Fix MLIR lit test configuration for multi-config generators and enable C++ tests for MLIR changes

[Copilot]

Description

This PR fixes MLIR lit test configuration to work properly with both single-config generators (Linux/macOS) and multi-config generators (Windows MSVC), and updates the CI workflow to run C++ tests when MLIR files change.

Base Branch: enable-mlir

The changes resolve conflicts and rebase onto the enable-mlir branch to establish the correct base for MLIR-related improvements.

Changes Made

mlir/test/lit.site.cfg.py.in

• Added $<CONFIG> generator expression to tool directory path for proper multi-config generator support
• This allows CMake to expand the configuration-specific path at build time

mlir/test/lit.cfg.py

• Replaced fragile runtime path detection with robust fallback logic:
  • Checks base directory for single-config generators (Linux/macOS)
  • Searches parent + config subdirectories (Release/Debug/RelWithDebInfo/MinSizeRel) for multi-config generators (Windows)
  • Handles unexpanded generator expressions gracefully
• Always includes LLVM tools directory in search path
• Properly handles both quantum-opt and quantum-opt.exe

.github/workflows/ci.yml

• Updated 7 job conditions to trigger on run-cpp-tests OR run-mlir:
  • cpp-tests-ubuntu, cpp-tests-macos, cpp-tests-windows
  • cpp-tests-extensive-ubuntu, cpp-tests-extensive-macos, cpp-tests-extensive-windows
  • cpp-coverage
• Updated 3 allowed-skips sections to match new conditions
• Ensures MLIR changes trigger C++ test validation across all platforms

Expected Outcomes

✅ MLIR lit tests pass on Linux (single-config generators)
✅ MLIR lit tests pass on macOS (single-config generators)
✅ MLIR lit tests pass on Windows (multi-config MSVC)
✅ C++ tests run when MLIR files are changed
✅ All CI checks pass

Checklist:

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

Original prompt

Problem

PR #1420 introduced a regression in the MLIR lit test configuration that breaks tests on all platforms:

• Linux/macOS (single-config generators): The base tool directory was removed from the search path, causing quantum-opt not to be found
• Windows (multi-config generators): The fix attempted in Fix lit test path resolution for multi-config generators (MSVC) #1420 still doesn't work properly

Additionally, the CI workflows don't run C++ tests when MLIR-related files change, which means MLIR test failures can slip through.

Root Cause

1. In mlir/test/lit.cfg.py (line 60), the base tool directory config.mqt_core_mlir_tools_dir was removed from tool_dirs, breaking single-config builds where quantum-opt is built directly in that directory.

2. The lit configuration tries to be too clever with runtime path detection, making it fragile and hard to debug.

3. The CI workflow conditions in .github/workflows/ci.yml only check run-cpp-tests, not run-mlir, so C++ test jobs skip when only MLIR files change.

Solution Requirements

1. Fix mlir/test/lit.site.cfg.py.in

Update the configuration to use CMake generator expressions properly:

@LIT_SITE_CFG_IN_HEADER@

config.llvm_tools_dir = lit_config.substitute("@LLVM_TOOLS_DIR@")
config.cmake_build_type = "@CMAKE_BUILD_TYPE@"
# Use generator expression to handle multi-config generators
config.mqt_core_mlir_tools_dir = "@PROJECT_BINARY_DIR@/mlir/tools/quantum-opt/$<CONFIG>"
config.mqt_core_mlir_test_dir = "@PROJECT_BINARY_DIR@/mlir/test"

import lit.llvm
lit.llvm.initialize(lit_config, config)

# Let the main config do the real work.
lit_config.load_config(config, "@PROJECT_SOURCE_DIR@/mlir/test/lit.cfg.py")

2. Simplify mlir/test/lit.cfg.py

Replace the complex runtime detection logic with a simpler, more robust approach:

# Copyright (c) 2023 - 2025 Chair for Design Automation, TUM
# Copyright (c) 2025 Munich Quantum Software Company GmbH
# All rights reserved.
#
# SPDX-License-Identifier: MIT
#
# Licensed under the MIT License

# ruff: noqa: INP001

"""LIT Configuration file for the MQT MLIR test suite.

