[compiler][rfc] enablePreserveMemo treats manual deps as non-nullable

The `@enablePreserveExistingMemoizationGuarantees` mode can still fail to preserve manual memoization due to mismtached dependencies. Specifically, where the user's dependencies are more precise than the compiler infers bc the compiler is being conservative about what might be nullable. In this mode though we're intentionally using information from the manual memoization and can also rely on the deps as a signal for what's non-nullable.

The idea of the PR — which I need to test with optional chains still — is that we treat manual memo deps just like other inferred-as-non-nullable objects during PropagateScopeDeps. We're careful to not treat the full path as non-nullable, only up to the last property index. So `x.y.z` as a manual dep treats `x.y` as non-nullable, allowing us to preserve a conditional dependency on `x.y.z`.

I still need to handle optionals and think about what should happen for manual deps like `x?.y?.z`.

Author: josephsavona

compiler/packages/babel-plugin-react-compiler/src/HIR/CollectHoistablePropertyLoads.ts

@@ -454,6 +454,31 @@ function collectNonNullsInBlocks(
             assumedNonNullObjects.add(entry);
           }
         }
+      } else if (
+        fn.env.config.enablePreserveExistingMemoizationGuarantees &&
+        instr.value.kind === 'StartMemoize' &&
+        instr.value.deps != null
+      ) {
+        for (const dep of instr.value.deps) {
+          if (dep.root.kind === 'NamedLocal') {
+            if (
+              !isImmutableAtInstr(dep.root.value.identifier, instr.id, context)
+            ) {
+              continue;
+            }
+            for (let i = 0; i < dep.path.length; i++) {
+              const pathEntry = dep.path[i]!;
+              if (!pathEntry.optional) {
+                const depNode = context.registry.getOrCreateProperty({
+                  identifier: dep.root.value.identifier,
+                  path: dep.path.slice(0, i),
+                  reactive: dep.root.value.reactive,
+                });
+                assumedNonNullObjects.add(depNode);
+              }
+            }
+          }
+        }
       }
     }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-preserve-memo-deps-mixed-optional-nonoptional-property-chain.expect.md

@@ -0,0 +1,91 @@
+
+## Input
+
+```javascript
+// @enablePreserveExistingMemoizationGuarantees @validatePreserveExistingMemoizationGuarantees @enableOptionalDependencies @enableTreatFunctionDepsAsConditional:false
+
+import {useMemo} from 'react';
+import {identity, ValidateMemoization} from 'shared-runtime';
+
+function Component({x}) {
+  const object = useMemo(() => {
+    return identity({
+      callback: () => {
+        // This is a bug in our dependency inference: we stop capturing dependencies
+        // after x.a.b?.c. But what this dependency is telling us is that if `x.a.b`
+        // was non-nullish, then we can access `.c.d?.e`. Thus we should take the
+        // full property chain, exactly as-is with optionals/non-optionals, as a
+        // dependency
+        return identity(x.a.b?.c.d?.e);
+      },
+    });
+  }, [x.a.b?.c.d?.e]);
+  const result = useMemo(() => {
+    return [object.callback()];
+  }, [object]);
+  return <Inner x={x} result={result} />;
+}
+
+function Inner({x, result}) {
+  'use no memo';
+  return <ValidateMemoization inputs={[x.y.z]} output={result} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{x: {y: {z: 42}}}],
+  sequentialRenders: [
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 3.14}}},
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 3.14}}},
+    {x: {y: {z: 42}}},
+  ],
+};
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Compilation Skipped: Existing memoization could not be preserved
+
+React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected. The inferred dependency was `x.a.b?.c`, but the source dependencies were [x.a.b?.c.d?.e]. Inferred less specific property than source.
+
+error.todo-preserve-memo-deps-mixed-optional-nonoptional-property-chain.ts:7:25
+   5 |
+   6 | function Component({x}) {
+>  7 |   const object = useMemo(() => {
+     |                          ^^^^^^^
+>  8 |     return identity({
+     | ^^^^^^^^^^^^^^^^^^^^^
+>  9 |       callback: () => {
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 10 |         // This is a bug in our dependency inference: we stop capturing dependencies
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 11 |         // after x.a.b?.c. But what this dependency is telling us is that if `x.a.b`
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 12 |         // was non-nullish, then we can access `.c.d?.e`. Thus we should take the
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 13 |         // full property chain, exactly as-is with optionals/non-optionals, as a
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 14 |         // dependency
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 15 |         return identity(x.a.b?.c.d?.e);
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 16 |       },
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 17 |     });
+     | ^^^^^^^^^^^^^^^^^^^^^
+> 18 |   }, [x.a.b?.c.d?.e]);
+     | ^^^^ Could not preserve existing manual memoization
+  19 |   const result = useMemo(() => {
+  20 |     return [object.callback()];
+  21 |   }, [object]);
+```
+          
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-preserve-memo-deps-mixed-optional-nonoptional-property-chain.js

