Save and restore warnings from cached files

There's a concurrency issue between stdout and stderr prints so lines are interleaved at the moment (when parallel compilation is active).

Author: facchinm

builder_utils/utils.go

@@ -230,12 +230,18 @@ func compileFileWithRecipe(ctx *types.Context, sourcePath string, source string,
 	}
 
 	if !objIsUpToDate {
-		_, _, err = ExecRecipe(ctx, properties, recipe, false /* stdout */, utils.ShowIfVerbose /* stderr */, utils.Show)
+		_, stderrCache, err := ExecRecipe(ctx, properties, recipe, false /* stdout */, utils.ShowIfVerbose /* stderr */, utils.Show)
 		if err != nil {
 			return "", i18n.WrapError(err)
 		}
-	} else if ctx.Verbose {
-		logger.Println(constants.LOG_LEVEL_INFO, constants.MSG_USING_PREVIOUS_COMPILED_FILE, properties[constants.BUILD_PROPERTIES_OBJECT_FILE])
+		ctx.WarningsCache[source] = string(stderrCache)
+	} else {
+		if ctx.Verbose {
+			logger.Println(constants.LOG_LEVEL_INFO, constants.MSG_USING_PREVIOUS_COMPILED_FILE, properties[constants.BUILD_PROPERTIES_OBJECT_FILE])
+		}
+		if ctx.WarningsCache[source] != "" {
+			logger.UnformattedFprintln(os.Stderr, ctx.WarningsCache[source])
+		}
 	}
 
 	return properties[constants.BUILD_PROPERTIES_OBJECT_FILE], nil