src: dump snapshot source with node:generate_default_snapshot_source

joyeecheung · aduh95 · commit a96256524cc4 · 2026-02-24T00:37:13.000+01:00
This helps diffing snapshots when the reproducibility gets broken. PR-URL: #61101 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
diff --git a/src/node.cc b/src/node.cc
@@ -1422,6 +1422,21 @@ ExitCode GenerateAndWriteSnapshotData(const SnapshotData** snapshot_data_ptr,
   DCHECK(snapshot_config.builder_script_path.has_value());
   const std::string& builder_script =
       snapshot_config.builder_script_path.value();
+
+  // For the special builder node:generate_default_snapshot_source, generate
+  // the snapshot as C++ source and write it to snapshot.cc (for testing).
+  if (builder_script == "node:generate_default_snapshot_source") {
+    // Reset to empty to generate from scratch.
+    snapshot_config.builder_script_path = {};
+    exit_code =
+        node::SnapshotBuilder::GenerateAsSource("snapshot.cc",
+                                                args_maybe_patched,
+                                                result->exec_args(),
+                                                snapshot_config,
+                                                true /* use_array_literals */);
+    return exit_code;
+  }
+
   // node:embedded_snapshot_main indicates that we are using the
   // embedded snapshot and we are not supposed to clean it up.
   if (builder_script == "node:embedded_snapshot_main") {
diff --git a/test/parallel/test-snapshot-reproducible.js b/test/parallel/test-snapshot-reproducible.js
@@ -23,7 +23,7 @@ function generateSnapshot() {
       '--random_seed=42',
       '--predictable',
       '--build-snapshot',
-      'node:generate_default_snapshot',
+      'node:generate_default_snapshot_source',
     ],
     {
       env: { ...process.env, NODE_DEBUG_NATIVE: 'SNAPSHOT_SERDES' },
@@ -40,33 +40,10 @@ function generateSnapshot() {
       },
     }
   );
-  const blobPath = tmpdir.resolve('snapshot.blob');
-  return fs.readFileSync(blobPath);
+  const outputPath = tmpdir.resolve('snapshot.cc');
+  return fs.readFileSync(outputPath, 'utf-8').split('\n');
 }
 
-const buf1 = generateSnapshot();
-const buf2 = generateSnapshot();
-
-const diff = [];
-let offset = 0;
-const step = 16;
-do {
-  const length = Math.min(buf1.length - offset, step);
-  const slice1 = buf1.slice(offset, offset + length).toString('hex');
-  const slice2 = buf2.slice(offset, offset + length).toString('hex');
-  if (slice1 !== slice2) {
-    diff.push({ offset: '0x' + (offset).toString(16), slice1, slice2 });
-  }
-  offset += length;
-} while (offset < buf1.length);
-
-assert.strictEqual(offset, buf1.length);
-if (offset < buf2.length) {
-  const length = Math.min(buf2.length - offset, step);
-  const slice2 = buf2.slice(offset, offset + length).toString('hex');
-  diff.push({ offset, slice1: '', slice2 });
-  offset += length;
-} while (offset < buf2.length);
-
-assert.deepStrictEqual(diff, []);
-assert.strictEqual(buf1.length, buf2.length);
+const source1 = generateSnapshot();
+const source2 = generateSnapshot();
+assert.deepStrictEqual(source1, source2);