@@ -0,0 +1,41 @@
+// @enablePreserveExistingMemoizationGuarantees @validatePreserveExistingMemoizationGuarantees @enableOptionalDependencies @enableTreatFunctionDepsAsConditional:false
+
+import {useMemo} from 'react';
+import {identity, ValidateMemoization} from 'shared-runtime';
+
+function Component({x}) {
+  const object = useMemo(() => {
+    return identity({
+      callback: () => {
+        // This is a bug in our dependency inference: we stop capturing dependencies
+        // after x.a.b?.c. But what this dependency is telling us is that if `x.a.b`
+        // was non-nullish, then we can access `.c.d?.e`. Thus we should take the
+        // full property chain, exactly as-is with optionals/non-optionals, as a
+        // dependency
+        return identity(x.a.b?.c.d?.e);
+      },
+    });
+  }, [x.a.b?.c.d?.e]);
+  const result = useMemo(() => {
+    return [object.callback()];
+  }, [object]);
+  return <Inner x={x} result={result} />;
+}
+
+function Inner({x, result}) {
+  'use no memo';
+  return <ValidateMemoization inputs={[x.y.z]} output={result} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{x: {y: {z: 42}}}],
+  sequentialRenders: [
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 3.14}}},
+    {x: {y: {z: 42}}},
+    {x: {y: {z: 3.14}}},
+    {x: {y: {z: 42}}},
+  ],
+};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-deps-conditional-property-chain-less-precise-deps.expect.md

@@ -0,0 +1,122 @@
+
+## Input
+
+```javascript
+// @enablePreserveExistingMemoizationGuarantees @validatePreserveExistingMemoizationGuarantees @enableOptionalDependencies @enableTreatFunctionDepsAsConditional:false
+
+import {useMemo} from 'react';
+import {identity, ValidateMemoization} from 'shared-runtime';
+
+function Component({x}) {
+  const object = useMemo(() => {
+    return identity({
+      callback: () => {
+        return identity(x.y.z); // accesses more levels of properties than the manual memo
+      },
+    });
+    // x.y as a manual dep only tells us that x is non-nullable, not that x.y is non-nullable
+    // we can only take a dep on x.y, not x.y.z
+  }, [x.y]);
+  const result = useMemo(() => {
+    return [object.callback()];
+  }, [object]);
+  return <ValidateMemoization inputs={[x.y]} output={result} />;
+}
+
+const input1 = {x: {y: {z: 42}}};
+const input1b = {x: {y: {z: 42}}};
+const input2 = {x: {y: {z: 3.14}}};
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [input1],
+  sequentialRenders: [
+    input1,
+    input1,
+    input1b, // should reset even though .z didn't change
+    input1,
+    input2,
+  ],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enablePreserveExistingMemoizationGuarantees @validatePreserveExistingMemoizationGuarantees @enableOptionalDependencies @enableTreatFunctionDepsAsConditional:false
+
+import { useMemo } from "react";
+import { identity, ValidateMemoization } from "shared-runtime";
+
+function Component(t0) {
+  const $ = _c(11);
+  const { x } = t0;
+  let t1;
+  if ($[0] !== x.y) {
+    t1 = identity({ callback: () => identity(x.y.z) });
+    $[0] = x.y;
+    $[1] = t1;
+  } else {
+    t1 = $[1];
+  }
+  const object = t1;
+  let t2;
+  if ($[2] !== object) {
+    t2 = object.callback();
+    $[2] = object;
+    $[3] = t2;
+  } else {
+    t2 = $[3];
+  }
+  let t3;
+  if ($[4] !== t2) {
+    t3 = [t2];
+    $[4] = t2;
+    $[5] = t3;
+  } else {
+    t3 = $[5];
+  }
+  const result = t3;
+  let t4;
+  if ($[6] !== x.y) {
+    t4 = [x.y];
+    $[6] = x.y;
+    $[7] = t4;
+  } else {
+    t4 = $[7];
+  }
+  let t5;
+  if ($[8] !== result || $[9] !== t4) {
+    t5 = <ValidateMemoization inputs={t4} output={result} />;
+    $[8] = result;
+    $[9] = t4;
+    $[10] = t5;
+  } else {
+    t5 = $[10];
+  }
+  return t5;
+}
+
+const input1 = { x: { y: { z: 42 } } };
+const input1b = { x: { y: { z: 42 } } };
+const input2 = { x: { y: { z: 3.14 } } };
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [input1],
+  sequentialRenders: [
+    input1,
+    input1,
+    input1b, // should reset even though .z didn't change
+    input1,
+    input2,
+  ],
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>{"inputs":[{"z":42}],"output":[42]}</div>
+<div>{"inputs":[{"z":42}],"output":[42]}</div>
+<div>{"inputs":[{"z":42}],"output":[42]}</div>
+<div>{"inputs":[{"z":42}],"output":[42]}</div>
+<div>{"inputs":[{"z":3.14}],"output":[3.14]}</div>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/preserve-memo-deps-conditional-property-chain-less-precise-deps.js

@@ -0,0 +1,35 @@
+// @enablePreserveExistingMemoizationGuarantees @validatePreserveExistingMemoizationGuarantees @enableOptionalDependencies @enableTreatFunctionDepsAsConditional:false
+
+import {useMemo} from 'react';
+import {identity, ValidateMemoization} from 'shared-runtime';
+
+function Component({x}) {
+  const object = useMemo(() => {
+    return identity({
+      callback: () => {
+        return identity(x.y.z); // accesses more levels of properties than the manual memo
+      },
+    });
+    // x.y as a manual dep only tells us that x is non-nullable, not that x.y is non-nullable
+    // we can only take a dep on x.y, not x.y.z
+  }, [x.y]);
+  const result = useMemo(() => {
+    return [object.callback()];
+  }, [object]);
+  return <ValidateMemoization inputs={[x.y]} output={result} />;
+}
+
+const input1 = {x: {y: {z: 42}}};
+const input1b = {x: {y: {z: 42}}};
+const input2 = {x: {y: {z: 3.14}}};
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [input1],
+  sequentialRenders: [
+    input1,
+    input1,
+    input1b, // should reset even though .z didn't change
+    input1,
+    input2,
+  ],
+};