Rollup of 6 pull requests

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -368,7 +368,7 @@ fn check_opaque_type_well_formed<'tcx>(
     if errors.is_empty() {
         Ok(definition_ty)
     } else {
-        Err(infcx.err_ctxt().report_fulfillment_errors(&errors))
+        Err(infcx.err_ctxt().report_fulfillment_errors(errors))
     }
 }
 

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -743,7 +743,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
                 let errors = ocx.select_all_or_error();
                 if !errors.is_empty() {
-                    infcx.err_ctxt().report_fulfillment_errors(&errors);
+                    infcx.err_ctxt().report_fulfillment_errors(errors);
                 }
 
                 // Attempting to call a trait method?

compiler/rustc_error_codes/src/error_codes/E0282.md

@@ -3,29 +3,32 @@ The compiler could not infer a type and asked for a type annotation.
 Erroneous code example:
 
 ```compile_fail,E0282
-let x = "hello".chars().rev().collect();
+let x = Vec::new();
 ```
 
 This error indicates that type inference did not result in one unique possible
 type, and extra information is required. In most cases this can be provided
 by adding a type annotation. Sometimes you need to specify a generic type
 parameter manually.
 
-A common example is the `collect` method on `Iterator`. It has a generic type
-parameter with a `FromIterator` bound, which for a `char` iterator is
-implemented by `Vec` and `String` among others. Consider the following snippet
-that reverses the characters of a string:
+In the example above, type `Vec` has a type parameter `T`. When calling
+`Vec::new`, barring any other later usage of the variable `x` that allows the
+compiler to infer what type `T` is, the compiler needs to be told what it is.
 
-In the first code example, the compiler cannot infer what the type of `x` should
-be: `Vec<char>` and `String` are both suitable candidates. To specify which type
-to use, you can use a type annotation on `x`:
+The type can be specified on the variable:
 
 ```
-let x: Vec<char> = "hello".chars().rev().collect();
+let x: Vec<i32> = Vec::new();
 ```
 
-It is not necessary to annotate the full type. Once the ambiguity is resolved,
-the compiler can infer the rest:
+The type can also be specified in the path of the expression:
+
+```
+let x = Vec::<i32>::new();
+```
+
+In cases with more complex types, it is not necessary to annotate the full
+type. Once the ambiguity is resolved, the compiler can infer the rest:
 
 ```
 let x: Vec<_> = "hello".chars().rev().collect();

compiler/rustc_error_codes/src/error_codes/E0283.md

@@ -1,7 +1,51 @@
-An implementation cannot be chosen unambiguously because of lack of information.
+The compiler could not infer a type and asked for a type annotation.
 
 Erroneous code example:
 
+```compile_fail,E0283
+let x = "hello".chars().rev().collect();
+```
+
+This error indicates that type inference did not result in one unique possible
+type, and extra information is required. In most cases this can be provided
+by adding a type annotation. Sometimes you need to specify a generic type
+parameter manually.
+
+A common example is the `collect` method on `Iterator`. It has a generic type
+parameter with a `FromIterator` bound, which for a `char` iterator is
+implemented by `Vec` and `String` among others. Consider the following snippet
+that reverses the characters of a string:
+
+In the first code example, the compiler cannot infer what the type of `x` should
+be: `Vec<char>` and `String` are both suitable candidates. To specify which type
+to use, you can use a type annotation on `x`:
+
+```
+let x: Vec<char> = "hello".chars().rev().collect();
+```
+
+It is not necessary to annotate the full type. Once the ambiguity is resolved,
+the compiler can infer the rest:
+
+```
+let x: Vec<_> = "hello".chars().rev().collect();
+```
+
+Another way to provide the compiler with enough information, is to specify the
+generic type parameter:
+
+```
+let x = "hello".chars().rev().collect::<Vec<char>>();
+```
+
+Again, you need not specify the full type if the compiler can infer it:
+
+```
+let x = "hello".chars().rev().collect::<Vec<_>>();
+```
+
+We can see a self-contained example below:
+
 ```compile_fail,E0283
 struct Foo;
 

compiler/rustc_errors/src/lib.rs

@@ -1376,16 +1376,16 @@ impl HandlerInner {
                 self.emitted_diagnostic_codes.insert(code.clone());
             }
 
-            let already_emitted = |this: &mut Self| {
+            let already_emitted = {
                 let mut hasher = StableHasher::new();
                 diagnostic.hash(&mut hasher);
                 let diagnostic_hash = hasher.finish();
-                !this.emitted_diagnostics.insert(diagnostic_hash)
+                !self.emitted_diagnostics.insert(diagnostic_hash)
             };
 
