feat(toolchain): MSVC system-toolchain detection & selection (msvc@system) — 0.0.88#208
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…stem) (0.0.88) MSVC joins as the first *system* toolchain: mcpp locates and identifies an installed Visual Studio / Build Tools (vswhere → env → well-known paths; cl.exe banner → compiler version/arch, localization-tolerant) but never installs or removes MSVC itself. - toolchain default msvc: detect + report (VS product, VC tools, cl version, std.ixx availability), persist stable 'msvc@system'; absent → install guidance (VS Installer C++ workload / winget BuildTools), exit non-zero. msvc@<prefix> acts as pin-verify against the detected install. - toolchain list: Windows 'System:' section; install msvc reports what's there or guides; remove msvc refuses (system component). - self doctor: Windows 'msvc (system)' check section. - manifest [toolchain] windows = "msvc@system" now actually works; msvc specs on non-Windows hosts error clearly. - build: native cl.exe (.ifc) pipeline is gated off with one owned message pointing at llvm@20.1.7 (MSVC-ABI Clang) until it lands. - detect(): cl.exe classification path (filename short-circuit, banner enrich); bmi_traits gains the MSVC .ifc branch. - tests: unit (banner/guidance/spec/traits) + e2e 95 (Windows, requires msvc cap) / 96 (non-Windows rejection); run_all.sh msvc capability. - design: .agents/docs/2026-07-13-msvc-system-toolchain-detection-design.md
toolchain list stars the *effective* default; the repo root's mcpp.toml [toolchain] windows=llvm@20.1.7 would shadow the freshly-set global msvc@system when run_all.sh executes from the workspace.
The rebuild cleans target/, invalidating the job's $MCPP_SELF fingerprint path — the MSVC step then failed with exit 127 (binary gone).
windows-latest now installs VS under 'Microsoft Visual Studio\18\Enterprise' (major version, not year branding) — vswhere finds it, but the strategy-3 path scan should too.
…poraries GCC/libstdc++ and Clang/MSVC-STL accepted 'auto&' here; Clang/libc++ (macOS job) correctly rejects binding a non-const lvalue ref to the temporary.
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Summary
MSVC joins as mcpp's first system toolchain: mcpp locates and identifies an installed Visual Studio / Build Tools but never installs or removes MSVC itself (detection-first; the native cl.exe/.ifc build pipeline is a later phase).
Design doc:
.agents/docs/2026-07-13-msvc-system-toolchain-detection-design.mdImplementation plan:
.agents/docs/2026-07-13-msvc-system-toolchain-implementation-plan.mdWhat works
mcpp toolchain default msvc— three-strategy discovery (vswhere →VSINSTALLDIR/VS*COMNTOOLS→ well-known paths, incl. new major-version dirs like…\18\Enterprise), identifies VS product / VC tools / cl.exe banner version (localization-tolerant token parsing), reportsimport std(std.ixx) availability, persists the stable specmsvc@system(survives VS updates). Absent MSVC → actionable install guidance (VS Installer C++ workload /winget install Microsoft.VisualStudio.2022.BuildTools) + non-zero exit.msvc@<prefix>(e.g.msvc@19.51) — pin-verify against the detected install.mcpp toolchain list— WindowsSystem:section with effective-default star;install msvcreports what's there or guides;remove msvcrefuses (system component).mcpp self doctor— Windows "msvc (system)" check section.[toolchain] windows = "msvc@system"now actually works (the schema documented in types.cppm since long ago); msvc specs on non-Windows hosts error clearly.mcpp buildwith msvc selected fails early with one owned message naming the detected version and pointing atllvm@20.1.7(MSVC-ABI Clang) — never an incidental error deep in GCC/Clang-shaped flag machinery.detect()classifies cl.exe (filename short-circuit; banner → version/arch/triple;driverIdentfrom the banner so MSVC patch updates invalidate BMI fingerprints correctly);bmi_traitsgains the.ifcbranch for the future pipeline.Verified on real Windows CI (temp PR #207, green)
Tests
tests/unit/test_toolchain_msvc.cpp(banner incl. localized/arm64, guidance, spec classification,msvc@systemdefault matching,.ifctraits) — 9 tests95_msvc_system_toolchain.sh(requires: msvc, passed on Windows CI) +96_msvc_unavailable_nonwindows.sh(requires: unix-shell, passed locally)Version
0.0.88 (mcpp.toml + fingerprint.cppm + CHANGELOG)