Make handling of input sourcemaps less flaky

Signed-off-by: Karthik Ganeshram <[email protected]>

Author: karthik2804

packages/build-tools/src/index.ts

@@ -7,6 +7,7 @@ import {
   calculateChecksum,
   chainSourceMaps,
   fileExists,
+  getSourceMapFromFile,
   saveBuildData,
 } from './utils.js';
 import { getCliArgs } from './cli.js';
@@ -17,6 +18,7 @@ import { mergeWit } from '../lib/wit_tools.js';
 import { precompile } from "./precompile.js"
 import path from 'node:path'
 import { SourceMapInput } from '@ampproject/remapping';
+import { get } from 'node:http';
 
 async function main() {
   try {
@@ -70,9 +72,8 @@ async function main() {
     const source = await readFile(src, 'utf8');
     let { content: precompiledSource, sourceMap: precompiledSourceMap } = precompile(source, src, true, 'precompiled-source.js') as { content: string; sourceMap: SourceMapInput };
     // Check if input file has a source map because if we does, we need to chain it with the precompiled source map
-    // TODO: check using the sourcemap comment instead of the file existence and also deal with base64 encoded source maps
-    if (await fileExists(src + '.map')) {
-      const inputSourceMap = JSON.parse(await readFile(src + '.map', 'utf8')) as SourceMapInput;
+    let inputSourceMap = await getSourceMapFromFile(src);
+    if (inputSourceMap) {
       precompiledSourceMap = chainSourceMaps(precompiledSourceMap, { [src]: inputSourceMap }) as SourceMapInput;
     }
 

packages/build-tools/src/utils.ts

@@ -2,6 +2,7 @@ import { readFile } from 'fs/promises';
 import { createHash } from 'node:crypto';
 import { access, writeFile } from 'node:fs/promises';
 import remapping, { SourceMapInput } from '@ampproject/remapping';
+import path from 'path';
 
 type FileName = string;
 type SourceMapLookup = Record<FileName, SourceMapInput>;
@@ -73,3 +74,35 @@ export async function saveBuildData(
     throw error;
   }
 }
+
+export async function getSourceMapFromFile(filePath: string): Promise<SourceMapInput | null> {
+  try {
+    const content = await readFile(filePath, 'utf8');
+
+    // Look for the sourceMappingURL comment
+    const sourceMapRegex = /\/\/[#@]\s*sourceMappingURL=(.+)$/m;
+    const match = content.match(sourceMapRegex);
+
+    if (!match) return null;
+
+    const sourceMapUrl = match[1].trim();
+
+    if (sourceMapUrl.startsWith('data:application/json;base64,')) {
+      // Inline base64-encoded source map
+      const base64 = sourceMapUrl.slice('data:application/json;base64,'.length);
+      const rawMap = Buffer.from(base64, 'base64').toString('utf8');
+      return JSON.parse(rawMap);
+    } else {
+      // External .map file
+      const mapPath = path.resolve(path.dirname(filePath), sourceMapUrl);
+      try {
+        const rawMap = await readFile(mapPath, 'utf8');
+        return JSON.parse(rawMap);
+      } catch (e) {
+        return null; // map file not found or invalid
+      }
+    }
+  } catch (err) {
+    return null; // file doesn't exist or can't be read
+  }
+}