[internal] Error when using cgo files (#13172)

Cgo files are `.go` files that use C: https://pkg.go.dev/cmd/cgo. We do not have the infrastructure to support them yet, so we instead want to eagerly redirect users to file a feature request. 

Note that users cannot use other file types like `.h` and `.m` files already because the Sources field bans them. Only cgo files are possible because they end in `.go`.

[ci skip-rust]
[ci skip-build-wheels]

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

@@ -93,7 +93,11 @@ class GoModPackageSourcesField(StringSequenceField, AsyncFieldMixin):
     default = ("**/*.go", "**/*.s")
     help = (
         "What sources to generate `go_first_party_package` targets for.\n\n"
-        "Pants will generate one target per matching directory."
+        "Pants will generate one target per matching directory.\n\n"
+        "Pants does not yet support some file types like `.c` and `.h` files, along with cgo "
+        "files. If you need to use these files, please open a feature request at "
+        "https://github.com/pantsbuild/pants/issues/new/choose so that we know to "
+        "prioritize adding support."
     )
 
     def _prefix_glob_with_address(self, glob: str) -> str:

src/python/pants/backend/go/util_rules/first_party_pkg.py

@@ -86,6 +86,15 @@ async def compute_first_party_package_info(
         ),
     )
     metadata = json.loads(result.stdout)
+
+    if "CgoFiles" in metadata:
+        raise NotImplementedError(
+            f"The first-party package {request.address} includes `CgoFiles`, which Pants does "
+            "not yet support. Please open a feature request at "
+            "https://github.com/pantsbuild/pants/issues/new/choose so that we know to "
+            "prioritize adding support."
+        )
+
     return FirstPartyPkgInfo(
         digest=pkg_sources.snapshot.digest,
         imports=tuple(metadata.get("Imports", [])),

src/python/pants/backend/go/util_rules/first_party_pkg_test.py

@@ -14,7 +14,7 @@
 from pants.engine.addresses import Address
 from pants.engine.fs import PathGlobs, Snapshot
 from pants.engine.rules import QueryRule
-from pants.testutil.rule_runner import RuleRunner
+from pants.testutil.rule_runner import RuleRunner, engine_error
 
 
 @pytest.fixture
@@ -34,7 +34,7 @@ def rule_runner() -> RuleRunner:
     return rule_runner
 
 
-def test_resolve_go_package(rule_runner: RuleRunner) -> None:
+def test_package_info(rule_runner: RuleRunner) -> None:
     rule_runner.write_files(
         {
             "foo/BUILD": "go_mod()\n",
@@ -118,3 +118,39 @@ def assert_info(
         test_files=["bar_test.go"],
         xtest_files=[],
     )
+
+
+def test_cgo_not_supported(rule_runner: RuleRunner) -> None:
+    rule_runner.write_files(
+        {
+            "BUILD": "go_mod(name='mod')\n",
+            "go.mod": dedent(
+                """\
+                module go.example.com/foo
+                go 1.17
+                """
+            ),
+            "hello.go": dedent(
+                """\
+                package main
+
+                // int fortytwo()
+                // {
+                //	    return 42;
+                // }
+                import "C"
+                import "fmt"
+
+                func main() {
+                    f := C.intFunc(C.fortytwo)
+                    fmt.Println(C.intFunc(C.fortytwo))
+                }
+                """
+            ),
+        }
+    )
+    with engine_error(NotImplementedError):
+        rule_runner.request(
+            FirstPartyPkgInfo,
+            [FirstPartyPkgInfoRequest(Address("", target_name="mod", generated_name="./"))],
+        )