test(NODE-7493): Enable source maps for accurate test debugging

.mocharc.js

@@ -5,8 +5,8 @@ const [major] = process.versions.node.split('.');
 /** @type {import("mocha").MochaOptions} */
 module.exports = {
   require: [
-    'source-map-support/register',
     'ts-node/register',
+    'test/tools/runner/source_map.cjs',
     'test/tools/runner/throw_rejections.cjs',
     'test/tools/runner/chai_addons.ts',
     'test/tools/runner/ee_checker.ts'
@@ -18,5 +18,8 @@ module.exports = {
   reporter: 'test/tools/reporter/mongodb_reporter.js',
   sort: true,
   color: true,
-  'node-option': Number(major) >= 23 ? ['no-experimental-strip-types'] : undefined
+  'node-option':
+    Number(major) >= 23
+      ? ['enable-source-maps', 'no-experimental-strip-types']
+      : ['enable-source-maps']
 };

package.json

@@ -160,7 +160,7 @@
     "build:bundle": "npm run bundle:driver && npm run bundle:types && npm run build:runtime-barrel",
     "build:runtime-barrel": "node etc/build-runtime-barrel.mjs",
     "bundle:driver": "node etc/bundle-driver.mjs",
-    "bundle:types": "npx tsc --project ./tsconfig.json --declaration --emitDeclarationOnly --declarationDir test/tools/runner/bundle/types",
+    "bundle:types": "node ./node_modules/typescript/bin/tsc --project ./tsconfig.json --declaration --emitDeclarationOnly --declarationDir test/tools/runner/bundle/types",
     "fix:eslint": "npm run check:eslint -- --fix",
     "prepare": "node etc/prepare.js",
     "preview:docs": "ts-node etc/docs/preview.ts",

test/manual/mocharc.js

@@ -7,12 +7,16 @@ const [major] = process.versions.node.split('.');
 module.exports = {
   require: [
     'ts-node/register',
+    'test/tools/runner/source_map.cjs',
     'test/tools/runner/throw_rejections.cjs',
     'test/tools/runner/chai_addons.ts'
   ],
   reporter: 'test/tools/reporter/mongodb_reporter.js',
   failZero: true,
   color: true,
   timeout: 10000,
-  'node-option': Number(major) >= 23 ? ['no-experimental-strip-types'] : undefined
+  'node-option':
+    Number(major) >= 23
+      ? ['enable-source-maps', 'no-experimental-strip-types']
+      : ['enable-source-maps']
 };

test/mocha_lambda.js

@@ -17,5 +17,8 @@ module.exports = {
   reporter: 'test/tools/reporter/mongodb_reporter.js',
   sort: true,
   color: true,
-  'node-option': Number(major) >= 23 ? ['no-experimental-strip-types'] : undefined
+  'node-option':
+    Number(major) >= 23
+      ? ['enable-source-maps', 'no-experimental-strip-types']
+      : ['enable-source-maps']
 };

test/mocha_mongodb.js

@@ -6,8 +6,8 @@ const [major] = process.versions.node.split('.');
 /** @type {import("mocha").MochaOptions} */
 module.exports = {
   require: [
-    'source-map-support/register',
     'ts-node/register',
+    'test/tools/runner/source_map.cjs',
     'test/tools/runner/throw_rejections.cjs',
     'test/tools/runner/chai_addons.ts',
     'test/tools/runner/ee_checker.ts',
@@ -31,5 +31,8 @@ module.exports = {
     'test/integration/node-specific/examples/transactions.test.js',
     'test/integration/node-specific/examples/versioned_api.js'
   ],
-  'node-option': Number(major) >= 23 ? ['no-experimental-strip-types'] : undefined
+  'node-option':
+    Number(major) >= 23
+      ? ['enable-source-maps', 'no-experimental-strip-types']
+      : ['enable-source-maps']
 };

test/tools/runner/hooks/configuration.ts

@@ -1,10 +1,5 @@
 /* eslint-disable simple-import-sort/imports */
 
-// eslint-disable-next-line @typescript-eslint/no-require-imports
-require('source-map-support').install({
-  hookRequire: true
-});
-
 import * as process from 'process';
 import * as os from 'os';
 

