Incorrect proto_library deps when strip_import_prefix, --index=false and mode=file

[nchepanov]

What version of gazelle are you using?

Latest, v.0.39.0

What version of rules_go are you using? / What version of Bazel are you using? / Does this issue reproduce with the latest releases of all the above?

N.A.

What operating system and processor architecture are you using?

Darwin nchepanov-mac 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:30 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6000 arm64 MacOS 14.6.1

What did you do?

Reproducer https://github.com/nchepanov/gazelle-strip-import-prefix-index-off/

In our repository all protos live in a special directory within the monorepo. For historical reasons they reference each other relative to the directory, not the repository root. We are trying to speed up gazelle by using --index=false but it seems to break the proto_strip_import_prefix directive rewriting of the imports during language/proto/resolve.go:resolveProto()

In essence, --index=false + strip_import_prefix results in dropping the //prefix in deps that was there with indexing on

diff --git a/prefix/foo/BUILD.bazel b/prefix/foo/BUILD.bazel
index fab6b89..037722e 100644
--- a/prefix/foo/BUILD.bazel
+++ b/prefix/foo/BUILD.bazel
@@ -5,5 +5,5 @@ proto_library(
    srcs = ["foo.proto"],
    strip_import_prefix = "/prefix",
    visibility = ["//visibility:public"],
-    deps = ["//prefix/moo:moo_proto"],
+    deps = ["//moo:moo_proto"],
)

What did you expect to see?

The strip_import_prefix attribute is generated in both situations, so the root BUILD.bazel file was read with or without indexing. The deps attribute should be the same in both cases.

[nchepanov]

UPD: In a general case, such mapping is impossible without indexing, however in our case with mode=file, index=false, strip_import_prefix=set the tail end of the resolveProto() function can actually use this knowledge to map import to deps without index: https://github.com/bazelbuild/bazel-gazelle/blob/d16fc424cfcfdbd8893a267e500ec5d04ec0bbf0/language/proto/resolve.go#L145-L152

The following work in progress PR (please ignore changes to resolve.go) nchepanov#1 contains a fully functional test that fails as expected, showcasing the unsupported edge-case.

For now, I don't have more time to dig more into this, I ended up solving this in our custom language by using CrossResolve that was introduced in #771 to support a very similar use-case: full indexing is too slow.

For reference, a super simple CrossResolve impelmentation ended up looking like this

func (l *customLang) CrossResolve(c *config.Config, ix *resolve.RuleIndex, imp resolve.ImportSpec, lang string) []resolve.FindResult {
	if lang == "proto" && imp.Lang == "proto" {
		rel := path.Dir(imp.Imp)
		if rel == "." {
			rel = ""
		}
		filename := strings.TrimSuffix(path.Base(imp.Imp), ".proto")
		return []resolve.FindResult{
			{Label: label.New("", path.Join("prefix", rel), proto.RuleName(filename))},
		}
	}
	return nil
}