From 96fc81c00a9b0ef3431ae50591f063cdbf596f7d Mon Sep 17 00:00:00 2001
From: brandon s allbery kf8nh <allbery.b@gmail.com>
Date: Sat, 24 Aug 2024 12:33:49 -0400
Subject: [PATCH] split "validate old ghcs" into a separate workflow

I am not convinced this is a good idea, for the same reason that
Artem wants it: complexity. I'm very worried that this will
break things, although as far as I can tell it should be okay as
long as nobody commits anything overriding branch protection.

All branch protection rules will need to be updated to check for
"Validate old ghcs post job" the same way they check for
"Bootstrap post job" and "Validate post job".
---
 .github/workflows/old-ghcs.skip.yml |  39 ++++++++++
 .github/workflows/old-ghcs.yml      | 114 ++++++++++++++++++++++++++++
 .github/workflows/validate.yml      |  69 ++---------------
 3 files changed, 161 insertions(+), 61 deletions(-)
 create mode 100644 .github/workflows/old-ghcs.skip.yml
 create mode 100644 .github/workflows/old-ghcs.yml

diff --git a/.github/workflows/old-ghcs.skip.yml b/.github/workflows/old-ghcs.skip.yml
new file mode 100644
index 00000000000..c2d7e6e70ee
--- /dev/null
+++ b/.github/workflows/old-ghcs.skip.yml
@@ -0,0 +1,39 @@
+name: Validate old ghcs Skip
+
+# This Workflow is special and contains a workaround for a known limitation of GitHub CI.
+#
+# The problem: We don't want to run the "old ghcs" jobs on PRs which contain only changes
+# to the docs, since these jobs take a long time to complete without providing any benefit.
+# We therefore use path-filtering in the workflow triggers for the old ghcs jobs, namely
+# "paths-ignore: doc/**". But the "Validate old ghcs post job" is a required job, therefore
+# a PR cannot be merged unless the "Validate old ghcs post job" completes succesfully, which
+# it doesn't do if we filter it out.
+#
+# The solution: We use a second job with the same name which always returns the exit code 0.
+# The logic implemented for "required" workflows accepts if 1) at least one job with that name
+# runs through, AND 2) If multiple jobs of that name exist, then all jobs of that name have to
+# finish successfully.
+on:
+  push:
+    paths:
+      - 'doc/**'
+      - '**/README.md'
+      - 'CONTRIBUTING.md'
+    branches:
+      - master
+  pull_request:
+    paths:
+      - 'doc/**'
+      - '**/README.md'
+      - 'CONTRIBUTING.md'
+  release:
+    types:
+      - created
+
+jobs:
+  validate-old-ghcs-post-job:
+    if: always()
+    name: Validate old ghcs post job
+    runs-on: ubuntu-latest
+    steps:
+      - run: exit 0
diff --git a/.github/workflows/old-ghcs.yml b/.github/workflows/old-ghcs.yml
new file mode 100644
index 00000000000..519040d9e23
--- /dev/null
+++ b/.github/workflows/old-ghcs.yml
@@ -0,0 +1,114 @@
+name: Validate old ghcs
+
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
+# Note: This workflow file contains the required job "Validate old ghcs post job". We are using path
+# filtering here to ignore PRs which only change documentation. This can cause a problem, see the
+# workflow file "old-ghcs.skip.yml" for a description of the problem and the solution provided in
+# that file.
+on:
+  push:
+    paths-ignore:
+      - "doc/**"
+      - "**/README.md"
+      - "CONTRIBUTING.md"
+    branches:
+      - master
+  pull_request:
+    paths-ignore:
+      - "doc/**"
+      - "**/README.md"
+      - "CONTRIBUTING.md"
+  release:
+    types:
+      - created
+  workflow_call:
+
+env:
+  # We choose a stable ghc version across all os's
+  # which will be used to do the next release
+  GHC_FOR_RELEASE: "9.4.8"
+  COMMON_FLAGS: "-j 2 -v"
+
+jobs:
+
+  validate-old-ghcs:
+    name: Validate old ghcs ${{ matrix.extra-ghc }}
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        extra-ghc:
+          ["8.4.4", "8.2.2", "8.0.2"]
+          ## GHC 7.10.3 does not install on ubuntu-22.04 with ghcup.
+          ## Older GHCs are not supported by ghcup in the first place.
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install prerequisites for old GHCs
+        run: |
+          sudo apt-get update
+          sudo apt-get install libncurses5 libtinfo5
+
+      - name: Install extra compiler
+        run: ghcup install ghc ${{ matrix.extra-ghc }}
+
+      - name: GHCup logs
+        if: always()
+        run: cat /usr/local/.ghcup/logs/*
+
+      - name: Install primary compiler
+        uses: haskell-actions/setup@v2
+        id: setup-haskell
+        with:
+          ghc-version: ${{ env.GHC_FOR_RELEASE }}
+          cabal-version: latest
+
+      - name: GHC versions
+        run: |
+          ghc --version
+          "ghc-${{ matrix.extra-ghc }}" --version
+
+      # As we are reusing the cached build dir from the previous step
+      # the generated artifacts are available here,
+      # including the cabal executable and the test suite
+      # @@@ not any more, we don't get the cache from validate.yml
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ${{ steps.setup-haskell.outputs.cabal-store }}
+            dist-*
+          key: ${{ runner.os }}-${{ env.GHC_FOR_RELEASE }}-${{ github.sha }}
+          restore-keys: ${{ runner.os }}-${{ env.GHC_FOR_RELEASE }}-
+
+      - name: Validate build
+        run: sh validate.sh ${{ env.COMMON_FLAGS }} -s build
+
+      - name: "Validate lib-suite-extras --extra-hc ghc-${{ matrix.extra-ghc }}"
+        env:
+          EXTRA_GHC: ghc-${{ matrix.extra-ghc }}
+        run: sh validate.sh ${{ env.COMMON_FLAGS }} --lib-only -s lib-suite-extras --extra-hc "${{ env.EXTRA_GHC }}"
+
+  # We use this job as a summary of the workflow
+  # It will fail if any of the previous jobs does
+  # This way we can use it exclusively in branch protection rules
+  # and abstract away the concrete jobs of the workflow, including their names
+  validate-old-ghcs-post-job:
+    if: always()
+    name: Validate old ghcs post job
+    runs-on: ubuntu-latest
+    # IMPORTANT! Any job added to the workflow should be added here too
+    # (This one is true because of the abstraction described above, and the
+    # corresponding branch protection rules. ++bsa)
+    needs: [validate-old-ghcs]
+
+    steps:
+      - run: |
+          echo "jobs info: ${{ toJSON(needs) }}"
+      - if: contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')
+        run: exit 1
diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 2d8be7f02a3..17148400179 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -231,65 +231,6 @@ jobs:
         if: matrix.ghc == env.GHC_FOR_SOLVER_BENCHMARKS
         run: sh validate.sh $FLAGS -s solver-benchmarks-run
 
