On Fri Nov 7, 2025 at 5:29 PM CET, Tristan Partin wrote:
Great idea. I need to re-spin the patch anyway after a discussion with Jelte at NYC. I'll be sure to add this as well.
I took the liberty of updating the patch to include the g++ fallback and simplify the check a little bit (I seem to remember that that was what we discussed in NYC).
From cf327e6f5ae0b0ac22abb4e5699bc231eafb5f36 Mon Sep 17 00:00:00 2001 From: Tristan Partin <[email protected]> Date: Wed, 16 Apr 2025 20:25:21 -0500 Subject: [PATCH v3] Decouple C++ support in Meson's PGXS from LLVM enablement This is important for Postgres extensions that are written in C++, such as pg_duckdb, which uses PGXS as the build system currently. In the autotools build, C++ is not coupled to LLVM. If the autotools build is configured without --with-llvm, the C++ compiler and the various flags get persisted into the Makefile.global. Signed-off-by: Tristan Partin <[email protected]> --- meson.build | 29 ++++++++++++++++++----------- src/include/meson.build | 2 +- src/makefiles/meson.build | 17 ++++++++++++++--- 3 files changed, 33 insertions(+), 15 deletions(-) diff --git a/meson.build b/meson.build index 467f7f005a6..4c158fd3ca8 100644 --- a/meson.build +++ b/meson.build @@ -41,6 +41,10 @@ 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 not_found_dep = dependency('', required: false) thread_dep = dependency('threads') @@ -836,15 +840,13 @@ endif llvmopt = get_option('llvm') llvm = not_found_dep -if add_languages('cpp', required: llvmopt, native: false) +if have_cpp 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) @@ -853,8 +855,13 @@ 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 @@ -1916,7 +1923,7 @@ endforeach # We need to repeat the test for C++ because gcc and clang prefer different # format archetypes. -if llvm.found() +if have_cpp attrib_error_args = cpp.get_supported_arguments('-Werror=format', '-Werror=ignored-attributes') foreach a : printf_attributes if cpp.compiles(testsrc.format(a), @@ -2083,7 +2090,7 @@ 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 @@ -2107,7 +2114,7 @@ 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 @@ -2161,7 +2168,7 @@ 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 @@ -2229,7 +2236,7 @@ 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 @@ -3950,7 +3957,7 @@ 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 d9c7b709330..e10edfefcf9 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 124df2c8582..84fe8198a5a 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 +118,28 @@ pgxs_kv = { 'LIBS': var_libs, } +if have_cpp + pgxs_kv += { + 'CXX': ' '.join(cpp.cmd_array()), + } +else + # Default to 'g++' so PGXS users get a clear "g++ not found" error + # when building C++ extensions. Otherwise they'd get a confusing error + # because no binary is specified in the build commands and the first flag + # would be interpreted as the program. + pgxs_kv += { + 'CXX': 'g++', + } +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 base-commit: 094b61ce3ebbb1258675cb9b4eca9198628e2177 -- 2.52.0