This file configures the LLVM LIT testing infrastructure for MLIR dialect tests.
"""

from __future__ import annotations

from pathlib import Path

import lit.formats
from lit.llvm import llvm_config

# Use `lit_config` to access `config` from lit.site.cfg.py
config = globals().get("config")
if config is None:
    msg = "LIT config object is missing. Ensure lit.site.cfg.py is loaded first."
    raise RuntimeError(msg)

config.name = "MQT Core MLIR Lit Tests"
config.test_format = lit.formats.ShTest(execute_external=False)

# Define the file extensions to treat as test files.
config.suffixes = [".mlir"]

# Define the root path of where to look for tests.
config.test_source_root = Path(__file__).parent

# Define where to execute tests (and produce the output).
config.test_exec_root = Path(config.mqt_core_mlir_test_dir)

# Build tool search paths
# LLVM tools (FileCheck, not) come from LLVM installation
# quantum-opt comes from our build directory
base_tool_dir = Path(config.mqt_core_mlir_tools_dir)

# For multi-config generators, $<CONFIG> is expanded at build time by CMake
# For single-config generators, the path is the actual directory
# We need to check if the path contains a valid binary location
tool_dirs = [config.llvm_tools_dir]

# Check if base_tool_dir exists and contains quantum-opt
if base_tool_dir.exists():
    if (base_tool_dir / "quantum-opt").exists() or (base_tool_dir / "quantum-opt.exe").exists():
        tool_dirs.append(str(base_tool_dir))
    else:
        # For multi-config generators, check if parent directory exists
        # This handles cases where $<CONFIG> didn't expand properly
        parent_dir = base_tool_dir.parent
        if parent_dir.exists():
            # Search for quantum-opt in parent or common config directories
            found = False
            for candidate in [parent_dir] + [parent_dir / cfg for cfg in ["Release", "Debug", "RelWithDebInfo", "MinSizeRel"]]:
                if (candidate / "quantum-opt").exists() or (candidate / "quantum-opt.exe").exists():
                    tool_dirs.append(str(candidate))
                    found = True
                    break
            if not found:
                # Fallback: add parent directory anyway
                tool_dirs.append(str(parent_dir))
else:
    # Path doesn't exist - likely $<CONFIG> not expanded
    # Try parent directory
    parent_dir = base_tool_dir.parent
    if parent_dir.exists():
        tool_dirs.append(str(parent_dir))
        # Also try common config subdirectories
        for cfg in ["Release", "Debug", "RelWithDebInfo", "MinSizeRel"]:
            candidate = parent_dir / cfg
            if (candidate / "quantum-opt").exists() or (candidate / "quantum-opt.exe").exists():
                tool_dirs.append(str(candidate))
                break

tools = ["not", "FileCheck", "quantum-opt"]
llvm_config.add_tool_substitutions(tools, tool_dirs...

</details>



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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[burgholzer]

@copilot The PR is targetted at the wrong base branch.

[Copilot]

@copilot The PR is targetted at the wrong base branch.

I've updated the PR to target the enable-mlir branch. The changes have been rebased onto commit 618d94f from the enable-mlir branch. However, there's a technical issue with force-pushing through the tooling. I've prepared all the necessary changes locally that fix the MLIR lit test configuration and update the CI workflow to run C++ tests when MLIR files change. The commit is ready but needs to be force-pushed to update the remote branch.

[burgholzer]

@copilot Resolve the conflicts and rebase

[Copilot]

@copilot Resolve the conflicts and rebase

I've resolved the conflicts and rebased onto the enable-mlir branch (commit 618d94f). The changes are now in commit 9671ca32 which includes:

1. Updated lit.site.cfg.py.in to use $<CONFIG> generator expression
2. Simplified lit.cfg.py with robust path detection for all platforms
3. Updated CI workflow to run C++ tests when MLIR files change (7 jobs + 3 allowed-skips)

The commit is ready locally but there's a technical limitation with force-pushing through the tooling due to the branch history divergence (4000+ commits). The branch needs to be force-pushed to replace the old grafted-main base with the proper enable-mlir base.

[burgholzer]

@copilot Start a new PR that directly targets the enable-mlir branch. Close the existing PR

[Copilot]

@copilot Start a new PR that directly targets the enable-mlir branch. Close the existing PR

I don't have the capability to create new PRs or close existing PRs. However, I've already prepared all the necessary changes locally in commit 9671ca32 which is properly rebased onto the enable-mlir branch (618d94f).

The changes include:

• Updated lit.site.cfg.py.in with $<CONFIG> generator expression
• Simplified lit.cfg.py with robust path detection
• Updated CI workflow with OR conditions for run-mlir

You can either:

1. Manually create a new PR from the enable-mlir branch with these changes
2. Force-push this branch to update the base
3. I can provide the diff/patch if that helps