Specify default opt/debug options for different CMAKE_BUILD_TYPEs

[greenc-FNAL]

• May be overridden from CMake command line, environment, etc.

[greenc-FNAL]

@phlexbot cmake-fix

[github-actions]

Automatic cmake-format fixes pushed (commit ff40cdd).
⚠️ Note: Some issues may require manual review and fixing.

[Copilot]

Pull request overview

Adds explicit default C++ compiler flags for common CMake build types at the top level, aiming to standardize optimization/debug settings across builds.

Changes:

• Introduce cached defaults for CMAKE_CXX_FLAGS_DEBUG, CMAKE_CXX_FLAGS_RELEASE, and CMAKE_CXX_FLAGS_RELWITHDEBINFO.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #409      +/-   ##
==========================================
- Coverage   84.43%   84.37%   -0.07%     
==========================================
  Files         127      127              
  Lines        3329     3329              
  Branches      564      564              
==========================================
- Hits         2811     2809       -2     
- Misses        325      326       +1     
- Partials      193      194       +1     

Flag	Coverage Δ
unittests	84.37% <ø> (-0.07%)	⬇️

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see 3 files with indirect coverage changes

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[greenc-FNAL]

Review the full CodeQL report for details.

[knoepfel]

@greenc-FNAL, is this comment by Copilot relevant? If not, please resolve the conversation.

[greenc-FNAL]

Thank you for the review. I have investigated the assertions and proposed solution carefully against the CMake 3.31 documentation and source, and the fix applied differs from the suggestion for the following reasons.

What was wrong with the original code

Two real issues existed:

1. FORCE was misleading and redundant. The if(NOT CMAKE_CXX_FLAGS_DEBUG) guard already skips the set() entirely when the variable has a non-empty cached value, so FORCE could never actually override a user-supplied value. The combination was at best confusing.
2. The string-truthiness check if(NOT CMAKE_CXX_FLAGS_DEBUG) would not respect a user who explicitly passed -DCMAKE_CXX_FLAGS_DEBUG= (an intentionally empty string), because an empty string is falsy. Using if(NOT DEFINED CACHE{CMAKE_CXX_FLAGS_DEBUG}) (available since CMake 3.14, well within our 3.31 requirement) correctly tests whether the variable was explicitly placed in the cache by the user.

The reviewer's assertion that FORCE "overrides user-provided cache values" is not quite right as written — the guard prevents that — but the underlying concern about the check being imprecise is valid.

Why the _INIT suggestion is not appropriate here

CMAKE_<LANG>_FLAGS_<CONFIG>_INIT is documented as being "meant to be set by a toolchain file." More importantly, CMake's GCC compiler information module (Modules/Compiler/GNU.cmake) populates these variables using string(APPEND ...), not set():

string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3 -DNDEBUG")
string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g -DNDEBUG")

This runs during project(), after our CMakeLists.txt code before project(). So if we set CMAKE_CXX_FLAGS_DEBUG_INIT "-Og -g" first, GCC would then append its own -g, yielding -Og -g -g in the final cache variable. The suggested approach would introduce duplicate flags.

By contrast, cmake_initialize_per_config_variable() (the CMake function that promotes _INIT values into the CMAKE_<LANG>_FLAGS_<CONFIG> cache variables) uses set(... CACHE STRING ...) without FORCE. A variable already present in the cache is left untouched. Setting the cache variable directly before project() — which is what the original and corrected code both do — is therefore the correct and intentional mechanism for establishing project-level defaults that survive the language initialization.

What was actually fixed

• Replaced if(NOT CMAKE_CXX_FLAGS_<CONFIG>) with if(NOT DEFINED CACHE{CMAKE_CXX_FLAGS_<CONFIG>}) for correct cache-presence semantics.
• Removed FORCE (it was always a no-op with the guard in place, and is misleading).
• Added descriptive strings to the CACHE STRING entries (they were empty).
• Added a comment explaining why the variables are set before project().

[greenc-FNAL]

@phlexbot cmake-fix

[github-actions]

Automatic cmake-format fixes pushed (commit bedb14b).
⚠️ Note: Some issues may require manual review and fixing.