[compiler] Factor out function effects from reference effects

Summary:
This PR performs a major refactor of InferReferenceEffects to separate out the work on marking places with Effects from inferring FunctionEffects. The behavior should be identical after this change (see [internal sync](https://www.internalfb.com/intern/everpaste/?handle=GN74VxscnUaztTYDAL8q0CRWBIxibsIXAAAB)) but the FunctionEffect logic should be easier to work with.

These analyses are unfortunately still deeply linked--the FunctionEffect analysis needs to reason about the "current" value kind for each point in the program, while the InferReferenceEffects algorithm performs global updates on the state of the program (e.g. freezing). In the future, it might be possible to make these entirely separate passes if we store the ValueKind directly on places.

For the most part, the logic of reference effects and function effects can be cleanly separated: for each instruction and terminal, we visit its places and infer their effects, and then we visit its places and infer any function effects that they cause. The biggest wrinkle here is that when a transitive function freeze operation occurs, it has to happen *after* inferring the function effects on the place, because otherwise we may convert a value from Context to Frozen, which will cause the ContextualMutation function effect to be converted to a ReactMutation effect too early. This can be observed in a case like this:

```
export default component C() {
  foo(() => {
    const p = {};
    return () => {
      p['a'] = 1
    };
  });
}
```
Here when the outer function returns the inner function, it freezes the inner function which transitively freezes `p`. But before that freeze happens, we need to replay the ContextualMutation on the inner function to determine that the value is mutable in the outer context. If we froze `p` first, we would instead convert the ContextualMutation to a ReactMutation and error.

To handle this, InferReferenceEffects now delays the exection of the freezeValue action until after it's called the helper functions that generate function effects. So the order of operations on a given place is now

set effect --> generate function effects --> transitively freeze dependencies, if applicable

ghstack-source-id: 21cb50c14054e7e7a307acb595ef30b54c2f2a52
Pull Request resolved: #30920

compiler/packages/babel-plugin-react-compiler/src/Inference/InferFunctionEffects.ts

