Let ExecRecipeCollectStdErr return []byte for stderr

Previously, the return value was converted to string. Letting callers
convert to string makes it easier to write the sterr contents to
os.Stderr again in a future commit.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>

Author: matthijskooijman

builder_utils/utils.go

@@ -452,16 +452,16 @@ func PrepareCommandForRecipe(buildProperties properties.Map, recipe string, remo
 	return command, nil
 }
 
-func ExecRecipeCollectStdErr(buildProperties properties.Map, recipe string, removeUnsetProperties bool, echoCommandLine bool, echoOutput bool, logger i18n.Logger) (string, error) {
+func ExecRecipeCollectStdErr(buildProperties properties.Map, recipe string, removeUnsetProperties bool, echoCommandLine bool, echoOutput bool, logger i18n.Logger) ([]byte, error) {
 	command, err := PrepareCommandForRecipe(buildProperties, recipe, removeUnsetProperties, echoCommandLine, echoOutput, logger)
 	if err != nil {
-		return "", i18n.WrapError(err)
+		return nil, i18n.WrapError(err)
 	}
 
 	buffer := &bytes.Buffer{}
 	command.Stderr = buffer
 	err = command.Run()
-	return string(buffer.Bytes()), err
+	return buffer.Bytes(), err
 }
 
 func RemoveHyphenMDDFlagFromGCCCommandLine(buildProperties properties.Map) {

container_find_includes.go

@@ -333,7 +333,7 @@ func findIncludesUntilDone(ctx *types.Context, cache *includeCache, sourceFile t
 			if err != nil && !is_exit_error {
 				return i18n.WrapError(err)
 			}
-			include = IncludesFinderWithRegExp(ctx, stderr)
+			include = IncludesFinderWithRegExp(ctx, string(stderr))
 		}
 
 		if include == "" {

gcc_preproc_runner.go

@@ -61,10 +61,10 @@ func GCCPreprocRunner(ctx *types.Context, sourceFilePath string, targetFilePath
 	return nil
 }
 
-func GCCPreprocRunnerForDiscoveringIncludes(ctx *types.Context, sourceFilePath string, targetFilePath string, includes []string) (string, error) {
+func GCCPreprocRunnerForDiscoveringIncludes(ctx *types.Context, sourceFilePath string, targetFilePath string, includes []string) ([]byte, error) {
 	properties, err := prepareGCCPreprocRecipeProperties(ctx, sourceFilePath, targetFilePath, includes)
 	if err != nil {
-		return "", i18n.WrapError(err)
+		return nil, i18n.WrapError(err)
 	}
 
 	verbose := ctx.Verbose
@@ -77,10 +77,10 @@ func GCCPreprocRunnerForDiscoveringIncludes(ctx *types.Context, sourceFilePath s
 
 	stderr, err := builder_utils.ExecRecipeCollectStdErr(properties, constants.RECIPE_PREPROC_MACROS, true, verbose, verbose, logger)
 	if err != nil {
-		return string(stderr), i18n.WrapError(err)
+		return stderr, i18n.WrapError(err)
 	}
 
-	return string(stderr), nil
+	return stderr, nil
 }
 
 func prepareGCCPreprocRecipeProperties(ctx *types.Context, sourceFilePath string, targetFilePath string, includes []string) (properties.Map, error) {