gopls/internal/cache: prune broken edges to command-line-arguments pkgs

Fix two bugs discovered during the investigation of golang/go#66109,
which revealed the strange and broken intermediate test variant form
"path/to/command/package [command-line-arguments.test]", referenced from
the equally broken
"command-line-arguments [command-line-arguments.test]". This latter
package was *also* detected as an ITV, which is why we never tried to
type check it in gopls@v0.14.2.

- Snapshot.orphanedFileDiagnostics was not pruning intermediate test
  variants, causing it to be the one place where we were now type
  checking ITVs.
- Fix the latent bug that caused gopls to record a dangling edge between
  the two ITVs.

There is a third bug in go/packages, filed as golang/go#66126.

Fixes golang/go#66109

Change-Id: Ie5795b6d5a4831bf2f73217c8eb22c6ba18e59cd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/569035
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

gopls/internal/cache/load.go

@@ -336,7 +336,11 @@ func (m *moduleErrorMap) Error() string {
 // buildMetadata populates the updates map with metadata updates to
 // apply, based on the given pkg. It recurs through pkg.Imports to ensure that
 // metadata exists for all dependencies.
-func buildMetadata(updates map[PackageID]*metadata.Package, pkg *packages.Package, loadDir string, standalone bool) {
+//
+// Returns the metadata.Package that was built (or which was already present in
+// updates), or nil if the package could not be built. Notably, the resulting
+// metadata.Package may have an ID that differs from pkg.ID.
+func buildMetadata(updates map[PackageID]*metadata.Package, pkg *packages.Package, loadDir string, standalone bool) *metadata.Package {
 	// Allow for multiple ad-hoc packages in the workspace (see #47584).
 	pkgPath := PackagePath(pkg.PkgPath)
 	id := PackageID(pkg.ID)
@@ -351,27 +355,27 @@ func buildMetadata(updates map[PackageID]*metadata.Package, pkg *packages.Packag
 			// (Can this happen? #64557)
 			if len(pkg.CompiledGoFiles) > 1 {
 				bug.Reportf("unexpected files in command-line-arguments package: %v", pkg.CompiledGoFiles)
-				return
+				return nil
 			}
 		} else if len(pkg.IgnoredFiles) > 0 {
 			// A file=empty.go query results in IgnoredFiles=[empty.go].
 			f = pkg.IgnoredFiles[0]
 		} else {
 			bug.Reportf("command-line-arguments package has neither CompiledGoFiles nor IgnoredFiles: %#v", "") //*pkg.Metadata)
-			return
+			return nil
 		}
 		id = PackageID(pkg.ID + f)
 		pkgPath = PackagePath(pkg.PkgPath + f)
 	}
 
 	// Duplicate?
-	if _, ok := updates[id]; ok {
+	if existing, ok := updates[id]; ok {
 		// A package was encountered twice due to shared
 		// subgraphs (common) or cycles (rare). Although "go
 		// list" usually breaks cycles, we don't rely on it.
 		// breakImportCycles in metadataGraph.Clone takes care
 		// of it later.
-		return
+		return existing
 	}
 
 	if pkg.TypesSizes == nil {
@@ -492,15 +496,21 @@ func buildMetadata(updates map[PackageID]*metadata.Package, pkg *packages.Packag
 			continue
 		}
 
-		buildMetadata(updates, imported, loadDir, false) // only top level packages can be standalone
+		dep := buildMetadata(updates, imported, loadDir, false) // only top level packages can be standalone
 
 		// Don't record edges to packages with no name, as they cause trouble for
 		// the importer (golang/go#60952).
 		//
+		// Also don't record edges to packages whose ID was modified (i.e.
+		// command-line-arguments packages), as encountered in golang/go#66109. In
+		// this case, we could theoretically keep the edge through dep.ID, but
+		// since this import doesn't make any sense in the first place, we instead
+		// choose to consider it invalid.
+		//
 		// However, we do want to insert these packages into the update map
 		// (buildMetadata above), so that we get type-checking diagnostics for the
 		// invalid packages.
-		if imported.Name == "" {
+		if dep == nil || dep.ID != PackageID(imported.ID) || imported.Name == "" {
 			depsByImpPath[importPath] = "" // missing
 			continue
 		}
@@ -510,6 +520,7 @@ func buildMetadata(updates map[PackageID]*metadata.Package, pkg *packages.Packag
 	}
 	mp.DepsByImpPath = depsByImpPath
 	mp.DepsByPkgPath = depsByPkgPath
+	return mp
 
 	// m.Diagnostics is set later in the loading pass, using
 	// computeLoadDiagnostics.

gopls/internal/cache/snapshot.go

@@ -1441,6 +1441,8 @@ searchOverlays:
 				continue searchOverlays
 			}
 		}
+		metadata.RemoveIntermediateTestVariants(&mps)
+
 		// With zero-config gopls (golang/go#57979), orphaned file diagnostics
 		// include diagnostics for orphaned files -- not just diagnostics relating
 		// to the reason the files are opened.

gopls/internal/test/marker/testdata/fixedbugs/issue66109.txt

@@ -0,0 +1,25 @@
+This test exercises the crash in golang/go#66109: a dangling reference due to
+test variants of a command-line-arguments package.
+
+-- flags --
+-min_go=go1.22
+
+-- go.mod --
+module example.com/tools
+
+go 1.22
+
+-- tools_test.go --
+//go:build tools
+
+package tools //@diag("tools", re"No packages found")
+
+import (
+	_ "example.com/tools/tool"
+)
+
+-- tool/tool.go --
+package main
+
+func main() {
+}