👷 add windows CI for MLIR (#952)

## Description

This PR adds MLIR CI tests for windows runners.
This is achieved by building MLIR from source so the first execution
should take a bit longer.
Afterwards, the cache will be used to store the built versions of MLIR.

This PR contributes to #925

**Note:** To install a specific version, the runner clones the tag
`llvmorg-{version}.1.0`. It seems that the first release of a new major
`llvm-project` version is typically called `{version}.1.0` so this
should keep working, but there is no guarantee.

## Checklist:

- [x] The pull request only contains commits that are focused and
relevant to this change.
- [x] I have added appropriate tests that cover the new/changed
functionality.
- [x] I have updated the documentation to reflect these changes.
- [x] I have added entries to the changelog for any noteworthy
additions, changes, fixes or removals.
- [x] I have added migration instructions to the upgrade guide (if
needed).
- [x] The changes follow the project's style guidelines and introduce no
new warnings.
- [x] The changes are fully tested and pass the CI checks.
- [x] I have reviewed my own code changes.

---------

Signed-off-by: burgholzer <[email protected]>
Co-authored-by: burgholzer <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

.github/workflows/ci_mlir.yml

@@ -18,7 +18,7 @@ concurrency:
 
 jobs:
   cpp-test-mlir:
-    name: 🇨‌ Test MLIR with LLVM@${{ matrix.llvm-version }}
+    name: 🐧 Test MLIR with LLVM@${{ matrix.llvm-version }}
     runs-on: ubuntu-24.04
     strategy:
       matrix:
@@ -90,3 +90,108 @@ jobs:
       # build the project and run the tests
       - name: Build MLIR components and directly run lit tests
         run: cmake --build build --config Release --target check-quantum-opt
+
+  cpp-test-mlir-windows:
+    name: 🏁 Test MLIR with LLVM@${{ matrix.llvm-version }}
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        llvm-version: [19, 20]
+    env:
+      CMAKE_BUILD_PARALLEL_LEVEL: 4
+      CTEST_PARALLEL_LEVEL: 4
+      FORCE_COLOR: 3
+    outputs:
+      llvm-latest-tag: ${{ steps.get-latest.outputs.latest }}
+    steps:
+      # check out the repository
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Find latest release of llvm-project
+        id: get-latest
+        run: |
+          $tag = git ls-remote --tags https://github.com/llvm/llvm-project.git "llvmorg-${{ matrix.llvm-version }}.*" |
+                  Where-Object { $_ -match "llvmorg-\d+\.\d+\.\d+" } |
+                  Sort-Object -Property {
+                    if ($_ -match "llvmorg-(\d+)\.(\d+)\.(\d+)") {
+                      [int]$Matches[1]*10000 + [int]$Matches[2]*100 + [int]$Matches[3]
+                    }
+                  } |
+                  Select-Object -Last 1
+          $latest = $tag | ForEach-Object {
+                  if ($_ -match "refs/tags/llvmorg-(\d+\.\d+\.\d+)") {
+                    $Matches[1]  # Extract just the version number (e.g., "20.1.0")
+                  }
+                } |
+                Where-Object { $_ -ne $null }
+          echo "Latest tag: $tag"
+          echo "latest=$latest" >> $env:GITHUB_OUTPUT
+
+      - name: Try to get MLIR from cache
+        uses: actions/cache@v4
+        id: mlir-cache
+        with:
+          path: ${{ github.workspace }}/llvm-install
+          key: ${{ runner.os }}-llvm-${{ steps.get-latest.outputs.latest }}
+          restore-keys: |
+            ${{ runner.os }}-llvm-${{ steps.get-latest.outputs.latest }}
+
+      # build the llvm-project from source
+      - name: Install llvm and mlir
+        if: steps.mlir-cache.outputs.cache-hit != 'true'
+        run: |
+          git clone --depth 1 https://github.com/llvm/llvm-project.git --branch llvmorg-${{ steps.get-latest.outputs.latest }}
+          cd llvm-project
+          cmake -S llvm -B build_llvm `
+            -DLLVM_ENABLE_PROJECTS=mlir `
+            -DLLVM_BUILD_EXAMPLES=OFF `
+            -DLLVM_TARGETS_TO_BUILD="X86" `
+            -DCMAKE_BUILD_TYPE=Release `
+            -DLLVM_BUILD_TESTS=OFF `
+            -DLLVM_INCLUDE_TESTS=OFF `
+            -DLLVM_INCLUDE_EXAMPLES=OFF `
+            -DLLVM_ENABLE_ASSERTIONS=ON `
+            -DLLVM_ENABLE_UTILS=ON `
+            -DLLVM_INSTALL_UTILS=ON `
+            -DCMAKE_INSTALL_PREFIX=${{ github.workspace }}\llvm-install
+          cmake --build build_llvm --target install --config Release
+
+      # set up uv for faster Python package management
+      - name: Install the latest version of uv
+        uses: astral-sh/setup-uv@v6
+        with:
+          python-version: 3.13
+          activate-environment: true
+
+      # make sure the lit test runner is installed
+      - name: Install lit
+        run: |
+          uv pip install lit
+
+      # configure the project with CMake
+      - name: Configure CMake for MLIR
+        run: |
+          cmake -S . -B build `
+            -DCMAKE_BUILD_TYPE=Release `
+            -DBUILD_MQT_CORE_MLIR=ON `
+            -DCMAKE_PREFIX_PATH=${{ github.workspace }}\llvm-install `
+            -DLLVM_EXTERNAL_LIT=${{ github.workspace }}\.venv\Scripts\lit.exe
+
+      # build the project and run the tests
+      - name: Build MLIR components and directly run lit tests
+        run: |
+          cmake --build build --config Release --target quantum-opt
+
+          $targetPath = "${{ github.workspace }}\\build\\mlir\\tools\\quantum-opt\\Release\\quantum-opt.exe"
+          $batchContent = '"{0}" "$@"' -f $targetPath
+
+          # Write to a directory that's definitely in PATH
+          $batchContent | Out-File -FilePath "C:\Windows\quantum-opt" -Encoding ascii
+
+          # Verify the batch file
+          Get-Content "C:\Windows\quantum-opt"
+          Write-Output "Batch file created at C:\Windows\quantum-opt pointing to $targetPath"
+
+          cmake --build build --config Release --target check-quantum-opt