ci: Split downgrade CI into its own workflow (#81)

* Separate downgrade CI workflow and run on Julia v1.11

The downgrade CI workflow was failing because it downgrades DimensionalData
to a version that doesn't work correctly on Julia v1.12. Following
Pathfinder.jl's approach:

- Create separate Downgrade.yml workflow file
- Run downgrade tests on Julia v1.11 instead of latest
- Remove downgrade matrix from main CI.yml workflow

This ensures backward compatibility testing without the Julia v1.12
DimensionalData incompatibility issue.

* Simplify DOCUMENTER_KEY in CI.yml

Since docs workflow only runs on Julia v1, the conditional check is unnecessary.

---------

Co-authored-by: Claude <[email protected]>

Author: sethaxen

.github/workflows/CI.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   test:
-    name: ${{ matrix.downgrade && 'Downgrade / ' || '' }}Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.num_threads }} threads
+    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.num_threads }} threads
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -20,17 +20,11 @@ jobs:
           - '1'
           - 'pre'
         os: ['ubuntu-latest']
-        downgrade: [false]
         num_threads: [2]
         include:
           - version: '1'
             os: 'ubuntu-latest'
             num_threads: 1
-            downgrade: false
-          - version: 1
-            os: 'ubuntu-latest'
-            num_threads: 2
-            downgrade: true
 
     steps:
       - uses: actions/checkout@v6
@@ -40,11 +34,6 @@ jobs:
           version: ${{ matrix.version }}
           arch: x64
       - uses: julia-actions/cache@v2
-      - uses: julia-actions/julia-downgrade-compat@v2
-        with:
-          skip: LinearAlgebra,Printf,Statistics
-          julia_version: ${{ steps['setup-julia'].outputs.julia-version }}
-        if: matrix.downgrade
       - uses: julia-actions/julia-buildpkg@latest
       - uses: julia-actions/julia-runtest@latest
         env:
@@ -54,28 +43,21 @@ jobs:
         with:
           file: lcov.info
   docs:
-    name: ${{ matrix.downgrade && 'Downgrade / ' || '' }}Documentation - Julia ${{ matrix.version }}
+    name: Documentation - Julia ${{ matrix.version }}
     runs-on: ubuntu-latest
     strategy:
       matrix:
         version: ['1']
-        downgrade: [false, true]
     steps:
       - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         id: setup-julia
         with:
           version: ${{ matrix.version }}
       - uses: julia-actions/cache@v2
-      - uses: julia-actions/julia-downgrade-compat@v2
-        with:
-          skip: LinearAlgebra,Printf,PSIS,Statistics
-          projects: ., docs
-          julia_version: ${{ steps['setup-julia'].outputs.julia-version }}
-        if: matrix.downgrade
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-docdeploy@v1
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          DOCUMENTER_KEY: ${{ matrix.version == '1' && secrets.DOCUMENTER_KEY || '' }}
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}
           GKSwstype: "100" # https://discourse.julialang.org/t/generation-of-documentation-fails-qt-qpa-xcb-could-not-connect-to-display/60988

.github/workflows/Downgrade.yml

@@ -0,0 +1,68 @@
+name: Downgrade
+on:
+  pull_request:
+  push:
+    branches: [main]
+    paths-ignore:
+      - 'docs/**'
+  workflow_dispatch:
+
+jobs:
+  test:
+    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.num_threads }} threads
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+          - '1.11'
+        os: ['ubuntu-latest']
+        num_threads: [1, 2]
+
+    steps:
+      - uses: actions/checkout@v6
+      - uses: julia-actions/setup-julia@v2
+        id: setup-julia
+        with:
+          version: ${{ matrix.version }}
+          arch: x64
+      - uses: julia-actions/cache@v2
+      - uses: julia-actions/julia-downgrade-compat@v2
+        with:
+          skip: LinearAlgebra,Printf,Statistics
+          julia_version: ${{ steps['setup-julia'].outputs.julia-version }}
+      - uses: julia-actions/julia-buildpkg@latest
+      - uses: julia-actions/julia-runtest@latest
+        with:
+          allow_reresolve: false
+          force_latest_compatible_version: false
+        env:
+          JULIA_NUM_THREADS: ${{ matrix.num_threads }}
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v5
+        with:
+          file: lcov.info
+
+  docs:
+    name: Documentation - Julia ${{ matrix.version }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: ['1.11']
+    steps:
+      - uses: actions/checkout@v6
+      - uses: julia-actions/setup-julia@v2
+        id: setup-julia
+        with:
+          version: ${{ matrix.version }}
+      - uses: julia-actions/cache@v2
+      - uses: julia-actions/julia-downgrade-compat@v2
+        with:
+          skip: LinearAlgebra,Printf,PSIS,Statistics
+          projects: ., docs
+          julia_version: ${{ steps['setup-julia'].outputs.julia-version }}
+      - uses: julia-actions/julia-buildpkg@v1
+      - uses: julia-actions/julia-docdeploy@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GKSwstype: "100"