[compiler] Feature flag cleanup (facebook#35825)

Cleans up feature flags that do not have an active experiment and which
we don't currently plan to ship, one commit per flag. Notable removals:
* Automatic (inferred) effect dependencies / Fire: abandoned due to
early feedback. Shipped useEffectEvent which addresses some of the
use-cases.
* Inline JSX transform (experimented, not a consistent win)
* Context selectors (experimented, not a sufficient/consistent win given
the benefit the compiler already provides)
* Instruction Reordering (will try a different approach)

To decide which features to remove, I looked at Meta's internal repos as
well as eslint-pugin-react-hooks to see which flags were never
overridden anywhere. That gave a longer list of flags, from which I then
removed some features that I know are used in OSS.

Author: josephsavona

compiler/CLAUDE.md

@@ -215,12 +215,12 @@ const UseEffectEventHook = addHook(
 Feature flags are configured in `src/HIR/Environment.ts`, for example `enableJsxOutlining`. Test fixtures can override the active feature flags used for that fixture via a comment pragma on the first line of the fixture input, for example:
 
 ```javascript
-// enableJsxOutlining @enableChangeVariableCodegen:false
+// enableJsxOutlining @enableNameAnonymousFunctions:false
 
 ...code...
 ```
 
-Would enable the `enableJsxOutlining` feature and disable the `enableChangeVariableCodegen` feature.
+Would enable the `enableJsxOutlining` feature and disable the `enableNameAnonymousFunctions` feature.
 
 ## Debugging Tips
 

compiler/apps/playground/__tests__/e2e/__snapshots__/page.spec.ts/disableMemoizationForDebugging-output.txt

@@ -283,37 +283,6 @@ test('error is displayed when config has validation error', async ({page}) => {
   expect(output.replace(/\s+/g, ' ')).toContain('Unexpected compilationMode');
 });
 
-test('disableMemoizationForDebugging flag works as expected', async ({
-  page,
-}) => {
-  const store: Store = {
-    source: TEST_SOURCE,
-    config: `import type { PluginOptions } from 'babel-plugin-react-compiler/dist';
-
-({
-  environment: {
-    disableMemoizationForDebugging: true
-  }
-} satisfies PluginOptions);`,
-    showInternals: false,
-  };
-  const hash = encodeStore(store);
-  await page.goto(`/#${hash}`, {waitUntil: 'networkidle'});
-  await page.waitForFunction(isMonacoLoaded);
-  await expandConfigs(page);
-  await page.screenshot({
-    fullPage: true,
-    path: 'test-results/07-config-disableMemoizationForDebugging-flag.png',
-  });
-
-  const text =
-    (await page.locator('.monaco-editor-output').allInnerTexts()) ?? [];
-  const output = await formatPrint(text);
-
-  expect(output).not.toEqual('');
-  expect(output).toMatchSnapshot('disableMemoizationForDebugging-output.txt');
-});
-
 test('error is displayed when source has syntax error', async ({page}) => {
   const syntaxErrorSource = `function TestComponent(props) {
   const oops = props.

compiler/apps/playground/__tests__/e2e/page.spec.ts

@@ -70,9 +70,6 @@ The `occursCheck` method prevents infinite types by detecting when a type variab
 - `DeclareContext` and `LoadContext` generate no type equations (intentionally untyped)
 - `StoreContext` with `Const` kind does propagate the rvalue type to enable ref inference through context variables
 
-### Event Handler Inference
-When `enableInferEventHandlers` is enabled, JSX props starting with "on" (e.g., `onClick`) on built-in DOM elements (excluding web components with hyphens) are inferred as `Function<BuiltInEventHandlerId>`.
-
 ## TODOs
 1. **Hook vs Function type ambiguity**:
    > "TODO: callee could be a hook or a function, so this type equation isn't correct. We should change Hook to a subtype of Function or change unifier logic."

compiler/packages/babel-plugin-react-compiler/docs/passes/06-inferTypes.md

@@ -205,8 +205,6 @@ if ($[0] !== "source_hash_abc123") {
 }
 ```
 
-### Change Detection for Debugging
-When `enableChangeDetectionForDebugging` is configured, additional code is generated to detect when cached values unexpectedly change.
 
 ### Labeled Breaks
 Control flow with labeled breaks (for early returns or loop exits) uses `codegenLabel` to generate consistent label names:
@@ -231,7 +229,6 @@ type CodegenFunction = {
   prunedMemoBlocks: number;  // Scopes that were pruned
   prunedMemoValues: number;  // Values in pruned scopes
   hasInferredEffect: boolean;
-  hasFireRewrite: boolean;
 };
 ```