build: PCH + ccache launcher + fast-linker autodetect#6
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Three build-time levers, all guarded/no-op where tooling is absent: - PCH on lci_lib for the heaviest, most widely-included headers — nlohmann/json (~25k lines, 26 TUs) and absl flat_hash_map (39 TUs) plus ubiquitous std headers (<string> 134 TUs, <vector> 100). Parsed once instead of per-TU; the largest clean-build compile-time win for the 95-TU library. - ccache as CMAKE_CXX/C_COMPILER_LAUNCHER when installed, set before project(). Automatic for local dev builds (CI already passed it explicitly; guarded by NOT DEFINED so the CI override wins). - Fast linker autodetect: mold > lld via find_program, add_link_options -fuse-ld=...; no-op if neither present or on MSVC. Speeds the link of `lci` and the monolithic lci_tests (~1700 tests + all deps). lci_lib + lci_tests build clean with the PCH; full suite 1692/1692 green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Mach-O has no mold support and Apple's ld64 is fine; guard the -fuse-ld override with NOT APPLE so the macOS leg keeps its default linker. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Build-time optimizations identified from the actual build profile. All guarded / no-op where tooling is absent.
Changes
lci_lib— the heaviest widely-included headers parsed once instead of per-TU:nlohmann/json.hpp(~25k lines, 26 TUs),absl/container/flat_hash_map.h(39 TUs), plus ubiquitous std (<string>134,<vector>100). Largest clean-build compile win for the 95-TU library.project()when installed; automatic for local dev (CI already passed it explicitly;NOT DEFINEDguard lets the CI override win).mold>lldviafind_program+-fuse-ld=; no-op if absent or MSVC. Speeds linkinglci+ the monolithiclci_tests.Verification
lci_lib+lci_testsbuild clean with PCH (a broken PCH fails the build).Follow-ups (not here, need more care): unity build for lci_lib, splitting lci_tests, and the vcpkg setup reliability/pre-bake that caused the recent Windows runner hang.
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