go: add go_module and go_external_module targets

[tdyas]

• Add go_module target which represents a first-party Go module.
• Add go_external_module target which is a third-party Go module.
• Add a rule to infer a dependency between a go_package and the nearest sibling or ancestor go_module.

Note: This PR does not include a dependency inference rule to infer the external modules listed in a go.mod file as dependencies of the applicable go_module. That will be done in a follow-up.

[ci skip-rust]

[ci skip-build-wheels]

[tdyas]

diff --git a/src/python/pants/backend/go/target_type_rules.py b/src/python/pants/backend/go/target_type_rules.py
index f22448740..9ba4b7a05 100644
--- a/src/python/pants/backend/go/target_type_rules.py
+++ b/src/python/pants/backend/go/target_type_rules.py
@@ -1,6 +1,6 @@
 # Copyright 2021 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
-from pants.backend.go.target_types import GoModuleGoVersion, GoPackageDependencies
+from pants.backend.go.target_types import GoModuleSources, GoPackageDependencies
 from pants.base.specs import AddressSpecs, AscendantAddresses, SiblingAddresses
 from pants.build_graph.address import Address
 from pants.engine.internals.selectors import Get
@@ -25,12 +25,13 @@ async def inject_go_module_dependency(request: InjectGoModuleDependency) -> Inje
     candidate_targets = await Get(
         Targets, AddressSpecs([AscendantAddresses(spec_path), SiblingAddresses(spec_path)])
     )
+    print(f"candidate_targets={candidate_targets}")
     go_module_targets = [
-        (tgt.address.spec_path, tgt)
-        for tgt in candidate_targets
-        if tgt.has_field(GoModuleGoVersion)
+        (tgt.address.spec_path, tgt) for tgt in candidate_targets if tgt.has_field(GoModuleSources) and not tgt.address.is_file_target
     ]
+    print(f"go_module_targets={go_module_targets}")
     sorted_go_module_targets = sorted(go_module_targets, key=lambda x: x[0], reverse=True)
+    print(f"sorted_go_module_targets={sorted_go_module_targets}")
     if sorted_go_module_targets:
         nearest_go_module_target = sorted_go_module_targets[0][1]
         return InjectedDependencies([nearest_go_module_target.address])
diff --git a/src/python/pants/backend/go/target_type_rules_test.py b/src/python/pants/backend/go/target_type_rules_test.py
index 9b2a03e21..265da7396 100644
--- a/src/python/pants/backend/go/target_type_rules_test.py
+++ b/src/python/pants/backend/go/target_type_rules_test.py
@@ -3,7 +3,7 @@
 import pytest
 
 from pants.backend.go import target_type_rules
-from pants.backend.go.target_types import GoModule, GoModuleGoVersion, GoPackage
+from pants.backend.go.target_types import GoModule, GoModuleSources, GoPackage
 from pants.build_graph.address import Address
 from pants.engine.addresses import Addresses
 from pants.engine.rules import QueryRule
@@ -25,7 +25,7 @@ def rule_runner() -> RuleRunner:
 def assert_go_module_address(rule_runner: RuleRunner, target: Target, expected_address: Address):
     addresses = rule_runner.request(Addresses, [DependenciesRequest(target[Dependencies])])
     targets = rule_runner.request(Targets, [addresses])
-    go_module_targets = [tgt for tgt in targets if tgt.has_field(GoModuleGoVersion)]
+    go_module_targets = [tgt for tgt in targets if tgt.has_field(GoModuleSources)]
     assert len(go_module_targets) == 1
     assert go_module_targets[0].address == expected_address
 
diff --git a/src/python/pants/backend/go/target_types.py b/src/python/pants/backend/go/target_types.py
index df16b9f6f..f94152979 100644
--- a/src/python/pants/backend/go/target_types.py
+++ b/src/python/pants/backend/go/target_types.py
@@ -31,33 +31,8 @@ class GoPackage(Target):
 # `go_module` target
 
 
-class GoModuleGoVersion(StringField):
-    alias = "go_version"
-    # TODO: Set default to match the active `GoLangDisribution`.
-    default = "1.16"
-
-
-# class GoModuleGoModSource(Sources):
-#     alias = "gomod"
-#     default = ["go.mod"]
-#     # TODO: This does not handle a missing go.mod file.
-#     expected_num_files = 1
-#
-#
-# class GoModuleGoSumSource(Sources):
-#     alias = "gosum"
-#     default = ["go.sum"]
-#     # TODO: This does not handle a missing go.sum file.
-#     expected_num_files = 1
-#     help = "The source file containing the go.sum file."
-#
-#
-# class GoModuleImportPathReplacements(StringSequenceField):
-#     alias = "replacements"
-#     help = (
-#         "Import path replacements where each item is in the form ORIGINAL,REPLACEMENT. "
-#         "This will be inferred from the go.mod file."
-#     )
+class GoModuleSources(Sources):
+    default = ("go.mod", "go.sum")
 
 
 class GoModule(Target):
@@ -65,10 +40,7 @@ class GoModule(Target):
     core_fields = (
         *COMMON_TARGET_FIELDS,
         Dependencies,
-        GoModuleGoVersion,
-        GoImportPath,
-        # GoModuleGoModSource,
-        # GoModuleGoSumSource,
+        GoModuleSources,
     )
 

I tried the above diff to add a Sources field to go_module but now I get a GoModule target per go.mod and go.sum file instead of a single GoModule target. How do I get a single GoModule target again?

[tdyas]

I switched to requesting UnexpandedTargets in the rule. This seemed to prevent the file target expansion.

[Eric-Arellano]

Thanks!

[Eric-Arellano]

Simpler is probably to not store a tuple in the above collection, and sort by lambda tgt: tgt.address.spec_path. That should simplify a couple lines in this rule

[Eric-Arellano]

Consider using this style:

pants/src/python/pants/engine/internals/graph.py

Lines 89 to 91 in e01e353

	# -----------------------------------------------------------------------------------------------
	# Address -> Target(s)
	# -----------------------------------------------------------------------------------------------

[tdyas]

There are no rules in this file. This comment style doesn't make sense for just the target type definitions. It would make sense for the files with rules in them.

[Eric-Arellano]

We use it for python/target_types.py too:

pants/src/python/pants/backend/python/target_types.py

Lines 85 to 87 in e392457

	# -----------------------------------------------------------------------------------------------
	# `pex_binary` target
	# -----------------------------------------------------------------------------------------------

The general idea is to have section headers that more clearly delineate the file, sort of like chapters in a book.

[tdyas]

Ah, I had thought you were referring to the Foo -> Bar notation and not the dashes. Yeah the dashes would be relevant to the comments here.