[compiler] Add data flow tree to compiler error for no-deriving-state-in-effects

Author: jorge-cab

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoDerivedComputationsInEffects_exp.ts

@@ -23,6 +23,7 @@ import {
   GeneratedSource,
   SourceLocation,
 } from '../HIR';
+import {printInstruction} from '../HIR/PrintHIR';
 import {eachInstructionLValue, eachInstructionOperand} from '../HIR/visitors';
 import {isMutable} from '../ReactiveScopes/InferReactiveScopeVariables';
 import {assertExhaustive} from '../Utils/utils';
@@ -102,31 +103,24 @@ class DerivationCache {
       typeOfValue: typeOfValue ?? 'ignored',
     };
 
-    if (sourcesIds !== undefined) {
-      for (const id of sourcesIds) {
-        const sourcePlace = this.cache.get(id)?.place;
+    if (isNamedIdentifier(derivedVar)) {
+      newValue.sourcesIds.add(derivedVar.identifier.id);
+    }
 
-        if (sourcePlace === undefined) {
-          continue;
-        }
+    for (const id of sourcesIds) {
+      const sourceMetadata = this.cache.get(id);
 
-        /*
-         * If the identifier of the source is a promoted identifier, then
-         *  we should set the target as the source.
-         */
-        if (
-          sourcePlace.identifier.name === null ||
-          sourcePlace.identifier.name?.kind === 'promoted'
-        ) {
-          newValue.sourcesIds.add(derivedVar.identifier.id);
-        } else {
-          newValue.sourcesIds.add(sourcePlace.identifier.id);
-        }
+      if (sourceMetadata === undefined) {
+        continue;
       }
-    }
 
-    if (newValue.sourcesIds.size === 0) {
-      newValue.sourcesIds.add(derivedVar.identifier.id);
+      if (isNamedIdentifier(sourceMetadata.place)) {
+        newValue.sourcesIds.add(sourceMetadata.place.identifier.id);
+      } else {
+        for (const sourcesSourceId of sourceMetadata.sourcesIds) {
+          newValue.sourcesIds.add(sourcesSourceId);
+        }
+      }
     }
 
     this.cache.set(derivedVar.identifier.id, newValue);
@@ -151,6 +145,12 @@ class DerivationCache {
   }
 }
 
+function isNamedIdentifier(place: Place): Boolean {
+  return (
+    place.identifier.name !== null && place.identifier.name?.kind === 'named'
+  );
+}
+
 /**
  * Validates that useEffect is not used for derived computations which could/should
  * be performed in render.
@@ -202,7 +202,9 @@ export function validateNoDerivedComputationsInEffects_exp(
       if (param.kind === 'Identifier') {
         context.derivationCache.cache.set(param.identifier.id, {
           place: param,
-          sourcesIds: new Set([param.identifier.id]),
+          sourcesIds: new Set(
+            isNamedIdentifier(param) ? [param.identifier.id] : [],
+          ),
           typeOfValue: 'fromProps',
         });
       }
@@ -212,7 +214,9 @@ export function validateNoDerivedComputationsInEffects_exp(
     if (props != null && props.kind === 'Identifier') {
       context.derivationCache.cache.set(props.identifier.id, {
         place: props,
-        sourcesIds: new Set([props.identifier.id]),
+        sourcesIds: new Set(
+          isNamedIdentifier(props) ? [props.identifier.id] : [],
+        ),
         typeOfValue: 'fromProps',
       });
     }
@@ -223,10 +227,10 @@ export function validateNoDerivedComputationsInEffects_exp(
     context.derivationCache.takeSnapshot();
 
     for (const block of fn.body.blocks.values()) {
+      recordPhiDerivations(block, context);
       for (const instr of block.instructions) {
         recordInstructionDerivations(instr, context, isFirstPass);
       }
-      recordPhiDerivations(block, context);
     }
 
     context.derivationCache.checkForChanges();
@@ -237,6 +241,7 @@ export function validateNoDerivedComputationsInEffects_exp(
     validateEffect(effect, context);
   }
 
+  console.log(derivationCache.cache);
   if (errors.hasAnyErrors()) {
     throw errors;
   }
@@ -293,6 +298,7 @@ function recordInstructionDerivations(
   if (value.kind === 'FunctionExpression') {
     context.functions.set(lvalue.identifier.id, value);
     for (const [, block] of value.loweredFunc.func.body.blocks) {
+      recordPhiDerivations(block, context);
       for (const instr of block.instructions) {
         recordInstructionDerivations(instr, context, isFirstPass);
       }
@@ -341,9 +347,7 @@ function recordInstructionDerivations(
     }
 
     typeOfValue = joinValue(typeOfValue, operandMetadata.typeOfValue);
-    for (const id of operandMetadata.sourcesIds) {
-      sources.add(id);
-    }
+    sources.add(operand.identifier.id);
   }
 
   if (typeOfValue === 'ignored') {
@@ -406,6 +410,60 @@ function recordInstructionDerivations(
   }
 }
 
