From 634203727cdf49eff8a185bcfbfdbe44648ded84 Mon Sep 17 00:00:00 2001
From: Tim Keir <tkeir@atlassian.com>
Date: Thu, 4 Jun 2026 15:09:20 +1000
Subject: [PATCH] Ignore cache misses prior to fetch step

---
 .yarn/versions/216387e5.yml                 | 36 +++++++++++++++++++++
 packages/yarnpkg-core/sources/Project.ts    | 11 +++++--
 packages/yarnpkg-core/tests/Project.test.ts | 33 +++++++++++++++----
 3 files changed, 71 insertions(+), 9 deletions(-)
 create mode 100644 .yarn/versions/216387e5.yml

diff --git a/.yarn/versions/216387e5.yml b/.yarn/versions/216387e5.yml
new file mode 100644
index 000000000000..6c24923445d8
--- /dev/null
+++ b/.yarn/versions/216387e5.yml
@@ -0,0 +1,36 @@
+releases:
+  "@yarnpkg/core": patch
+
+declined:
+  - "@yarnpkg/plugin-catalog"
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-essentials"
+  - "@yarnpkg/plugin-exec"
+  - "@yarnpkg/plugin-file"
+  - "@yarnpkg/plugin-git"
+  - "@yarnpkg/plugin-github"
+  - "@yarnpkg/plugin-http"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-jsr"
+  - "@yarnpkg/plugin-link"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/cli"
+  - "@yarnpkg/doctor"
+  - "@yarnpkg/extensions"
+  - "@yarnpkg/nm"
+  - "@yarnpkg/pnpify"
+  - "@yarnpkg/sdks"
diff --git a/packages/yarnpkg-core/sources/Project.ts b/packages/yarnpkg-core/sources/Project.ts
index 8e42251dc68c..ebe9089d09bd 100644
--- a/packages/yarnpkg-core/sources/Project.ts
+++ b/packages/yarnpkg-core/sources/Project.ts
@@ -1097,6 +1097,7 @@ export class Project {
       mockedPackages: this.disabledLocators,
       unstablePackages: this.conditionalLocators,
     };
+    const initialCacheMisses = new Set(report.cacheMisses);
 
     const fetcher = userFetcher || this.configuration.makeFetcher();
     const fetcherOptions = {checksums: this.storedChecksums, project: this, cache, fetcher, report, cacheOptions};
@@ -1165,8 +1166,12 @@ export class Project {
       ? await this.cacheCleanup({cache, report})
       : null;
 
-    if (report.cacheMisses.size > 0 || cleanInfo) {
-      const addedSizes = await Promise.all([...report.cacheMisses].map(async locatorHash => {
+    const fetchCacheMisses = [...report.cacheMisses].filter(locatorHash => {
+      return !initialCacheMisses.has(locatorHash);
+    });
+
+    if (fetchCacheMisses.length > 0 || cleanInfo) {
+      const addedSizes = await Promise.all(fetchCacheMisses.map(async locatorHash => {
         const locator = this.storedPackages.get(locatorHash);
         const checksum = this.storedChecksums.get(locatorHash) ?? null;
 
@@ -1178,7 +1183,7 @@ export class Project {
 
       const finalSizeChange = addedSizes.reduce((sum, size) => sum + size, 0) - (cleanInfo?.size ?? 0);
 
-      const addedCount = report.cacheMisses.size;
+      const addedCount = fetchCacheMisses.length;
       const removedCount = cleanInfo?.count ?? 0;
 
       const addedLine = `${miscUtils.plural(addedCount, {
diff --git a/packages/yarnpkg-core/tests/Project.test.ts b/packages/yarnpkg-core/tests/Project.test.ts
index c00b449da738..f345856c0854 100644
--- a/packages/yarnpkg-core/tests/Project.test.ts
+++ b/packages/yarnpkg-core/tests/Project.test.ts
@@ -1,10 +1,10 @@
-import {Cache, Configuration, Project, ThrowReport, structUtils, LocatorHash, Package} from '@yarnpkg/core';
-import {Filename, PortablePath, ppath, xfs}                                            from '@yarnpkg/fslib';
-import LinkPlugin                                                                      from '@yarnpkg/plugin-link';
-import PnpPlugin                                                                       from '@yarnpkg/plugin-pnp';
-import v8                                                                              from 'v8';
+import {Cache, Configuration, Project, ThrowReport, structUtils, LocatorHash, Package, InstallMode} from '@yarnpkg/core';
+import {Filename, PortablePath, ppath, xfs}                                                         from '@yarnpkg/fslib';
+import LinkPlugin                                                                                   from '@yarnpkg/plugin-link';
+import PnpPlugin                                                                                    from '@yarnpkg/plugin-pnp';
+import v8                                                                                           from 'v8';
 
-import {TestPlugin}                                                                    from './TestPlugin';
+import {TestPlugin}                                                                                 from './TestPlugin';
 
 const getConfiguration = (p: PortablePath) => {
   return Configuration.create(p, p, new Map([
@@ -301,4 +301,25 @@ describe(`Project`, () => {
       await expect(project.restoreInstallState()).resolves.toBeUndefined();
     });
   });
+
+  it(`should ignore cache misses recorded before the fetch step`, async() => {
+    await xfs.mktempPromise(async dir => {
+      await xfs.writeJsonPromise(ppath.join(dir, Filename.manifest), {name: `foo`});
+      await xfs.writeFilePromise(ppath.join(dir, Filename.lockfile), ``);
+
+      const configuration = getConfiguration(dir);
+      const {project} = await Project.find(configuration, dir);
+      const cache = await Cache.find(configuration);
+      const report = new ThrowReport();
+
+      report.cacheMisses.add(`preexisting-cache-miss` as LocatorHash);
+
+      await expect(project.fetchEverything({
+        cache,
+        report,
+        mode: InstallMode.UpdateLockfile,
+        persistProject: false,
+      })).resolves.toBeUndefined();
+    });
+  });
 });