diff --git a/compiler/rustc_target/src/spec/json.rs b/compiler/rustc_target/src/spec/json.rs
new file mode 100644
index 0000000000000..206766325aa16
--- /dev/null
+++ b/compiler/rustc_target/src/spec/json.rs
@@ -0,0 +1,798 @@
+use std::borrow::Cow;
+use std::collections::BTreeMap;
+use std::str::FromStr;
+
+use serde_json::Value;
+
+use super::{Target, TargetKind, TargetOptions, TargetWarnings};
+use crate::json::{Json, ToJson};
+
+impl Target {
+    /// Loads a target descriptor from a JSON object.
+    pub fn from_json(obj: Json) -> Result<(Target, TargetWarnings), String> {
+        // While ugly, this code must remain this way to retain
+        // compatibility with existing JSON fields and the internal
+        // expected naming of the Target and TargetOptions structs.
+        // To ensure compatibility is retained, the built-in targets
+        // are round-tripped through this code to catch cases where
+        // the JSON parser is not updated to match the structs.
+
+        let mut obj = match obj {
+            Value::Object(obj) => obj,
+            _ => return Err("Expected JSON object for target")?,
+        };
+
+        let mut get_req_field = |name: &str| {
+            obj.remove(name)
+                .and_then(|j| j.as_str().map(str::to_string))
+                .ok_or_else(|| format!("Field {name} in target specification is required"))
+        };
+
+        let mut base = Target {
+            llvm_target: get_req_field("llvm-target")?.into(),
+            metadata: Default::default(),
+            pointer_width: get_req_field("target-pointer-width")?
+                .parse::<u32>()
+                .map_err(|_| "target-pointer-width must be an integer".to_string())?,
+            data_layout: get_req_field("data-layout")?.into(),
+            arch: get_req_field("arch")?.into(),
+            options: Default::default(),
+        };
+
+        // FIXME: This doesn't properly validate anything and just ignores the data if it's invalid.
+        // That's okay for now, the only use of this is when generating docs, which we don't do for
+        // custom targets.
+        if let Some(Json::Object(mut metadata)) = obj.remove("metadata") {
+            base.metadata.description = metadata
+                .remove("description")
+                .and_then(|desc| desc.as_str().map(|desc| desc.to_owned().into()));
+            base.metadata.tier = metadata
+                .remove("tier")
+                .and_then(|tier| tier.as_u64())
+                .filter(|tier| (1..=3).contains(tier));
+            base.metadata.host_tools =
+                metadata.remove("host_tools").and_then(|host| host.as_bool());
+            base.metadata.std = metadata.remove("std").and_then(|host| host.as_bool());
+        }
+
+        let mut incorrect_type = vec![];
+
+        macro_rules! key {
+            ($key_name:ident) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(s) = obj.remove(&name).and_then(|s| s.as_str().map(str::to_string).map(Cow::from)) {
+                    base.$key_name = s;
+                }
+            } );
+            ($key_name:ident = $json_name:expr) => ( {
+                let name = $json_name;
+                if let Some(s) = obj.remove(name).and_then(|s| s.as_str().map(str::to_string).map(Cow::from)) {
+                    base.$key_name = s;
+                }
+            } );
+            ($key_name:ident, bool) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(s) = obj.remove(&name).and_then(|b| b.as_bool()) {
+                    base.$key_name = s;
+                }
+            } );
+            ($key_name:ident = $json_name:expr, bool) => ( {
+                let name = $json_name;
+                if let Some(s) = obj.remove(name).and_then(|b| b.as_bool()) {
+                    base.$key_name = s;
+                }
+            } );
+            ($key_name:ident, u32) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(s) = obj.remove(&name).and_then(|b| b.as_u64()) {
+                    if s < 1 || s > 5 {
+                        return Err("Not a valid DWARF version number".into());
+                    }
+                    base.$key_name = s as u32;
+                }
+            } );
+            ($key_name:ident, Option<bool>) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(s) = obj.remove(&name).and_then(|b| b.as_bool()) {
+                    base.$key_name = Some(s);
+                }
+            } );
+            ($key_name:ident, Option<u64>) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(s) = obj.remove(&name).and_then(|b| b.as_u64()) {
+                    base.$key_name = Some(s);
+                }
+            } );
+            ($key_name:ident, MergeFunctions) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::MergeFunctions>() {
+                        Ok(mergefunc) => base.$key_name = mergefunc,
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      merge-functions. Use 'disabled', \
+                                                      'trampolines', or 'aliases'.",
+                                                      s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, RelocModel) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::RelocModel>() {
+                        Ok(relocation_model) => base.$key_name = relocation_model,
+                        _ => return Some(Err(format!("'{}' is not a valid relocation model. \
+                                                      Run `rustc --print relocation-models` to \
+                                                      see the list of supported values.", s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, CodeModel) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::CodeModel>() {
+                        Ok(code_model) => base.$key_name = Some(code_model),
+                        _ => return Some(Err(format!("'{}' is not a valid code model. \
+                                                      Run `rustc --print code-models` to \
+                                                      see the list of supported values.", s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, TlsModel) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::TlsModel>() {
+                        Ok(tls_model) => base.$key_name = tls_model,
+                        _ => return Some(Err(format!("'{}' is not a valid TLS model. \
+                                                      Run `rustc --print tls-models` to \
+                                                      see the list of supported values.", s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, SmallDataThresholdSupport) => ( {
+                obj.remove("small-data-threshold-support").and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::SmallDataThresholdSupport>() {
+                        Ok(support) => base.small_data_threshold_support = support,
+                        _ => return Some(Err(format!("'{s}' is not a valid value for small-data-threshold-support."))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, PanicStrategy) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s {
+                        "unwind" => base.$key_name = super::PanicStrategy::Unwind,
+                        "abort" => base.$key_name = super::PanicStrategy::Abort,
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      panic-strategy. Use 'unwind' or 'abort'.",
+                                                     s))),
+                }
+                Some(Ok(()))
+            })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, RelroLevel) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::RelroLevel>() {
+                        Ok(level) => base.$key_name = level,
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      relro-level. Use 'full', 'partial, or 'off'.",
+                                                      s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, Option<SymbolVisibility>) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::SymbolVisibility>() {
+                        Ok(level) => base.$key_name = Some(level),
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      symbol-visibility. Use 'hidden', 'protected, or 'interposable'.",
+                                                      s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, DebuginfoKind) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::DebuginfoKind>() {
+                        Ok(level) => base.$key_name = level,
+                        _ => return Some(Err(
+                            format!("'{s}' is not a valid value for debuginfo-kind. Use 'dwarf', \
+                                  'dwarf-dsym' or 'pdb'.")
