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
From a220d781b3a53565c799ea48b92460467c089f6c Mon Sep 17 00:00:00 2001 From: Tristan Partin <[email protected]> Date: Wed, 16 Apr 2025 20:25:21 -0500 Subject: [PATCH] meson: warn when no C++ compiler is found --- meson.build | 34 +++++++++++++++++++++++----------- src/include/meson.build | 2 +- src/makefiles/meson.build | 9 ++++++--- 3 files changed, 30 insertions(+), 15 deletions(-) diff --git a/meson.build b/meson.build index 395416a606..a0afb0d5a8 100644 --- a/meson.build +++ b/meson.build @@ -41,13 +41,22 @@ build_system = build_machine.system() host_cpu = host_machine.cpu_family() cc = meson.get_compiler('c') +have_cpp = add_languages('cpp', required: false, native: false) +if have_cpp + cpp = meson.get_compiler('cpp') +endif +# === USER WARNING: No C++ compiler found === +if not have_cpp + warning('No C++ compiler found on your system.\n' + + ' Extensions using C++ (e.g. pg_duckdb) will FAIL to build.\n' + + ' Install g++ or clang++ to enable C++ support.') +endif not_found_dep = dependency('', required: false) thread_dep = dependency('threads') auto_features = get_option('auto_features') - ############################################################### # Safety first ############################################################### @@ -827,15 +836,13 @@ endif llvmopt = get_option('llvm') llvm = not_found_dep -if add_languages('cpp', required: llvmopt, native: false) +if have_cpp and not llvmopt.disabled() llvm = dependency('llvm', version: '>=14', method: 'config-tool', required: llvmopt) if llvm.found() cdata.set('USE_LLVM', 1) - cpp = meson.get_compiler('cpp') - llvm_binpath = llvm.get_variable(configtool: 'bindir') ccache = find_program('ccache', native: true, required: false) @@ -844,8 +851,13 @@ if add_languages('cpp', required: llvmopt, native: false) # find via PATH, too. clang = find_program(llvm_binpath / 'clang', 'clang', required: true) endif -elif llvmopt.auto() - message('llvm requires a C++ compiler') +else + msg = 'llvm requires a C++ compiler' + if llvmopt.auto() + message(msg) + elif llvmopt.enabled() + error(msg) + endif endif @@ -2061,7 +2073,7 @@ common_functional_flags = [ ] cflags += cc.get_supported_arguments(common_functional_flags) -if llvm.found() +if have_cpp cxxflags += cpp.get_supported_arguments(common_functional_flags) endif @@ -2085,7 +2097,7 @@ common_warning_flags = [ ] cflags_warn += cc.get_supported_arguments(common_warning_flags) -if llvm.found() +if have_cpp cxxflags_warn += cpp.get_supported_arguments(common_warning_flags) endif @@ -2139,7 +2151,7 @@ foreach w : negative_warning_flags if cc.has_argument('-W' + w) cflags_warn += '-Wno-' + w endif - if llvm.found() and cpp.has_argument('-W' + w) + if have_cpp and cpp.has_argument('-W' + w) cxxflags_warn += '-Wno-' + w endif endforeach @@ -2200,7 +2212,7 @@ elif optimization == 's' endif cflags_builtin = cc.get_supported_arguments(common_builtin_flags) -if llvm.found() +if have_cpp cxxflags_builtin = cpp.get_supported_arguments(common_builtin_flags) endif @@ -3929,7 +3941,7 @@ summary( section: 'Compiler Flags', ) -if llvm.found() +if have_cpp summary( { 'C++ compiler': '@0@ @1@'.format(cpp.get_id(), cpp.version()), diff --git a/src/include/meson.build b/src/include/meson.build index 7cb3075da2..9be2f25e4a 100644 --- a/src/include/meson.build +++ b/src/include/meson.build @@ -36,7 +36,7 @@ config_paths_data.set_quoted('MANDIR', dir_prefix / dir_man) var_cc = ' '.join(cc.cmd_array()) var_cpp = ' '.join(cc.cmd_array() + ['-E']) var_cflags = ' '.join(cflags + cflags_builtin + cflags_warn + get_option('c_args')) -if llvm.found() +if have_cpp var_cxxflags = ' '.join(cxxflags + cxxflags_builtin + cxxflags_warn + get_option('cpp_args')) else var_cxxflags = '' diff --git a/src/makefiles/meson.build b/src/makefiles/meson.build index 0def244c90..ff62200e5f 100644 --- a/src/makefiles/meson.build +++ b/src/makefiles/meson.build @@ -31,7 +31,6 @@ if not working_strip strip_shared_cmd = [':'] endif - pgxs_kv = { 'PACKAGE_URL': pg_url, 'PACKAGE_VERSION': pg_version, @@ -119,16 +118,20 @@ pgxs_kv = { 'LIBS': var_libs, } +if have_cpp + pgxs_kv += { + 'CXX': ' '.join(cpp.cmd_array()), + } +endif + if llvm.found() pgxs_kv += { 'CLANG': clang.full_path(), - 'CXX': ' '.join(cpp.cmd_array()), 'LLVM_BINPATH': llvm_binpath, } else pgxs_kv += { 'CLANG': '', - 'CXX': '', 'LLVM_BINPATH': '', } endif -- 2.39.5
