[compiler] Alternate take on ref validation

Some of the false positives we've seen have to do with the need to align our ref validation with our understanding of which functions may be called during render. The new mutability/aliasing model makes this much more explicit, with the ability to create Impure effects which we then throw as errors if they are reachable during render. This means we can now revisit ref validation by just emitting impure effects.

That's what this new pass does. It's a bit simpler: it implements the check for `ref.current == null` guarded if blocks. Otherwise it disallows access to `ref.current` specifically. Unlike before, we intentionally allow passing ref objects to functions — we just see a lot of many false positives on disallowing things like `children({ref})` or similar.

Open to feedback! This is also still WIP.

Author: josephsavona

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts

@@ -285,7 +285,7 @@ function runWithEnvironment(
     }
 
     if (env.config.validateRefAccessDuringRender) {
-      validateNoRefAccessInRender(hir).unwrap();
+      // validateNoRefAccessInRender(hir).unwrap();
     }
 
     if (env.config.validateNoSetStateInRender) {

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

@@ -28,7 +28,9 @@ import {
   isMapType,
   isPrimitiveType,
   isRefOrRefValue,
+  isRefValueType,
   isSetType,
+  isUseRefType,
   makeIdentifierId,
   Phi,
   Place,
@@ -219,6 +221,9 @@ export function inferMutationAliasingEffects(
       }
     }
   }
+  if (fn.env.config.validateRefAccessDuringRender) {
+    inferRefAccessEffects(fn, isFunctionExpression);
+  }
   return Ok(undefined);
 }
 
@@ -2513,3 +2518,127 @@ export type AbstractValue = {
   kind: ValueKind;
   reason: ReadonlySet<ValueReason>;
 };
+
+function inferRefAccessEffects(
+  fn: HIRFunction,
+  _isFunctionExpression: boolean,
+): void {
+  const nullish = new Set<IdentifierId>();
+  const nullishTest = new Map<IdentifierId, Place>();
+  let guard: {ref: IdentifierId; fallthrough: BlockId} | null = null;
+  const temporaries: Map<IdentifierId, Place> = new Map();
+
+  function visitOperand(operand: Place): AliasingEffect | null {
+    const nullTestRef = nullishTest.get(operand.identifier.id);
+    if (isRefValueType(operand.identifier) || nullTestRef != null) {
+      const refOperand = nullTestRef ?? operand;
+      return {
+        kind: 'Impure',
+        error: {
+          severity: ErrorSeverity.InvalidReact,
+          reason:
+            'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+          loc: refOperand.loc,
+          description:
+            refOperand.identifier.name !== null &&
+            refOperand.identifier.name.kind === 'named'
+              ? `Cannot access ref value \`${refOperand.identifier.name.value}\``
+              : null,
+          suggestions: null,
+        },
+        place: refOperand,
+      };
+    }
+    return null;
+  }
+
+  for (const block of fn.body.blocks.values()) {
+    if (guard !== null && guard.fallthrough === block.id) {
+      guard = null;
+    }
+    for (const instr of block.instructions) {
+      const {lvalue, value} = instr;
+      if (value.kind === 'LoadLocal' && isUseRefType(value.place.identifier)) {
+        temporaries.set(lvalue.identifier.id, value.place);
+      } else if (
+        value.kind === 'StoreLocal' &&
+        isUseRefType(value.value.identifier)
+      ) {
+        temporaries.set(value.lvalue.place.identifier.id, value.value);
+        temporaries.set(lvalue.identifier.id, value.value);
+      } else if (
+        value.kind === 'BinaryExpression' &&
+        ((isRefValueType(value.left.identifier) &&
+          nullish.has(value.right.identifier.id)) ||
+          (nullish.has(value.left.identifier.id) &&
+            isRefValueType(value.right.identifier)))
+      ) {
+        const refOperand = isRefValueType(value.left.identifier)
+          ? value.left
+          : value.right;
+        const operand = temporaries.get(refOperand.identifier.id) ?? refOperand;
+        nullishTest.set(lvalue.identifier.id, operand);
+      } else if (value.kind === 'Primitive' && value.value == null) {
+        nullish.add(lvalue.identifier.id);
+      } else if (
+        value.kind === 'PropertyLoad' &&
+        isUseRefType(value.object.identifier) &&
+        value.property === 'current'
+      ) {
+        const refOperand =
+          temporaries.get(value.object.identifier.id) ?? value.object;
+        temporaries.set(lvalue.identifier.id, refOperand);
+      } else if (
+        value.kind === 'PropertyStore' &&
+        value.property === 'current' &&
+        isUseRefType(value.object.identifier)
+      ) {
+        const refOperand =
+          temporaries.get(value.object.identifier.id) ?? value.object;
+        if (guard != null && refOperand.identifier.id === guard.ref) {
+          // Allow a single write within the guard
+          guard = null;
+        } else {
+          instr.effects ??= [];
+          instr.effects.push({
+            kind: 'Impure',
+            error: {
+              severity: ErrorSeverity.InvalidReact,
+              reason:
+                'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+              loc: value.loc,
+              description:
+                value.object.identifier.name !== null &&
+                value.object.identifier.name.kind === 'named'
+                  ? `Cannot access ref value \`${value.object.identifier.name.value}\``
+                  : null,
+              suggestions: null,
+            },
+            place: value.object,
+          });
+        }
+      } else {
+        for (const operand of eachInstructionValueOperand(value)) {
+          const error = visitOperand(operand);
+          if (error) {
+            instr.effects ??= [];
+            instr.effects.push(error);
+          }
+        }
+      }
+    }
+    if (
+      guard == null &&
+      block.terminal.kind === 'if' &&
+      nullishTest.has(block.terminal.test.identifier.id)
+    ) {
+      const ref = nullishTest.get(block.terminal.test.identifier.id)!;
+      guard = {ref: ref.identifier.id, fallthrough: block.terminal.fallthrough};
+    } else {
+      for (const operand of eachTerminalOperand(block.terminal)) {
+        const _effect = visitOperand(operand);
+        // TODO: need a place to store terminal effects generically
+      }
+    }
+  }
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hook-ref-value.expect.md