+                        )),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, SplitDebuginfo) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::SplitDebuginfo>() {
+                        Ok(level) => base.$key_name = level,
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      split-debuginfo. Use 'off' or 'dsymutil'.",
+                                                      s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, list) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(j) = obj.remove(&name) {
+                    if let Some(v) = j.as_array() {
+                        base.$key_name = v.iter()
+                            .map(|a| a.as_str().unwrap().to_string().into())
+                            .collect();
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                }
+            } );
+            ($key_name:ident, opt_list) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(j) = obj.remove(&name) {
+                    if let Some(v) = j.as_array() {
+                        base.$key_name = Some(v.iter()
+                            .map(|a| a.as_str().unwrap().to_string().into())
+                            .collect());
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                }
+            } );
+            ($key_name:ident, fallible_list) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|j| {
+                    if let Some(v) = j.as_array() {
+                        match v.iter().map(|a| FromStr::from_str(a.as_str().unwrap())).collect() {
+                            Ok(l) => { base.$key_name = l },
+                            // FIXME: `fallible_list` can't re-use the `key!` macro for list
+                            // elements and the error messages from that macro, so it has a bad
+                            // generic message instead
+                            Err(_) => return Some(Err(
+                                format!("`{:?}` is not a valid value for `{}`", j, name)
+                            )),
+                        }
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                    Some(Ok(()))
+                }).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, optional) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(o) = obj.remove(&name) {
+                    base.$key_name = o
+                        .as_str()
+                        .map(|s| s.to_string().into());
+                }
+            } );
+            ($key_name:ident = $json_name:expr, LldFlavor) => ( {
+                let name = $json_name;
+                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
+                    if let Some(flavor) = super::LldFlavor::from_str(&s) {
+                        base.$key_name = flavor;
+                    } else {
+                        return Some(Err(format!(
+                            "'{}' is not a valid value for lld-flavor. \
+                             Use 'darwin', 'gnu', 'link' or 'wasm'.",
+                            s)))
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident = $json_name:expr, LinkerFlavorCli) => ( {
+                let name = $json_name;
+                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
+                    match super::LinkerFlavorCli::from_str(s) {
+                        Some(linker_flavor) => base.$key_name = linker_flavor,
+                        _ => return Some(Err(format!("'{}' is not a valid value for linker-flavor. \
+                                                      Use {}", s, super::LinkerFlavorCli::one_of()))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, StackProbeType) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| match super::StackProbeType::from_json(&o) {
+                    Ok(v) => {
+                        base.$key_name = v;
+                        Some(Ok(()))
+                    },
+                    Err(s) => Some(Err(
+                        format!("`{:?}` is not a valid value for `{}`: {}", o, name, s)
+                    )),
+                }).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident, SanitizerSet) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(o) = obj.remove(&name) {
+                    if let Some(a) = o.as_array() {
+                        for s in a {
+                            use super::SanitizerSet;
+                            base.$key_name |= match s.as_str() {
+                                Some("address") => SanitizerSet::ADDRESS,
+                                Some("cfi") => SanitizerSet::CFI,
+                                Some("dataflow") => SanitizerSet::DATAFLOW,
+                                Some("kcfi") => SanitizerSet::KCFI,
+                                Some("kernel-address") => SanitizerSet::KERNELADDRESS,
+                                Some("leak") => SanitizerSet::LEAK,
+                                Some("memory") => SanitizerSet::MEMORY,
+                                Some("memtag") => SanitizerSet::MEMTAG,
+                                Some("safestack") => SanitizerSet::SAFESTACK,
+                                Some("shadow-call-stack") => SanitizerSet::SHADOWCALLSTACK,
+                                Some("thread") => SanitizerSet::THREAD,
+                                Some("hwaddress") => SanitizerSet::HWADDRESS,
+                                Some(s) => return Err(format!("unknown sanitizer {}", s)),
+                                _ => return Err(format!("not a string: {:?}", s)),
+                            };
+                        }
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                }
+                Ok::<(), String>(())
+            } );
+            ($key_name:ident, link_self_contained_components) => ( {
+                // Skeleton of what needs to be parsed:
+                //
+                // ```
+                // $name: {
+                //     "components": [
+                //         <array of strings>
+                //     ]
+                // }
+                // ```
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(o) = obj.remove(&name) {
+                    if let Some(o) = o.as_object() {
+                        let component_array = o.get("components")
+                            .ok_or_else(|| format!("{name}: expected a \
+                                JSON object with a `components` field."))?;
+                        let component_array = component_array.as_array()
+                            .ok_or_else(|| format!("{name}.components: expected a JSON array"))?;
+                        let mut components = super::LinkSelfContainedComponents::empty();
+                        for s in component_array {
+                            components |= match s.as_str() {
+                                Some(s) => {
+                                    super::LinkSelfContainedComponents::from_str(s)
+                                        .ok_or_else(|| format!("unknown \
+                                        `-Clink-self-contained` component: {s}"))?
+                                },
+                                _ => return Err(format!("not a string: {:?}", s)),
+                            };
+                        }
+                        base.$key_name = super::LinkSelfContainedDefault::WithComponents(components);
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                }
+                Ok::<(), String>(())
+            } );
+            ($key_name:ident = $json_name:expr, link_self_contained_backwards_compatible) => ( {
+                let name = $json_name;
+                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::LinkSelfContainedDefault>() {
+                        Ok(lsc_default) => base.$key_name = lsc_default,
+                        _ => return Some(Err(format!("'{}' is not a valid `-Clink-self-contained` default. \
+                                                      Use 'false', 'true', 'musl' or 'mingw'", s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
+            ($key_name:ident = $json_name:expr, link_objects) => ( {
+                let name = $json_name;
+                if let Some(val) = obj.remove(name) {
+                    let obj = val.as_object().ok_or_else(|| format!("{}: expected a \
+                        JSON object with fields per CRT object kind.", name))?;
+                    let mut args = super::CrtObjects::new();
+                    for (k, v) in obj {
+                        let kind = super::LinkOutputKind::from_str(&k).ok_or_else(|| {
+                            format!("{}: '{}' is not a valid value for CRT object kind. \
+                                     Use '(dynamic,static)-(nopic,pic)-exe' or \
+                                     '(dynamic,static)-dylib' or 'wasi-reactor-exe'", name, k)
+                        })?;
+
+                        let v = v.as_array().ok_or_else(||
+                            format!("{}.{}: expected a JSON array", name, k)
+                        )?.iter().enumerate()
+                            .map(|(i,s)| {
+                                let s = s.as_str().ok_or_else(||
+                                    format!("{}.{}[{}]: expected a JSON string", name, k, i))?;
