Add GCC 15 warning support

[laurynas-biveinis]

Tweak old-compilers.yml at the same time.

Summary by CodeRabbit

• Chores
  • Updated build system to support flexible GCC version configuration.
  • Extended compiler support to GCC 15.0+ with improved warning detection.

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[coderabbitai]

Walkthrough

This PR adds GCC 15 compiler support to the build system and parameterizes the GitHub Actions workflow for flexible compiler installation. Changes include new warning flags for C++15+, compiler version checks, and a parameterized installation step.

Changes

Cohort / File(s)	Summary
GitHub Actions workflow parameterization .github/workflows/old-compilers.yml	Replaces hardcoded g++-13 installation with g++-${VERSION} variable for flexible compiler version selection.
GCC 15+ compiler support CMakeLists.txt	Adds GCC_GE_15_CXX_WARNING_FLAGS with whitespace-related warning flags; introduces cxx_ge_15 version check against 15.0; defines is_gxx_ge_15 conditional; integrates new flags into COMMON_TARGET_PROPERTIES via generator expression.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• CMakeLists.txt generator expressions and flag definitions should be verified for correctness
• Confirm is_gxx_ge_15 conditional logic properly gates the warning flags for standalone builds

Possibly related PRs

• Add GCC 15 support, excluding CI #803: Adds GCC 15 to CMake presets, complementing the compiler-version checks introduced here
• Bump GCC version in build.yml to 14 #801: Modifies GCC installation logic in the same workflow file with different version handling
• Silence Google Test build warnings under GCC 14 #784: Restructures compiler-warning flags in CMakeLists.txt for GCC 14 and above

Poem

🔨 From thirteen to fifteen we climb,
New warnings flag the whitespace crime,
Variables flow through workflows bright,
GCC marches on to compile the night. 🌙

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding GCC 15 warning support to CMakeLists.txt, which is the primary objective of this pull request.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch gcc-15-partial

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📜 Recent review details

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 0b20e68 and a748522.

📒 Files selected for processing (2)

• .github/workflows/old-compilers.yml (1 hunks)
• CMakeLists.txt (4 hunks)

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🔇 Additional comments (4)

.github/workflows/old-compilers.yml (1)

776-781: Parameterization is correct, but GCC 15 is missing from the test matrix.

Line 780 now uses g++-${VERSION} instead of hardcoded g++-13, which properly aligns with the parameterized workflow. However, the workflow matrix (lines 518–732) only defines GCC versions 10–13. To fully support GCC 15 as claimed in the PR title, you need to add GCC 15 test matrix entries.

Verify whether GCC 15 packages are available in the Ubuntu 22.04 repository or require a PPA. If available, add matrix entries following the existing GCC 13 pattern. If not available, consider either updating the runner OS or clarifying that GCC 15 support is limited to CMake configuration only.

CMakeLists.txt (3)

416-427: Version check and combined condition follow the established pattern.

Lines 416–427 correctly introduce cxx_ge_15 and is_gxx_ge_15 following the existing pattern for other GCC versions (e.g., cxx_ge_14 and is_gxx_ge_14). The generator expressions are syntactically correct and properly combine the GCC compiler ID with the version constraint.

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740-740: Warning flags are correctly applied with proper conditional.

Line 740 applies GCC_GE_15_CXX_WARNING_FLAGS using the correct generator expression pattern: $<$<AND:${is_standalone},${is_gxx_ge_15}>:...>. This mirrors the existing conditional logic for other version-specific warning sets (lines 737–739).

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122-123: The warning flags -Wleading-whitespace=spaces and -Wtrailing-whitespace=any are both valid in GCC 15. These flags are documented in the GCC 15 manual and were newly added in GCC 15. The implementation is correct.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.33%. Comparing base (0b20e68) to head (a748522).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #825      +/-   ##
==========================================
+ Coverage   98.16%   98.33%   +0.16%     
==========================================
  Files          35       35              
  Lines        6492     6492              
==========================================
+ Hits         6373     6384      +11     
+ Misses        119      108      -11     

Flag	Coverage Δ
Debug	98.33% <ø> (+0.20%)	⬆️
Release	97.46% <ø> (-0.11%)	⬇️

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