[compiler] Add snap subcommand to minimize a test input (#35663)

Snap now supports subcommands 'test' (default) and 'minimize`. The
minimize subcommand attempts to minimize a single failing input fixture
by incrementally simplifying the ast so long as the same error occurs. I
spot-checked it and it seemed to work pretty well. This is intended for
use in a new subagent designed for investigating bugs — fixture
simplification is an important part of the process and we can automate
this rather than light tokens on fire.

Example Input:

```js
function Component(props) {
  const x = [];
  let result;
  for (let i = 0; i < 10; i++) {
    if (cond) {
      try {
        result = {key: bar([props.cond && props.foo])};
      } catch (e) {
        console.log(e);
      }
    }
  }
  x.push(result);
  return <Stringify x={x} />;
}
```

Command output:

```
$ yarn snap minimize --path .../input.js
Minimizing: .../input.js

Minimizing................

--- Minimized Code ---
function Component(props) {
  try {
    props && props;
  } catch (e) {}
}

Reduced from 16 lines to 5 lines
```

This demonstrates things like:
* Removing one statement at at time
* Replacing if/else with the test, consequent, or alternate. Similar for
other control-flow statements including try/catch
* Removing individual array/object expression properties
* Replacing single-value array/object with the value
* Replacing control-flow expression (logical, consequent) w the test or
left/right values
* Removing call arguments
* Replacing calls with a single argument with the argument
* Replacing calls with multiple arguments with an array of the arguments
* Replacing optional member/call with non-optional versions
* Replacing member expression with the object. If computed, also try
replacing w the key
* And a bunch more strategies, see the code

compiler/packages/snap/package.json

@@ -22,6 +22,7 @@
   },
   "dependencies": {
     "@babel/code-frame": "^7.22.5",
+    "@babel/generator": "^7.19.1",
     "@babel/plugin-syntax-jsx": "^7.18.6",
     "@babel/preset-flow": "^7.7.4",
     "@babel/preset-typescript": "^7.26.0",
@@ -58,6 +59,7 @@
   "resolutions": {
     "./**/@babel/parser": "7.7.4",
     "./**/@babel/types": "7.7.4",
+    "@babel/generator": "7.2.0",
     "@babel/preset-flow": "7.22.5"
   }
 }

compiler/packages/snap/src/runner.ts

@@ -23,6 +23,7 @@ import {
 } from './runner-watch';
 import * as runnerWorker from './runner-worker';
 import {execSync} from 'child_process';
+import {runMinimize} from './minimize';
 
 const WORKER_PATH = require.resolve('./runner-worker.js');
 const NUM_WORKERS = cpus().length - 1;
@@ -38,40 +39,76 @@ type RunnerOptions = {
   debug: boolean;
 };
 
-const opts: RunnerOptions = yargs
+async function runTestCommand(opts: RunnerOptions): Promise<void> {
-  .boolean('sync')
+  await main(opts);
-  .describe(
+}
-    'sync',
+
-    'Run compiler in main thread (instead of using worker threads or subprocesses). Defaults to false.',
+async function runMinimizeCommand(path: string): Promise<void> {
+  await runMinimize({path});
+}
+
+yargs(hideBin(process.argv))
+  .command(
+    ['test', '$0'],
+    'Run compiler tests',
+    yargs => {
+      return yargs
+        .boolean('sync')
+        .describe(
+          'sync',
+          'Run compiler in main thread (instead of using worker threads or subprocesses). Defaults to false.',
+        )
+        .default('sync', false)
+        .boolean('worker-threads')
+        .describe(
+          'worker-threads',
+          'Run compiler in worker threads (instead of subprocesses). Defaults to true.',
+        )
+        .default('worker-threads', true)
+        .boolean('watch')
+        .describe(
+          'watch',
+          'Run compiler in watch mode, re-running after changes',
+        )
+        .alias('w', 'watch')
+        .default('watch', false)
+        .boolean('update')
+        .alias('u', 'update')
+        .describe('update', 'Update fixtures')
+        .default('update', false)
+        .string('pattern')
+        .alias('p', 'pattern')
+        .describe(
+          'pattern',
+          'Optional glob pattern to filter fixtures (e.g., "error.*", "use-memo")',
+        )
+        .boolean('debug')
+        .alias('d', 'debug')
+        .describe('debug', 'Enable debug logging to print HIR for each pass')
+        .default('debug', false);
+    },
+    async argv => {
+      await runTestCommand(argv as RunnerOptions);
+    },
   )
-  .default('sync', false)
+  .command(
-  .boolean('worker-threads')
+    'minimize',
-  .describe(
+    'Minimize a test case to reproduce a compiler error',
-    'worker-threads',
+    yargs => {
-    'Run compiler in worker threads (instead of subprocesses). Defaults to true.',
+      return yargs
+        .string('path')
+        .alias('p', 'path')
+        .describe('path', 'Path to the file to minimize')
+        .demandOption('path');
+    },
+    async argv => {
+      await runMinimizeCommand(argv.path as string);
+    },
   )
-  .default('worker-threads', true)
-  .boolean('watch')
-  .describe('watch', 'Run compiler in watch mode, re-running after changes')
-  .alias('w', 'watch')
-  .default('watch', false)
-  .boolean('update')
-  .alias('u', 'update')
-  .describe('update', 'Update fixtures')
-  .default('update', false)
-  .string('pattern')
-  .alias('p', 'pattern')
-  .describe(
-    'pattern',
-    'Optional glob pattern to filter fixtures (e.g., "error.*", "use-memo")',
-  )
-  .boolean('debug')
-  .alias('d', 'debug')
-  .describe('debug', 'Enable debug logging to print HIR for each pass')
-  .default('debug', false)
   .help('help')
   .strict()
-  .parseSync(hideBin(process.argv)) as RunnerOptions;
+  .demandCommand()
+  .parse();
 