+                                Ok(s.to_string().into())
+                            })
+                            .collect::<Result<Vec<_>, String>>()?;
+
+                        args.insert(kind, v);
+                    }
+                    base.$key_name = args;
+                }
+            } );
+            ($key_name:ident = $json_name:expr, link_args) => ( {
+                let name = $json_name;
+                if let Some(val) = obj.remove(name) {
+                    let obj = val.as_object().ok_or_else(|| format!("{}: expected a \
+                        JSON object with fields per linker-flavor.", name))?;
+                    let mut args = super::LinkArgsCli::new();
+                    for (k, v) in obj {
+                        let flavor = super::LinkerFlavorCli::from_str(&k).ok_or_else(|| {
+                            format!("{}: '{}' is not a valid value for linker-flavor. \
+                                     Use 'em', 'gcc', 'ld' or 'msvc'", name, k)
+                        })?;
+
+                        let v = v.as_array().ok_or_else(||
+                            format!("{}.{}: expected a JSON array", name, k)
+                        )?.iter().enumerate()
+                            .map(|(i,s)| {
+                                let s = s.as_str().ok_or_else(||
+                                    format!("{}.{}[{}]: expected a JSON string", name, k, i))?;
+                                Ok(s.to_string().into())
+                            })
+                            .collect::<Result<Vec<_>, String>>()?;
+
+                        args.insert(flavor, v);
+                    }
+                    base.$key_name = args;
+                }
+            } );
+            ($key_name:ident, env) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                if let Some(o) = obj.remove(&name) {
+                    if let Some(a) = o.as_array() {
+                        for o in a {
+                            if let Some(s) = o.as_str() {
+                                if let [k, v] = *s.split('=').collect::<Vec<_>>() {
+                                    base.$key_name
+                                        .to_mut()
+                                        .push((k.to_string().into(), v.to_string().into()))
+                                }
+                            }
+                        }
+                    } else {
+                        incorrect_type.push(name)
+                    }
+                }
+            } );
+            ($key_name:ident, target_families) => ( {
+                if let Some(value) = obj.remove("target-family") {
+                    if let Some(v) = value.as_array() {
+                        base.$key_name = v.iter()
+                            .map(|a| a.as_str().unwrap().to_string().into())
+                            .collect();
+                    } else if let Some(v) = value.as_str() {
+                        base.$key_name = vec![v.to_string().into()].into();
+                    }
+                }
+            } );
+            ($key_name:ident, Conv) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match super::Conv::from_str(s) {
+                        Ok(c) => {
+                            base.$key_name = c;
+                            Some(Ok(()))
+                        }
+                        Err(e) => Some(Err(e))
+                    }
+                })).unwrap_or(Ok(()))
+            } );
+        }
+
+        if let Some(j) = obj.remove("target-endian") {
+            if let Some(s) = j.as_str() {
+                base.endian = s.parse()?;
+            } else {
+                incorrect_type.push("target-endian".into())
+            }
+        }
+
+        if let Some(fp) = obj.remove("frame-pointer") {
+            if let Some(s) = fp.as_str() {
+                base.frame_pointer = s
+                    .parse()
+                    .map_err(|()| format!("'{s}' is not a valid value for frame-pointer"))?;
+            } else {
+                incorrect_type.push("frame-pointer".into())
+            }
+        }
+
+        key!(c_int_width = "target-c-int-width");
+        key!(c_enum_min_bits, Option<u64>); // if None, matches c_int_width
+        key!(os);
+        key!(env);
+        key!(abi);
+        key!(vendor);
+        key!(linker, optional);
+        key!(linker_flavor_json = "linker-flavor", LinkerFlavorCli)?;
+        key!(lld_flavor_json = "lld-flavor", LldFlavor)?;
+        key!(linker_is_gnu_json = "linker-is-gnu", bool);
+        key!(pre_link_objects = "pre-link-objects", link_objects);
+        key!(post_link_objects = "post-link-objects", link_objects);
+        key!(pre_link_objects_self_contained = "pre-link-objects-fallback", link_objects);
+        key!(post_link_objects_self_contained = "post-link-objects-fallback", link_objects);
+        // Deserializes the backwards-compatible variants of `-Clink-self-contained`
+        key!(
+            link_self_contained = "crt-objects-fallback",
+            link_self_contained_backwards_compatible
+        )?;
+        // Deserializes the components variant of `-Clink-self-contained`
+        key!(link_self_contained, link_self_contained_components)?;
+        key!(pre_link_args_json = "pre-link-args", link_args);
+        key!(late_link_args_json = "late-link-args", link_args);
+        key!(late_link_args_dynamic_json = "late-link-args-dynamic", link_args);
+        key!(late_link_args_static_json = "late-link-args-static", link_args);
+        key!(post_link_args_json = "post-link-args", link_args);
+        key!(link_script, optional);
+        key!(link_env, env);
+        key!(link_env_remove, list);
+        key!(asm_args, list);
+        key!(cpu);
+        key!(features);
+        key!(dynamic_linking, bool);
+        key!(direct_access_external_data, Option<bool>);
+        key!(dll_tls_export, bool);
+        key!(only_cdylib, bool);
+        key!(executables, bool);
+        key!(relocation_model, RelocModel)?;
+        key!(code_model, CodeModel)?;
+        key!(tls_model, TlsModel)?;
+        key!(disable_redzone, bool);
+        key!(function_sections, bool);
+        key!(dll_prefix);
+        key!(dll_suffix);
+        key!(exe_suffix);
+        key!(staticlib_prefix);
+        key!(staticlib_suffix);
+        key!(families, target_families);
+        key!(abi_return_struct_as_int, bool);
+        key!(is_like_aix, bool);
+        key!(is_like_osx, bool);
+        key!(is_like_solaris, bool);
+        key!(is_like_windows, bool);
+        key!(is_like_msvc, bool);
+        key!(is_like_wasm, bool);
+        key!(is_like_android, bool);
+        key!(default_dwarf_version, u32);
+        key!(allows_weak_linkage, bool);
+        key!(has_rpath, bool);
+        key!(no_default_libraries, bool);
+        key!(position_independent_executables, bool);
+        key!(static_position_independent_executables, bool);
+        key!(plt_by_default, bool);
+        key!(relro_level, RelroLevel)?;
+        key!(archive_format);
+        key!(allow_asm, bool);
+        key!(main_needs_argc_argv, bool);
+        key!(has_thread_local, bool);
+        key!(obj_is_bitcode, bool);
+        key!(bitcode_llvm_cmdline);
+        key!(max_atomic_width, Option<u64>);
+        key!(min_atomic_width, Option<u64>);
+        key!(atomic_cas, bool);
+        key!(panic_strategy, PanicStrategy)?;
+        key!(crt_static_allows_dylibs, bool);
+        key!(crt_static_default, bool);
+        key!(crt_static_respected, bool);
+        key!(stack_probes, StackProbeType)?;
+        key!(min_global_align, Option<u64>);
+        key!(default_codegen_units, Option<u64>);
+        key!(trap_unreachable, bool);
+        key!(requires_lto, bool);
+        key!(singlethread, bool);
+        key!(no_builtins, bool);
+        key!(default_visibility, Option<SymbolVisibility>)?;
+        key!(emit_debug_gdb_scripts, bool);
+        key!(requires_uwtable, bool);
+        key!(default_uwtable, bool);
+        key!(simd_types_indirect, bool);
+        key!(limit_rdylib_exports, bool);
+        key!(override_export_symbols, opt_list);
+        key!(merge_functions, MergeFunctions)?;
+        key!(mcount = "target-mcount");
+        key!(llvm_mcount_intrinsic, optional);
+        key!(llvm_abiname);
+        key!(relax_elf_relocations, bool);
+        key!(llvm_args, list);
+        key!(use_ctors_section, bool);
+        key!(eh_frame_header, bool);
+        key!(has_thumb_interworking, bool);
+        key!(debuginfo_kind, DebuginfoKind)?;
+        key!(split_debuginfo, SplitDebuginfo)?;
+        key!(supported_split_debuginfo, fallible_list)?;
+        key!(supported_sanitizers, SanitizerSet)?;
+        key!(generate_arange_section, bool);
+        key!(supports_stack_protector, bool);
+        key!(small_data_threshold_support, SmallDataThresholdSupport)?;
+        key!(entry_name);
+        key!(entry_abi, Conv)?;
+        key!(supports_xray, bool);
+
+        base.update_from_cli();
+        base.check_consistency(TargetKind::Json)?;
+
+        // Each field should have been read using `Json::remove` so any keys remaining are unused.
