[compiler] Add DependencyPath optional property

Adds an `optional: boolean` property to each token in a DependencyPath, currently always set to false. Also updates the equality and printing logic for paths to account for this field.

Subsequent PRs will update our logic to determine which manual dependencies were optional, then we can start inferring optional deps as well.

[ghstack-poisoned]

compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts

@@ -1500,10 +1500,13 @@ export type ReactiveScopeDependency = {
 export function areEqualPaths(a: DependencyPath, b: DependencyPath): boolean {
   return (
     a.length === b.length &&
-    a.every((item, ix) => item.property === b[ix].property)
+    a.every(
+      (item, ix) =>
+        item.property === b[ix].property && item.optional === b[ix].optional,
+    )
   );
 }
-export type DependencyPath = Array<{property: string}>;
+export type DependencyPath = Array<{property: string; optional: boolean}>;
 
 /*
  * Simulated opaque type for BlockIds to prevent using normal numbers as block ids

compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts

@@ -869,7 +869,7 @@ export function printManualMemoDependency(
       ? val.root.value.identifier.name.value
       : printIdentifier(val.root.value.identifier);
   }
-  return `${rootStr}${val.path.length > 0 ? '.' : ''}${val.path.join('.')}`;
+  return `${rootStr}${val.path.map(v => `${v.optional ? '?.' : '.'}${v.property}`).join('')}`;
 }
 export function printType(type: Type): string {
   if (type.kind === 'Type') return '';

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

@@ -68,7 +68,8 @@ export function collectMaybeMemoDependencies(
       if (object != null) {
         return {
           root: object.root,
-          path: [...object.path, {property: value.property}],
+          // TODO: determine if the access is optional
+          path: [...object.path, {property: value.property, optional: false}],
         };
       }
       break;

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

@@ -6,7 +6,7 @@
  */
 
 import {CompilerError} from '../CompilerError';
-import {Identifier, ReactiveScopeDependency} from '../HIR';
+import {DependencyPath, Identifier, ReactiveScopeDependency} from '../HIR';
 import {printIdentifier} from '../HIR/PrintHIR';
 import {assertExhaustive} from '../Utils/utils';
 
@@ -252,7 +252,7 @@ type DependencyNode = {
 };
 
 type ReduceResultNode = {
-  relativePath: Array<{property: string}>;
+  relativePath: DependencyPath;
   accessType: PropertyAccessType;
 };
 
@@ -283,7 +283,10 @@ function deriveMinimalDependenciesInSubtree(
     const childResult = deriveMinimalDependenciesInSubtree(childNode).map(
       ({relativePath, accessType}) => {
         return {
-          relativePath: [{property: childName}, ...relativePath],
+          relativePath: [
+            {property: childName, optional: false},
+            ...relativePath,
+          ],
           accessType,
         };
       },

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

@@ -485,7 +485,7 @@ class Context {
       };
     }
 
-    objectDependency.path.push({property});
+    objectDependency.path.push({property, optional: false});
 
     return objectDependency;
   }

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

@@ -116,7 +116,7 @@ function prettyPrintScopeDependency(val: ReactiveScopeDependency): string {
   } else {
     rootStr = '[unnamed]';
   }
-  return `${rootStr}${val.path.length > 0 ? '.' : ''}${val.path.join('.')}`;
+  return `${rootStr}${val.path.map(v => `${v.optional ? '?.' : '.'}${v.property}`).join('')}`;
 }
 
 enum CompareDependencyResult {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-optional-member-expression-as-memo-dep.expect.md

@@ -0,0 +1,32 @@
+
+## Input
+
+```javascript
+// @validatePreserveExistingMemoizationGuarantees
+function Component(props) {
+  const data = useMemo(() => {
+    return props.items?.edges?.nodes ?? [];
+  }, [props.items?.edges?.nodes]);
+  return <Foo data={data} />;
+}
+
+```
+
+
+## Error
+
+```
+  1 | // @validatePreserveExistingMemoizationGuarantees
+  2 | function Component(props) {
+> 3 |   const data = useMemo(() => {
+    |                        ^^^^^^^
+> 4 |     return props.items?.edges?.nodes ?? [];
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+> 5 |   }, [props.items?.edges?.nodes]);
+    | ^^^^ CannotPreserveMemoization: React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected (3:5)
+  6 |   return <Foo data={data} />;
+  7 | }
+  8 |
+```
+          
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-optional-member-expression-as-memo-dep.js

@@ -0,0 +1,7 @@
+// @validatePreserveExistingMemoizationGuarantees
+function Component(props) {
+  const data = useMemo(() => {
+    return props.items?.edges?.nodes ?? [];
+  }, [props.items?.edges?.nodes]);
+  return <Foo data={data} />;
+}