feat: add Alpine image by pat-s · Pull Request #1949 · j178/prek

pat-s · 2026-04-18T08:27:42Z

fix #1946

Copilot

Pull request overview

Adds an Alpine-based Docker image variant for prek (to cover common hook runtime dependencies) and updates docs/CI publishing to support it.

Changes:

Document two published images (scratch minimal and alpine) in Docker integration docs.
Extend the root Dockerfile with an alpine:3.23 target that installs common hook dependencies and includes the prek binary.
Update the Docker build/publish GitHub Actions workflow to build and publish both minimal and alpine image variants for multiple platforms.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
`docs/integrations.md`	Documents the new `ghcr.io/j178/prek-alpine` image and clarifies the minimal scratch image section.
`Dockerfile`	Adds `minimal` and `alpine` build targets; Alpine target installs common hook dependencies and copies `prek` to `/usr/local/bin`.
`.github/workflows/build-docker.yml`	Builds/publishes both image variants across `linux/amd64` and `linux/arm64`, and separates digest artifacts per image+platform.

Copilot · 2026-04-18T08:32:02Z

@@ -87,10 +99,11 @@ jobs:
        with:
          context: .
          platforms: ${{ matrix.platform }}
-          cache-from: type=gha,scope=prek-${{ env.PLATFORM_TUPLE }}
-          cache-to: type=gha,mode=min,scope=prek-${{ env.PLATFORM_TUPLE }}
+          target: ${{ matrix.image }}
+          cache-from: type=gha,scope=prek-${{ matrix.image }}-${{ env.PLATFORM_TUPLE }}
+          cache-to: type=gha,mode=min,scope=prek-${{ matrix.image }}-${{ env.PLATFORM_TUPLE }}
          labels: ${{ steps.meta.outputs.labels }}
-          outputs: type=image,name=${{ env.PREK_BASE_IMG }},push-by-digest=true,name-canonical=true,push=${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
+          outputs: type=image,name=${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}


IMAGE_NAME is set via $GITHUB_ENV in a previous step, but later you reference it via the expression context (${{ env.IMAGE_NAME }}) in with: inputs. Environment variables written to $GITHUB_ENV are available to subsequent run: steps, but they are not reliably available for expression evaluation in later steps, which can cause images:/outputs: to be empty or incorrect. Prefer computing the image name directly in the expression (e.g., conditional on matrix.image), or set it as a step output and reference steps.<id>.outputs.* instead.

Copilot · 2026-04-18T08:32:03Z

@@ -136,7 +163,7 @@ jobs:
        env:
          DOCKER_METADATA_ANNOTATIONS_LEVELS: index
        with:
-          images: ${{ env.PREK_BASE_IMG }}
+          images: ${{ env.IMAGE_NAME }}
          # Order is on purpose such that the label org.opencontainers.image.version has the first pattern with the full version
          tags: |
            type=raw,value=${{ fromJson(inputs.plan).announcement_tag }}
@@ -151,27 +178,23 @@ jobs:
      # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
      - name: Create manifest list and push
        working-directory: /tmp/digests
-        # The jq command expands the docker/metadata json "tags" array entry to `-t tag1 -t tag2 ...` for each tag in the array
-        # The printf will expand the base image with the `<PREK_BASE_IMG>@sha256:<sha256> ...` for each sha256 in the directory
-        # The final command becomes `docker buildx imagetools create -t tag1 -t tag2 ... <PREK_BASE_IMG>@sha256:<sha256_1> <PREK_BASE_IMG>@sha256:<sha256_2> ...`
        run: |
          # shellcheck disable=SC2046
          readarray -t lines <<< "$DOCKER_METADATA_OUTPUT_ANNOTATIONS"; annotations=(); for line in "${lines[@]}"; do annotations+=(--annotation "$line"); done

          docker buildx imagetools create \
            "${annotations[@]}" \
            $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf "${PREK_BASE_IMG}@sha256:%s " *)
+            $(printf "${IMAGE_NAME}@sha256:%s " *)

      - name: Export manifest digest
        id: manifest-digest
        env:
-          IMAGE: ${{ env.PREK_BASE_IMG }}
          VERSION: ${{ steps.meta.outputs.version }}
        run: |
          digest="$(
            docker buildx imagetools inspect \
-              "${IMAGE}:${VERSION}" \
+              "${IMAGE_NAME}:${VERSION}" \
              --format '{{json .Manifest}}' \
            | jq -r '.digest'
          )"
@@ -180,5 +203,5 @@ jobs:
      - name: Generate artifact attestation
        uses: actions/attest@59d89421af93a897026c735860bf21b6eb4f7b26 # v4.1.0
        with:
-          subject-name: ${{ env.PREK_BASE_IMG }}
+          subject-name: ${{ env.IMAGE_NAME }}
          subject-digest: ${{ steps.manifest-digest.outputs.digest }}


Same issue as in the build job: IMAGE_NAME is set via $GITHUB_ENV, but later used in expression contexts (${{ env.IMAGE_NAME }}) for docker/metadata-action and actions/attest. This can result in publishing/attesting with an empty or wrong image name. Compute IMAGE_NAME via expressions (based on matrix.image) or expose it as a step output and reference steps.<id>.outputs.image_name.