+        let remaining_keys = obj.keys();
+        Ok((base, TargetWarnings {
+            unused_fields: remaining_keys.cloned().collect(),
+            incorrect_type,
+        }))
+    }
+}
+
+impl ToJson for Target {
+    fn to_json(&self) -> Json {
+        let mut d = serde_json::Map::new();
+        let default: TargetOptions = Default::default();
+        let mut target = self.clone();
+        target.update_to_cli();
+
+        macro_rules! target_val {
+            ($attr:ident) => {{
+                let name = (stringify!($attr)).replace("_", "-");
+                d.insert(name, target.$attr.to_json());
+            }};
+        }
+
+        macro_rules! target_option_val {
+            ($attr:ident) => {{
+                let name = (stringify!($attr)).replace("_", "-");
+                if default.$attr != target.$attr {
+                    d.insert(name, target.$attr.to_json());
+                }
+            }};
+            ($attr:ident, $json_name:expr) => {{
+                let name = $json_name;
+                if default.$attr != target.$attr {
+                    d.insert(name.into(), target.$attr.to_json());
+                }
+            }};
+            (link_args - $attr:ident, $json_name:expr) => {{
+                let name = $json_name;
+                if default.$attr != target.$attr {
+                    let obj = target
+                        .$attr
+                        .iter()
+                        .map(|(k, v)| (k.desc().to_string(), v.clone()))
+                        .collect::<BTreeMap<_, _>>();
+                    d.insert(name.to_string(), obj.to_json());
+                }
+            }};
+            (env - $attr:ident) => {{
+                let name = (stringify!($attr)).replace("_", "-");
+                if default.$attr != target.$attr {
+                    let obj = target
+                        .$attr
+                        .iter()
+                        .map(|&(ref k, ref v)| format!("{k}={v}"))
+                        .collect::<Vec<_>>();
+                    d.insert(name, obj.to_json());
+                }
+            }};
+        }
+
+        target_val!(llvm_target);
+        target_val!(metadata);
+        d.insert("target-pointer-width".to_string(), self.pointer_width.to_string().to_json());
+        target_val!(arch);
+        target_val!(data_layout);
+
+        target_option_val!(endian, "target-endian");
+        target_option_val!(c_int_width, "target-c-int-width");
+        target_option_val!(os);
+        target_option_val!(env);
+        target_option_val!(abi);
+        target_option_val!(vendor);
+        target_option_val!(linker);
+        target_option_val!(linker_flavor_json, "linker-flavor");
+        target_option_val!(lld_flavor_json, "lld-flavor");
+        target_option_val!(linker_is_gnu_json, "linker-is-gnu");
+        target_option_val!(pre_link_objects);
+        target_option_val!(post_link_objects);
+        target_option_val!(pre_link_objects_self_contained, "pre-link-objects-fallback");
+        target_option_val!(post_link_objects_self_contained, "post-link-objects-fallback");
+        target_option_val!(link_args - pre_link_args_json, "pre-link-args");
+        target_option_val!(link_args - late_link_args_json, "late-link-args");
+        target_option_val!(link_args - late_link_args_dynamic_json, "late-link-args-dynamic");
+        target_option_val!(link_args - late_link_args_static_json, "late-link-args-static");
+        target_option_val!(link_args - post_link_args_json, "post-link-args");
+        target_option_val!(link_script);
+        target_option_val!(env - link_env);
+        target_option_val!(link_env_remove);
+        target_option_val!(asm_args);
+        target_option_val!(cpu);
+        target_option_val!(features);
+        target_option_val!(dynamic_linking);
+        target_option_val!(direct_access_external_data);
+        target_option_val!(dll_tls_export);
+        target_option_val!(only_cdylib);
+        target_option_val!(executables);
+        target_option_val!(relocation_model);
+        target_option_val!(code_model);
+        target_option_val!(tls_model);
+        target_option_val!(disable_redzone);
+        target_option_val!(frame_pointer);
+        target_option_val!(function_sections);
+        target_option_val!(dll_prefix);
+        target_option_val!(dll_suffix);
+        target_option_val!(exe_suffix);
+        target_option_val!(staticlib_prefix);
+        target_option_val!(staticlib_suffix);
+        target_option_val!(families, "target-family");
+        target_option_val!(abi_return_struct_as_int);
+        target_option_val!(is_like_aix);
+        target_option_val!(is_like_osx);
+        target_option_val!(is_like_solaris);
+        target_option_val!(is_like_windows);
+        target_option_val!(is_like_msvc);
+        target_option_val!(is_like_wasm);
+        target_option_val!(is_like_android);
+        target_option_val!(default_dwarf_version);
+        target_option_val!(allows_weak_linkage);
+        target_option_val!(has_rpath);
+        target_option_val!(no_default_libraries);
+        target_option_val!(position_independent_executables);
+        target_option_val!(static_position_independent_executables);
+        target_option_val!(plt_by_default);
+        target_option_val!(relro_level);
+        target_option_val!(archive_format);
+        target_option_val!(allow_asm);
+        target_option_val!(main_needs_argc_argv);
+        target_option_val!(has_thread_local);
+        target_option_val!(obj_is_bitcode);
+        target_option_val!(bitcode_llvm_cmdline);
+        target_option_val!(min_atomic_width);
+        target_option_val!(max_atomic_width);
+        target_option_val!(atomic_cas);
+        target_option_val!(panic_strategy);
+        target_option_val!(crt_static_allows_dylibs);
+        target_option_val!(crt_static_default);
+        target_option_val!(crt_static_respected);
+        target_option_val!(stack_probes);
+        target_option_val!(min_global_align);
+        target_option_val!(default_codegen_units);
+        target_option_val!(trap_unreachable);
+        target_option_val!(requires_lto);
+        target_option_val!(singlethread);
+        target_option_val!(no_builtins);
+        target_option_val!(default_visibility);
+        target_option_val!(emit_debug_gdb_scripts);
+        target_option_val!(requires_uwtable);
+        target_option_val!(default_uwtable);
+        target_option_val!(simd_types_indirect);
+        target_option_val!(limit_rdylib_exports);
+        target_option_val!(override_export_symbols);
+        target_option_val!(merge_functions);
+        target_option_val!(mcount, "target-mcount");
+        target_option_val!(llvm_mcount_intrinsic);
+        target_option_val!(llvm_abiname);
+        target_option_val!(relax_elf_relocations);
+        target_option_val!(llvm_args);
+        target_option_val!(use_ctors_section);
+        target_option_val!(eh_frame_header);
+        target_option_val!(has_thumb_interworking);
+        target_option_val!(debuginfo_kind);
+        target_option_val!(split_debuginfo);
+        target_option_val!(supported_split_debuginfo);
+        target_option_val!(supported_sanitizers);
+        target_option_val!(c_enum_min_bits);
+        target_option_val!(generate_arange_section);
+        target_option_val!(supports_stack_protector);
+        target_option_val!(small_data_threshold_support);
+        target_option_val!(entry_name);
+        target_option_val!(entry_abi);
+        target_option_val!(supports_xray);
+
+        // Serializing `-Clink-self-contained` needs a dynamic key to support the
+        // backwards-compatible variants.
+        d.insert(self.link_self_contained.json_key().into(), self.link_self_contained.to_json());
+
+        Json::Object(d)
+    }
+}
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 1c7d473447acf..a2e9430830a22 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -34,8 +34,6 @@
 //! the target's settings, though `target-feature` and `link-args` will *add*
 //! to the list specified by the target, rather than replace.
 
-// ignore-tidy-filelength
-
 use std::borrow::Cow;
 use std::collections::BTreeMap;
 use std::hash::{Hash, Hasher};
@@ -68,6 +66,8 @@ pub mod abi {
 }
 
 mod base;
+mod json;
+
 pub use base::avr_gnu::ef_avr_arch;
 
 /// Linker is called through a C/C++ compiler.
