Log cached fetches during HMR refreshes if enabled in logging config (#68287)

In #67925 we decided not to log any fetches during HMR refreshes (i.e.
when editing server components). With this PR, we introduce a new
logging config (`logging.fetches.hmrRefreshes`) so that users can opt in
to logging of `fetch` requests that are restored from the Server
Components HMR cache.

<img width="806" alt="hmr cache logs"
src="https://github.com/user-attachments/assets/ea789520-8490-479a-a4f0-1febb42388e2">

Author: unstubbable

docs/02-app/02-api-reference/05-next-config-js/logging.mdx

@@ -19,6 +19,19 @@ module.exports = {
 }
 ```
 
+{/* TODO: Cross-reference severComponentsHmrCache page when #67839 has landed. */}
+Any `fetch` requests that are restored from the Server Components HMR cache are not logged by default. However, this can be enabled by setting `logging.fetches.hmrRefreshes` to `true`.
+
+```js filename="next.config.js"
+module.exports = {
+  logging: {
+    fetches: {
+      hmrRefreshes: true,
+    },
+  },
+}
+```
+
 In addition, you can disable the development logging by setting `logging` to `false`.
 
 ```js filename="next.config.js"

packages/next/src/server/config-schema.ts

@@ -539,6 +539,7 @@ export const configSchema: zod.ZodType<NextConfig> = z.lazy(() =>
           fetches: z
             .object({
               fullUrl: z.boolean().optional(),
+              hmrRefreshes: z.boolean().optional(),
             })
             .optional(),
         }),

packages/next/src/server/config-shared.ts

@@ -202,6 +202,11 @@ export interface ReactCompilerOptions {
 export interface LoggingConfig {
   fetches?: {
     fullUrl?: boolean
+    /**
+     * If true, fetch requests that are restored from the HMR cache are logged
+     * during an HMR refresh request, i.e. when editing a server component.
+     */
+    hmrRefreshes?: boolean
   }
 }
 

packages/next/src/server/dev/log-requests.ts

@@ -80,8 +80,9 @@ function logFetchMetric(
     url,
   } = fetchMetric
 
-  if (cacheStatus === 'hmr') {
-    // Cache hits during HMR refreshes are intentionally not logged.
+  if (cacheStatus === 'hmr' && !loggingConfig?.fetches?.hmrRefreshes) {
+    // Cache hits during HMR refreshes are intentionally not logged, unless
+    // explicitly enabled in the logging config.
     return
   }
 
@@ -138,8 +139,13 @@ function truncateUrl(url: string): string {
   )
 }
 
-function formatCacheStatus(cacheStatus: 'hit' | 'miss' | 'skip'): string {
-  const color = cacheStatus === 'hit' ? green : yellow
-
-  return color(`(cache ${cacheStatus})`)
+function formatCacheStatus(cacheStatus: FetchMetric['cacheStatus']): string {
+  switch (cacheStatus) {
+    case 'hmr':
+      return green('(HMR cache)')
+    case 'hit':
+      return green('(cache hit)')
+    default:
+      return yellow(`(cache ${cacheStatus})`)
+  }
 }

test/e2e/app-dir/logging/app/fetch-no-store/page.js

@@ -8,5 +8,5 @@ export default async function Page() {
     }
   )
 
-  return <div>Hello World!</div>
+  return <h1>Hello World!</h1>
 }

test/e2e/app-dir/logging/fetch-logging.test.ts

@@ -227,23 +227,69 @@ describe('app-dir - logging', () => {
         })
 
         it('should not log requests for HMR refreshes', async () => {
-          const browser = await next.browser('/default-cache')
+          const browser = await next.browser('/fetch-no-store')
           let headline = await browser.waitForElementByCss('h1').text()
-          expect(headline).toBe('Default Cache')
+          expect(headline).toBe('Hello World!')
           const outputIndex = next.cliOutput.length
 
           await next.patchFile(
-            'app/default-cache/page.js',
-            (content) => content.replace('Default Cache', 'Hello!'),
+            'app/fetch-no-store/page.js',
+            (content) => content.replace('Hello World!', 'Hello Test!'),
             async () =>
               retry(async () => {
                 headline = await browser.waitForElementByCss('h1').text()
-                expect(headline).toBe('Hello!')
+                expect(headline).toBe('Hello Test!')
                 const logs = stripAnsi(next.cliOutput.slice(outputIndex))
+                expect(logs).toInclude(' GET /fetch-no-store')
                 expect(logs).not.toInclude(` │ GET `)
               })
           )
         })
+
+        describe('when logging.fetches.hmrRefreshes is true', () => {
+          beforeAll(async () => {
+            await next.patchFile('next.config.js', (content) =>
+              content.replace('// hmrRefreshes: true', 'hmrRefreshes: true')
+            )
+          })
+
+          afterAll(async () => {
+            await next.patchFile('next.config.js', (content) =>
+              content.replace('hmrRefreshes: true', '// hmrRefreshes: true')
+            )
+          })
+
+          it('should log requests for HMR refreshes', async () => {
+            const browser = await next.browser('/fetch-no-store')
+            let headline = await browser.waitForElementByCss('h1').text()
+            expect(headline).toBe('Hello World!')
+            const outputIndex = next.cliOutput.length
+
+            await next.patchFile(
+              'app/fetch-no-store/page.js',
+              (content) => content.replace('Hello World!', 'Hello Test!'),
+              async () => {
+                const expectedUrl = withFullUrlFetches
+                  ? 'https://next-data-api-endpoint.vercel.app/api/random'
+                  : 'https://next-data-api-en../api/random'
+
+                return retry(async () => {
+                  headline = await browser.waitForElementByCss('h1').text()
+                  expect(headline).toBe('Hello Test!')
+
+                  const logs = stripAnsi(
+                    next.cliOutput.slice(outputIndex)
+                  ).replace(/\d+ms/g, '1ms')
+
+                  expect(logs).toInclude(' GET /fetch-no-store')
+                  expect(logs).toInclude(
+                    ` │ GET ${expectedUrl}?request-input 200 in 1ms (HMR cache)`
+                  )
+                })
+              }
+            )
+          })
+        })
       }
     } else {
       // No fetches logging enabled

test/e2e/app-dir/logging/next.config.js

@@ -2,6 +2,7 @@ module.exports = {
   logging: {
     fetches: {
       fullUrl: true,
+      // hmrRefreshes: true,
     },
   },
 }