fix: trim leading newline

We trim this so we don't trigger stylelint's rules which disallow empty
first lines. In JS sources, an empty first line makes sense.

We also have to set `beforeStart` explicitly on the root's raws until
stylelint fixes stylelint/stylelint#5767.

src/locationCorrection.ts

@@ -5,7 +5,8 @@ import {createPlaceholder} from './util.js';
 const correctLocation = (
   node: TaggedTemplateExpression,
   loc: Position,
-  baseIndentations: Map<number, number>
+  baseIndentations: Map<number, number>,
+  prefixOffsets?: {lines: number; offset: number}
 ): Position => {
   if (!node.quasi.loc || !node.quasi.range) {
     return loc;
@@ -19,6 +20,11 @@ const correctLocation = (
   let currentLine = 1;
   let columnOffset = nodeLoc.start.column + 1;
 
+  if (prefixOffsets) {
+    lineOffset += prefixOffsets.lines;
+    newOffset += prefixOffsets.offset;
+  }
+
   for (let i = 0; i < node.quasi.expressions.length; i++) {
     const expr = node.quasi.expressions[i];
     const previousQuasi = node.quasi.quasis[i];
@@ -72,9 +78,7 @@ const correctLocation = (
   if (loc.line === currentLine) {
     loc.column += columnOffset;
   }
-  if (loc.line !== 1) {
-    loc.column += baseIndentation;
-  }
+  loc.column += baseIndentation;
 
   loc.offset = newOffset + indentationOffset;
 
@@ -94,7 +98,7 @@ function computeBeforeAfter(
 ): void {
   if (
     node.raws['before'] &&
-    node.raws['before'].includes('\n') &&
+    (node.raws['before'].includes('\n') || node.parent?.type === 'root') &&
     node.source?.start
   ) {
     const raw = node.raws['before'];
@@ -140,14 +144,16 @@ export function locationCorrectionWalker(
       node.source.start = correctLocation(
         expr,
         node.source.start,
-        baseIndentations
+        baseIndentations,
+        root.raws['litPrefixOffsets']
       );
     }
     if (node.source?.end) {
       node.source.end = correctLocation(
         expr,
         node.source.end,
-        baseIndentations
+        baseIndentations,
+        root.raws['litPrefixOffsets']
       );
     }
   };

src/parse.ts

@@ -70,7 +70,15 @@ export const parse: Parser<Root | Document> = (
     const sourceLines = styleText.split('\n');
     const baseIndentations = new Map<number, number>();
     const indentationPattern = new RegExp(`^[ \\t]{${baseIndentation}}`);
+    const emptyLinePattern = /^[ \\t\r]*$/;
     const deindentedLines: string[] = [];
+    const prefixOffsets = {lines: 0, offset: 0};
+
+    if (sourceLines[0] !== undefined && emptyLinePattern.test(sourceLines[0])) {
+      prefixOffsets.lines = 1;
+      prefixOffsets.offset = sourceLines[0].length + 1;
+      sourceLines.shift();
+    }
 
     for (let i = 0; i < sourceLines.length; i++) {
       const sourceLine = sourceLines[i];
@@ -95,9 +103,19 @@ export const parse: Parser<Root | Document> = (
       map: false
     }) as Root;
 
+    root.raws['litPrefixOffsets'] = prefixOffsets;
     root.raws['litTemplateExpressions'] = expressionStrings;
     root.raws['litBaseIndentations'] = baseIndentations;
-    root.raws.codeBefore = sourceAsString.slice(currentOffset, startIndex);
+    // TODO (43081j): remove this if stylelint/stylelint#5767 ever gets fixed,
+    // or they drop the indentation rule. Their indentation rule depends on
+    // `beforeStart` existing as they unsafely try to call `endsWith` on it.
+    if (!root.raws['beforeStart']) {
+      root.raws['beforeStart'] = '';
+    }
+    root.raws.codeBefore = sourceAsString.slice(
+      currentOffset,
+      startIndex + prefixOffsets.offset
+    );
     root.parent = doc;
     // TODO (43081j): stylelint relies on this existing, really unsure why.
     // it could just access root.parent to get the document...

src/test/parse_test.ts

@@ -16,7 +16,7 @@ describe('parse', () => {
     assert.equal(root.type, 'root');
     assert.equal(rule.type, 'rule');
     assert.equal(colour.type, 'decl');
-    assert.equal(root.raws.codeBefore, '\n      css`');
+    assert.equal(root.raws.codeBefore, '\n      css`\n');
     assert.equal(root.parent, ast);
     assert.equal(root.raws.codeAfter, '`;\n    ');
     assert.deepEqual(ast.source!.start, {
@@ -73,7 +73,7 @@ describe('parse', () => {
     const root2 = ast.nodes[1] as Root;
 
     assert.equal(root1.type, 'root');
-    assert.equal(root1.raws.codeBefore, '\n      css`');
+    assert.equal(root1.raws.codeBefore, '\n      css`\n');
     assert.equal(root1.raws.codeAfter, undefined);
     assert.equal(root1.parent, ast);
     assert.equal(root2.type, 'root');

src/test/postcss_test.ts

@@ -25,7 +25,7 @@ describe('postcss', () => {
     assert.equal(root.type, 'root');
     assert.equal(rule.type, 'rule');
     assert.equal(colour.type, 'decl');
-    assert.equal(root.raws.codeBefore, '\n      css`');
+    assert.equal(root.raws.codeBefore, '\n      css`\n');
     assert.equal(root.parent, ast);
     assert.equal(root.raws.codeAfter, '`;\n    ');
     assert.deepEqual(ast.source!.start, {