test/tools/runner/source_map.cjs

@@ -0,0 +1,4 @@
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+require('source-map-support').install({
+    hookRequire: true
+});

test/tsconfig.json

@@ -3,7 +3,8 @@
     "compilerOptions": {
         "strict": false,
         "allowJs": true,
-        "checkJs": false
+        "checkJs": false,
+        "sourceMap": true
     },
     "include": [
         "../node_modules/@types/mocha/index.d.ts",

test/unit/source_map.test.ts

@@ -0,0 +1,76 @@
+// These import-type lines are completely erased by the TypeScript compiler
+// (no blank-line placeholder is left behind), so the compiled JS has fewer
+// lines than this source file.  That shifts every subsequent line upward in
+// the JS output.
+import type { Document as _Doc } from 'bson';
+import { expect } from 'chai';
+
+import type {
+  AbstractCursor as _AbC,
+  AggregationCursor as _AC,
+  ChangeStream as _CS,
+  ClientSession as _Sess,
+  Collection as _Col,
+  Db as _Db,
+  FindCursor as _FC,
+  GridFSBucket as _GB,
+  MongoClient as _MC
+} from '../../mongodb';
+
+// ─── This Error is created at line 31 in the TypeScript source. ───────────
+// The twelve `import type` lines above are erased without replacement, so
+// in the compiled JS this falls on line 31 − 12 = line 19.
+//
+// ts-node's bundled `@cspotcode/source-map-support` patches
+// Error.prepareStackTrace so `error.stack` already shows the correct TS
+// line. We DISABLE that patch to see what V8 reports natively.
+//
+//   OLD commit (no --enable-source-maps): V8 says line 19  ← WRONG
+//   NEW commit (   --enable-source-maps): V8 says line 31  ← correct
+const TS_SOURCE_LINE = 31; // must match the line below
+const errorAtKnownLine = new Error('source-map probe'); // ← line 31
+
+/**
+ * Capture a raw V8 stack frame by temporarily removing
+ * `@cspotcode/source-map-support`'s prepareStackTrace override (installed
+ * by ts-node) so we see exactly what V8 reports — with or without its own
+ * source-map awareness.
+ */
+function rawV8FrameOf(err: Error): {
+  file: string | null;
+  line: number | null;
+  col: number | null;
+} {
+  const saved = Error.prepareStackTrace;
+  // Null → V8 uses its built-in formatter (honours --enable-source-maps).
+  Error.prepareStackTrace = undefined as unknown as typeof Error.prepareStackTrace;
+  const raw = err.stack ?? ''; // triggers V8 formatting with no hook
+  Error.prepareStackTrace = saved;
+
+  // First "at …" line: "    at Object.<anonymous> (/abs/path/file.ts:LINE:COL)"
+  const match = raw.split('\n')[1]?.match(/\((.+):(\d+):(\d+)\)$/);
+  if (!match) return { file: null, line: null, col: null };
+  return { file: match[1], line: Number(match[2]), col: Number(match[3]) };
+}
+
+describe('Source maps', function () {
+  it('report the correct line number when enabled', function () {
+    const frame = rawV8FrameOf(errorAtKnownLine);
+
+    if (process.env.VERBOSE) {
+      console.error('\n  ── raw V8 frame (prepareStackTrace bypassed) ──');
+      console.error(`  file : ${frame.file}`);
+      console.error(`  line : ${frame.line}  (TypeScript source line is ${TS_SOURCE_LINE})`);
+      console.error(`  col  : ${frame.col}`);
+      console.error(
+        `  ${frame.line === TS_SOURCE_LINE ? '✔ line matches TS source' : `✘ line ${frame.line} ≠ TS source line ${TS_SOURCE_LINE} — source maps not applied by V8`}`
+      );
+    }
+    expect(frame.line).to.equal(
+      TS_SOURCE_LINE,
+      `V8 reported line ${frame.line} but TypeScript source line is ${TS_SOURCE_LINE}. ` +
+      `This means --enable-source-maps is absent and V8 is reading the compiled-JS ` +
+      `line number instead of the original TypeScript line.`
+    );
+  });
+});