Reverse CI for FerriteGmsh and FerriteMeshParser (#797)

.github/workflows/Downstream.yml

@@ -0,0 +1,59 @@
+# Based on https://github.com/JuliaDiff/ChainRulesCore.jl/blob/main/.github/workflows/IntegrationTest.yml
+name: Downstream
+
+on:
+  push:
+    branches: ['master']
+    tags: ['*']
+  pull_request:
+
+concurrency:
+  # Skip intermediate builds: always.
+  # Cancel intermediate builds: only if it is a pull request build.
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
+
+jobs:
+  test:
+    name: ${{ matrix.package.repo }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        julia-version: ['1']
+        os: ['ubuntu-latest']
+        package:
+          # - {user: 'Ferrite-FEM', repo: 'FerriteDistributed.jl'} # Requires more efforts to be updated to 1.0
+          - {user: 'Ferrite-FEM', repo: 'FerriteGmsh.jl'}
+          - {user: 'Ferrite-FEM', repo: 'FerriteMeshParser.jl'}
+          # - {user: 'Ferrite-FEM', repo: 'FerriteViz.jl'} # Requires release
+    steps:
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
+        with:
+          version: ${{ matrix.julia-version }}
+      - uses: julia-actions/cache@v2
+      # - uses: julia-actions/julia-buildpkg@v1
+      - name: Clone Downstream
+        uses: actions/checkout@v4
+        with:
+          repository: ${{ matrix.package.user }}/${{ matrix.package.repo }}
+          path: downstream
+      - name: Load this and run the downstream 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
+              rethrow() # Currently all packages tested are under Ferrite-FEM control so don't expect breakage
+              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