@@ -3206,622 +3206,6 @@ impl Target {
             || (self.env == "sgx" && self.vendor == "fortanix")
     }
 
-    /// Loads a target descriptor from a JSON object.
-    pub fn from_json(obj: Json) -> Result<(Target, TargetWarnings), String> {
-        // While ugly, this code must remain this way to retain
-        // compatibility with existing JSON fields and the internal
-        // expected naming of the Target and TargetOptions structs.
-        // To ensure compatibility is retained, the built-in targets
-        // are round-tripped through this code to catch cases where
-        // the JSON parser is not updated to match the structs.
-
-        let mut obj = match obj {
-            Value::Object(obj) => obj,
-            _ => return Err("Expected JSON object for target")?,
-        };
-
-        let mut get_req_field = |name: &str| {
-            obj.remove(name)
-                .and_then(|j| j.as_str().map(str::to_string))
-                .ok_or_else(|| format!("Field {name} in target specification is required"))
-        };
-
-        let mut base = Target {
-            llvm_target: get_req_field("llvm-target")?.into(),
-            metadata: Default::default(),
-            pointer_width: get_req_field("target-pointer-width")?
-                .parse::<u32>()
-                .map_err(|_| "target-pointer-width must be an integer".to_string())?,
-            data_layout: get_req_field("data-layout")?.into(),
-            arch: get_req_field("arch")?.into(),
-            options: Default::default(),
-        };
-
-        // FIXME: This doesn't properly validate anything and just ignores the data if it's invalid.
-        // That's okay for now, the only use of this is when generating docs, which we don't do for
-        // custom targets.
-        if let Some(Json::Object(mut metadata)) = obj.remove("metadata") {
-            base.metadata.description = metadata
-                .remove("description")
-                .and_then(|desc| desc.as_str().map(|desc| desc.to_owned().into()));
-            base.metadata.tier = metadata
-                .remove("tier")
-                .and_then(|tier| tier.as_u64())
-                .filter(|tier| (1..=3).contains(tier));
-            base.metadata.host_tools =
-                metadata.remove("host_tools").and_then(|host| host.as_bool());
-            base.metadata.std = metadata.remove("std").and_then(|host| host.as_bool());
-        }
-
-        let mut incorrect_type = vec![];
-
-        macro_rules! key {
-            ($key_name:ident) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(s) = obj.remove(&name).and_then(|s| s.as_str().map(str::to_string).map(Cow::from)) {
-                    base.$key_name = s;
-                }
-            } );
-            ($key_name:ident = $json_name:expr) => ( {
-                let name = $json_name;
-                if let Some(s) = obj.remove(name).and_then(|s| s.as_str().map(str::to_string).map(Cow::from)) {
-                    base.$key_name = s;
-                }
-            } );
-            ($key_name:ident, bool) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(s) = obj.remove(&name).and_then(|b| b.as_bool()) {
-                    base.$key_name = s;
-                }
-            } );
-            ($key_name:ident = $json_name:expr, bool) => ( {
-                let name = $json_name;
-                if let Some(s) = obj.remove(name).and_then(|b| b.as_bool()) {
-                    base.$key_name = s;
-                }
-            } );
-            ($key_name:ident, u32) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(s) = obj.remove(&name).and_then(|b| b.as_u64()) {
-                    if s < 1 || s > 5 {
-                        return Err("Not a valid DWARF version number".into());
-                    }
-                    base.$key_name = s as u32;
-                }
-            } );
-            ($key_name:ident, Option<bool>) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(s) = obj.remove(&name).and_then(|b| b.as_bool()) {
-                    base.$key_name = Some(s);
-                }
-            } );
-            ($key_name:ident, Option<u64>) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(s) = obj.remove(&name).and_then(|b| b.as_u64()) {
-                    base.$key_name = Some(s);
-                }
-            } );
-            ($key_name:ident, MergeFunctions) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<MergeFunctions>() {
-                        Ok(mergefunc) => base.$key_name = mergefunc,
-                        _ => return Some(Err(format!("'{}' is not a valid value for \
-                                                      merge-functions. Use 'disabled', \
-                                                      'trampolines', or 'aliases'.",
-                                                      s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, RelocModel) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<RelocModel>() {
-                        Ok(relocation_model) => base.$key_name = relocation_model,
-                        _ => return Some(Err(format!("'{}' is not a valid relocation model. \
-                                                      Run `rustc --print relocation-models` to \
-                                                      see the list of supported values.", s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, CodeModel) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<CodeModel>() {
-                        Ok(code_model) => base.$key_name = Some(code_model),
-                        _ => return Some(Err(format!("'{}' is not a valid code model. \
-                                                      Run `rustc --print code-models` to \
-                                                      see the list of supported values.", s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, TlsModel) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<TlsModel>() {
-                        Ok(tls_model) => base.$key_name = tls_model,
-                        _ => return Some(Err(format!("'{}' is not a valid TLS model. \
-                                                      Run `rustc --print tls-models` to \
-                                                      see the list of supported values.", s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, SmallDataThresholdSupport) => ( {
-                obj.remove("small-data-threshold-support").and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<SmallDataThresholdSupport>() {
-                        Ok(support) => base.small_data_threshold_support = support,
-                        _ => return Some(Err(format!("'{s}' is not a valid value for small-data-threshold-support."))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, PanicStrategy) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s {
-                        "unwind" => base.$key_name = PanicStrategy::Unwind,
-                        "abort" => base.$key_name = PanicStrategy::Abort,
-                        _ => return Some(Err(format!("'{}' is not a valid value for \
-                                                      panic-strategy. Use 'unwind' or 'abort'.",
-                                                     s))),
-                }
-                Some(Ok(()))
-            })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, RelroLevel) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<RelroLevel>() {
-                        Ok(level) => base.$key_name = level,
-                        _ => return Some(Err(format!("'{}' is not a valid value for \
-                                                      relro-level. Use 'full', 'partial, or 'off'.",
-                                                      s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, Option<SymbolVisibility>) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<SymbolVisibility>() {
-                        Ok(level) => base.$key_name = Some(level),
-                        _ => return Some(Err(format!("'{}' is not a valid value for \
-                                                      symbol-visibility. Use 'hidden', 'protected, or 'interposable'.",
-                                                      s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, DebuginfoKind) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<DebuginfoKind>() {
-                        Ok(level) => base.$key_name = level,
-                        _ => return Some(Err(
-                            format!("'{s}' is not a valid value for debuginfo-kind. Use 'dwarf', \
-                                  'dwarf-dsym' or 'pdb'.")
