Release validation source bytes after checks

internal/validation/tree_test.go

@@ -78,6 +78,56 @@ func TestReadCandidateTreeUsesCapturedCommitAndEnumeratesGitEntries(t *testing.T
 	}
 }
 
+func TestReadFileReturnsOwnedBytesAndCachesOnlySymlinkTargets(t *testing.T) {
+	repository := newTreeRepository(t)
+	writeTreeFile(t, repository, "source.txt", []byte("committed content"))
+	if err := os.Symlink("source.txt", filepath.Join(repository, "alias.txt")); err != nil {
+		t.Fatal(err)
+	}
+	commit := commitCandidateTree(t, repository)
+	tree, err := ReadCandidateTree(context.Background(), repository, commit)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cleanupCandidateTree(t, tree)
+
+	first, err := tree.ReadFile(context.Background(), "source.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	first[0] = 'X'
+	second, err := tree.ReadFile(context.Background(), "source.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(second) != "committed content" {
+		t.Fatalf("second regular-file read = %q, want committed content", second)
+	}
+	if &first[0] == &second[0] {
+		t.Fatal("regular-file reads share a backing byte slice")
+	}
+
+	linkFirst, err := tree.ReadFile(context.Background(), "alias.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	linkFirst[0] = 'X'
+	linkSecond, err := tree.ReadFile(context.Background(), "alias.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(linkSecond) != "source.txt" {
+		t.Fatalf("second symlink read = %q, want source.txt", linkSecond)
+	}
+	if len(tree.symlinkTargets) != 1 {
+		t.Fatalf("cached symlink target count = %d, want 1", len(tree.symlinkTargets))
+	}
+	destination, err := tree.ResolveDestination(context.Background(), "README.md", "alias.txt")
+	if err != nil || destination.Kind != DestinationEntry || destination.Path != "source.txt" {
+		t.Fatalf("ResolveDestination() = %#v, %v; want source.txt entry", destination, err)
+	}
+}
+
 func cleanupCandidateTree(tb testing.TB, tree *CandidateTree) {
 	tb.Helper()
 	tb.Cleanup(func() { _ = tree.Close() })