             // Only emit the diagnostic if we've been asked to deduplicate or
             // haven't already emitted an equivalent diagnostic.
-            if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
+            if !(self.flags.deduplicate_diagnostics && already_emitted) {
                 debug!(?diagnostic);
                 debug!(?self.emitted_diagnostics);
                 let already_emitted_sub = |sub: &mut SubDiagnostic| {
@@ -1401,6 +1401,11 @@ impl HandlerInner {
                 };
 
                 diagnostic.children.extract_if(already_emitted_sub).for_each(|_| {});
+                if already_emitted {
+                    diagnostic.note(
+                        "duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`",
+                    );
+                }
 
                 self.emitter.emit_diagnostic(diagnostic);
                 if diagnostic.is_error() {

compiler/rustc_hir_analysis/src/check/check.rs

@@ -327,7 +327,7 @@ fn check_opaque_meets_bounds<'tcx>(
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        let guar = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let guar = infcx.err_ctxt().report_fulfillment_errors(errors);
         return Err(guar);
     }
     match origin {
@@ -1512,6 +1512,6 @@ pub(super) fn check_generator_obligations(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     let errors = fulfillment_cx.select_all_or_error(&infcx);
     debug!(?errors);
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        infcx.err_ctxt().report_fulfillment_errors(errors);
     }
 }

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -323,7 +323,7 @@ fn compare_method_predicate_entailment<'tcx>(
         // FIXME(-Ztrait-solver=next): Not needed when the hack below is removed.
         let errors = ocx.select_where_possible();
         if !errors.is_empty() {
-            let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
+            let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
             return Err(reported);
         }
 
@@ -394,7 +394,7 @@ fn compare_method_predicate_entailment<'tcx>(
                 });
             }
             CheckImpliedWfMode::Skip => {
-                let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
+                let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
                 return Err(reported);
             }
         }
@@ -874,7 +874,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     // RPITs.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
         return Err(reported);
     }
 
@@ -2050,7 +2050,7 @@ fn compare_const_predicate_entailment<'tcx>(
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        return Err(infcx.err_ctxt().report_fulfillment_errors(&errors));
+        return Err(infcx.err_ctxt().report_fulfillment_errors(errors));
     }
 
     let outlives_env = OutlivesEnvironment::new(param_env);
@@ -2143,7 +2143,7 @@ fn compare_type_predicate_entailment<'tcx>(
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
         return Err(reported);
     }
 
@@ -2358,7 +2358,7 @@ pub(super) fn check_type_bounds<'tcx>(
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
         return Err(reported);
     }
 

compiler/rustc_hir_analysis/src/check/entry.rs

@@ -158,7 +158,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         ocx.register_bound(cause, param_env, norm_return_ty, term_did);
         let errors = ocx.select_all_or_error();
         if !errors.is_empty() {
-            infcx.err_ctxt().report_fulfillment_errors(&errors);
+            infcx.err_ctxt().report_fulfillment_errors(errors);
             error = true;
         }
         // now we can take the return type of the given main function

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -588,7 +588,7 @@ pub fn check_function_signature<'tcx>(
         Ok(()) => {
             let errors = ocx.select_all_or_error();
             if !errors.is_empty() {
-                infcx.err_ctxt().report_fulfillment_errors(&errors);
+                infcx.err_ctxt().report_fulfillment_errors(errors);
                 return;
             }
         }

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -116,7 +116,7 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
 
     let errors = wfcx.select_all_or_error();
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        infcx.err_ctxt().report_fulfillment_errors(errors);
         return;
     }
 

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -261,7 +261,7 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                 }
                 let errors = ocx.select_all_or_error();
                 if !errors.is_empty() {
-                    infcx.err_ctxt().report_fulfillment_errors(&errors);
+                    infcx.err_ctxt().report_fulfillment_errors(errors);
                 }
 
                 // Finally, resolve all regions.
@@ -470,7 +470,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
     ocx.register_obligation(obligation);
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        infcx.err_ctxt().report_fulfillment_errors(errors);
     }
 
     // Finally, resolve all regions.

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -196,7 +196,7 @@ fn get_impl_args(
 
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        let guar = ocx.infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let guar = ocx.infcx.err_ctxt().report_fulfillment_errors(errors);
         return Err(guar);
     }
 

compiler/rustc_hir_typeck/src/expr.rs

@@ -2958,7 +2958,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // There should be at least one error reported. If not, we
             // will still delay a span bug in `report_fulfillment_errors`.
             Ok::<_, NoSolution>((
-                self.err_ctxt().report_fulfillment_errors(&errors),
+                self.err_ctxt().report_fulfillment_errors(errors),
                 impl_trait_ref.args.type_at(1),
                 element_ty,
             ))

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -564,7 +564,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         if !errors.is_empty() {
             self.adjust_fulfillment_errors_for_expr_obligation(&mut errors);
-            self.err_ctxt().report_fulfillment_errors(&errors);
+            self.err_ctxt().report_fulfillment_errors(errors);
         }
     }
 
