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[compiler] Add fault tolerance test fixtures

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Joe Savona
2026-02-20 12:48:55 -08:00
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1
compiler/fault-tolerance-overview.md
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@@ -327,4 +327,5 @@ Walk through `runWithEnvironment` and wrap each pass call site. This is the inte
* **Phase 3 (BuildHIR) revealed that most error sites already used `builder.errors.push()` for accumulation.** The existing lowering code was designed to accumulate errors rather than throw. The main changes were: (1) changing `lower()` return type from `Result` to `HIRFunction`, (2) recording builder errors on env, (3) adding a try/catch around body lowering to catch thrown CompilerErrors from sub-calls like `resolveBinding()`, (4) treating `var` as `let` instead of skipping declarations, and (5) fixing ForStatement init/test handling to produce valid CFG structure.
* **Partial HIR can trigger downstream invariants.** When lowering skips or partially handles constructs (e.g., unreachable hoisted functions, `var` declarations before the fix), downstream passes like `InferMutationAliasingEffects` may encounter uninitialized identifiers and throw invariants. This is acceptable since the function still correctly bails out of compilation, but error messages may be less specific. The fix for `var` (treating as `let`) demonstrates how to avoid this: continue lowering with a best-effort representation rather than skipping entirely.
* **Errors accumulated on `env` are lost when an invariant propagates out of the pipeline.** Since invariant CompilerErrors always re-throw through `tryRecord()`, they exit the pipeline as exceptions. The caller only sees the invariant error, not any errors previously recorded on `env`. This is a design limitation that could be addressed by aggregating env errors with caught exceptions in `tryCompileFunction()`.
* **Dedicated fault tolerance test fixtures** were added in `__tests__/fixtures/compiler/fault-tolerance/`. Each fixture combines two or more errors from different passes to verify the compiler reports all of them rather than short-circuiting on the first. Coverage includes: `var`+props mutation (BuildHIR→InferMutationAliasingEffects), `var`+ref access (BuildHIR→ValidateNoRefAccessInRender), `try/finally`+props mutation (BuildHIR→InferMutationAliasingEffects), `try/finally`+ref access (BuildHIR→ValidateNoRefAccessInRender), and a 3-error test combining try/finally+ref access+props mutation.

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md Normal file
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## Input
```javascript
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
// Error: try/finally (Todo from BuildHIR)
try {
doWork();
} finally {
doCleanup();
}
// Error: mutating frozen props
props.value = 1;
return <div>{props.value}</div>;
}
```
## Error
```
Found 2 errors:
Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
error.try-finally-and-mutation-of-props.ts:9:2
7 | function Component(props) {
8 | // Error: try/finally (Todo from BuildHIR)
> 9 | try {
| ^^^^^
> 10 | doWork();
| ^^^^^^^^^^^^^
> 11 | } finally {
| ^^^^^^^^^^^^^
> 12 | doCleanup();
| ^^^^^^^^^^^^^
> 13 | }
| ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
14 |
15 | // Error: mutating frozen props
16 | props.value = 1;
Error: This value cannot be modified
Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
error.try-finally-and-mutation-of-props.ts:16:2
14 |
15 | // Error: mutating frozen props
> 16 | props.value = 1;
| ^^^^^ value cannot be modified
17 |
18 | return <div>{props.value}</div>;
19 | }
```

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js Normal file
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/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
// Error: try/finally (Todo from BuildHIR)
try {
doWork();
} finally {
doCleanup();
}
// Error: mutating frozen props
props.value = 1;
return <div>{props.value}</div>;
}

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.expect.md Normal file
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## Input
```javascript
// @validateRefAccessDuringRender
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
*/
function Component() {
const ref = useRef(null);
// Error: try/finally (Todo from BuildHIR)
try {
doSomething();
} finally {
cleanup();
}
// Error: reading ref during render
const value = ref.current;
return <div>{value}</div>;
}
```
## Error
```
Found 2 errors:
Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
error.try-finally-and-ref-access.ts:12:2
10 |
11 | // Error: try/finally (Todo from BuildHIR)
> 12 | try {
| ^^^^^
> 13 | doSomething();
| ^^^^^^^^^^^^^^^^^^
> 14 | } finally {
| ^^^^^^^^^^^^^^^^^^
> 15 | cleanup();
| ^^^^^^^^^^^^^^^^^^
> 16 | }
| ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
17 |
18 | // Error: reading ref during render
19 | const value = ref.current;
Error: Cannot access refs during render
React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
error.try-finally-and-ref-access.ts:19:16
17 |
18 | // Error: reading ref during render
> 19 | const value = ref.current;
| ^^^^^^^^^^^ Cannot access ref value during render
20 |
21 | return <div>{value}</div>;
22 | }
```

