vcpkg manifest still builds dependencies regardless of the cache

[HappySeaFox]

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Hi everyone! 👋

My project has a vcpkg.json, and vcpkg install is supposed to build the dependencies directly inside the vcpkg tree. As far as I understand, at the end of the workflow the entire vcpkg directory with all build artifacts should be cached.

However, when the workflow runs again, it restores the vcpkg directory from the cache but still recompiles all dependencies from scratch, which takes 20+ minutes.

Based on Cache API responses, the cache size is reasonable (around 1.5 GB):

    {
      "id": 1886518243,
      "ref": "refs/heads/master",
      "key": "vcpkg-Windows-Shared Combined-10c1067d795963ce2187c3a0ce27350b47dc14f0db2682f80fcb55963a37350d",
      "version": "ab49189a60a482bc1c2e1a4c155056fa0c670dfa1d2507ab12de506e6c5d5d93",
      "last_accessed_at": "2025-11-30T11:55:47.752686000Z",
      "created_at": "2025-11-30T11:55:47.752686000Z",
      "size_in_bytes": 1666344384
    },

The job where I updated vcpkg baseline to force the cache to be updated: https://github.com/HappySeaFox/sail/actions/runs/19798162265/job/56721466416
The next job https://github.com/HappySeaFox/sail/actions/runs/19798530799/job/56722342031 should not build dependencies. However, it still builds a lot of them.

Any ideas on how to fix it?

[TanishqCh07]

It looks like the cache is being restored correctly, but vcpkg is still rebuilding because the restored tree isn’t in a fully “ready-to-use” state for binary reuse.

A few things to check:

1. vcpkg binary caching must be enabled

By default, vcpkg will rebuild if binary caching isn’t turned on explicitly:

vcpkg install --binarysource=clear --binarysource=files:$(VCPKG_ROOT)/archives

Or in vcpkg.json:

{
"binarySources": [
"files:./vcpkg/archives,readwrite"
]
}

If binary caching isn’t configured, vcpkg treats the restored directory as empty and rebuilds everything.

2. The cache may not include the archives/ folder

vcpkg’s actual binary packages live in:

vcpkg/installed/
vcpkg/buildtrees/
vcpkg/packages/
vcpkg/archives/ ← IMPORTANT

Many workflows only cache vcpkg/installed but forget archives, so vcpkg has no local binaries to extract.
Make sure your cache includes the entire vcpkg root:

path: |
./vcpkg

3. Triplet / baseline mismatch = full rebuild

If your workflow changes:

triplet

compiler version

vcpkg baseline

host OS image version

…then vcpkg will rebuild because binaries don’t match the expected hash.

Even a small baseline update causes invalidation.

4. GitHub Actions cache key must not change between runs

Your key seems to include a hash:

vcpkg-Windows-Shared Combined-10c1067d...

If that hash is derived from:

commit SHA

vcpkg.json hash

baseline hash

then any small change produces a new cache.
vcpkg will rebuild because the restored state isn’t from the previous successful build.

You may want a separate restore key:

restore-keys: |
vcpkg-Windows-

5. vcpkg may detect "dirty" buildtrees and rebuild

If buildtrees/ contains partial builds, vcpkg will rebuild the port to ensure consistency.
Try caching only:

vcpkg/installed
vcpkg/archives

instead of the entire folder.

[HappySeaFox]

Thanks a lot! Setting VCPKG_DEFAULT_BINARY_CACHE to ${{ github.workspace }}/vcpkg/archives fixed the issue. The problem was that vcpkg caches the built archives not in its root, but in a user directory. That's why the cache action never cached them.

[TanishqCh07]

No worries mate!