[internal] Infer main field for go_binary

src/python/pants/backend/experimental/go/register.py

@@ -2,13 +2,17 @@
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
 from pants.backend.go import target_type_rules
-from pants.backend.go import target_types as go_target_types
 from pants.backend.go.goals import custom_goals, package_binary, tailor
 from pants.backend.go.lint import fmt
 from pants.backend.go.lint.gofmt import skip_field as gofmt_skip_field
 from pants.backend.go.lint.gofmt.rules import rules as gofmt_rules
 from pants.backend.go.subsystems import golang
-from pants.backend.go.target_types import GoBinary, GoExternalPackageTarget, GoModTarget, GoPackage
+from pants.backend.go.target_types import (
+    GoBinaryTarget,
+    GoExternalPackageTarget,
+    GoModTarget,
+    GoPackage,
+)
 from pants.backend.go.util_rules import (
     assembly,
     build_go_pkg,
@@ -24,7 +28,7 @@
 
 
 def target_types():
-    return [GoBinary, GoPackage, GoModTarget, GoExternalPackageTarget]
+    return [GoModTarget, GoPackage, GoExternalPackageTarget, GoBinaryTarget]
 
 
 def rules():
@@ -34,7 +38,6 @@ def rules():
         *compile.rules(),
         *external_module.rules(),
         *golang.rules(),
-        *go_target_types.rules(),
         *import_analysis.rules(),
         *go_mod.rules(),
         *go_pkg.rules(),

src/python/pants/backend/go/goals/package_binary.py

@@ -4,11 +4,14 @@
 from dataclasses import dataclass
 from pathlib import PurePath
 
-from pants.backend.go.target_types import GoBinaryMainAddress
+from pants.backend.go.target_types import (
+    GoBinaryMainPackage,
+    GoBinaryMainPackageField,
+    GoBinaryMainPackageRequest,
+)
 from pants.backend.go.util_rules.build_go_pkg import BuildGoPackageRequest, BuiltGoPackage
 from pants.backend.go.util_rules.import_analysis import ImportConfig, ImportConfigRequest
 from pants.backend.go.util_rules.link import LinkedGoBinary, LinkGoBinaryRequest
-from pants.build_graph.address import Address, AddressInput
 from pants.core.goals.package import (
     BuiltPackage,
     BuiltPackageArtifact,
@@ -23,23 +26,16 @@
 
 @dataclass(frozen=True)
 class GoBinaryFieldSet(PackageFieldSet):
-    required_fields = (GoBinaryMainAddress,)
+    required_fields = (GoBinaryMainPackageField,)
 
-    main_address: GoBinaryMainAddress
+    main: GoBinaryMainPackageField
     output_path: OutputPathField
 
 
 @rule
 async def package_go_binary(field_set: GoBinaryFieldSet) -> BuiltPackage:
-    main_go_package_address = await Get(
-        Address,
-        AddressInput,
-        AddressInput.parse(field_set.main_address.value, relative_to=field_set.address.spec_path),
-    )
-
-    built_package = await Get(
-        BuiltGoPackage, BuildGoPackageRequest(main_go_package_address, is_main=True)
-    )
+    main_pkg = await Get(GoBinaryMainPackage, GoBinaryMainPackageRequest(field_set.main))
+    built_package = await Get(BuiltGoPackage, BuildGoPackageRequest(main_pkg.address, is_main=True))
     main_pkg_path = built_package.import_paths_to_pkg_a_files["main"]
     import_config = await Get(
         ImportConfig, ImportConfigRequest(built_package.import_paths_to_pkg_a_files)

src/python/pants/backend/go/goals/package_binary_integration_test.py

@@ -12,7 +12,7 @@
 from pants.backend.go import target_type_rules
 from pants.backend.go.goals import package_binary
 from pants.backend.go.goals.package_binary import GoBinaryFieldSet
-from pants.backend.go.target_types import GoBinary, GoModTarget, GoPackage
+from pants.backend.go.target_types import GoBinaryTarget, GoModTarget, GoPackage
 from pants.backend.go.util_rules import (
     assembly,
     build_go_pkg,
@@ -50,7 +50,7 @@ def rule_runner() -> RuleRunner:
             *sdk.rules(),
             QueryRule(BuiltPackage, (GoBinaryFieldSet,)),
         ],
-        target_types=[GoBinary, GoPackage, GoModTarget],
+        target_types=[GoBinaryTarget, GoPackage, GoModTarget],
     )
     rule_runner.set_options([], env_inherit={"PATH"})
     return rule_runner
@@ -88,8 +88,8 @@ def test_package_simple(rule_runner: RuleRunner) -> None:
             "BUILD": dedent(
                 """\
                 go_mod(name='mod')
-                go_package(name='main')
-                go_binary(name='bin', main=':main')
+                go_package(name='pkg')
+                go_binary(name='bin')
                 """
             ),
         }
@@ -165,8 +165,8 @@ def test_package_with_dependencies(rule_runner: RuleRunner) -> None:
             "BUILD": dedent(
                 """\
                 go_mod(name='mod')
-                go_package(name='main')
-                go_binary(name='bin', main=':main')
+                go_package(name='pkg')
+                go_binary(name='bin')
                 """
             ),
         }

