compiler: Log metrics on pruned memo blocks/values

Adds additional information to the CompileSuccess LoggerEvent:
* `prunedMemoBlocks` is the number of reactive scopes that were pruned for some reason.
* `prunedMemoValues` is the number of unique _values_ produced by those scopes.

Both numbers exclude blocks that are just a hook call - ie although we create and prune a scope for eg `useState()`, that's just an artifact of the sequencing of our pipeline. So what this metric is counting is cases of _other_ values that go unmemoized. See the new fixture, which takes advantage of improvements in the snap runner to optionally emit the logger events in the .expect.md file if you include the "logger" pragma in a fixture.

ghstack-source-id: c2015bb556
Pull Request resolved: https://github.com/facebook/react/pull/29810

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts

@@ -22,6 +22,7 @@ import {
   ObjectPropertyKey,
   Pattern,
   Place,
+  PrunedReactiveScopeBlock,
   ReactiveBlock,
   ReactiveFunction,
   ReactiveInstruction,
@@ -67,6 +68,23 @@ export type CodegenFunction = {
    * how many inputs/outputs each block has
    */
   memoBlocks: number;
+
+  /**
+   * Number of memoized values across all reactive scopes
+   */
+  memoValues: number;
+
+  /**
+   * The number of reactive scopes that were created but had to be discarded
+   * because they contained hook calls.
+   */
+  prunedMemoBlocks: number;
+
+  /**
+   * The total number of values that should have been memoized but weren't
+   * because they were part of a pruned memo block.
+   */
+  prunedMemoValues: number;
 };
 
 export function codegenFunction(
@@ -272,7 +290,7 @@ function codegenReactiveFunction(
     return Err(cx.errors);
   }
 
-  const countMemoBlockVisitor = new CountMemoBlockVisitor();
+  const countMemoBlockVisitor = new CountMemoBlockVisitor(fn.env);
   visitReactiveFunction(fn, countMemoBlockVisitor, undefined);
 
   return Ok({
@@ -284,16 +302,59 @@ function codegenReactiveFunction(
     generator: fn.generator,
     async: fn.async,
     memoSlotsUsed: cx.nextCacheIndex,
-    memoBlocks: countMemoBlockVisitor.count,
+    memoBlocks: countMemoBlockVisitor.memoBlocks,
+    memoValues: countMemoBlockVisitor.memoValues,
+    prunedMemoBlocks: countMemoBlockVisitor.prunedMemoBlocks,
+    prunedMemoValues: countMemoBlockVisitor.prunedMemoValues,
   });
 }
 
 class CountMemoBlockVisitor extends ReactiveFunctionVisitor<void> {
-  count: number = 0;
+  env: Environment;
+  memoBlocks: number = 0;
+  memoValues: number = 0;
+  prunedMemoBlocks: number = 0;
+  prunedMemoValues: number = 0;
 
-  override visitScope(scope: ReactiveScopeBlock, state: void): void {
-    this.count += 1;
-    this.traverseScope(scope, state);
+  constructor(env: Environment) {
+    super();
+    this.env = env;
+  }
+
+  override visitScope(scopeBlock: ReactiveScopeBlock, state: void): void {
+    this.memoBlocks += 1;
+    this.memoValues += scopeBlock.scope.declarations.size;
+    this.traverseScope(scopeBlock, state);
+  }
+
+  override visitPrunedScope(
+    scopeBlock: PrunedReactiveScopeBlock,
+    state: void
+  ): void {
+    let isHookOnlyMemoBlock = false;
+    if (
+      scopeBlock.instructions.length === 1 &&
+      scopeBlock.instructions[0].kind === "instruction"
+    ) {
+      const instr = scopeBlock.instructions[0]!.instruction;
+      if (
+        instr.value.kind === "MethodCall" ||
+        instr.value.kind === "CallExpression"
+      ) {
+        const callee =
+          instr.value.kind === "MethodCall"
+            ? instr.value.property
+            : instr.value.callee;
+        if (getHookKind(this.env, callee.identifier) != null) {
+          isHookOnlyMemoBlock = true;
+        }
+      }
+    }
+    if (!isHookOnlyMemoBlock) {
+      this.prunedMemoBlocks += 1;
+      this.prunedMemoValues += scopeBlock.scope.declarations.size;
+    }
+    this.traversePrunedScope(scopeBlock, state);
   }
 }