chore: try provided readmeFilename before starting the fallback batch

Author: trivikr

server/utils/readme-loaders.ts

@@ -26,11 +26,9 @@ export function isStandardReadme(filename: string | undefined): boolean {
 }
 
 function buildReadmeFetchCandidates(readmeFilename: string | undefined): string[] {
-  if (!readmeFilename) {
-    return standardReadmeFilenames
-  }
-
-  return [readmeFilename, ...standardReadmeFilenames.filter(name => name !== readmeFilename)]
+  return readmeFilename
+    ? standardReadmeFilenames.filter(name => name !== readmeFilename)
+    : standardReadmeFilenames
 }
 
 /**
@@ -105,13 +103,20 @@ export const resolvePackageReadmeSource = defineCachedFunction(
       !isStandardReadme(readmeFilename) ||
       readmeContent!.length >= NPM_README_TRUNCATION_THRESHOLD
     ) {
-      const readmeCandidates = buildReadmeFetchCandidates(readmeFilename)
       const resolvedVersion = version ?? packageData['dist-tags']?.latest
-      const jsdelivrReadme = await fetchReadmeFromJsdelivr(
-        packageName,
-        readmeCandidates,
-        resolvedVersion,
-      )
+      let jsdelivrReadme =
+        readmeFilename &&
+        (await fetchReadmeFromJsdelivr(packageName, [readmeFilename], resolvedVersion))
+
+      if (!jsdelivrReadme) {
+        const readmeCandidates = buildReadmeFetchCandidates(readmeFilename)
+        jsdelivrReadme = await fetchReadmeFromJsdelivr(
+          packageName,
+          readmeCandidates,
+          resolvedVersion,
+        )
+      }
+
       if (jsdelivrReadme) {
         readmeContent = jsdelivrReadme
       }

test/unit/server/utils/readme-loaders.spec.ts

@@ -259,6 +259,79 @@ describe('resolvePackageReadmeSource', () => {
     expect(fetchMock).toHaveBeenNthCalledWith(1, 'https://cdn.jsdelivr.net/npm/pkg/DOCS.md')
   })
 
+  it('tries a provided readmeFilename before starting the fallback batch', async () => {
+    let resolveDocs!: (value: { ok: false }) => void
+    let resolveReadmeMd!: (value: { ok: false }) => void
+    let resolveLowercase!: (value: { ok: false }) => void
+    let resolveReadmeCase!: (value: { ok: true; text: () => Promise<string> }) => void
+
+    fetchNpmPackageMock.mockResolvedValue({
+      readme: undefined,
+      readmeFilename: 'DOCS.md',
+      repository: undefined,
+      versions: {},
+    })
+    parseRepositoryInfoMock.mockReturnValue(undefined)
+
+    const fetchMock = vi.fn((url: string) => {
+      if (url.endsWith('/DOCS.md')) {
+        return new Promise(resolve => {
+          resolveDocs = resolve
+        })
+      }
+
+      if (url.endsWith('/README.md')) {
+        return new Promise(resolve => {
+          resolveReadmeMd = resolve
+        })
+      }
+
+      if (url.endsWith('/readme.md')) {
+        return new Promise(resolve => {
+          resolveLowercase = resolve
+        })
+      }
+
+      if (url.endsWith('/Readme.md')) {
+        return new Promise(resolve => {
+          resolveReadmeCase = resolve
+        })
+      }
+
+      return Promise.resolve({ ok: false })
+    })
+    vi.stubGlobal('fetch', fetchMock)
+
+    const resultPromise = resolvePackageReadmeSource('pkg')
+
+    await new Promise(resolve => setTimeout(resolve, 0))
+    expect(fetchMock).toHaveBeenCalledTimes(1)
+    expect(fetchMock).toHaveBeenNthCalledWith(1, 'https://cdn.jsdelivr.net/npm/pkg/DOCS.md')
+
+    resolveDocs({ ok: false })
+
+    await new Promise(resolve => setTimeout(resolve, 0))
+    expect(fetchMock).toHaveBeenCalledTimes(4)
+    expect(fetchMock.mock.calls.slice(1).map(([url]) => url)).toEqual([
+      'https://cdn.jsdelivr.net/npm/pkg/README.md',
+      'https://cdn.jsdelivr.net/npm/pkg/readme.md',
+      'https://cdn.jsdelivr.net/npm/pkg/Readme.md',
+    ])
+
+    resolveReadmeMd({ ok: false })
+    resolveLowercase({ ok: false })
+    resolveReadmeCase({
+      ok: true,
+      text: async () => '# From fallback batch',
+    })
+
+    await expect(resultPromise).resolves.toMatchObject({
+      packageName: 'pkg',
+      markdown: '# From fallback batch',
+      repoInfo: undefined,
+    })
+  })
+
   it('returns undefined markdown when no content and jsdelivr fails', async () => {
     fetchNpmPackageMock.mockResolvedValue({
       readme: undefined,