-                        )),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, SplitDebuginfo) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<SplitDebuginfo>() {
-                        Ok(level) => base.$key_name = level,
-                        _ => return Some(Err(format!("'{}' is not a valid value for \
-                                                      split-debuginfo. Use 'off' or 'dsymutil'.",
-                                                      s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, list) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(j) = obj.remove(&name) {
-                    if let Some(v) = j.as_array() {
-                        base.$key_name = v.iter()
-                            .map(|a| a.as_str().unwrap().to_string().into())
-                            .collect();
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                }
-            } );
-            ($key_name:ident, opt_list) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(j) = obj.remove(&name) {
-                    if let Some(v) = j.as_array() {
-                        base.$key_name = Some(v.iter()
-                            .map(|a| a.as_str().unwrap().to_string().into())
-                            .collect());
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                }
-            } );
-            ($key_name:ident, fallible_list) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|j| {
-                    if let Some(v) = j.as_array() {
-                        match v.iter().map(|a| FromStr::from_str(a.as_str().unwrap())).collect() {
-                            Ok(l) => { base.$key_name = l },
-                            // FIXME: `fallible_list` can't re-use the `key!` macro for list
-                            // elements and the error messages from that macro, so it has a bad
-                            // generic message instead
-                            Err(_) => return Some(Err(
-                                format!("`{:?}` is not a valid value for `{}`", j, name)
-                            )),
-                        }
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                    Some(Ok(()))
-                }).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, optional) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(o) = obj.remove(&name) {
-                    base.$key_name = o
-                        .as_str()
-                        .map(|s| s.to_string().into());
-                }
-            } );
-            ($key_name:ident = $json_name:expr, LldFlavor) => ( {
-                let name = $json_name;
-                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
-                    if let Some(flavor) = LldFlavor::from_str(&s) {
-                        base.$key_name = flavor;
-                    } else {
-                        return Some(Err(format!(
-                            "'{}' is not a valid value for lld-flavor. \
-                             Use 'darwin', 'gnu', 'link' or 'wasm'.",
-                            s)))
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident = $json_name:expr, LinkerFlavor) => ( {
-                let name = $json_name;
-                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
-                    match LinkerFlavorCli::from_str(s) {
-                        Some(linker_flavor) => base.$key_name = linker_flavor,
-                        _ => return Some(Err(format!("'{}' is not a valid value for linker-flavor. \
-                                                      Use {}", s, LinkerFlavorCli::one_of()))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, StackProbeType) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| match StackProbeType::from_json(&o) {
-                    Ok(v) => {
-                        base.$key_name = v;
-                        Some(Ok(()))
-                    },
-                    Err(s) => Some(Err(
-                        format!("`{:?}` is not a valid value for `{}`: {}", o, name, s)
-                    )),
-                }).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident, SanitizerSet) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(o) = obj.remove(&name) {
-                    if let Some(a) = o.as_array() {
-                        for s in a {
-                            base.$key_name |= match s.as_str() {
-                                Some("address") => SanitizerSet::ADDRESS,
-                                Some("cfi") => SanitizerSet::CFI,
-                                Some("dataflow") => SanitizerSet::DATAFLOW,
-                                Some("kcfi") => SanitizerSet::KCFI,
-                                Some("kernel-address") => SanitizerSet::KERNELADDRESS,
-                                Some("leak") => SanitizerSet::LEAK,
-                                Some("memory") => SanitizerSet::MEMORY,
-                                Some("memtag") => SanitizerSet::MEMTAG,
-                                Some("safestack") => SanitizerSet::SAFESTACK,
-                                Some("shadow-call-stack") => SanitizerSet::SHADOWCALLSTACK,
-                                Some("thread") => SanitizerSet::THREAD,
-                                Some("hwaddress") => SanitizerSet::HWADDRESS,
-                                Some(s) => return Err(format!("unknown sanitizer {}", s)),
-                                _ => return Err(format!("not a string: {:?}", s)),
-                            };
-                        }
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                }
-                Ok::<(), String>(())
-            } );
-            ($key_name:ident, link_self_contained_components) => ( {
-                // Skeleton of what needs to be parsed:
-                //
-                // ```
-                // $name: {
-                //     "components": [
-                //         <array of strings>
-                //     ]
-                // }
-                // ```
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(o) = obj.remove(&name) {
-                    if let Some(o) = o.as_object() {
-                        let component_array = o.get("components")
-                            .ok_or_else(|| format!("{name}: expected a \
-                                JSON object with a `components` field."))?;
-                        let component_array = component_array.as_array()
-                            .ok_or_else(|| format!("{name}.components: expected a JSON array"))?;
-                        let mut components = LinkSelfContainedComponents::empty();
-                        for s in component_array {
-                            components |= match s.as_str() {
-                                Some(s) => {
-                                    LinkSelfContainedComponents::from_str(s)
-                                        .ok_or_else(|| format!("unknown \
-                                        `-Clink-self-contained` component: {s}"))?
-                                },
-                                _ => return Err(format!("not a string: {:?}", s)),
-                            };
-                        }
-                        base.$key_name = LinkSelfContainedDefault::WithComponents(components);
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                }
-                Ok::<(), String>(())
-            } );
-            ($key_name:ident = $json_name:expr, link_self_contained_backwards_compatible) => ( {
-                let name = $json_name;
-                obj.remove(name).and_then(|o| o.as_str().and_then(|s| {
-                    match s.parse::<LinkSelfContainedDefault>() {
-                        Ok(lsc_default) => base.$key_name = lsc_default,
-                        _ => return Some(Err(format!("'{}' is not a valid `-Clink-self-contained` default. \
-                                                      Use 'false', 'true', 'musl' or 'mingw'", s))),
-                    }
-                    Some(Ok(()))
-                })).unwrap_or(Ok(()))
-            } );
-            ($key_name:ident = $json_name:expr, link_objects) => ( {
-                let name = $json_name;
-                if let Some(val) = obj.remove(name) {
-                    let obj = val.as_object().ok_or_else(|| format!("{}: expected a \
-                        JSON object with fields per CRT object kind.", name))?;
-                    let mut args = CrtObjects::new();
-                    for (k, v) in obj {
-                        let kind = LinkOutputKind::from_str(&k).ok_or_else(|| {
-                            format!("{}: '{}' is not a valid value for CRT object kind. \
-                                     Use '(dynamic,static)-(nopic,pic)-exe' or \
-                                     '(dynamic,static)-dylib' or 'wasi-reactor-exe'", name, k)
-                        })?;
-
-                        let v = v.as_array().ok_or_else(||
-                            format!("{}.{}: expected a JSON array", name, k)
-                        )?.iter().enumerate()
-                            .map(|(i,s)| {
-                                let s = s.as_str().ok_or_else(||
-                                    format!("{}.{}[{}]: expected a JSON string", name, k, i))?;
