[esrrhs]

Summary

Re-applies the wiped #47 coverage work onto current master (a6fe459, which already includes #48). The old PR had been merged, then disappeared when master was force-updated; this branch cherry-picks only the coverage commits (with #48 conflict resolutions preserved).

Enable usable Codecov signal for GCC JIT-emitted runtime C under USE_COV.

Changes

1. GCC JIT gcov (USE_COV) — When coverage is on, pass -fprofile-arcs / -ftest-coverage / --coverage into the GCC JIT compile/link of generated C, place temps under build/jit_cov, use a two-step .c→.o→.so so .gcno/.gcda stay harvestable, and keep the .c after unload for lcov. TCC path unchanged.
2. CI extract includes jit_cov — After one lcov --directory build capture, --extract keeps src/*, include/*, and build/jit_cov/* so JIT hits are not dropped before Codecov upload. Adds --ignore-errors inconsistent for #line → .lua end-line noise.
3. View header + #line mapping — Codecov cannot usefully browse build/jit_cov/fakelua_jit_*.c. Add checked-in src/compile/c_runtime_cov.h (byte-identical view of kCRuntimeHeader) and wrap the paste with #line 1 \"src/compile/c_runtime_cov.h\" so Fl* runtime hits map to an in-repo src/ path. Reset to <fakelua-generated> afterward so preamble / #line→.lua stay unchanged.
4. Sync test — Unit test asserts the view file stays byte-identical to the raw-string body (kCRuntimeHeader remains the compile-time source of truth).
5. cppcheck / CVar.flag_ — Exclude the Codecov twin from cppcheck; initialize key CVar.flag_ = 0 while keeping master's UNLIKELY (perf(jit): optimize loop advance, closure call, condition comparisons and itoa #48) behavior.

Caveats

• TCC still blind — TCC JIT is not instrumented; only GCC JIT contributes coverage under USE_COV.
• Local coverage — Full local cov on c_runtime_cov.h is ~87.8% in the measured run; residual gaps are expected for cold error/edge paths.
• build/jit_cov and coverage.info remain gitignored artifacts — not committed.

Commits

• 15f9a8e exp: instrument GCC JIT emitted C with gcov when USE_COV
• 62197d7 ci(cov): include build/jit_cov GCC JIT temps in Codecov upload
• bd90271 exp(cov): map GCC JIT Fl* runtime hits onto checked-in c_runtime_cov.h
• bf5ebe3 fix(ci): silence cppcheck on c_runtime_cov view and init CVar.flag_

Do not merge from this bot turn; review CI / Codecov first.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 79.31034% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.49%. Comparing base (a6fe459) to head (bf5ebe3).

Files with missing lines	Patch %	Lines
src/jit/gcc_jit.cpp	78.82%	18 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
+ Coverage   88.45%   88.49%   +0.04%     
==========================================
  Files         124      125       +1     
  Lines       26109    27211    +1102     
==========================================
+ Hits        23095    24081     +986     
- Misses       3014     3130     +116     

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