Support input sourceMaps

lib/index.d.ts

@@ -7,6 +7,8 @@
  *   original.
  * @prop {boolean} [noOriginal] Do not run tests on the original code, only
  *   on the generated code.
+ * @prop {boolean} [inputSourceMap] Read sourceMap information from the input
+ *   file.  Use it to filter the generated sourceMap information.
  */
 /**
  * Test the basic functionality of a Peggy grammar, to make coverage easier.
@@ -113,4 +115,9 @@ export type TestPeggyOptions = {
      * on the generated code.
      */
     noOriginal?: boolean | undefined;
+    /**
+     * Read sourceMap information from the input
+     * file.  Use it to filter the generated sourceMap information.
+     */
+    inputSourceMap?: boolean | undefined;
 };

lib/index.js

@@ -1,16 +1,19 @@
+import { SourceMapConsumer, SourceNode } from "source-map";
 import {
   deepEqual,
   equal,
   fail,
   ok,
   throws,
 } from "node:assert/strict";
-import { SourceNode } from "source-map";
 import { fileURLToPath } from "node:url";
 import fs from "node:fs/promises";
 import path from "node:path";
 
 const INVALID = "\uffff";
+const START = "//#"; // c8: THIS file is not mapped.
+const sourceMapRE = new RegExp(`^${START}\\s*sourceMappingURL\\s*=\\s*([^\r\n]+)`, "m");
+const startRuleRE = /^\s*peg\$result = peg\$startRuleFunction\(\);/;
 let counter = 0;
 
 /**
@@ -258,6 +261,8 @@ function checkParserStarts(grammar, starts, modified, counts) {
  *   original.
  * @prop {boolean} [noOriginal] Do not run tests on the original code, only
  *   on the generated code.
+ * @prop {boolean} [inputSourceMap] Read sourceMap information from the input
+ *   file.  Use it to filter the generated sourceMap information.
  */
 
 /**
@@ -333,13 +338,47 @@ export async function testPeggy(grammarUrl, starts, opts) {
     ok(grammarJs);
     equal(typeof grammarJs, "string");
 
+    /** @type {SourceMapConsumer|null} */
+    let ism = null;
+    if (opts?.inputSourceMap) {
+      const m = grammarJs.match(sourceMapRE);
+      if (m) {
+        const map = m[1].startsWith("data:")
+          ? await (await fetch(m[1])).json()
+          : JSON.parse(
+              await fs.readFile(
+                path.resolve(process.cwd(), path.dirname(grammarPath), m[1]),
+                "utf8"
+              )
+            );
+        ism = await new SourceMapConsumer(map);
+      }
+    }
+
     // Approach: generate a new file next to the existing grammar file, with
     // test code injected just before the parser runs.  Source map information
     // embedded in the new file will make coverage show up on the original file.
     const src = new SourceNode();
     let lineNum = 1;
     for (const line of grammarJs.split(/(?<=\n)/)) {
-      if (/^\s*peg\$result = peg\$startRuleFunction\(\);/.test(line)) {
+      let sn = null;
+      if (ism) {
+        const pos = ism.originalPositionFor({
+          line: lineNum,
+          column: 0,
+        });
+        if (pos) {
+          sn = new SourceNode(pos.line, pos.column, pos.source, line);
+        }
+      }
+      if (!sn) {
+        sn = new SourceNode(lineNum, 0, grammarPath, line);
+      }
+      lineNum++;
+
+      if (sourceMapRE.test(line)) {
+        // No-op, never output sourcemapurl line.
+      } else if (startRuleRE.test(line)) {
         src.add(`\
   //#region Inserted by @peggyjs/coverage
   let replacements = Object.create(null);
@@ -440,7 +479,7 @@ export async function testPeggy(grammarUrl, starts, opts) {
   //#endregion
 
 `);
-        src.add(new SourceNode(lineNum++, 0, grammarPath, line));
+        src.add(sn);
         src.add(`
   //#region Inserted by @peggyjs/coverage
   for (const [name, orig] of Object.entries(replacements)) {
@@ -450,7 +489,7 @@ export async function testPeggy(grammarUrl, starts, opts) {
   //#endregion
 `);
       } else {
-        src.add(new SourceNode(lineNum++, 0, grammarPath, line));
+        src.add(sn);
       }
     }
 
@@ -460,17 +499,15 @@ export async function testPeggy(grammarUrl, starts, opts) {
     let sm = starts.every(s => !s.options?.peg$debugger);
     if (opts && Object.prototype.hasOwnProperty.call(opts, "noMap")) {
       sm = !opts.noMap;
-    } else {
-      if (!sm) {
-        console.error("WARNING: sourcemap disabled due to peg$debugger");
-      }
+    } else if (!sm) {
+      console.error("WARNING: sourcemap disabled due to peg$debugger");
     }
-    const start = "//#"; // c8: THIS file is not mapped.
     if (sm) {
       code += `
-${start} sourceMappingURL=data:application/json;charset=utf-8;base64,${map}
+${START} sourceMappingURL=data:application/json;charset=utf-8;base64,${map}
 `;
     }
+    ism?.destroy();
     await fs.writeFile(modifiedPath, code);
     try {
       const agrammar = /** @type {Parser} */ (

package.json

@@ -37,10 +37,10 @@
   },
   "devDependencies": {
     "@peggyjs/eslint-config": "6.0.0",
-    "@types/node": "22.15.3",
+    "@types/node": "22.15.14",
     "c8": "10.1.3",
     "eslint": "9.26.0",
-    "typedoc": "0.28.3",
+    "typedoc": "0.28.4",
     "typescript": "5.8.3"
   },
   "packageManager": "[email protected]",