From 2ce112dbf2442c87f89b649e31dd132c170d64fd Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Fri, 22 Mar 2024 21:49:39 -0700
Subject: [PATCH] Repro for missing dep with while/if using externally declared
 "index" variable

What happens here is that the phi node for `i` has its mutable range set to
start at 0, because it has a back edge and we haven't initialized the mutable
ranges of all its operands yet when we iterate the operands and set range.start
= min(start of operand starts).

Then the corresponding scope has its range set to start at 0 too. When
PropagateScopeDeps runs it sees that `b` is from instruction 1, which is after
the start of the scope (0), so it thinks `b` isn't a valid dependency.

The fix is in InferMutableRanges, where we need to make sure that phis ignore
their operand's ranges until those ranges are initialized.
---
 ...ssing-dependency-if-within-while.expect.md | 79 +++++++++++++++++++
 ...epro-missing-dependency-if-within-while.js | 28 +++++++
 .../packages/snap/src/SproutTodoFilter.ts     |  1 +
 3 files changed, 108 insertions(+)
 create mode 100644 compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.js

diff --git a/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.expect.md b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.expect.md
new file mode 100644
index 0000000000..cacf7df91a
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.expect.md
@@ -0,0 +1,79 @@
+
+## Input
+
+```javascript
+const someGlobal = true;
+export default function Component(props) {
+  const { b } = props;
+  const items = [];
+  let i = 0;
+  while (i < 10) {
+    if (someGlobal) {
+      items.push(<div key={i}>{b}</div>);
+      i++;
+    }
+  }
+  return <>{items}</>;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ b: 42 }],
+  sequentialRenders: [
+    { b: 0 },
+    { b: 0 },
+    { b: 42 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+  ],
+};
+
+```
+
+## Code
+
+```javascript
+import { unstable_useMemoCache as useMemoCache } from "react";
+const someGlobal = true;
+export default function Component(props) {
+  const $ = useMemoCache(1);
+  const { b } = props;
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const items = [];
+    let i = 0;
+    while (i < 10) {
+      if (someGlobal) {
+        items.push(<div key={i}>{b}</div>);
+        i++;
+      }
+    }
+
+    t0 = <>{items}</>;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ b: 42 }],
+  sequentialRenders: [
+    { b: 0 },
+    { b: 0 },
+    { b: 42 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+  ],
+};
+
+```
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.js b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.js
new file mode 100644
index 0000000000..9b07b42fbf
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/bug-repro-missing-dependency-if-within-while.js
@@ -0,0 +1,28 @@
+const someGlobal = true;
+export default function Component(props) {
+  const { b } = props;
+  const items = [];
+  let i = 0;
+  while (i < 10) {
+    if (someGlobal) {
+      items.push(<div key={i}>{b}</div>);
+      i++;
+    }
+  }
+  return <>{items}</>;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ b: 42 }],
+  sequentialRenders: [
+    { b: 0 },
+    { b: 0 },
+    { b: 42 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+    { b: 0 },
+    { b: 42 },
+  ],
+};
diff --git a/compiler/packages/snap/src/SproutTodoFilter.ts b/compiler/packages/snap/src/SproutTodoFilter.ts
index fef339c363..cbc2edd572 100644
--- a/compiler/packages/snap/src/SproutTodoFilter.ts
+++ b/compiler/packages/snap/src/SproutTodoFilter.ts
@@ -534,6 +534,7 @@ const skipFilter = new Set([
   // bugs
   "bug-reduce-reactive-deps-return-in-scope",
   "bug-reduce-reactive-deps-break-in-scope",
+  "bug-repro-missing-dependency-if-within-while",
 
   // 'react-forget-runtime' not yet supported
   "flag-enable-emit-hook-guards",