@@ -0,0 +1,335 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {CompilerError, ErrorSeverity, ValueKind} from '..';
+import {
+  AbstractValue,
+  BasicBlock,
+  Effect,
+  Environment,
+  FunctionEffect,
+  Instruction,
+  InstructionValue,
+  Place,
+  ValueReason,
+  getHookKind,
+  isRefOrRefValue,
+} from '../HIR';
+import {eachInstructionOperand, eachTerminalOperand} from '../HIR/visitors';
+import {assertExhaustive} from '../Utils/utils';
+
+interface State {
+  kind(place: Place): AbstractValue;
+  values(place: Place): Array<InstructionValue>;
+  isDefined(place: Place): boolean;
+}
+
+function inferOperandEffect(state: State, place: Place): null | FunctionEffect {
+  const value = state.kind(place);
+  CompilerError.invariant(value != null, {
+    reason: 'Expected operand to have a kind',
+    loc: null,
+  });
+
+  switch (place.effect) {
+    case Effect.Store:
+    case Effect.Mutate: {
+      if (isRefOrRefValue(place.identifier)) {
+        break;
+      } else if (value.kind === ValueKind.Context) {
+        return {
+          kind: 'ContextMutation',
+          loc: place.loc,
+          effect: place.effect,
+          places: value.context.size === 0 ? new Set([place]) : value.context,
+        };
+      } else if (
+        value.kind !== ValueKind.Mutable &&
+        // We ignore mutations of primitives since this is not a React-specific problem
+        value.kind !== ValueKind.Primitive
+      ) {
+        let reason = getWriteErrorReason(value);
+        return {
+          kind:
+            value.reason.size === 1 && value.reason.has(ValueReason.Global)
+              ? 'GlobalMutation'
+              : 'ReactMutation',
+          error: {
+            reason,
+            description:
+              place.identifier.name !== null &&
+              place.identifier.name.kind === 'named'
+                ? `Found mutation of \`${place.identifier.name.value}\``
+                : null,
+            loc: place.loc,
+            suggestions: null,
+            severity: ErrorSeverity.InvalidReact,
+          },
+        };
+      }
+      break;
+    }
+  }
+  return null;
+}
+
+function inheritFunctionEffects(
+  state: State,
+  place: Place,
+): Array<FunctionEffect> {
+  const effects = inferFunctionInstrEffects(state, place);
+
+  return effects
+    .flatMap(effect => {
+      if (effect.kind === 'GlobalMutation' || effect.kind === 'ReactMutation') {
+        return [effect];
+      } else {
+        const effects: Array<FunctionEffect | null> = [];
+        CompilerError.invariant(effect.kind === 'ContextMutation', {
+          reason: 'Expected ContextMutation',
+          loc: null,
+        });
+        /**
+         * Contextual effects need to be replayed against the current inference
+         * state, which may know more about the value to which the effect applied.
+         * The main cases are:
+         * 1. The mutated context value is _still_ a context value in the current scope,
+         *    so we have to continue propagating the original context mutation.
+         * 2. The mutated context value is a mutable value in the current scope,
+         *    so the context mutation was fine and we can skip propagating the effect.
+         * 3. The mutated context value  is an immutable value in the current scope,
+         *    resulting in a non-ContextMutation FunctionEffect. We propagate that new,
+         *    more detailed effect to the current function context.
+         */
+        for (const place of effect.places) {
+          if (state.isDefined(place)) {
+            const replayedEffect = inferOperandEffect(state, {
+              ...place,
+              loc: effect.loc,
+              effect: effect.effect,
+            });
+            if (replayedEffect != null) {
+              if (replayedEffect.kind === 'ContextMutation') {
+                // Case 1, still a context value so propagate the original effect
+                effects.push(effect);
+              } else {
+                // Case 3, immutable value so propagate the more precise effect
+                effects.push(replayedEffect);
+              }
+            } // else case 2, local mutable value so this effect was fine
+          }
+        }
+        return effects;
+      }
+    })
+    .filter((effect): effect is FunctionEffect => effect != null);
+}
+
+function inferFunctionInstrEffects(
+  state: State,
+  place: Place,
+): Array<FunctionEffect> {
+  const effects: Array<FunctionEffect> = [];
+  const instrs = state.values(place);
+  CompilerError.invariant(instrs != null, {
+    reason: 'Expected operand to have instructions',
+    loc: null,
+  });
+
+  for (const instr of instrs) {
+    if (
+      (instr.kind === 'FunctionExpression' || instr.kind === 'ObjectMethod') &&
+      instr.loweredFunc.func.effects != null
+    ) {
+      effects.push(...instr.loweredFunc.func.effects);
+    }
+  }
+
+  return effects;
+}
+
+function operandEffects(
+  state: State,
+  place: Place,
+  filterRenderSafe: boolean,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  const effect = inferOperandEffect(state, place);
+  effect && functionEffects.push(effect);
+  functionEffects.push(...inheritFunctionEffects(state, place));
+  if (filterRenderSafe) {
+    return functionEffects.filter(effect => !isEffectSafeOutsideRender(effect));
+  } else {
+    return functionEffects;
+  }
+}
+
+export function inferInstructionFunctionEffects(
+  env: Environment,
+  state: State,
+  instr: Instruction,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  switch (instr.value.kind) {
+    case 'JsxExpression': {
+      if (instr.value.tag.kind === 'Identifier') {
+        functionEffects.push(...operandEffects(state, instr.value.tag, false));
+      }
+      instr.value.children?.forEach(child =>
