Fix build compatibility with macOS 26 and Apple Clang 21

.github/actions/ccache-push/action.yml

@@ -15,10 +15,10 @@ inputs:
     description: 'PR number for tag. Auto-detected from ref_name when empty.'
     required: false
     default: ''
-  delta-threshold:
-    description: 'Skip push if cache file count changed by less than this percentage. Set to 0 to always push.'
+  miss-threshold:
+    description: 'Skip push if ccache miss rate is below this percentage. Set to 0 to always push.'
     required: false
-    default: '10'
+    default: '5'
   ref-name:
     description: 'Branch name used for tag when not a PR build'
     required: false
@@ -42,7 +42,7 @@ runs:
       shell: bash
       run: |
         cache_path="${{ inputs.cache-path }}"
-        delta_threshold="${{ inputs.delta-threshold }}"
+        miss_threshold="${{ inputs.miss-threshold }}"
 
         # Validate cache path has content
         if [ ! -d "$cache_path" ] || [ -z "$(ls -A "$cache_path" 2>/dev/null)" ]; then
@@ -53,35 +53,30 @@ runs:
 
         # Print stats for visibility: prefer _build_stats.txt from Docker
         # export, fall back to querying ccache on the host (native builds).
+        stats_output=""
         stats_file="$cache_path/_build_stats.txt"
         if [ -f "$stats_file" ]; then
           echo "=== ccache stats (from Docker build) ==="
-          cat "$stats_file"
+          stats_output=$(cat "$stats_file")
+          echo "$stats_output"
         elif command -v ccache &>/dev/null; then
           echo "=== ccache stats ==="
-          ccache -s 2>/dev/null || true
+          stats_output=$(ccache -s 2>/dev/null || true)
+          echo "$stats_output"
         fi
 
-        # Compute cache delta: compare current file count to the baseline
-        # recorded at restore time. This measures how much the cache
-        # actually changed, regardless of whether the build ran natively
-        # or inside Docker.
-        restore_count_file="$cache_path/_restore_file_count.txt"
-        current_count=$(find "$cache_path" -type f | wc -l | tr -d ' ')
-        if [ -f "$restore_count_file" ]; then
-          restore_count=$(cat "$restore_count_file" | tr -d ' ')
-        else
-          restore_count=0
-        fi
-        new_files=$((current_count - restore_count))
-        if [ "$restore_count" -gt 0 ]; then
-          delta_pct=$((new_files * 100 / restore_count))
-        elif [ "$current_count" -gt 0 ]; then
-          delta_pct=100
-        else
-          delta_pct=0
+        # Use ccache's miss rate to decide whether the cache is worth saving.
+        # File-count growth is a poor proxy: a small percentage change can still
+        # represent hundreds of missed compile results in a large cache.
+        cacheable_calls=$(echo "$stats_output" | awk '/^Cacheable calls:/ {print $3; exit}')
+        cache_misses=$(echo "$stats_output" | awk '/^  Misses:/ {print $2; exit}')
+        miss_pct=""
+        if [[ "$cacheable_calls" =~ ^[0-9]+$ ]] && \
+           [[ "$cache_misses" =~ ^[0-9]+$ ]] && \
+           [ "$cacheable_calls" -gt 0 ]; then
+          miss_pct=$((cache_misses * 100 / cacheable_calls))
+          echo "Cache miss rate: ${miss_pct}% (${cache_misses} misses / ${cacheable_calls} cacheable calls)"
         fi
-        echo "Cache delta: ${new_files} new files (${delta_pct}% change, ${restore_count} -> ${current_count})"
 