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js Normal file
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// @validateRefAccessDuringRender
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
*/
function Component() {
const ref = useRef(null);
// Error: try/finally (Todo from BuildHIR)
try {
doSomething();
} finally {
cleanup();
}
// Error: reading ref during render
const value = ref.current;
return <div>{value}</div>;
}

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md Normal file
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## Input
```javascript
// @validateRefAccessDuringRender
/**
* Fault tolerance test: three independent errors should all be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
* Error 3 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
const ref = useRef(null);
// Error: try/finally (Todo from BuildHIR)
try {
doWork();
} finally {
cleanup();
}
// Error: reading ref during render
const value = ref.current;
// Error: mutating frozen props
props.items = [];
return <div>{value}</div>;
}
```
## Error
```
Found 3 errors:
Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
error.try-finally-ref-access-and-mutation.ts:13:2
11 |
12 | // Error: try/finally (Todo from BuildHIR)
> 13 | try {
| ^^^^^
> 14 | doWork();
| ^^^^^^^^^^^^^
> 15 | } finally {
| ^^^^^^^^^^^^^
> 16 | cleanup();
| ^^^^^^^^^^^^^
> 17 | }
| ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
18 |
19 | // Error: reading ref during render
20 | const value = ref.current;
Error: This value cannot be modified
Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
error.try-finally-ref-access-and-mutation.ts:23:2
21 |
22 | // Error: mutating frozen props
> 23 | props.items = [];
| ^^^^^ value cannot be modified
24 |
25 | return <div>{value}</div>;
26 | }
Error: Cannot access refs during render
React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
error.try-finally-ref-access-and-mutation.ts:20:16
18 |
19 | // Error: reading ref during render
> 20 | const value = ref.current;
| ^^^^^^^^^^^ Cannot access ref value during render
21 |
22 | // Error: mutating frozen props
23 | props.items = [];
```

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js Normal file
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// @validateRefAccessDuringRender
/**
* Fault tolerance test: three independent errors should all be reported.
*
* Error 1 (BuildHIR): `try/finally` is not supported
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
* Error 3 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
const ref = useRef(null);
// Error: try/finally (Todo from BuildHIR)
try {
doWork();
} finally {
cleanup();
}
// Error: reading ref during render
const value = ref.current;
// Error: mutating frozen props
props.items = [];
return <div>{value}</div>;
}

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md Normal file
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## Input
```javascript
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
* Error 2 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
// Error: var declaration (Todo from BuildHIR)
var items = props.items;
// Error: mutating frozen props (detected during inference)
props.items = [];
return <div>{items.length}</div>;
}
```
## Error
```
Found 2 errors:
Todo: (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
error.var-declaration-and-mutation-of-props.ts:9:2
7 | function Component(props) {
8 | // Error: var declaration (Todo from BuildHIR)
> 9 | var items = props.items;
| ^^^^^^^^^^^^^^^^^^^^^^^^ (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
10 |
11 | // Error: mutating frozen props (detected during inference)
12 | props.items = [];
Error: This value cannot be modified
Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
error.var-declaration-and-mutation-of-props.ts:12:2
10 |
11 | // Error: mutating frozen props (detected during inference)
> 12 | props.items = [];
| ^^^^^ value cannot be modified
13 |
14 | return <div>{items.length}</div>;
15 | }
```

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js Normal file
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/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
* Error 2 (InferMutationAliasingEffects): Mutation of frozen props
*/
function Component(props) {
// Error: var declaration (Todo from BuildHIR)
var items = props.items;
// Error: mutating frozen props (detected during inference)
props.items = [];
return <div>{items.length}</div>;
}

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md Normal file
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## Input
```javascript
// @validateRefAccessDuringRender
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
*/
function Component() {
const ref = useRef(null);
// Error: var declaration (Todo from BuildHIR)
var items = [1, 2, 3];
// Error: reading ref during render
const value = ref.current;
return <div>{value}{items.length}</div>;
}
```
## Error
```
Found 2 errors:
Todo: (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
error.var-declaration-and-ref-access.ts:12:2
10 |
11 | // Error: var declaration (Todo from BuildHIR)
> 12 | var items = [1, 2, 3];
| ^^^^^^^^^^^^^^^^^^^^^^ (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
13 |
14 | // Error: reading ref during render
15 | const value = ref.current;
Error: Cannot access refs during render
React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
error.var-declaration-and-ref-access.ts:15:16
13 |
14 | // Error: reading ref during render
> 15 | const value = ref.current;
| ^^^^^^^^^^^ Cannot access ref value during render
16 |
17 | return <div>{value}{items.length}</div>;
18 | }
```

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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.js Normal file
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// @validateRefAccessDuringRender
/**
* Fault tolerance test: two independent errors should both be reported.
*
* Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
* Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
*/
function Component() {
const ref = useRef(null);
// Error: var declaration (Todo from BuildHIR)
var items = [1, 2, 3];
// Error: reading ref during render
const value = ref.current;
return (
<div>
{value}
{items.length}
</div>
);
}