-                                Ok(s.to_string().into())
-                            })
-                            .collect::<Result<Vec<_>, String>>()?;
-
-                        args.insert(kind, v);
-                    }
-                    base.$key_name = args;
-                }
-            } );
-            ($key_name:ident = $json_name:expr, link_args) => ( {
-                let name = $json_name;
-                if let Some(val) = obj.remove(name) {
-                    let obj = val.as_object().ok_or_else(|| format!("{}: expected a \
-                        JSON object with fields per linker-flavor.", name))?;
-                    let mut args = LinkArgsCli::new();
-                    for (k, v) in obj {
-                        let flavor = LinkerFlavorCli::from_str(&k).ok_or_else(|| {
-                            format!("{}: '{}' is not a valid value for linker-flavor. \
-                                     Use 'em', 'gcc', 'ld' or 'msvc'", name, k)
-                        })?;
-
-                        let v = v.as_array().ok_or_else(||
-                            format!("{}.{}: expected a JSON array", name, k)
-                        )?.iter().enumerate()
-                            .map(|(i,s)| {
-                                let s = s.as_str().ok_or_else(||
-                                    format!("{}.{}[{}]: expected a JSON string", name, k, i))?;
-                                Ok(s.to_string().into())
-                            })
-                            .collect::<Result<Vec<_>, String>>()?;
-
-                        args.insert(flavor, v);
-                    }
-                    base.$key_name = args;
-                }
-            } );
-            ($key_name:ident, env) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                if let Some(o) = obj.remove(&name) {
-                    if let Some(a) = o.as_array() {
-                        for o in a {
-                            if let Some(s) = o.as_str() {
-                                if let [k, v] = *s.split('=').collect::<Vec<_>>() {
-                                    base.$key_name
-                                        .to_mut()
-                                        .push((k.to_string().into(), v.to_string().into()))
-                                }
-                            }
-                        }
-                    } else {
-                        incorrect_type.push(name)
-                    }
-                }
-            } );
-            ($key_name:ident, TargetFamilies) => ( {
-                if let Some(value) = obj.remove("target-family") {
-                    if let Some(v) = value.as_array() {
-                        base.$key_name = v.iter()
-                            .map(|a| a.as_str().unwrap().to_string().into())
-                            .collect();
-                    } else if let Some(v) = value.as_str() {
-                        base.$key_name = vec![v.to_string().into()].into();
-                    }
-                }
-            } );
-            ($key_name:ident, Conv) => ( {
-                let name = (stringify!($key_name)).replace("_", "-");
-                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
-                    match Conv::from_str(s) {
-                        Ok(c) => {
-                            base.$key_name = c;
-                            Some(Ok(()))
-                        }
-                        Err(e) => Some(Err(e))
-                    }
-                })).unwrap_or(Ok(()))
-            } );
-        }
-
-        if let Some(j) = obj.remove("target-endian") {
-            if let Some(s) = j.as_str() {
-                base.endian = s.parse()?;
-            } else {
-                incorrect_type.push("target-endian".into())
-            }
-        }
-
-        if let Some(fp) = obj.remove("frame-pointer") {
-            if let Some(s) = fp.as_str() {
-                base.frame_pointer = s
-                    .parse()
-                    .map_err(|()| format!("'{s}' is not a valid value for frame-pointer"))?;
-            } else {
-                incorrect_type.push("frame-pointer".into())
-            }
-        }
-
-        key!(c_int_width = "target-c-int-width");
-        key!(c_enum_min_bits, Option<u64>); // if None, matches c_int_width
-        key!(os);
-        key!(env);
-        key!(abi);
-        key!(vendor);
-        key!(linker, optional);
-        key!(linker_flavor_json = "linker-flavor", LinkerFlavor)?;
-        key!(lld_flavor_json = "lld-flavor", LldFlavor)?;
-        key!(linker_is_gnu_json = "linker-is-gnu", bool);
-        key!(pre_link_objects = "pre-link-objects", link_objects);
-        key!(post_link_objects = "post-link-objects", link_objects);
-        key!(pre_link_objects_self_contained = "pre-link-objects-fallback", link_objects);
-        key!(post_link_objects_self_contained = "post-link-objects-fallback", link_objects);
-        // Deserializes the backwards-compatible variants of `-Clink-self-contained`
-        key!(
-            link_self_contained = "crt-objects-fallback",
-            link_self_contained_backwards_compatible
-        )?;
-        // Deserializes the components variant of `-Clink-self-contained`
-        key!(link_self_contained, link_self_contained_components)?;
-        key!(pre_link_args_json = "pre-link-args", link_args);
-        key!(late_link_args_json = "late-link-args", link_args);
-        key!(late_link_args_dynamic_json = "late-link-args-dynamic", link_args);
-        key!(late_link_args_static_json = "late-link-args-static", link_args);
-        key!(post_link_args_json = "post-link-args", link_args);
-        key!(link_script, optional);
-        key!(link_env, env);
-        key!(link_env_remove, list);
-        key!(asm_args, list);
-        key!(cpu);
-        key!(features);
-        key!(dynamic_linking, bool);
-        key!(direct_access_external_data, Option<bool>);
-        key!(dll_tls_export, bool);
-        key!(only_cdylib, bool);
-        key!(executables, bool);
-        key!(relocation_model, RelocModel)?;
-        key!(code_model, CodeModel)?;
-        key!(tls_model, TlsModel)?;
-        key!(disable_redzone, bool);
-        key!(function_sections, bool);
-        key!(dll_prefix);
-        key!(dll_suffix);
-        key!(exe_suffix);
-        key!(staticlib_prefix);
-        key!(staticlib_suffix);
-        key!(families, TargetFamilies);
-        key!(abi_return_struct_as_int, bool);
-        key!(is_like_aix, bool);
-        key!(is_like_osx, bool);
-        key!(is_like_solaris, bool);
-        key!(is_like_windows, bool);
-        key!(is_like_msvc, bool);
-        key!(is_like_wasm, bool);
-        key!(is_like_android, bool);
-        key!(default_dwarf_version, u32);
-        key!(allows_weak_linkage, bool);
-        key!(has_rpath, bool);
-        key!(no_default_libraries, bool);
-        key!(position_independent_executables, bool);
-        key!(static_position_independent_executables, bool);
-        key!(plt_by_default, bool);
-        key!(relro_level, RelroLevel)?;
-        key!(archive_format);
-        key!(allow_asm, bool);
-        key!(main_needs_argc_argv, bool);
-        key!(has_thread_local, bool);
-        key!(obj_is_bitcode, bool);
-        key!(bitcode_llvm_cmdline);
-        key!(max_atomic_width, Option<u64>);
-        key!(min_atomic_width, Option<u64>);
-        key!(atomic_cas, bool);
-        key!(panic_strategy, PanicStrategy)?;
-        key!(crt_static_allows_dylibs, bool);
-        key!(crt_static_default, bool);
-        key!(crt_static_respected, bool);
-        key!(stack_probes, StackProbeType)?;
-        key!(min_global_align, Option<u64>);
-        key!(default_codegen_units, Option<u64>);
-        key!(trap_unreachable, bool);
-        key!(requires_lto, bool);
-        key!(singlethread, bool);
-        key!(no_builtins, bool);
-        key!(default_visibility, Option<SymbolVisibility>)?;
-        key!(emit_debug_gdb_scripts, bool);
-        key!(requires_uwtable, bool);
-        key!(default_uwtable, bool);
-        key!(simd_types_indirect, bool);
-        key!(limit_rdylib_exports, bool);
-        key!(override_export_symbols, opt_list);
-        key!(merge_functions, MergeFunctions)?;
-        key!(mcount = "target-mcount");
-        key!(llvm_mcount_intrinsic, optional);
-        key!(llvm_abiname);
-        key!(relax_elf_relocations, bool);
-        key!(llvm_args, list);
-        key!(use_ctors_section, bool);
-        key!(eh_frame_header, bool);
-        key!(has_thumb_interworking, bool);
-        key!(debuginfo_kind, DebuginfoKind)?;
-        key!(split_debuginfo, SplitDebuginfo)?;
-        key!(supported_split_debuginfo, fallible_list)?;
-        key!(supported_sanitizers, SanitizerSet)?;
-        key!(generate_arange_section, bool);
-        key!(supports_stack_protector, bool);
-        key!(small_data_threshold_support, SmallDataThresholdSupport)?;
-        key!(entry_name);
-        key!(entry_abi, Conv)?;
-        key!(supports_xray, bool);
-
-        base.update_from_cli();
-        base.check_consistency(TargetKind::Json)?;
-
-        // Each field should have been read using `Json::remove` so any keys remaining are unused.