Copilot · 2026-04-18T08:32:03Z

+  py3-pip
+COPY --from=build /prek /usr/local/bin/prek
+WORKDIR /io
+ENTRYPOINT ["prek"]


Because the alpine stage is now the last stage in the Dockerfile, running docker build . without --target will produce the Alpine image rather than the previously default scratch/minimal image. If consumers rely on the default being the minimal image, consider keeping the minimal stage as the final/default stage (e.g., add a final FROM minimal stage at the end, or reorder stages) while still allowing --target alpine for the Alpine variant.

Suggested change

ENTRYPOINT ["prek"]

ENTRYPOINT ["prek"]

FROM minimal

codecov · 2026-04-18T08:36:02Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.25%. Comparing base (de7ac64) to head (ac73e8d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1949   +/-   ##
=======================================
  Coverage   93.25%   93.25%           
=======================================
  Files         127      127           
  Lines       27988    27988           
=======================================
  Hits        26099    26099           
  Misses       1889     1889

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Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

j178 · 2026-04-27T09:51:06Z

Sorry for the back and forth here. After thinking more about the long-term maintenance tradeoff, I think the official prek image should stay as the minimal scratch-based image.

That keeps the image contract clear: we ship the prek binary, not a maintained set of hook runtimes and system packages. For CI setups that need git, Python, Node, etc., I think the better path is to copy/install prek into the project’s own base image.

Thanks again for the proposal and the PR. I’m going to close this and #1946 for now.

pat-s · 2026-04-27T10:10:59Z

Uff, that's quite a bummer.

I didn't mean to replace the scratch image, just add an Alpine one on the side which will save multiple seconds and bandwith in CI on every run. There's almost no effort to build these in addition to the already existing base image.

It's easy to do this in the main source repo. By denying this, you indirectly force many individual's to build the same images and keep up with releases in a dynamic way etc. That is a lot of (unnecessary) overhead.

For CI setups that need git, Python, Node, etc., I think the better path is to copy/install prek into the project’s own base image.

A sophisticated use of prek in CI almost always needs these. The scratch image can't be used out-of-the box in a meaningful way.

prek-ci-bot · 2026-04-27T16:52:27Z

📦 Cargo Bloat Comparison

Binary size change: +0.00% (25.8 MiB → 25.8 MiB)

Expand for cargo-bloat output

Head Branch Results

 File  .text     Size             Crate Name
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_encrypt_avx512
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_decrypt_avx512
 0.3%   0.7%  84.0KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.7%  82.0KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.2%   0.5%  60.9KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.4%  56.8KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  53.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  46.8KiB              prek prek::run::{{closure}}
 0.2%   0.3%  41.3KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  33.3KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  28.0KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2%  27.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble
 0.1%   0.2%  26.9KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  26.3KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  22.8KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  22.5KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  22.3KiB         [Unknown] Lp384_montjscalarmul_alt_p384_montjadd
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.2%  86.3%  10.6MiB                   And 23718 smaller methods. Use -n N to show more.
47.8% 100.0%  12.3MiB                   .text section size, the file size is 25.8MiB

Base Branch Results

 File  .text     Size             Crate Name
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_encrypt_avx512
 1.3%   2.6% 332.0KiB        aws_lc_sys aws_lc_0_39_1_aes_gcm_decrypt_avx512
 0.3%   0.7%  88.9KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  81.6KiB              prek prek::languages::<impl prek::config::Language>::run::{{closure}}::{{closure}}
 0.3%   0.6%  71.8KiB             prek? <prek::cli::Command as clap_builder::derive::Subcommand>::augment_subcommands
 0.2%   0.5%  56.8KiB              prek prek::languages::<impl prek::config::Language>::install::{{closure}}
 0.2%   0.4%  53.3KiB annotate_snippets annotate_snippets::renderer::render::render
 0.2%   0.4%  46.7KiB              prek prek::run::{{closure}}
 0.2%   0.3%  40.9KiB              prek prek::cli::run::run::run::{{closure}}
 0.1%   0.3%  32.6KiB             prek? <prek::cli::RunArgs as clap_builder::derive::Args>::augment_args
 0.1%   0.2%  30.0KiB             prek? <prek::config::_::<impl serde_core::de::Deserialize for prek::config::Config>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map
 0.1%   0.2%  28.0KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble_alt
 0.1%   0.2%  27.6KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  27.5KiB        aws_lc_sys aws_lc_0_39_1_edwards25519_scalarmuldouble
 0.1%   0.2%  27.1KiB               std core::ptr::drop_in_place<prek::languages::<impl prek::config::Language>::install::{{closure}}>
 0.1%   0.2%  26.4KiB              prek prek::cli::try_repo::try_repo::{{closure}}
 0.1%   0.2%  23.2KiB              prek prek::hooks::meta_hooks::MetaHooks::run::{{closure}}
 0.1%   0.2%  22.5KiB      serde_saphyr saphyr_parser_bw::scanner::Scanner<T>::fetch_more_tokens
 0.1%   0.2%  22.3KiB         [Unknown] Lp384_montjscalarmul_alt_p384_montjadd
 0.1%   0.2%  21.5KiB      clap_builder clap_builder::parser::parser::Parser::get_matches_with
41.0%  86.1%  10.6MiB                   And 23756 smaller methods. Use -n N to show more.
47.6% 100.0%  12.3MiB                   .text section size, the file size is 25.8MiB

Copilot

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Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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pat-s · 2026-07-09T14:46:36Z

@j178 Tried to make all automated reviewers happy. Would be great if you could take a look again if this would work for you!

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feat(docker): add curl to alpine image

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fix(docker): register QEMU for arm64 alpine build and fix verify exam…

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