 /**
  * Do a test run and return the test results
@@ -82,6 +119,7 @@ async function runFixtures(
   compilerVersion: number,
   debug: boolean,
   requireSingleFixture: boolean,
+  sync: boolean,
 ): Promise<TestResults> {
   // We could in theory be fancy about tracking the contents of the fixtures
   // directory via our file subscription, but it's simpler to just re-read
@@ -91,7 +129,7 @@ async function runFixtures(
   const shouldLog = debug && (!requireSingleFixture || isOnlyFixture);
 
   let entries: Array<[string, TestResult]>;
-  if (!opts.sync) {
+  if (!sync) {
     // Note: promise.all to ensure parallelism when enabled
     const work: Array<Promise<[string, TestResult]>> = [];
     for (const [fixtureName, fixture] of fixtures) {
@@ -123,6 +161,7 @@ async function runFixtures(
 async function onChange(
   worker: Worker & typeof runnerWorker,
   state: RunnerState,
+  sync: boolean,
 ) {
   const {compilerVersion, isCompilerBuildValid, mode, filter, debug} = state;
   if (isCompilerBuildValid) {
@@ -140,6 +179,7 @@ async function onChange(
       compilerVersion,
       debug,
       true, // requireSingleFixture in watch mode
+      sync,
     );
     const end = performance.now();
 
@@ -192,7 +232,11 @@ export async function main(opts: RunnerOptions): Promise<void> {
   const shouldWatch = opts.watch;
 
   if (shouldWatch) {
-    makeWatchRunner(state => onChange(worker, state), opts.debug, opts.pattern);
+    makeWatchRunner(
+      state => onChange(worker, state, opts.sync),
+      opts.debug,
+      opts.pattern,
+    );
     if (opts.pattern) {
       /**
        * Warm up wormers when in watch mode. Loading the Forget babel plugin
@@ -251,6 +295,7 @@ export async function main(opts: RunnerOptions): Promise<void> {
                 0,
                 opts.debug,
                 false, // no requireSingleFixture in non-watch mode
+                opts.sync,
               );
               if (opts.update) {
                 update(results);
@@ -269,5 +314,3 @@ export async function main(opts: RunnerOptions): Promise<void> {
       );
   }
 }
-
-main(opts).catch(error => console.error(error));

compiler/yarn.lock

@@ -268,6 +268,17 @@
     source-map "^0.5.0"
     trim-right "^1.0.1"
 
+"@babel/generator@^7.19.1":
+  version "7.28.6"
+  resolved "https://registry.yarnpkg.com/@babel/generator/-/generator-7.28.6.tgz#48dcc65d98fcc8626a48f72b62e263d25fc3c3f1"
+  integrity sha512-lOoVRwADj8hjf7al89tvQ2a1lf53Z+7tiXMgpZJL3maQPDxh0DgLMN62B2MKUOFcoodBHLMbDM6WAbKgNy5Suw==
+  dependencies:
+    "@babel/parser" "^7.28.6"
+    "@babel/types" "^7.28.6"
+    "@jridgewell/gen-mapping" "^0.3.12"
+    "@jridgewell/trace-mapping" "^0.3.28"
+    jsesc "^3.0.2"
+
 "@babel/generator@^7.2.0", "@babel/generator@^7.26.0", "@babel/generator@^7.26.10", "@babel/generator@^7.26.3", "@babel/generator@^7.27.0", "@babel/generator@^7.7.2", "@babel/generator@^7.7.4":
   version "7.27.0"
   resolved "https://registry.npmjs.org/@babel/generator/-/generator-7.27.0.tgz"
@@ -662,6 +673,13 @@
   resolved "https://registry.npmjs.org/@babel/parser/-/parser-7.24.4.tgz"
   integrity sha512-zTvEBcghmeBma9QIGunWevvBAp4/Qu9Bdq+2k0Ot4fVMD6v3dsC9WOcRSKk7tRRyBM/53yKMJko9xOatGQAwSg==
 
