Remove automatic fetch cache instrumentation (#28896)

This removes the automatic patching of the global `fetch` function in
Server Components environments to dedupe requests using `React.cache`, a
behavior that some RSC framework maintainers have objected to.

We may revisit this decision in the future, but for now it's not worth
the controversy.

Frameworks that have already shipped this behavior, like Next.js, can
reimplement it in userspace.

I considered keeping the implementation in the codebase and disabling it
by setting `enableFetchInstrumentation` to `false` everywhere, but since
that also disables the tests, it doesn't seem worth it because without
test coverage the behavior is likely to drift regardless. We can just
revert this PR later if desired.

Author: acdlite

packages/react/src/ReactFetch.js

@@ -7,9 +7,6 @@
  * @flow
  */
 
-// Patch fetch
-import './ReactFetch';
-
 export {default as __SERVER_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE} from './ReactSharedInternalsServer';
 
 import {forEach, map, count, toArray, only} from './ReactChildren';

packages/react/src/ReactServer.experimental.js

@@ -7,9 +7,6 @@
  * @flow
  */
 
-// Patch fetch
-import './ReactFetch';
-
 export {default as __SERVER_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE} from './ReactSharedInternalsServer';
 
 import {forEach, map, count, toArray, only} from './ReactChildren';

packages/react/src/ReactServer.js

@@ -78,7 +78,6 @@ export const enableLegacyFBSupport = false;
 
 export const enableCache = true;
 export const enableLegacyCache = __EXPERIMENTAL__;
-export const enableFetchInstrumentation = true;
 
 export const enableBinaryFlight = __EXPERIMENTAL__;
 export const enableFlightReadableStream = __EXPERIMENTAL__;

packages/react/src/__tests__/ReactFetch-test.js

@@ -43,7 +43,6 @@ export const enableProfilerNestedUpdatePhase = __PROFILE__;
 export const enableUpdaterTracking = __PROFILE__;
 export const enableCache = true;
 export const enableLegacyCache = false;
-export const enableFetchInstrumentation = false;
 export const enableBinaryFlight = true;
 export const enableFlightReadableStream = true;
 export const enableAsyncIterableChildren = false;

packages/react/src/__tests__/ReactFetchEdge-test.js

@@ -73,7 +73,6 @@ export const enableDebugTracing = false;
 export const enableAsyncDebugInfo = false;
 export const enableSchedulingProfiler = __PROFILE__;
 export const enableLegacyCache = false;
-export const enableFetchInstrumentation = false;
 export const enablePostpone = false;
 export const disableCommentsAsDOMContainers = true;
 export const disableInputAttributeSyncing = false;

packages/shared/ReactFeatureFlags.js

@@ -20,7 +20,6 @@ export const enableProfilerNestedUpdatePhase = __PROFILE__;
 export const enableUpdaterTracking = false;
 export const enableCache = true;
 export const enableLegacyCache = __EXPERIMENTAL__;
-export const enableFetchInstrumentation = true;
 export const enableBinaryFlight = true;
 export const enableFlightReadableStream = true;
 export const enableAsyncIterableChildren = false;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -20,7 +20,6 @@ export const enableProfilerNestedUpdatePhase = __PROFILE__;
 export const enableUpdaterTracking = false;
 export const enableCache = true;
 export const enableLegacyCache = false;
-export const enableFetchInstrumentation = false;
 export const enableBinaryFlight = true;
 export const enableFlightReadableStream = true;
 export const enableAsyncIterableChildren = false;

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -20,7 +20,6 @@ export const enableProfilerNestedUpdatePhase = __PROFILE__;
 export const enableUpdaterTracking = false;
 export const enableCache = true;
 export const enableLegacyCache = true;
-export const enableFetchInstrumentation = false;
 export const enableBinaryFlight = true;
 export const enableFlightReadableStream = true;
 export const enableAsyncIterableChildren = false;

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -69,7 +69,6 @@ export const renameElementSymbol = false;
 
 export const enableCache = true;
 export const enableLegacyCache = true;
-export const enableFetchInstrumentation = false;
 
 export const enableBinaryFlight = false;
 export const enableFlightReadableStream = false;