fix: source maps for esm modules

dist/index.mjs

@@ -18,6 +18,7 @@ import cjsModule from 'node:module';
 const __filename = cjsUrl.fileURLToPath(import.meta.url);
 const __dirname = cjsPath.dirname(__filename);
 const require = cjsModule.createRequire(import.meta.url);
+// -- End Shims --
 
 
 function getTrayBinPath(debug = false, copyDir = false) {

package.json

@@ -49,6 +49,7 @@
     "eslint-config-prettier": "^8.5.0",
     "eslint-plugin-prettier": "^4.2.1",
     "jest": "^29.3.1",
+    "magic-string": "^0.30.10",
     "prettier": "^2.8.1",
     "rimraf": "^5.0.5",
     "rollup": "^2.79.1",

rollup.config.mjs

@@ -4,6 +4,7 @@ import { readFile } from 'node:fs/promises';
 
 import typescript2 from 'rollup-plugin-typescript2';
 import json from '@rollup/plugin-json';
+import MagicString from 'magic-string';
 
 const packageJSON = JSON.parse(await readFile('./package.json', 'utf-8'));
 
@@ -70,13 +71,16 @@ const options = {
 export default options;
 
 /**
- * The original ESM shim plugin is broken, it inserts the shims
- * in wrong places causing syntax errors. This is a very simple
- * solution, which is not better, but at list does not brake for
- * this specific code.
+ * An alternative to @rollup/plugin-esm-shim (https://github.com/rollup/plugins/tree/master/packages/esm-shim).
  *
- * @todo post the improvement to the issue https://github.com/rollup/plugins/issues/1709
- * @todo use magic-string to also generate mappings. Right now this plugin removes mappings for esm builds.
+ * The original ESM shim plugin has a bug: it inserts the shims
+ * in wrong places causing syntax errors. This slightly modified
+ * version of it is a very simple solution, which surely will not work
+ * in every case, but at list does not brake specifically for my code.
+ *
+ * Whats different from the original?
+ * The regex used to find import statements is changed to a more
+ * simple one /^import\s.*';$/gm and the whole login is a lot simpler.
  */
 function esmShimCustom() {
   const ESMShim = `
@@ -87,14 +91,22 @@ import cjsModule from 'node:module';
 const __filename = cjsUrl.fileURLToPath(import.meta.url);
 const __dirname = cjsPath.dirname(__filename);
 const require = cjsModule.createRequire(import.meta.url);
+// -- End Shims --
 `;
+  const CJSyntaxRegex = /__filename|__dirname|require\(|require\.resolve\(/;
 
   return {
     name: 'esm-shim-custom',
 
     renderChunk(/** @type {string} */ code, _chunk, opts) {
       if (opts.format === 'es') {
+        if (code.includes(ESMShim) || !CJSyntaxRegex.test(code)) {
+          return null;
+        }
+
         let endIndexOfLastImport = -1;
+
+        // Find the last import statement and its ending index
         for (let match of code.matchAll(/^import\s.*';$/gm)) {
           if (match.length === 0 || typeof match.index !== 'number') {
             continue;
@@ -103,14 +115,32 @@ const require = cjsModule.createRequire(import.meta.url);
           endIndexOfLastImport = match.index + match[0].length;
         }
 
-        if (endIndexOfLastImport > -1) {
-          code =
-            code.slice(0, endIndexOfLastImport) +
-            ESMShim +
-            code.slice(endIndexOfLastImport);
+        const s = new MagicString(code);
+        s.appendRight(endIndexOfLastImport, ESMShim);
+
+        const sourceMap = s.generateMap({
+          includeContent: true,
+        });
+
+        /** @type {string[] | undefined} */
+        let sourcesContent;
+        if (Array.isArray(sourceMap.sourcesContent)) {
+          sourcesContent = [];
+          for (let i = 0; i < sourceMap.sourcesContent.length; i++) {
+            const content = sourceMap.sourcesContent[i];
+            if (typeof content === 'string') {
+              sourcesContent.push(content);
+            }
+          }
         }
 
-        return code;
+        return {
+          code: s.toString(),
+          map: {
+            ...sourceMap,
+            sourcesContent,
+          },
+        };
       }
 
       return null;

yarn.lock

@@ -599,7 +599,7 @@
   resolved "https://registry.yarnpkg.com/@jridgewell/set-array/-/set-array-1.1.2.tgz#7c6cf998d6d20b914c0a55a91ae928ff25965e72"
   integrity sha512-xnkseuNADM0gt2bs+BvhO0p78Mk762YnZdsuzFV018NoG1Sj1SCQvpSqa7XUaTam5vAGasABV9qXASMKnFMwMw==
 
-"@jridgewell/sourcemap-codec@^1.4.10", "@jridgewell/sourcemap-codec@^1.4.14":
+"@jridgewell/sourcemap-codec@^1.4.10", "@jridgewell/sourcemap-codec@^1.4.14", "@jridgewell/sourcemap-codec@^1.4.15":
   version "1.4.15"
   resolved "https://registry.yarnpkg.com/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.4.15.tgz#d7c6e6755c78567a951e04ab52ef0fd26de59f32"
   integrity sha512-eF2rxCRulEKXHTRiDrDy6erMYWqNw4LPdQ8UQA4huuxaQsVeRPFl2oM8oDGxMFhJUWZf9McpLtJasDDZb/Bpeg==
@@ -2531,6 +2531,13 @@ lunr@^2.3.9:
   resolved "https://registry.yarnpkg.com/lunr/-/lunr-2.3.9.tgz#18b123142832337dd6e964df1a5a7707b25d35e1"
   integrity sha512-zTU3DaZaF3Rt9rhN3uBMGQD3dD2/vFQqnvZCDv4dl5iOzq2IZQqTxu90r4E5J+nP70J3ilqVCrbho2eWaeW8Ow==
 
+magic-string@^0.30.10:
+  version "0.30.10"
+  resolved "https://registry.yarnpkg.com/magic-string/-/magic-string-0.30.10.tgz#123d9c41a0cb5640c892b041d4cfb3bd0aa4b39e"
+  integrity sha512-iIRwTIf0QKV3UAnYK4PU8uiEc4SRh5jX0mwpIwETPpHdhVM4f53RSwS/vXvN1JhGX+Cs7B8qIq3d6AH49O5fAQ==
+  dependencies:
+    "@jridgewell/sourcemap-codec" "^1.4.15"
+
 make-dir@^3.0.2:
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/make-dir/-/make-dir-3.1.0.tgz#415e967046b3a7f1d185277d84aa58203726a13f"