pkg/clangtool/tooltest: add LoadOutput helper

Add LoadOutput helper to use in future commits,
and switch to osutil.ReadJSON helper.

Author: dvyukov

pkg/clangtool/clangtool.go

@@ -42,12 +42,9 @@ type OutputDataPtr[T any] interface {
 // It always caches results, and optionally reuses previously cached results.
 func Run[Output any, OutputPtr OutputDataPtr[Output]](cfg *Config) (OutputPtr, error) {
 	if cfg.CacheFile != "" {
-		data, err := os.ReadFile(cfg.CacheFile)
+		out, err := osutil.ReadJSON[OutputPtr](cfg.CacheFile)
 		if err == nil {
-			out, err := unmarshal[Output, OutputPtr](data)
-			if err == nil {
-				return out, nil
-			}
+			return out, nil
 		}
 	}
 
@@ -111,7 +108,7 @@ func runTool[Output any, OutputPtr OutputDataPtr[Output]](cfg *Config, dbFile, f
 		}
 		return nil, err
 	}
-	out, err := unmarshal[Output, OutputPtr](data)
+	out, err := osutil.ParseJSON[OutputPtr](data)
 	if err != nil {
 		return nil, err
 	}
@@ -127,16 +124,6 @@ func runTool[Output any, OutputPtr OutputDataPtr[Output]](cfg *Config, dbFile, f
 	return out, nil
 }
 
-func unmarshal[Output any, OutputPtr OutputDataPtr[Output]](data []byte) (OutputPtr, error) {
-	dec := json.NewDecoder(bytes.NewReader(data))
-	dec.DisallowUnknownFields()
-	out := OutputPtr(new(Output))
-	if err := dec.Decode(out); err != nil {
-		return nil, fmt.Errorf("failed to unmarshal clang tool output: %w\n%s", err, data)
-	}
-	return out, nil
-}
-
 type compileCommand struct {
 	Command   string
 	Directory string

pkg/clangtool/tooltest/tooltest.go

@@ -39,6 +39,19 @@ func TestClangTool[Output any, OutputPtr clangtool.OutputDataPtr[Output]](t *tes
 	})
 }
 
+func LoadOutput[Output any, OutputPtr clangtool.OutputDataPtr[Output]](t *testing.T) OutputPtr {
+	out := OutputPtr(new(Output))
+	forEachTestFile(t, func(t *testing.T, file string) {
+		tmp, err := osutil.ReadJSON[OutputPtr](file + ".json")
+		if err != nil {
+			t.Fatal(err)
+		}
+		out.Merge(tmp)
+	})
+	out.SortAndDedup()
+	return out
+}
+
 func ForEachTestFile(t *testing.T, fn func(t *testing.T, cfg *clangtool.Config, file string)) {
 	forEachTestFile(t, func(t *testing.T, file string) {
 		t.Run(filepath.Base(file), func(t *testing.T) {