Simplify downstream package integration CI action (#809)

* Update downstream package CI action

Author: musm

.github/workflows/CI.yml

@@ -77,8 +77,8 @@ jobs:
         with:
           file: lcov.info
 
-  MAT-integration:
-    name: MAT.jl - julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }}
+  integration:
+    name: ${{ matrix.package.repo }} - julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -89,49 +89,38 @@ jobs:
           - ubuntu-latest
         arch:
           - x64
+        package:
+          - {user: JuliaIO, repo: MAT.jl}
+          - {user: JuliaIO, repo: JLD.jl}
     steps:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@latest
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
       - uses: julia-actions/julia-buildpkg@latest
-      - name: Clone MAT.jl
+      - name: Clone ${{ matrix.package.repo }}
         uses: actions/checkout@v2
         with:
-          repository: JuliaIO/MAT.jl
-          path: "MAT.jl"
-      - name: Run the tests
-        run: julia --project="MAT.jl" -e "using Pkg; Pkg.develop(PackageSpec(path=\"./\")); Pkg.update(); Pkg.test()"
-        shell: bash
-
-  JLD-integration:
-    name: JLD.jl - julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        version:
-          - '1'
-        os:
-          - ubuntu-latest
-        arch:
-          - x64
-    steps:
-      - uses: actions/checkout@v2
-      - uses: julia-actions/setup-julia@latest
-        with:
-          version: ${{ matrix.version }}
-          arch: ${{ matrix.arch }}
-      - uses: julia-actions/julia-buildpkg@latest
-      - name: Clone JLD.jl
-        uses: actions/checkout@v2
-        with:
-          repository: JuliaIO/JLD.jl
-          path: "JLD.jl"
-      - name: Run the tests
-        run: julia --project="JLD.jl" -e "using Pkg; Pkg.develop(PackageSpec(path=\"./\")); Pkg.update(); Pkg.test()"
-        shell: bash
+          repository: ${{ matrix.package.user }}/${{ matrix.package.repo }}
+          path: downstream
+      - name: Run ${{ matrix.package.repo }} tests
+        shell: julia --project=downstream {0}
+        run: |
+            using Pkg
+            try
+              # force it to use this PR's version of the package
+              Pkg.develop(PackageSpec(path="."))  # resolver may fail with main deps
+              Pkg.update()
+              Pkg.test()  # resolver may fail with test time deps
+            catch err
+              err isa Pkg.Resolve.ResolverError || rethrow()
+              # If we can't resolve that means this is incompatible by SemVer and this is fine
+              # It means we marked this as a breaking change, so we don't need to worry about
+              # Mistakenly introducing a breaking change, as we have intentionally made one
+              @info "Not compatible with this release. No problem." exception=err
+              exit(0)  #  Exit immediately, as a success
+            end
 
   docs:
       runs-on: ubuntu-latest