gopls/internal/lsp: support more cases of definition on linkname directive.

Handle the case where //go:linkname localname importpath.name
is used in a package with no transitive dependency, forwards or
reverse, to importpath.

Updates golang/go#57312

Change-Id: I0033b166558275931a371a967caa6044a1b089f3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/469695
Run-TryBot: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

2 files changed, 51 insertions, 41 deletions

diff --git a/gopls/internal/lsp/source/linkname.go b/gopls/internal/lsp/source/linkname.go
index 4fb667e68..9017d14ea 100644
--- a/gopls/internal/lsp/source/linkname.go
+++ b/gopls/internal/lsp/source/linkname.go
@@ -92,31 +92,23 @@ func findLinknameOnLine(pgf *ParsedGoFile, line int) (string, int) {
 // findLinkname searches dependencies of packages containing fh for an object
 // with linker name matching the given package path and name.
 func findLinkname(ctx context.Context, snapshot Snapshot, fh FileHandle, pos protocol.Position, pkgPath PackagePath, name string) ([]protocol.Location, error) {
-	metas, err := snapshot.MetadataForFile(ctx, fh.URI())
+	// Typically the linkname refers to a forward dependency
+	// or a reverse dependency, but in general it may refer
+	// to any package in the workspace.
+	var pkgMeta *Metadata
+	metas, err := snapshot.AllMetadata(ctx)
 	if err != nil {
 		return nil, err
 	}
-	if len(metas) == 0 {
-		return nil, fmt.Errorf("no package found for file %q", fh.URI())
+	metas = RemoveIntermediateTestVariants(metas)
+	for _, meta := range metas {
+		if meta.PkgPath == pkgPath {
+			pkgMeta = meta
+			break
+		}
 	}
-
-	// Find package starting from narrowest package metadata.
-	pkgMeta := findPackageInDeps(snapshot, metas[0], pkgPath)
 	if pkgMeta == nil {
-		// Fall back to searching reverse dependencies.
-		reverse, err := snapshot.ReverseDependencies(ctx, metas[0].ID, true /* transitive */)
-		if err != nil {
-			return nil, err
-		}
-		for _, dep := range reverse {
-			if dep.PkgPath == pkgPath {
-				pkgMeta = dep
-				break
-			}
-		}
-		if pkgMeta == nil {
-			return nil, fmt.Errorf("cannot find package %q", pkgPath)
-		}
+		return nil, fmt.Errorf("cannot find package %q", pkgPath)
 	}
 
 	// When found, type check the desired package (snapshot.TypeCheck in TypecheckFull mode),
@@ -142,24 +134,3 @@ func findLinkname(ctx context.Context, snapshot Snapshot, fh FileHandle, pos pro
 	}
 	return []protocol.Location{loc}, nil
 }
-
-// findPackageInDeps returns the dependency of meta of the specified package path, if any.
-func findPackageInDeps(snapshot Snapshot, meta *Metadata, pkgPath PackagePath) *Metadata {
-	seen := make(map[*Metadata]bool)
-	var visit func(*Metadata) *Metadata
-	visit = func(meta *Metadata) *Metadata {
-		if !seen[meta] {
-			seen[meta] = true
-			if meta.PkgPath == pkgPath {
-				return meta
-			}
-			for _, id := range meta.DepsByPkgPath {
-				if m := visit(snapshot.Metadata(id)); m != nil {
-					return m
-				}
-			}
-		}
-		return nil
-	}
-	return visit(meta)
-}
diff --git a/gopls/internal/regtest/misc/definition_test.go b/gopls/internal/regtest/misc/definition_test.go
index 7767ac5aa..c2dd67fc3 100644
--- a/gopls/internal/regtest/misc/definition_test.go
+++ b/gopls/internal/regtest/misc/definition_test.go
@@ -147,6 +147,45 @@ func TestGoToLinknameDefinitionInReverseDep(t *testing.T) {
 	})
 }
 
+// The linkname directive connects two packages not related in the import graph.
+const linknameDefinitionDisconnected = `
+-- go.mod --
+module mod.com
+
+-- a/a.go --
+package a
+
+import (
+	_ "unsafe"
+)
+
+//go:linkname foo mod.com/b.bar
+func foo() string
+
+-- b/b.go --
+package b
+
+func bar() string {
+	return "bar as foo"
+}`
+
+func TestGoToLinknameDefinitionDisconnected(t *testing.T) {
+	Run(t, linknameDefinitionDisconnected, func(t *testing.T, env *Env) {
+		env.OpenFile("a/a.go")
+
+		// Jump from directives 2nd arg.
+		start := env.RegexpSearch("a/a.go", `b.bar`)
+		loc := env.GoToDefinition(start)
+		name := env.Sandbox.Workdir.URIToPath(loc.URI)
+		if want := "b/b.go"; name != want {
+			t.Errorf("GoToDefinition: got file %q, want %q", name, want)
+		}
+		if want := env.RegexpSearch("b/b.go", `bar`); loc != want {
+			t.Errorf("GoToDefinition: got position %v, want %v", loc, want)
+		}
+	})
+}
+
 const stdlibDefinition = `
 -- go.mod --
 module mod.com