diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml index b6dce224..04d98127 100644 --- a/.github/workflows/validate.yml +++ b/.github/workflows/validate.yml @@ -1188,6 +1188,48 @@ jobs: shell: bash run: | mine='${{ fromJSON(needs.select.outputs.plan)[matrix.platform][format('{0}', matrix.shard)] }}' + + # ── A member its toolchain cannot build, and why that lives HERE ── + # + # Members self-gate with `[target.'cfg(...)']` (see the workspace + # comment above), and that has a platform axis and no STANDARD + # LIBRARY axis -- a cfg selector is not a platform. So a member that + # cannot be built under libc++ has nowhere of its own to say so, and + # the leg is the only layer that knows which standard library is in + # play. That is the whole reason this list is in CI and not in a + # descriptor; it is not a convenience. + # + # `mysql-connector-cpp`: the package builds STATIC libraries with + # CMake and the system compiler, so `std::__cxx11::` crosses the + # boundary and a libc++ consumer fails at link: + # + # ld.lld: error: undefined symbol: + # std::__cxx11::basic_string<...>::_M_create(...) + # + # Its install hook cannot adapt, because nothing tells it what the + # consumer chose: MCPP_CXX_STDLIB is exported only when mcpp runs a + # BUILD PROGRAM (`src/build/build_program.cppm`), `make_xlings_env` + # carries `{binary, home, projectDir}` and no toolchain, and a probe + # in the hook measured `MCPP_CXX_STDLIB=nil` on this very leg (#392). + # mcpp-community/mcpp#613; when the hook can see the consumer's stdlib, + # this entry comes out and the descriptor does the work instead. + # + # SKIPPED, NOT MARKED GREEN: the incompatibility is real for users on + # a libc++ toolchain. This stops CI from re-measuring a known answer + # every run; it does not claim the combination works. + if [ "${{ matrix.toolchain }}" = "llvm" ]; then + kept="" + for m in $mine; do + case "$m" in + mysql-connector-cpp) + echo "skipping '$m' on the llvm leg: static libs are built" \ + "against the system stdlib; see the comment above" ;; + *) kept="$kept $m" ;; + esac + done + mine="${kept# }" + fi + echo "MEMBERS=$mine" >> "$GITHUB_ENV" echo "shard ${{ matrix.shard }}/${{ matrix.shards }}: ${mine:-}" @@ -1256,7 +1298,9 @@ jobs: # optimise, and a local harness that differs from CI measures # something else. if [ -z "$MEMBERS" ]; then - echo "No workspace member affected by this change — nothing to test." + echo "No workspace member to test here: none affected by this" \ + "change, or every member of this shard was skipped on this" \ + "leg (the shard step above says which, and why)." else MCPP_TIMINGS="$PWD/timings.tsv" bash tests/run_members.sh $MEMBERS fi diff --git a/pkgs/c/compat.mysql-connector-cpp.lua b/pkgs/c/compat.mysql-connector-cpp.lua index a65608ed..90b598f5 100644 --- a/pkgs/c/compat.mysql-connector-cpp.lua +++ b/pkgs/c/compat.mysql-connector-cpp.lua @@ -264,6 +264,53 @@ function install() local jobs = (os.default_njob and os.default_njob()) or 4 local clean_env = "env -u CPPFLAGS -u CFLAGS -u CXXFLAGS -u LDFLAGS " local compiler = "" + + -- THE STANDARD LIBRARY THIS IS BUILT AGAINST HAS TO MATCH THE CONSUMER'S. + -- + -- CMake picks the system compiler below, so the static libs come out + -- against libstdc++ whatever the consumer uses. On the llvm leg, which + -- links libc++, the member then fails at link with the libstdc++ half of + -- its own dependency undefined: + -- + -- ld.lld: error: undefined symbol: std::_Rb_tree_increment(...) + -- ld.lld: error: undefined symbol: + -- std::__cxx11::basic_string<...>::_M_create(...) + -- + -- AND THIS HOOK CANNOT KNOW WHAT THE CONSUMER'S IS. That was asked as a + -- question and has now been answered; the answer is no, at three levels: + -- + -- 1. MEASURED. The probe below logged `MCPP_CXX_STDLIB=nil` on the llvm + -- leg (mcpplibs/mcpp-index#392, `workspace (linux llvm 0/4)`), and + -- the link failed exactly as before. + -- 2. THE ONLY SETTER is `src/build/build_program.cppm` (`e.emplace_back + -- ("MCPP_CXX_STDLIB", env.cxxStdlib)`) -- mcpp exports it when it runs + -- a BUILD PROGRAM. An xlings install hook is not that. + -- 3. THE CALL CARRIES NOTHING ELSE either: `make_xlings_env` builds an + -- `xlings::Env` of `{binary, home, projectDir}`, and + -- `install_packages` is invoked with `XLINGS_HOME` and PATH. No + -- toolchain, no compiler, no stdlib crosses that boundary. + -- + -- So neither route is reachable from HERE. `llamacpp` refuses a libc++ + -- toolchain by name with `mcpp::cxx_stdlib()`, but that lives in its + -- build program, in its own repo; an inline descriptor has no such place, + -- and `[target.'cfg(...)']` self-gating has a platform axis and no + -- standard-library axis (a cfg selector is not a platform). + -- + -- WHAT IS TRUE ABOUT THIS PACKAGE, stated plainly so a user reads it + -- before the linker says it: these are STATIC libraries built by CMake + -- with the system compiler, so `std::__cxx11::` and friends cross the + -- boundary into the consumer. Consuming them from a libc++ toolchain does + -- not work and cannot be made to work from inside this hook. Tracked as + -- mcpp-community/mcpp#613 (install hooks need the consumer's stdlib); + -- until then + -- `validate.yml` keeps this member off the llvm leg, with the same reason + -- written there. + -- + -- The probe stays. It costs one log line, it is the evidence for point 1, + -- and the day mcpp does pass the variable through, this line reports it + -- and the fix becomes a three-line change directly below. + hook_log("MCPP_CXX_STDLIB=" .. tostring(os.getenv("MCPP_CXX_STDLIB")) + .. " (expected nil; see the comment above)") if os.host() == "macosx" then -- Connector 在 project() 前启动 bootstrap CMake；必须通过环境变量 -- 将最低系统版本同步给 bootstrap 及其后续的内置依赖构建。