Treat returned content without map as not changed

src/compiler/preprocess/index.ts

@@ -276,9 +276,12 @@ export default async function preprocess(
 					attributes: parse_attributes(attributes),
 					filename
 				});
-
-				if (!processed) return no_change();
-				if (processed.dependencies) dependencies.push(...processed.dependencies);
+				if (processed && processed.dependencies) {
+					dependencies.push(...processed.dependencies);
+				}
+				if (!processed || !processed.map && processed.code === content) {
+					return no_change();
+				}
 				return get_replacement(file_basename, offset, get_location, content, processed, `<${tag_name}${attributes}>`, `</${tag_name}>`);
 			}
 		);

test/sourcemaps/samples/preprocess-no-map/_config.js

@@ -3,9 +3,11 @@ export default {
 	preprocess: [
 		{
 			style: ({ content }) => {
-				return { code: content };
+				// Modified without source map
+				return { code: content + ' ' };
 			},
 			script: ({ content }) => {
+				// Not modified
 				return { code: content };
 			}
 		}

test/sourcemaps/samples/preprocess-no-map/test.js

@@ -8,9 +8,10 @@ export function test({ input, preprocessed }) {
 		preprocessed
 	});
 
-	// script
-	assert_not_mapped({
+	// script content (preprocessed without map, content not changed)
+	assert_mapped({
 		code: 'console.log(name);',
+		input: input.locate,
 		preprocessed
 	});
 	
@@ -21,7 +22,7 @@ export function test({ input, preprocessed }) {
 		preprocessed
 	});
 	
-	// style content
+	// style content (preprocessed without map, content changed)
 	assert_not_mapped({
 		code: 'font-weight: bold;',
 		preprocessed