@@ -577,7 +577,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if !result.is_empty() {
             mutate_fulfillment_errors(&mut result);
             self.adjust_fulfillment_errors_for_expr_obligation(&mut result);
-            self.err_ctxt().report_fulfillment_errors(&result);
+            self.err_ctxt().report_fulfillment_errors(result);
         }
     }
 
@@ -1477,7 +1477,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             {
                 Ok(normalized_ty) => normalized_ty,
                 Err(errors) => {
-                    let guar = self.err_ctxt().report_fulfillment_errors(&errors);
+                    let guar = self.err_ctxt().report_fulfillment_errors(errors);
                     return Ty::new_error(self.tcx,guar);
                 }
             }

compiler/rustc_hir_typeck/src/lib.rs

@@ -5,7 +5,6 @@
 #![feature(box_patterns)]
 #![feature(min_specialization)]
 #![feature(control_flow_enum)]
-#![feature(option_as_slice)]
 #![recursion_limit = "256"]
 
 #[macro_use]

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -27,7 +27,7 @@ use std::iter;
 
 pub enum TypeAnnotationNeeded {
     /// ```compile_fail,E0282
-    /// let x = "hello".chars().rev().collect();
+    /// let x;
     /// ```
     E0282,
     /// An implementation cannot be chosen unambiguously because of lack of information.

compiler/rustc_mir_transform/src/add_subtyping_projections.rs

@@ -24,6 +24,11 @@ impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeChecker<'a, 'tcx> {
         rvalue: &mut Rvalue<'tcx>,
         location: Location,
     ) {
+        // We don't need to do anything for deref temps as they are
+        // not part of the source code, but used for desugaring purposes.
+        if self.local_decls[place.local].is_deref_temp() {
+            return;
+        }
         let mut place_ty = place.ty(self.local_decls, self.tcx).ty;
         let mut rval_ty = rvalue.ty(self.local_decls, self.tcx);
         // Not erasing this causes `Free Regions` errors in validator,
@@ -48,7 +53,6 @@ impl<'a, 'tcx> MutVisitor<'tcx> for SubTypeChecker<'a, 'tcx> {
 // // gets transformed to
 // let temp: rval_ty = rval;
 // let place: place_ty = temp as place_ty;
-//
 pub fn subtype_finder<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let patch = MirPatch::new(body);
     let mut checker = SubTypeChecker { tcx, patcher: patch, local_decls: &body.local_decls };

compiler/rustc_mir_transform/src/lib.rs

@@ -467,7 +467,6 @@ pub fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let passes: &[&dyn MirPass<'tcx>] = &[
-        &add_subtyping_projections::Subtyper,
         &cleanup_post_borrowck::CleanupPostBorrowck,
         &remove_noop_landing_pads::RemoveNoopLandingPads,
         &simplify::SimplifyCfg::EarlyOpt,
@@ -483,6 +482,7 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         // These next passes must be executed together
         &add_call_guards::CriticalCallEdges,
         &reveal_all::RevealAll, // has to be done before drop elaboration, since we need to drop opaque types, too.
+        &add_subtyping_projections::Subtyper, // calling this after reveal_all ensures that we don't deal with opaque types
         &elaborate_drops::ElaborateDrops,
         // This will remove extraneous landing pads which are no longer
         // necessary as well as well as forcing any call in a non-unwinding

compiler/rustc_mir_transform/src/reveal_all.rs

@@ -46,16 +46,18 @@ impl<'tcx> MutVisitor<'tcx> for RevealAllVisitor<'tcx> {
                 .filter(|elem| !matches!(elem, ProjectionElem::OpaqueCast(_)))
                 .collect::<Vec<_>>(),
         );
+        self.super_place(place, _context, _location);
     }
 
     #[inline]
-    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, _: Location) {
+    fn visit_constant(&mut self, constant: &mut ConstOperand<'tcx>, location: Location) {
         // We have to use `try_normalize_erasing_regions` here, since it's
         // possible that we visit impossible-to-satisfy where clauses here,
         // see #91745
         if let Ok(c) = self.tcx.try_normalize_erasing_regions(self.param_env, constant.const_) {
             constant.const_ = c;
         }
+        self.super_constant(constant, location);
     }
 
     #[inline]

compiler/rustc_passes/src/check_attr.rs

@@ -2373,7 +2373,7 @@ impl CheckAttrVisitor<'_> {
 
         let errors = ocx.select_all_or_error();
         if !errors.is_empty() {
-            infcx.err_ctxt().report_fulfillment_errors(&errors);
+            infcx.err_ctxt().report_fulfillment_errors(errors);
             self.abort.set(true);
         }
     }

compiler/rustc_passes/src/layout_test.rs

@@ -57,7 +57,7 @@ pub fn ensure_wf<'tcx>(
     ocx.register_obligation(obligation);
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        infcx.err_ctxt().report_fulfillment_errors(errors);
         false
     } else {
         // looks WF!