From f8360cad60a78bf59fc02d857d84c78c5dd8dcbf Mon Sep 17 00:00:00 2001
From: Claude Code <noreply@anthropic.com>
Date: Thu, 1 Jan 2026 03:21:55 -0500
Subject: [PATCH] Add downstream testing workflow for DI, Optimization, and
 Turing
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This addresses issue #97 by adding CI tests for the biggest downstream
users of ADTypes:

- DifferentiationInterface (JuliaDiff/DifferentiationInterface.jl)
- Optimization.jl (SciML/Optimization.jl)
- Turing.jl (TuringLang/Turing.jl)

The workflow runs on push to main and on pull requests, using the same
pattern as SciMLSensitivity's downstream testing. If a dependency
resolution fails due to SemVer incompatibility, it gracefully exits as
success since this indicates an intentional breaking change.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 .github/workflows/Downstream.yml | 59 ++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 .github/workflows/Downstream.yml

diff --git a/.github/workflows/Downstream.yml b/.github/workflows/Downstream.yml
new file mode 100644
index 0000000..7c0fb17
--- /dev/null
+++ b/.github/workflows/Downstream.yml
@@ -0,0 +1,59 @@
+name: Downstream
+on:
+  push:
+    branches: [main]
+    tags: [v*]
+  pull_request:
+
+jobs:
+  test:
+    name: ${{ matrix.package.repo }}/${{ matrix.julia-version }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        julia-version: ['1']
+        os: [ubuntu-latest]
+        package:
+          - {user: JuliaDiff, repo: DifferentiationInterface.jl, subdir: DifferentiationInterface}
+          - {user: SciML, repo: Optimization.jl, subdir: ""}
+          - {user: TuringLang, repo: Turing.jl, subdir: ""}
+
+    steps:
+      - uses: actions/checkout@v6
+      - uses: julia-actions/setup-julia@v2
+        with:
+          version: ${{ matrix.julia-version }}
+          arch: x64
+      - uses: julia-actions/julia-buildpkg@latest
+      - name: Clone Downstream
+        uses: actions/checkout@v6
+        with:
+          repository: ${{ matrix.package.user }}/${{ matrix.package.repo }}
+          path: downstream
+      - name: Load this and run the downstream tests
+        shell: julia --color=yes {0}
+        run: |
+          using Pkg
+          package_subdir = "${{ matrix.package.subdir }}"
+          downstream_dir = isempty(package_subdir) ? "downstream" : joinpath("downstream", package_subdir)
+          Pkg.activate(downstream_dir)
+          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(coverage=true)  # 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
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v5
+        with:
+          files: lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: false