fix(postcss): keep comment indentation stable

.changeset/calm-comments-stay.md

@@ -0,0 +1,7 @@
+---
+'@linaria/postcss-linaria': patch
+---
+
+Keep comment indentation stable through `stylelint --fix`
+
+Indented templates no longer add their base indentation before trailing comments or remove it from continuation lines inside multi-line comments. Repeated parse/stringify passes now preserve both forms byte-for-byte (#1502).

packages/postcss-linaria/__tests__/stringify.test.ts

@@ -298,6 +298,44 @@ describe('stringify', () => {
     expect(output).toEqual(source);
   });
 
+  // https://github.com/callstack/linaria/issues/1502. The whitespace before a
+  // trailing comment is not line indentation and must not grow on each pass.
+  it('should keep whitespace before a trailing comment unchanged', () => {
+    const source = `
+export const style = {
+  a: css\`
+    color: red; /* c */
+  \`,
+};
+`;
+
+    let current = source;
+    for (let pass = 0; pass < 3; pass += 1) {
+      const { ast } = createTestAst(current);
+      current = ast.toString(syntax);
+      expect(current).toEqual(source);
+    }
+  });
+
+  it('should keep indentation inside a multi-line comment unchanged', () => {
+    const source = `
+export const style = {
+  a: css\`
+    /* first line
+       second line */
+    color: red;
+  \`,
+};
+`;
+
+    let current = source;
+    for (let pass = 0; pass < 3; pass += 1) {
+      const { ast } = createTestAst(current);
+      current = ast.toString(syntax);
+      expect(current).toEqual(source);
+    }
+  });
+
   // Not the same as the placeholder cases above: these have no interpolations.
   it('should keep a comment inside a multi-line selector', () => {
     const { source, ast } = createTestAst(`

packages/postcss-linaria/src/locationCorrection.ts

@@ -178,20 +178,37 @@ function computeBeforeAfter(
   node: Document | Root | ChildNode,
   baseIndentations: Map<number, number>
 ): void {
+  const { before } = node.raws;
   if (
-    node.raws.before &&
-    (node.raws.before.includes('\n') || node.parent?.type === 'root') &&
+    before &&
+    (before.includes('\n') ||
+      (node.parent?.type === 'root' &&
+        node.source?.start &&
+        node.source.start.column === before.length + 1)) &&
     node.source?.start
   ) {
-    const numBeforeLines = node.raws.before.split('\n').length - 1;
+    const numBeforeLines = before.split('\n').length - 1;
     const corrected = computeCorrectedString(
-      node.raws.before,
+      before,
       node.source.start.line - numBeforeLines,
       baseIndentations
     );
     node.raws.linariaBefore = corrected;
   }
 
+  if (
+    node.type === 'comment' &&
+    node.text.includes('\n') &&
+    node.source?.start
+  ) {
+    const corrected = computeCorrectedString(
+      node.text,
+      node.source.start.line,
+      baseIndentations
+    );
+    node.raws.linariaText = corrected;
+  }
+
   if (
     node.raws.after &&
     node.raws.after.includes('\n') &&

packages/postcss-linaria/src/stringify.ts

@@ -174,7 +174,14 @@ class LinariaStringifier extends Stringifier {
       'left',
       this.raw(node, 'left', 'commentLeft')
     );
-    const text = escapeNodeField(node, 'text', node.text);
+    const text = escapeNodeField(
+      node,
+      'text',
+      typeof node.raws.linariaText === 'string' &&
+        isOriginalField(node, 'text', node.text)
+        ? node.raws.linariaText
+        : node.text
+    );
     const right = escapeRawField(
       node,
       'right',