@@ -24,8 +24,6 @@ export const FIXTURE_ENTRYPOINT = {
   4 |   const ref = useRef();
 > 5 |   useEffect(() => {}, [ref.current]);
     |                        ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (5:5)
-
-InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (5:5)
   6 | }
   7 |
   8 | export const FIXTURE_ENTRYPOINT = {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-access-ref-during-render.expect.md

@@ -19,6 +19,8 @@ function Component(props) {
   3 |   const ref = useRef(null);
 > 4 |   const value = ref.current;
     |                 ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (4:4)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef). Cannot access ref value `value` (5:5)
   5 |   return value;
   6 | }
   7 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-aliased-ref-in-callback-invoked-during-render-.expect.md

@@ -19,12 +19,17 @@ function Component(props) {
 ## Error
 
 ```
-   7 |     return <Foo item={item} current={current} />;
-   8 |   };
->  9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
-     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (9:9)
-  10 | }
-  11 |
+  4 |   const renderItem = item => {
+  5 |     const aliasedRef = ref;
+> 6 |     const current = aliasedRef.current;
+    |                     ^^^^^^^^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (6:6)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef). Cannot access ref value `current` (7:7)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (7:7)
+  7 |     return <Foo item={item} current={current} />;
+  8 |   };
+  9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-disallow-mutating-refs-in-render-transitive.expect.md

@@ -21,15 +21,13 @@ function Component() {
 ## Error
 
 ```
-   7 |   };
-   8 |   const changeRef = setRef;
->  9 |   changeRef();
-     |   ^^^^^^^^^ InvalidReact: This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef) (9:9)
-
-InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (9:9)
-  10 |
-  11 |   return <button ref={ref} />;
-  12 | }
+  4 |
+  5 |   const setRef = () => {
+> 6 |     ref.current = false;
+    |     ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (6:6)
+  7 |   };
+  8 |   const changeRef = setRef;
+  9 |   changeRef();
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-read-ref-prop-in-render-destructure.expect.md

@@ -18,6 +18,10 @@ function Component({ref}) {
   2 | function Component({ref}) {
 > 3 |   const value = ref.current;
     |                 ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (3:3)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef). Cannot access ref value `value` (4:4)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (4:4)
   4 |   return <div>{value}</div>;
   5 | }
   6 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-read-ref-prop-in-render-property-load.expect.md

@@ -18,6 +18,10 @@ function Component(props) {
   2 | function Component(props) {
 > 3 |   const value = props.ref.current;
     |                 ^^^^^^^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (3:3)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef). Cannot access ref value `value` (4:4)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (4:4)
   4 |   return <div>{value}</div>;
   5 | }
   6 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-ref-in-callback-invoked-during-render.expect.md

@@ -18,12 +18,17 @@ function Component(props) {
 ## Error
 
 ```
-   6 |     return <Foo item={item} current={current} />;
-   7 |   };
->  8 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
-     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (8:8)
-   9 | }
-  10 |
+  3 |   const ref = useRef(null);
+  4 |   const renderItem = item => {
+> 5 |     const current = ref.current;
+    |                     ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (5:5)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef). Cannot access ref value `current` (6:6)
+
+InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (6:6)
+  6 |     return <Foo item={item} current={current} />;
+  7 |   };
+  8 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-set-and-read-ref-during-render.expect.md

@@ -19,8 +19,6 @@ function Component(props) {
   3 |   const ref = useRef(null);
 > 4 |   ref.current = props.value;
     |   ^^^^^^^^^^^ InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (4:4)
-
-InvalidReact: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef) (5:5)
   5 |   return ref.current;
   6 | }
   7 |