From 8e4d2fb69d690695db0a33001fb1aee586bde15f Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Thu, 11 Jan 2024 16:52:57 -0800
Subject: [PATCH] Repro for false positive in validatePreserveMemoization on
 non-escaping value

This demonstrates a false positive in validatePreserveExistingManualMemoization.
We prune memoization of non-escaping values, but the validation pass just sees
that the value "should" have a scope and that scope doesn't exist, and thinks we
failed to preserve memoization.
---
 ...ve-memoization-nonescaping-value.expect.md | 28 +++++++++++++++++++
 ...-preserve-memoization-nonescaping-value.js | 13 +++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.js

diff --git a/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.expect.md b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.expect.md
new file mode 100644
index 0000000000..b7b4d75aed
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.expect.md
@@ -0,0 +1,28 @@
+
+## Input
+
+```javascript
+// @validatePreserveExistingMemoizationGuarantees @enableAssumeHooksFollowRulesOfReact @enableTransitivelyFreezeFunctionExpressions
+function Component({ entity, children }) {
+  // showMessage doesn't escape so we don't memoize it.
+  // However, validatePreserveExistingMemoizationGuarantees only sees that the scope
+  // doesn't exist, and thinks the memoization was missed instead of being intentionally dropped.
+  const showMessage = useCallback(() => entity != null);
+
+  if (!showMessage) {
+    return children;
+  }
+
+  return <Message>{children}</Message>;
+}
+
+```
+
+
+## Error
+
+```
+[ReactForget] InvalidReact: This value was manually memoized, but cannot be memoized under Forget because it may be mutated after it is memoized (6:6)
+```
+          
+      
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.js b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.js
new file mode 100644
index 0000000000..d917e72ea3
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.js
@@ -0,0 +1,13 @@
+// @validatePreserveExistingMemoizationGuarantees @enableAssumeHooksFollowRulesOfReact @enableTransitivelyFreezeFunctionExpressions
+function Component({ entity, children }) {
+  // showMessage doesn't escape so we don't memoize it.
+  // However, validatePreserveExistingMemoizationGuarantees only sees that the scope
+  // doesn't exist, and thinks the memoization was missed instead of being intentionally dropped.
+  const showMessage = useCallback(() => entity != null);
+
+  if (!showMessage) {
+    return children;
+  }
+
+  return <Message>{children}</Message>;
+}