+"@babel/parser@^7.28.6":
+  version "7.28.6"
+  resolved "https://registry.yarnpkg.com/@babel/parser/-/parser-7.28.6.tgz#f01a8885b7fa1e56dd8a155130226cd698ef13fd"
+  integrity sha512-TeR9zWR18BvbfPmGbLampPMW+uW1NZnJlRuuHso8i87QZNq2JRF9i6RgxRqtEq+wQGsS19NNTWr2duhnE49mfQ==
+  dependencies:
+    "@babel/types" "^7.28.6"
+
 "@babel/parser@^7.7.4":
   version "7.21.4"
   resolved "https://registry.npmjs.org/@babel/parser/-/parser-7.21.4.tgz"
@@ -1592,7 +1610,7 @@
     debug "^4.3.1"
     globals "^11.1.0"
 
-"@babel/types@7.26.3", "@babel/types@^7.0.0", "@babel/types@^7.19.0", "@babel/types@^7.2.0", "@babel/types@^7.2.2", "@babel/types@^7.20.2", "@babel/types@^7.20.7", "@babel/types@^7.21.2", "@babel/types@^7.24.7", "@babel/types@^7.25.9", "@babel/types@^7.26.0", "@babel/types@^7.26.10", "@babel/types@^7.26.3", "@babel/types@^7.27.0", "@babel/types@^7.27.1", "@babel/types@^7.3.0", "@babel/types@^7.3.3", "@babel/types@^7.4.4", "@babel/types@^7.7.4":
+"@babel/types@7.26.3", "@babel/types@^7.0.0", "@babel/types@^7.19.0", "@babel/types@^7.2.0", "@babel/types@^7.2.2", "@babel/types@^7.20.2", "@babel/types@^7.20.7", "@babel/types@^7.21.2", "@babel/types@^7.24.7", "@babel/types@^7.25.9", "@babel/types@^7.26.0", "@babel/types@^7.26.10", "@babel/types@^7.26.3", "@babel/types@^7.27.0", "@babel/types@^7.27.1", "@babel/types@^7.28.6", "@babel/types@^7.3.0", "@babel/types@^7.3.3", "@babel/types@^7.4.4", "@babel/types@^7.7.4":
   version "7.26.3"
   resolved "https://registry.yarnpkg.com/@babel/types/-/types-7.26.3.tgz#37e79830f04c2b5687acc77db97fbc75fb81f3c0"
   integrity sha512-vN5p+1kl59GVKMvTHt55NzzmYVxprfJD+ql7U9NFIfKCBkYE55LYtS+WtPlaYOyzydrKI8Nezd+aZextrd+FMA==
@@ -2732,6 +2750,14 @@
     "@types/yargs" "^17.0.8"
     chalk "^4.0.0"
 
+"@jridgewell/gen-mapping@^0.3.12":
+  version "0.3.13"
+  resolved "https://registry.yarnpkg.com/@jridgewell/gen-mapping/-/gen-mapping-0.3.13.tgz#6342a19f44347518c93e43b1ac69deb3c4656a1f"
+  integrity sha512-2kkt/7niJ6MgEPxF0bYdQ6etZaA+fQvDcLKckhy1yIQOzaoKjBBjSj63/aLVjYE3qhRt5dvM+uUyfCg6UKCBbA==
+  dependencies:
+    "@jridgewell/sourcemap-codec" "^1.5.0"
+    "@jridgewell/trace-mapping" "^0.3.24"
+
 "@jridgewell/gen-mapping@^0.3.2":
   version "0.3.8"
   resolved "https://registry.npmjs.org/@jridgewell/gen-mapping/-/gen-mapping-0.3.8.tgz"
@@ -2765,6 +2791,11 @@
   resolved "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.4.14.tgz"
   integrity sha512-XPSJHWmi394fuUuzDnGz1wiKqWfo1yXecHQMRf2l6hztTO+nPru658AyDngaBe7isIxEkRsPR3FZh+s7iVa4Uw==
 
+"@jridgewell/sourcemap-codec@^1.5.0":
+  version "1.5.5"
+  resolved "https://registry.yarnpkg.com/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz#6912b00d2c631c0d15ce1a7ab57cd657f2a8f8ba"
+  integrity sha512-cYQ9310grqxueWbl+WuIUIaiUaDcj7WOq5fVhEljNVgRfOUhY9fy2zTvfoqWsnebh8Sl70VScFbICvJnLKB0Og==
+
 "@jridgewell/trace-mapping@0.3.9":
   version "0.3.9"
   resolved "https://registry.npmjs.org/@jridgewell/trace-mapping/-/trace-mapping-0.3.9.tgz"
@@ -2789,6 +2820,14 @@
     "@jridgewell/resolve-uri" "3.1.0"
     "@jridgewell/sourcemap-codec" "1.4.14"
 
+"@jridgewell/trace-mapping@^0.3.28":
+  version "0.3.31"
+  resolved "https://registry.yarnpkg.com/@jridgewell/trace-mapping/-/trace-mapping-0.3.31.tgz#db15d6781c931f3a251a3dac39501c98a6082fd0"
+  integrity sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==
+  dependencies:
+    "@jridgewell/resolve-uri" "^3.1.0"
+    "@jridgewell/sourcemap-codec" "^1.4.14"
+
 "@modelcontextprotocol/sdk@^1.9.0":
   version "1.9.0"
   resolved "https://registry.npmjs.org/@modelcontextprotocol/sdk/-/sdk-1.9.0.tgz"