+function buildDataFlowTree(
+  sourceId: IdentifierId,
+  indent: string = '',
+  isLast: boolean = true,
+  context: ValidationContext,
+): string {
+  const sourceMetadata = context.derivationCache.cache.get(sourceId);
+  if (!sourceMetadata || !sourceMetadata.place.identifier.name?.value) {
+    return '';
+  }
+
+  const sourceName = sourceMetadata.place.identifier.name.value;
+  const prefix = indent + (isLast ? '└── ' : '├── ');
+  const childIndent = indent + (isLast ? '    ' : '│   ');
+
+  const childSourceIds = Array.from(sourceMetadata.sourcesIds).filter(
+    id => id !== sourceId,
+  );
+
+  const isOriginal = childSourceIds.length === 0;
+
+  let result = `${prefix}${sourceName}`;
+
+  if (isOriginal) {
+    let typeLabel: string;
+    if (sourceMetadata.typeOfValue === 'fromProps') {
+      typeLabel = 'Prop';
+    } else if (sourceMetadata.typeOfValue === 'fromState') {
+      typeLabel = 'State';
+    } else {
+      typeLabel = 'Prop and State';
+    }
+    result += ` (${typeLabel})`;
+  }
+
+  if (childSourceIds.length > 0) {
+    result += '\n';
+    childSourceIds.forEach((childId, index) => {
+      const childTree = buildDataFlowTree(
+        childId,
+        childIndent,
+        index === childSourceIds.length - 1,
+        context,
+      );
+      if (childTree) {
+        result += childTree + '\n';
+      }
+    });
+    result = result.slice(0, -1);
+  }
+
+  return result;
+}
+
 function validateEffect(
   effectFunction: HIRFunction,
   context: ValidationContext,
@@ -508,34 +566,68 @@ function validateEffect(
           .length -
           1
     ) {
-      const derivedDepsStr = Array.from(derivedSetStateCall.sourceIds)
-        .map(sourceId => {
-          const sourceMetadata = context.derivationCache.cache.get(sourceId);
-          return sourceMetadata?.place.identifier.name?.value;
-        })
-        .filter(Boolean)
-        .join(', ');
-
-      let description;
-
-      if (derivedSetStateCall.typeOfValue === 'fromProps') {
-        description = `From props: [${derivedDepsStr}]`;
-      } else if (derivedSetStateCall.typeOfValue === 'fromState') {
-        description = `From local state: [${derivedDepsStr}]`;
-      } else {
-        description = `From props and local state: [${derivedDepsStr}]`;
+      const allSourceIds = Array.from(derivedSetStateCall.sourceIds);
+      const trees = allSourceIds
+        .map((id, index) =>
+          buildDataFlowTree(id, '', index === allSourceIds.length - 1, context),
+        )
+        .filter(Boolean);
+
+      const propsSet = new Set<string>();
+      const stateSet = new Set<string>();
+
+      for (const sourceId of derivedSetStateCall.sourceIds) {
+        const sourceMetadata = context.derivationCache.cache.get(sourceId);
+        if (
+          sourceMetadata &&
+          sourceMetadata.place.identifier.name?.value &&
+          (sourceMetadata.sourcesIds.size === 0 ||
+            (sourceMetadata.sourcesIds.size === 1 &&
+              sourceMetadata.sourcesIds.has(sourceId)))
+        ) {
+          const name = sourceMetadata.place.identifier.name.value;
+          if (sourceMetadata.typeOfValue === 'fromProps') {
+            propsSet.add(name);
+          } else if (sourceMetadata.typeOfValue === 'fromState') {
+            stateSet.add(name);
+          } else if (sourceMetadata.typeOfValue === 'fromPropsAndState') {
+            propsSet.add(name);
+            stateSet.add(name);
+          }
+        }
+      }
+
+      const propsArr = Array.from(propsSet);
+      const stateArr = Array.from(stateSet);
+
+      let rootSources = '';
+      if (propsArr.length > 0) {
+        rootSources += `Props: [${propsArr.join(', ')}]`;
       }
+      if (stateArr.length > 0) {
+        if (rootSources) rootSources += '\n';
+        rootSources += `State: [${stateArr.join(', ')}]`;
+      }
+
+      const description = `This setState call is setting a derived value that depends on the following reactive sources:
+
+${rootSources}
+
+Data Flow Tree:
+${trees.join('\n')}
+
+See: https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state`;
 
       context.errors.pushDiagnostic(
         CompilerDiagnostic.create({
-          description: `Derived values (${description}) should be computed during render, rather than in effects. Using an effect triggers an additional render which can hurt performance and user experience, potentially briefly showing stale values to the user`,
+          description: description,
           category: ErrorCategory.EffectDerivationsOfState,
           reason:
-            'You might not need an effect. Derive values in render, not effects.',
+            'Avoid derived computations in effects. Compute values during render instead.',
         }).withDetails({
           kind: 'error',
           loc: derivedSetStateCall.value.callee.loc,
-          message: 'This should be computed during render, not in an effect',
+          message: 'Move this computation to render',
         }),
       );
     }