+        functionEffects.push(...operandEffects(state, child, false)),
+      );
+      for (const attr of instr.value.props) {
+        if (attr.kind === 'JsxSpreadAttribute') {
+          functionEffects.push(...operandEffects(state, attr.argument, false));
+        } else {
+          functionEffects.push(...operandEffects(state, attr.place, true));
+        }
+      }
+      break;
+    }
+    case 'ObjectMethod':
+    case 'FunctionExpression': {
+      /**
+       * If this function references other functions, propagate the referenced function's
+       * effects to this function.
+       *
+       * ```
+       * let f = () => global = true;
+       * let g = () => f();
+       * g();
+       * ```
+       *
+       * In this example, because `g` references `f`, we propagate the GlobalMutation from
+       * `f` to `g`. Thus, referencing `g` in `g()` will evaluate the GlobalMutation in the outer
+       * function effect context and report an error. But if instead we do:
+       *
+       * ```
+       * let f = () => global = true;
+       * let g = () => f();
+       * useEffect(() => g(), [g])
+       * ```
+       *
+       * Now `g`'s effects will be discarded since they're in a useEffect.
+       */
+      for (const operand of eachInstructionOperand(instr)) {
+        instr.value.loweredFunc.func.effects ??= [];
+        instr.value.loweredFunc.func.effects.push(
+          ...inferFunctionInstrEffects(state, operand),
+        );
+      }
+      break;
+    }
+    case 'MethodCall':
+    case 'CallExpression': {
+      let callee;
+      if (instr.value.kind === 'MethodCall') {
+        callee = instr.value.property;
+        functionEffects.push(
+          ...operandEffects(state, instr.value.receiver, false),
+        );
+      } else {
+        callee = instr.value.callee;
+      }
+      functionEffects.push(...operandEffects(state, callee, false));
+      let isHook = getHookKind(env, callee.identifier) != null;
+      for (const arg of instr.value.args) {
+        const place = arg.kind === 'Identifier' ? arg : arg.place;
+        /*
+         * Join the effects of the argument with the effects of the enclosing function,
+         * unless the we're detecting a global mutation inside a useEffect hook
+         */
+        functionEffects.push(...operandEffects(state, place, isHook));
+      }
+      break;
+    }
+    case 'StartMemoize':
+    case 'FinishMemoize':
+    case 'LoadLocal':
+    case 'StoreLocal': {
+      break;
+    }
+    case 'StoreGlobal': {
+      functionEffects.push({
+        kind: 'GlobalMutation',
+        error: {
+          reason:
+            'Unexpected reassignment of a variable which was defined outside of the component. Components and hooks should be pure and side-effect free, but variable reassignment is a form of side-effect. If this variable is used in rendering, use useState instead. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
+          loc: instr.loc,
+          suggestions: null,
+          severity: ErrorSeverity.InvalidReact,
+        },
+      });
+      break;
+    }
+    default: {
+      for (const operand of eachInstructionOperand(instr)) {
+        functionEffects.push(...operandEffects(state, operand, false));
+      }
+    }
+  }
+  return functionEffects;
+}
+
+export function inferTerminalFunctionEffects(
+  state: State,
+  block: BasicBlock,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  for (const operand of eachTerminalOperand(block.terminal)) {
+    functionEffects.push(...operandEffects(state, operand, true));
+  }
+  return functionEffects;
+}
+
+export function raiseFunctionEffectErrors(
+  functionEffects: Array<FunctionEffect>,
+): void {
+  functionEffects.forEach(eff => {
+    switch (eff.kind) {
+      case 'ReactMutation':
+      case 'GlobalMutation': {
+        CompilerError.throw(eff.error);
+      }
+      case 'ContextMutation': {
+        CompilerError.throw({
+          severity: ErrorSeverity.Invariant,
+          reason: `Unexpected ContextMutation in top-level function effects`,
+          loc: eff.loc,
+        });
+      }
+      default:
+        assertExhaustive(
+          eff,
+          `Unexpected function effect kind \`${(eff as any).kind}\``,
+        );
+    }
+  });
+}
+
+function isEffectSafeOutsideRender(effect: FunctionEffect): boolean {
+  return effect.kind === 'GlobalMutation';
+}
+
+function getWriteErrorReason(abstractValue: AbstractValue): string {
+  if (abstractValue.reason.has(ValueReason.Global)) {
+    return 'Writing to a variable defined outside a component or hook is not allowed. Consider using an effect';
+  } else if (abstractValue.reason.has(ValueReason.JsxCaptured)) {
+    return 'Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX';
+  } else if (abstractValue.reason.has(ValueReason.Context)) {
+    return `Mutating a value returned from 'useContext()', which should not be mutated`;
+  } else if (abstractValue.reason.has(ValueReason.KnownReturnSignature)) {
+    return 'Mutating a value returned from a function whose return value should not be mutated';
+  } else if (abstractValue.reason.has(ValueReason.ReactiveFunctionArgument)) {
+    return 'Mutating component props or hook arguments is not allowed. Consider using a local variable instead';
+  } else if (abstractValue.reason.has(ValueReason.State)) {
+    return "Mutating a value returned from 'useState()', which should not be mutated. Use the setter function to update instead";
+  } else if (abstractValue.reason.has(ValueReason.ReducerState)) {
+    return "Mutating a value returned from 'useReducer()', which should not be mutated. Use the dispatch function to update instead";
+  } else {
+    return 'This mutates a variable that React considers immutable';
+  }
+}