Hi Tristan, Andres, Jelte, and pgsql-hackers,
Thank you for the excellent work on decoupling C++ support in Meson from LLVM
SUMMARY: v2 PATCH TESTED AND WORKS PERFECTLY
- Built PostgreSQL 19devel (current master) with Meson
- Config: -Dllvm=disabled -Dcpp_support=auto
- Before patch: CXX = (empty) → extension fails with shell error
- After patch: CXX = ccache c++ → extension builds successfully
- Tested with minimal C++ extension → cpp_test.so created
REPRODUCTION & FIX STEPS
1. git remote add tristan https://github.com/tristan957/postgres.git
git fetch tristan
git checkout -b meson-cpp tristan/meson-cpp
2. meson setup build-fixed .. -Dllvm=disabled -Dcpp_support=auto
meson compile && meson install
3. Built test C++ extension:
cd ~/cpp_test_ext && make clean && make
VERIFIED OUTPUT
$ grep -E "^(CXX|CXXFLAGS) =" build-fixed/src/Makefile.global
CXX = ccache c++
CXXFLAGS = -fno-strict-aliasing -fwrapv -Wall -g -O0 ...
$ ls -l ~/cpp_test_ext/*.so
-rwxr-xr-x 1 boss boss 21568 Nov 4 12:18 /home/boss/cpp_test_ext/cpp_test.so
Patch applies cleanly and works perfectly on 19devel.
While testing the C++ PGXS patch, I noticed a usability gap:
> If no C++ compiler is installed (e.g., `g++` missing), Meson silently
> proceeds with C++ disabled — users only discover the issue when extensions
> like pg_duckdb fail with confusing build errors.
This patch adds a clear, single warning during configuration:
WARNING: No C++ compiler found on your system.
Extensions using C++ (e.g. pg_duckdb) will FAIL to build.
Install g++ or clang++ to enable C++ support.
- Only shown when `add_languages('cpp')` returns `false`
- No warning when C++ is available
- Tested on PostgreSQL 19devel (with and without `g++`)
Attached: `0001-meson-warn-when-no-C-compiler-is-found.patch`
Happy to revise if there are better ways to surface this — open to suggestions!
Thanks again for the great work on Meson C++ support.
Best regards,
Lakshmi
