---
# Throwaway diagnostic: why does master's ccache serve only ~14% of calls when a
# whole pull-request cache is restored?
#
# It builds the Arch leg's real command (`--server --debug --test`, the same as
# .github/workflows/desktop-build.yml) three times, with no Actions cache at all,
# so the repository's 10 GB quota is untouched:
#
#   1. cold, with a 6G bound that cannot be the limit: `du` and the ccache stats
#      give the true working set of one configuration.
#   2. again from a deleted build directory with the same image, sources and
#      flags: anything below ~95% hits means the hash inputs differ, not the size.
#   3. again after `ccache --recompress 1`, which is the candidate fix if one
#      configuration turns out to be larger than a per-leg bound: it measures what
#      the same configuration costs when the objects are compressed.
#
# Two runs of this workflow also compare the image id and the compiler's mtime,
# which is what ccache hashes by default (compiler_check = mtime).
name: ccache probe

on:
  push:
    branches:
      - ci/ccache-probe
  pull_request:
    branches:
      - master

concurrency:
  group: ${{ github.workflow }} @ ${{ github.ref_name }}
  cancel-in-progress: true

jobs:
  probe:
    name: Arch probe
    runs-on: ubuntu-latest
    timeout-minutes: 150
    env:
      NAME: Arch
      CACHE: ${{ github.workspace }}/.cache/Arch
      # Far above any candidate working set: a cache that evicts cannot be measured.
      CCACHE_BOUND: 6G
      # The leg's own invocation, so the probe cannot measure a configuration the
      # workflow does not build.
      LEG_ARGS: --server --debug --test --cmake-generator Ninja

    steps:
      - name: "Checkout"
        uses: actions/checkout@v7

      - name: "Build image and record the compiler's identity"
        shell: bash
        run: |
          source .ci/docker.sh --build
          echo "=== disk available to the build"
          df -h / | sed 's/^/  /'
          echo "=== image"
          docker image inspect --format 'image id: {{.Id}}' "$IMAGE_NAME"
          docker image inspect --format 'created: {{.Created}}' "$IMAGE_NAME"
          echo "=== compiler as ccache sees it (compiler_check = mtime hashes mtime and size)"
          docker run --rm "$IMAGE_NAME" bash -c 'for c in c++ cc gcc g++; do p="$(command -v $c)"; [ -n "$p" ] && stat -c "%n size=%s mtime=%Y" "$p"; done; c++ --version | head -1'

      - name: "Build 1 cold, 6G bound"
        shell: bash
        run: |
          source .ci/docker.sh
          RUN $LEG_ARGS --ccache "$CCACHE_BOUND"

      # du cannot see a size the cache was not allowed to keep, which is why the
      # bound is 6G here. The stats travel inside the cache directory, so the
      # numbers below are this run's, not a restored history.
      - name: "Working set of one configuration, uncompressed"
        shell: bash
        run: |
          source .ci/docker.sh
          echo "=== ccache dir on the host"
          du -sh "$CCACHE_DIR"
          find "$CCACHE_DIR" -type f -name '*.result' | wc -l | sed 's/^/result files: /'
          find "$CCACHE_DIR" -type f -name '*.manifest' | wc -l | sed 's/^/manifest files: /'
          echo "=== config in effect"
          docker run --rm --mount "type=bind,source=$CCACHE_DIR,target=/.ccache" \
            --env CCACHE_DIR=/.ccache "$IMAGE_NAME" ccache --show-config | grep -E 'compiler_check|hash_dir|compression|direct_mode|depend_mode'

      - name: "Build 2, same image, same sources, deleted build directory"
        shell: bash
        run: |
          rm -rf build
          source .ci/docker.sh
          RUN $LEG_ARGS --ccache "$CCACHE_BOUND"

      # A compressed cache is the only way one configuration can fit a per-leg
      # bound, so measure it on the cache build 2 just used.
      - name: "Working set after recompressing to level 1"
        shell: bash
        run: |
          source .ci/docker.sh
          docker run --rm --mount "type=bind,source=$CCACHE_DIR,target=/.ccache" \
            --env CCACHE_DIR=/.ccache "$IMAGE_NAME" ccache --recompress 1
          du -sh "$CCACHE_DIR"

      - name: "Build 3, compressed cache, deleted build directory"
        shell: bash
        run: |
          rm -rf build
          source .ci/docker.sh
          # Writes stay compressed, so this is the configuration a fix would ship.
          export RUN_ARGS="$RUN_ARGS -e CCACHE_COMPRESS=1"
          RUN $LEG_ARGS --ccache "$CCACHE_BOUND"
          echo "=== cache after build 3"
          du -sh "$CCACHE_DIR"