src/python/pants/backend/go/lint/gofmt/rules_integration_test.py

@@ -10,7 +10,7 @@
 from pants.backend.go.lint import fmt
 from pants.backend.go.lint.gofmt.rules import GofmtFieldSet, GofmtRequest
 from pants.backend.go.lint.gofmt.rules import rules as gofmt_rules
-from pants.backend.go.target_types import GoBinary, GoPackage
+from pants.backend.go.target_types import GoBinaryTarget, GoPackage
 from pants.core.goals.fmt import FmtResult
 from pants.core.goals.lint import LintResult, LintResults
 from pants.core.util_rules import source_files
@@ -24,7 +24,7 @@
 @pytest.fixture()
 def rule_runner() -> RuleRunner:
     return RuleRunner(
-        target_types=[GoBinary, GoPackage],
+        target_types=[GoBinaryTarget, GoPackage],
         rules=[
             *fmt.rules(),
             *gofmt_rules(),

src/python/pants/backend/go/target_type_rules.py

@@ -8,6 +8,10 @@
 from dataclasses import dataclass
 
 from pants.backend.go.target_types import (
+    GoBinaryDependenciesField,
+    GoBinaryMainPackage,
+    GoBinaryMainPackageField,
+    GoBinaryMainPackageRequest,
     GoExternalModulePathField,
     GoExternalModuleVersionField,
     GoExternalPackageDependencies,
@@ -33,22 +37,24 @@
 )
 from pants.backend.go.util_rules.go_pkg import ResolvedGoPackage, ResolveGoPackageRequest
 from pants.backend.go.util_rules.import_analysis import GoStdLibImports
+from pants.base.exceptions import ResolveError
 from pants.base.specs import (
     AddressSpecs,
     DescendantAddresses,
     MaybeEmptyDescendantAddresses,
     MaybeEmptySiblingAddresses,
+    SiblingAddresses,
 )
-from pants.build_graph.address import Address
-from pants.engine.internals.selectors import Get, MultiGet
-from pants.engine.rules import collect_rules, rule
+from pants.engine.addresses import Address, AddressInput
+from pants.engine.rules import Get, MultiGet, collect_rules, rule
 from pants.engine.target import (
     GeneratedTargets,
     GenerateTargetsRequest,
     InferDependenciesRequest,
     InferredDependencies,
     InjectDependenciesRequest,
     InjectedDependencies,
+    InvalidFieldException,
     Targets,
     WrappedTarget,
 )
@@ -285,6 +291,69 @@ def create_tgt(
     )
 
 
+# -----------------------------------------------------------------------------------------------
+# The `main` field for `go_binary`
+# -----------------------------------------------------------------------------------------------
+
+
+@rule
+async def determine_main_pkg_for_go_binary(
+    request: GoBinaryMainPackageRequest,
+) -> GoBinaryMainPackage:
+    addr = request.field.address
+    if request.field.value:
+        wrapped_specified_tgt = await Get(
+            WrappedTarget,
+            AddressInput,
+            AddressInput.parse(request.field.value, relative_to=addr.spec_path),
+        )
+        if not wrapped_specified_tgt.target.has_field(GoPackageSources):
+            raise InvalidFieldException(
+                f"The {repr(GoBinaryMainPackageField.alias)} field in target {addr} must point to "
+                "a `go_package` target, but was the address for a "
+                f"`{wrapped_specified_tgt.target.alias}` target.\n\n"
+                "Hint: consider leaving off this field so that Pants will find the `go_package` "
+                "target for you."
+            )
+        return GoBinaryMainPackage(wrapped_specified_tgt.target.address)
+
+    build_dir_targets = await Get(Targets, AddressSpecs([SiblingAddresses(addr.spec_path)]))
+    internal_pkg_targets = [tgt for tgt in build_dir_targets if tgt.has_field(GoPackageSources)]
+    if len(internal_pkg_targets) == 1:
+        return GoBinaryMainPackage(internal_pkg_targets[0].address)
+
+    wrapped_tgt = await Get(WrappedTarget, Address, addr)
+    alias = wrapped_tgt.target.alias
+    if not internal_pkg_targets:
+        raise ResolveError(
+            f"The `{alias}` target {addr} requires that there is a `go_package` "
+            "target in the same directory, but none were found."
+        )
+    raise ResolveError(
+        f"There are multiple `go_package` targets in the same directory of the `{alias}` "
+        f"target {addr}, so it is ambiguous what to use as the `main` package.\n\n"
+        f"To fix, please either set the `main` field for `{addr} or remove these "
+        "`go_package` targets so that only one remains: "
+        f"{sorted(tgt.address.spec for tgt in internal_pkg_targets)}"
+    )
+
+
+class InjectGoBinaryMainDependencyRequest(InjectDependenciesRequest):
+    inject_for = GoBinaryDependenciesField
+
+
+@rule
+async def inject_go_binary_main_dependency(
+    request: InjectGoBinaryMainDependencyRequest,
+) -> InjectedDependencies:
+    wrapped_tgt = await Get(WrappedTarget, Address, request.dependencies_field.address)
+    main_pkg = await Get(
+        GoBinaryMainPackage,
+        GoBinaryMainPackageRequest(wrapped_tgt.target[GoBinaryMainPackageField]),
+    )
+    return InjectedDependencies([main_pkg.address])
+
+
 def rules():
     return (
         *collect_rules(),
@@ -293,5 +362,6 @@ def rules():
         UnionRule(InjectDependenciesRequest, InjectGoPackageDependenciesRequest),
         UnionRule(InferDependenciesRequest, InferGoPackageDependenciesRequest),
         UnionRule(InjectDependenciesRequest, InjectGoExternalPackageDependenciesRequest),
+        UnionRule(InjectDependenciesRequest, InjectGoBinaryMainDependencyRequest),
         UnionRule(GenerateTargetsRequest, GenerateGoExternalPackageTargetsRequest),
     )