-        let remaining_keys = obj.keys();
-        Ok((base, TargetWarnings {
-            unused_fields: remaining_keys.cloned().collect(),
-            incorrect_type,
-        }))
-    }
-
     /// Load a built-in target
     pub fn expect_builtin(target_tuple: &TargetTuple) -> Target {
         match *target_tuple {
@@ -3924,177 +3308,6 @@ impl Target {
     }
 }
 
-impl ToJson for Target {
-    fn to_json(&self) -> Json {
-        let mut d = serde_json::Map::new();
-        let default: TargetOptions = Default::default();
-        let mut target = self.clone();
-        target.update_to_cli();
-
-        macro_rules! target_val {
-            ($attr:ident) => {{
-                let name = (stringify!($attr)).replace("_", "-");
-                d.insert(name, target.$attr.to_json());
-            }};
-        }
-
-        macro_rules! target_option_val {
-            ($attr:ident) => {{
-                let name = (stringify!($attr)).replace("_", "-");
-                if default.$attr != target.$attr {
-                    d.insert(name, target.$attr.to_json());
-                }
-            }};
-            ($attr:ident, $json_name:expr) => {{
-                let name = $json_name;
-                if default.$attr != target.$attr {
-                    d.insert(name.into(), target.$attr.to_json());
-                }
-            }};
-            (link_args - $attr:ident, $json_name:expr) => {{
-                let name = $json_name;
-                if default.$attr != target.$attr {
-                    let obj = target
-                        .$attr
-                        .iter()
-                        .map(|(k, v)| (k.desc().to_string(), v.clone()))
-                        .collect::<BTreeMap<_, _>>();
-                    d.insert(name.to_string(), obj.to_json());
-                }
-            }};
-            (env - $attr:ident) => {{
-                let name = (stringify!($attr)).replace("_", "-");
-                if default.$attr != target.$attr {
-                    let obj = target
-                        .$attr
-                        .iter()
-                        .map(|&(ref k, ref v)| format!("{k}={v}"))
-                        .collect::<Vec<_>>();
-                    d.insert(name, obj.to_json());
-                }
-            }};
-        }
-
-        target_val!(llvm_target);
-        target_val!(metadata);
-        d.insert("target-pointer-width".to_string(), self.pointer_width.to_string().to_json());
-        target_val!(arch);
-        target_val!(data_layout);
-
-        target_option_val!(endian, "target-endian");
-        target_option_val!(c_int_width, "target-c-int-width");
-        target_option_val!(os);
-        target_option_val!(env);
-        target_option_val!(abi);
-        target_option_val!(vendor);
-        target_option_val!(linker);
-        target_option_val!(linker_flavor_json, "linker-flavor");
-        target_option_val!(lld_flavor_json, "lld-flavor");
-        target_option_val!(linker_is_gnu_json, "linker-is-gnu");
-        target_option_val!(pre_link_objects);
-        target_option_val!(post_link_objects);
-        target_option_val!(pre_link_objects_self_contained, "pre-link-objects-fallback");
-        target_option_val!(post_link_objects_self_contained, "post-link-objects-fallback");
-        target_option_val!(link_args - pre_link_args_json, "pre-link-args");
-        target_option_val!(link_args - late_link_args_json, "late-link-args");
-        target_option_val!(link_args - late_link_args_dynamic_json, "late-link-args-dynamic");
-        target_option_val!(link_args - late_link_args_static_json, "late-link-args-static");
-        target_option_val!(link_args - post_link_args_json, "post-link-args");
-        target_option_val!(link_script);
-        target_option_val!(env - link_env);
-        target_option_val!(link_env_remove);
-        target_option_val!(asm_args);
-        target_option_val!(cpu);
-        target_option_val!(features);
-        target_option_val!(dynamic_linking);
-        target_option_val!(direct_access_external_data);
-        target_option_val!(dll_tls_export);
-        target_option_val!(only_cdylib);
-        target_option_val!(executables);
-        target_option_val!(relocation_model);
-        target_option_val!(code_model);
-        target_option_val!(tls_model);
-        target_option_val!(disable_redzone);
-        target_option_val!(frame_pointer);
-        target_option_val!(function_sections);
-        target_option_val!(dll_prefix);
-        target_option_val!(dll_suffix);
-        target_option_val!(exe_suffix);
-        target_option_val!(staticlib_prefix);
-        target_option_val!(staticlib_suffix);
-        target_option_val!(families, "target-family");
-        target_option_val!(abi_return_struct_as_int);
-        target_option_val!(is_like_aix);
-        target_option_val!(is_like_osx);
-        target_option_val!(is_like_solaris);
-        target_option_val!(is_like_windows);
-        target_option_val!(is_like_msvc);
-        target_option_val!(is_like_wasm);
-        target_option_val!(is_like_android);
-        target_option_val!(default_dwarf_version);
-        target_option_val!(allows_weak_linkage);
-        target_option_val!(has_rpath);
-        target_option_val!(no_default_libraries);
-        target_option_val!(position_independent_executables);
-        target_option_val!(static_position_independent_executables);
-        target_option_val!(plt_by_default);
-        target_option_val!(relro_level);
-        target_option_val!(archive_format);
-        target_option_val!(allow_asm);
-        target_option_val!(main_needs_argc_argv);
-        target_option_val!(has_thread_local);
-        target_option_val!(obj_is_bitcode);
-        target_option_val!(bitcode_llvm_cmdline);
-        target_option_val!(min_atomic_width);
-        target_option_val!(max_atomic_width);
-        target_option_val!(atomic_cas);
-        target_option_val!(panic_strategy);
-        target_option_val!(crt_static_allows_dylibs);
-        target_option_val!(crt_static_default);
-        target_option_val!(crt_static_respected);
-        target_option_val!(stack_probes);
-        target_option_val!(min_global_align);
-        target_option_val!(default_codegen_units);
-        target_option_val!(trap_unreachable);
-        target_option_val!(requires_lto);
-        target_option_val!(singlethread);
-        target_option_val!(no_builtins);
-        target_option_val!(default_visibility);
-        target_option_val!(emit_debug_gdb_scripts);
-        target_option_val!(requires_uwtable);
-        target_option_val!(default_uwtable);
-        target_option_val!(simd_types_indirect);
-        target_option_val!(limit_rdylib_exports);
-        target_option_val!(override_export_symbols);
-        target_option_val!(merge_functions);
-        target_option_val!(mcount, "target-mcount");
-        target_option_val!(llvm_mcount_intrinsic);
-        target_option_val!(llvm_abiname);
-        target_option_val!(relax_elf_relocations);
-        target_option_val!(llvm_args);
-        target_option_val!(use_ctors_section);
-        target_option_val!(eh_frame_header);
-        target_option_val!(has_thumb_interworking);
-        target_option_val!(debuginfo_kind);
-        target_option_val!(split_debuginfo);
-        target_option_val!(supported_split_debuginfo);
-        target_option_val!(supported_sanitizers);
-        target_option_val!(c_enum_min_bits);
-        target_option_val!(generate_arange_section);
-        target_option_val!(supports_stack_protector);
-        target_option_val!(small_data_threshold_support);
-        target_option_val!(entry_name);
-        target_option_val!(entry_abi);
-        target_option_val!(supports_xray);
-
-        // Serializing `-Clink-self-contained` needs a dynamic key to support the
-        // backwards-compatible variants.
-        d.insert(self.link_self_contained.json_key().into(), self.link_self_contained.to_json());
-
-        Json::Object(d)
-    }
-}
-
 /// Either a target tuple string or a path to a JSON file.
 #[derive(Clone, Debug)]
 pub enum TargetTuple {