         # Always push on the default branch to keep the baseline fresh.
         # This includes merge queue runs, which are the only path into
@@ -96,10 +91,14 @@ runs:
 
         if $is_default_branch; then
           echo "On default branch ($default_branch); always pushing to keep baseline fresh."
-        elif [ "$delta_threshold" -gt 0 ] 2>/dev/null && [ "$delta_pct" -lt "$delta_threshold" ]; then
-          echo "Cache changed by ${delta_pct}% (threshold: ${delta_threshold}%); skipping push."
-          echo "pushed=false" >> $GITHUB_OUTPUT
-          exit 0
+        elif [ "$miss_threshold" -gt 0 ] 2>/dev/null; then
+          if [ -z "$miss_pct" ]; then
+            echo "No ccache miss rate available; pushing cache."
+          elif [ "$miss_pct" -lt "$miss_threshold" ]; then
+            echo "Cache miss rate ${miss_pct}% is below threshold ${miss_threshold}%; skipping push."
+            echo "pushed=false" >> $GITHUB_OUTPUT
+            exit 0
+          fi
         fi
 
         # Extract log and stats from cache dir before tarring so they
@@ -108,7 +107,7 @@ runs:
         if [ -f "$cache_path/ccache.log" ]; then
           mv "$cache_path/ccache.log" "${GITHUB_WORKSPACE:-$(pwd)}/ccache.log"
         fi
-        rm -f "$stats_file" "$restore_count_file"
+        rm -f "$stats_file" "$cache_path/_restore_file_count.txt"
 
         # Determine tag
         repo_owner=$(echo "${{ github.repository_owner }}" | tr '[:upper:]' '[:lower:]')

.github/actions/setup-xcode-stable/action.yml

@@ -0,0 +1,94 @@
+name: Set up latest stable Xcode
+description: Select the newest non-beta Xcode installed on the macOS runner.
+
+outputs:
+  version:
+    description: Selected Xcode version.
+    value: ${{ steps.select.outputs.version }}
+  build:
+    description: Selected Xcode build number.
+    value: ${{ steps.select.outputs.build }}
+  path:
+    description: Selected Xcode application path.
+    value: ${{ steps.select.outputs.path }}
+  developer-dir:
+    description: Selected Xcode developer directory.
+    value: ${{ steps.select.outputs.developer-dir }}
+
+runs:
+  using: composite
+  steps:
+    - id: select
+      shell: bash
+      run: |
+        set -euo pipefail
+
+        # Mirrors the selection strategy from maxim-lobanov/setup-xcode
+        # (scan installed Xcode apps, ignore beta releases, choose newest
+        # stable), but keeps it local to avoid external-action allowlist issues.
+        selection_file=$(mktemp)
+        python3 > "$selection_file" <<'PY'
+        from pathlib import Path
+        import plistlib
+        import re
+        import sys
+
+        def semver_key(version):
+            return tuple(int(part) for part in re.findall(r"\d+", version))
+
+        versions = []
+        for app in Path("/Applications").iterdir():
+            if not app.is_dir() or app.is_symlink():
+                continue
+            if not re.match(r"^Xcode.*\.app$", app.name):
+                continue
+
+            version_plist = app / "Contents" / "version.plist"
+            license_plist = app / "Contents" / "Resources" / "LicenseInfo.plist"
+            if not version_plist.exists() or not license_plist.exists():
+                continue
+
+            with version_plist.open("rb") as handle:
+                version_info = plistlib.load(handle)
+            with license_plist.open("rb") as handle:
+                license_info = plistlib.load(handle)
+
+            version = str(version_info.get("CFBundleShortVersionString", ""))
+            build = str(version_info.get("ProductBuildVersion", ""))
+            license_type = str(license_info.get("licenseType", "")).lower()
+            if not version or not license_type or "beta" in license_type:
+                continue
+
+            versions.append((semver_key(version), version, build, str(app)))
+
+        if not versions:
+            print("No stable Xcode installation found in /Applications.", file=sys.stderr)
+            sys.exit(1)
+
+        _, version, build, path = sorted(versions, reverse=True)[0]
+        print(path)
+        print(version)
+        print(build)
+        PY
+
+        xcode_path=$(sed -n '1p' "$selection_file")
+        xcode_version=$(sed -n '2p' "$selection_file")
+        xcode_build=$(sed -n '3p' "$selection_file")
+        rm -f "$selection_file"
+
+        developer_dir="$xcode_path/Contents/Developer"
+        if [ ! -d "$developer_dir" ]; then
+          echo "Could not find Xcode developer directory: $developer_dir"
+          exit 1
+        fi
+
+        sudo xcode-select -s "$developer_dir"
+        echo "DEVELOPER_DIR=$developer_dir" >> "$GITHUB_ENV"
+        echo "MD_APPLE_SDK_ROOT=$xcode_path" >> "$GITHUB_ENV"
+
+        echo "path=$xcode_path" >> "$GITHUB_OUTPUT"
+        echo "version=$xcode_version" >> "$GITHUB_OUTPUT"
+        echo "build=$xcode_build" >> "$GITHUB_OUTPUT"
+        echo "developer-dir=$developer_dir" >> "$GITHUB_OUTPUT"
+
+        echo "Selected Xcode $xcode_version ($xcode_build) at $xcode_path"

