From f773cbc331428e57bac3d33e08b219723b5f24fe Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Fri, 20 Feb 2026 12:48:55 -0800
Subject: [PATCH] [compiler] Add fault tolerance test fixtures

---
 compiler/fault-tolerance-overview.md          |  1 +
 ...ry-finally-and-mutation-of-props.expect.md | 66 ++++++++++++++
 ...error.try-finally-and-mutation-of-props.js | 19 ++++
 ...error.try-finally-and-ref-access.expect.md | 69 +++++++++++++++
 .../error.try-finally-and-ref-access.js       | 22 +++++
 ...-finally-ref-access-and-mutation.expect.md | 86 +++++++++++++++++++
 ...ror.try-finally-ref-access-and-mutation.js | 26 ++++++
 ...eclaration-and-mutation-of-props.expect.md | 54 ++++++++++++
 ...r.var-declaration-and-mutation-of-props.js | 15 ++++
 ...r.var-declaration-and-ref-access.expect.md | 57 ++++++++++++
 .../error.var-declaration-and-ref-access.js   | 23 +++++
 11 files changed, 438 insertions(+)
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.js

diff --git a/compiler/fault-tolerance-overview.md b/compiler/fault-tolerance-overview.md
index 3010405dfa..aaeee21676 100644
--- a/compiler/fault-tolerance-overview.md
+++ b/compiler/fault-tolerance-overview.md
@@ -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.
 
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md
new file mode 100644
index 0000000000..750f35d7eb
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md
@@ -0,0 +1,66 @@
+
+## 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 | }
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js
new file mode 100644
index 0000000000..a26724daf6
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js
@@ -0,0 +1,19 @@
+/**
+ * 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>;
+}
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.expect.md
new file mode 100644
index 0000000000..45b637f104
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.expect.md
@@ -0,0 +1,69 @@
+
+## 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 | }
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js
new file mode 100644
index 0000000000..3d247c2c0b
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js
@@ -0,0 +1,22 @@
+// @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>;
+}
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md
new file mode 100644
index 0000000000..a21c72635b
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md
@@ -0,0 +1,86 @@
+
+## 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 = [];
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js
new file mode 100644
index 0000000000..f25a59c765
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js
@@ -0,0 +1,26 @@
+// @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>;
+}
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md
new file mode 100644
index 0000000000..ecb65622d4
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md
@@ -0,0 +1,54 @@
+
+## 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 | }
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js
new file mode 100644
index 0000000000..c0fd6a34fb
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js
@@ -0,0 +1,15 @@
+/**
+ * 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>;
+}
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md
new file mode 100644
index 0000000000..fa51122e92
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md
@@ -0,0 +1,57 @@
+
+## 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 | }
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.js b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.js
new file mode 100644
index 0000000000..60a14ecec3
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.js
@@ -0,0 +1,23 @@
+// @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>
+  );
+}