-  validate-old-ghcs:
-    name: Validate old ghcs ${{ matrix.extra-ghc }}
-    runs-on: ubuntu-latest
-    needs: validate
-
-    strategy:
-      matrix:
-        extra-ghc:
-          ["8.4.4", "8.2.2", "8.0.2"]
-          ## GHC 7.10.3 does not install on ubuntu-22.04 with ghcup.
-          ## Older GHCs are not supported by ghcup in the first place.
-      fail-fast: false
-
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Install prerequisites for old GHCs
-        run: |
-          sudo apt-get update
-          sudo apt-get install libncurses5 libtinfo5
-
-      - name: Install extra compiler
-        run: ghcup install ghc ${{ matrix.extra-ghc }}
-
-      - name: GHCup logs
-        if: always()
-        run: cat /usr/local/.ghcup/logs/*
-
-      - name: Install primary compiler
-        uses: haskell-actions/setup@v2
-        id: setup-haskell
-        with:
-          ghc-version: ${{ env.GHC_FOR_RELEASE }}
-          cabal-version: latest
-
-      - name: GHC versions
-        run: |
-          ghc --version
-          "ghc-${{ matrix.extra-ghc }}" --version
-
-      # As we are reusing the cached build dir from the previous step
-      # the generated artifacts are available here,
-      # including the cabal executable and the test suite
-      - uses: actions/cache@v4
-        with:
-          path: |
-            ${{ steps.setup-haskell.outputs.cabal-store }}
-            dist-*
-          key: ${{ runner.os }}-${{ env.GHC_FOR_RELEASE }}-${{ github.sha }}
-          restore-keys: ${{ runner.os }}-${{ env.GHC_FOR_RELEASE }}-
-
-      - name: Validate build
-        run: sh validate.sh ${{ env.COMMON_FLAGS }} -s build
-
-      - name: "Validate lib-suite-extras --extra-hc ghc-${{ matrix.extra-ghc }}"
-        env:
-          EXTRA_GHC: ghc-${{ matrix.extra-ghc }}
-        run: sh validate.sh ${{ env.COMMON_FLAGS }} --lib-only -s lib-suite-extras --extra-hc "${{ env.EXTRA_GHC }}"
-
   build-alpine:
     name: Build statically linked using alpine
     runs-on: ubuntu-latest
@@ -406,7 +347,11 @@ jobs:
     if: github.ref == 'refs/heads/master'
 
     # IMPORTANT! Any job added to the workflow should be added here too
-    needs: [validate, validate-old-ghcs, build-alpine, dogfooding]
+    # (This doesn't appear to be true, or we'd have merges with failed
+    # bootstrap tests. The pre-merge CI check is sufficient, but we do
+    # need validate and build-alpine to save the corresponding artifacts.
+    # ++bsa)
+    needs: [validate, build-alpine]
 
     steps:
       - uses: actions/download-artifact@v4
@@ -447,7 +392,9 @@ jobs:
     name: Validate post job
     runs-on: ubuntu-latest
     # IMPORTANT! Any job added to the workflow should be added here too
-    needs: [validate, validate-old-ghcs, build-alpine, dogfooding]
+    # (This one is true because of the abstraction described above, and the
+    # corresponding branch protection rules. ++bsa)
+    needs: [validate, build-alpine, dogfooding]
 
     steps:
       - run: |