.github/workflows/ci_macos.yml

@@ -128,6 +128,17 @@ jobs:
         with:
           python-version: '3.12'
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Set up ccache and ORAS
         uses: ./.github/actions/ccache-setup
 
@@ -158,7 +169,6 @@ jobs:
         run: |
           source scripts/set_env_defaults.sh
           Python3_EXECUTABLE="$(which python3)" \
-          LLVM_PROJECTS='clang;lld;mlir;openmp;python-bindings' \
           LLVM_SOURCE="$HOME/.llvm-project" \
           bash scripts/build_llvm.sh -c Release -v -j $(sysctl -n hw.ncpu)
 
@@ -209,6 +219,17 @@ jobs:
         with:
           python-version: ${{ matrix.python_version }}
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Set up ccache and ORAS
         uses: ./.github/actions/ccache-setup
 
@@ -235,7 +256,6 @@ jobs:
         run: |
           source scripts/set_env_defaults.sh
           Python3_EXECUTABLE="$(which python3)" \
-          LLVM_PROJECTS='clang;lld;mlir;openmp;python-bindings' \
           LLVM_SOURCE="$HOME/.llvm-project" \
           bash scripts/build_llvm.sh -c Release -v -j $(sysctl -n hw.ncpu)
 
@@ -291,6 +311,17 @@ jobs:
         with:
           python-version: ${{ matrix.python_version }}
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Download wheel artifact
         uses: actions/download-artifact@v4
         with:
@@ -339,6 +370,17 @@ jobs:
         with:
           python-version: '3.12'
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Set up ccache and ORAS
         uses: ./.github/actions/ccache-setup
 
@@ -367,7 +409,6 @@ jobs:
         run: |
           source scripts/set_env_defaults.sh
           Python3_EXECUTABLE="$(which python3)" \
-          LLVM_PROJECTS='clang;lld;mlir;openmp;python-bindings' \
           LLVM_SOURCE="$HOME/.llvm-project" \
           bash scripts/build_llvm.sh -c Release -v -j $(sysctl -n hw.ncpu)
 
@@ -418,6 +459,17 @@ jobs:
         with:
           python-version: '3.12'
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Download installer artifact
         uses: actions/download-artifact@v4
         with:

.github/workflows/dev_environment_macos.yml

@@ -94,6 +94,7 @@ jobs:
             scripts/install_prerequisites.sh \
             scripts/build_llvm.sh \
             scripts/set_env_defaults.sh \
+            cmake/caches/LLVM.cmake \
             .github/workflows/dev_environment_macos.yml \
             tpls/customizations/llvm/*.diff \
             | sha256sum | cut -c1-8)
@@ -142,17 +143,32 @@ jobs:
       - name: Log in to GitHub CR
         run: echo "${{ github.token }}" | oras login ghcr.io -u ${{ github.actor }} --password-stdin
 
+      - name: Select latest stable Xcode
+        uses: ./.github/actions/setup-xcode-stable
+
+      - name: Log macOS toolchain
+        run: |
+          sw_vers
+          xcodebuild -version
+          xcrun --show-sdk-path
+          xcrun --show-sdk-version
+          clang --version
+
       - name: Compute cache key
         id: cache_key
         run: |
           # Combine build scripts hash with the runner image version to detect
           # tool updates (cmake, compilers, etc.) that would invalidate the cache.
+          # Include the selected Xcode as well because the same runner image can
+          # contain multiple SDK/compiler releases.
           scripts_hash=${{ needs.metadata.outputs.scripts_hash }}
           runner_image=${ImageVersion:-unknown}
-          deps_hash=$(echo "${scripts_hash}-${runner_image}" | shasum -a 256 | cut -c1-8)
+          developer_dir=${DEVELOPER_DIR:-$(xcode-select -p 2>/dev/null || echo unknown)}
+          xcode_version=$(xcodebuild -version 2>/dev/null | shasum -a 256 | cut -c1-8 || echo unknown)
+          deps_hash=$(echo "${scripts_hash}-${runner_image}-${developer_dir}-${xcode_version}" | shasum -a 256 | cut -c1-8)
           image_name="${{ needs.metadata.outputs.image_name_base }}${deps_hash}"
           echo "image_name=$image_name" >> $GITHUB_OUTPUT
-          echo "Cache key: scripts_hash=$scripts_hash runner_image=$runner_image deps_hash=$deps_hash"
+          echo "Cache key: scripts_hash=$scripts_hash runner_image=$runner_image developer_dir=$developer_dir xcode_version=$xcode_version deps_hash=$deps_hash"
           echo "Image name: $image_name"
 
       - name: Check for cached image
@@ -186,7 +202,6 @@ jobs:
           git submodule update --init --recursive tpls/nanobind
 
           source scripts/set_env_defaults.sh
-          export LLVM_PROJECTS='clang;lld;mlir;openmp;python-bindings'
 
           echo "Building prerequisites..."
           echo "LLVM_INSTALL_PREFIX=$LLVM_INSTALL_PREFIX"

CMakeLists.txt

@@ -755,6 +755,7 @@ if (CUDAQ_ENABLE_PYTHON)
 endif()
 
 if(CUDAQ_BUILD_TESTS AND NOT CUDAQ_DISABLE_CPP_FRONTEND)
+  include(CheckCXXCompilerFlag)
   umbrella_lit_testsuite_begin(check-all)
   set(INSTALL_GTEST OFF)
   add_subdirectory(tpls/googletest-src)
@@ -773,6 +774,11 @@ if(CUDAQ_BUILD_TESTS AND NOT CUDAQ_DISABLE_CPP_FRONTEND)
   endif()
   if (CMAKE_CXX_COMPILER_ID MATCHES "^(Apple)?Clang$")
     target_compile_options(gtest PUBLIC -Wno-covered-switch-default)
+    check_cxx_compiler_flag("-Wno-character-conversion"
+                            CUDAQ_SUPPORTS_WNO_CHARACTER_CONVERSION)
+    if (CUDAQ_SUPPORTS_WNO_CHARACTER_CONVERSION)
+      target_compile_options(gtest PUBLIC -Wno-character-conversion)
+    endif()
   endif()
   include(GoogleTest)
   include(CTest)

runtime/cudaq/cudaq.cpp

@@ -270,7 +270,7 @@ void __nvqpp_initializer_list_to_vector_bool(std::vector<bool> &result,
                                              char *initList, std::size_t size) {
   // result is a sret return value. Make sure it is default initialized. Takes
   // advantage of default empty vector being all 0s.
-  std::memset(reinterpret_cast<void *>(&result), 0, sizeof(result));
+  std::memset(static_cast<void *>(&result), 0, sizeof(result));
   // Allocate space.
   result.reserve(size);
   // Copy in the initialization list data.