1 files changed, 56 insertions, 14 deletions

diff --git a/rakelib/gcc.rake b/rakelib/gcc.rake
index 558c8a2..7b6bf44 100644
--- a/rakelib/gcc.rake
+++ b/rakelib/gcc.rake
@@ -3,11 +3,36 @@
 # obtain one at https://mozilla.org/MPL/2.0/. -}
 # frozen_string_literal: true
 
+require 'fileutils'
 require 'uri'
 require 'net/http'
 require 'open3'
 require 'pathname'
 
+# Use Homebrew GCC if available (it uses libstdc++, avoiding
+# macOS-specific libc++ incompatibilities in GCC's own sources).
+class GCCConfiguration
+  attr_reader :target
+
+  def initialize(suffix, target, sysroot_sdk)
+    @suffix = suffix
+    @target = target
+    @sysroot_sdk = sysroot_sdk
+  end
+
+  def cc
+    "gcc#{@suffix}"
+  end
+
+  def cxx
+    "g++#{@suffix}"
+  end
+
+  def configure
+    @sysroot_sdk.nil? ? [] : ["--with-sysroot=#{@sysroot_sdk}"]
+  end
+end
+
 def gcc_verbose(gcc_binary)
   read, write = IO.pipe
   sh({'LC_ALL' => 'C'}, gcc_binary, '--verbose', err: write)
@@ -17,13 +42,21 @@ def gcc_verbose(gcc_binary)
   output
 end
 
-def find_build_target
-  gcc_verbose(ENV.fetch 'CC', 'gcc')
+def find_build_target(gcc_version)
+  if RUBY_PLATFORM =~ /darwin/
+    suffix = '-' + gcc_version.split('.').first
+    mac_os_sdk = '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk'
+  else
+    suffix = ''
+  end
+  build_target = gcc_verbose(ENV.fetch 'CC', "gcc#{suffix}")
     .lines
     .find { |line| line.start_with? 'Target: ' }
     .split(' ')
     .last
     .strip
+
+  GCCConfiguration.new suffix, build_target, mac_os_sdk
 end
 
 def download_and_pipe(url, target, command)
@@ -66,11 +99,12 @@ namespace :gcc do
   # Dependencies.
   GCC_VERSION = "16.1.0"
   HOST_GCC = 'build/host/gcc'
+  HOST_INSTALL = Pathname.new 'build/host/install'
   GCC_TREE = Pathname.new "build/tools/gcc-#{GCC_VERSION}"
   GCC_PATCH = 'https://raw.githubusercontent.com/Homebrew/homebrew-core/refs/heads/main/Patches/gcc/gcc-16.1.0.diff'
 
   directory HOST_GCC
-  directory 'build/host/install'
+  directory HOST_INSTALL.to_path
   directory 'build/tools'
 
   desc 'Download the bootstrap compiler and its prerequisites'
@@ -81,7 +115,7 @@ namespace :gcc do
     download_and_pipe URI.parse(GCC_PATCH), GCC_TREE, ['patch', '-p1']
 
     # GCC 16.1.0 registers 17 languages but CL_PARAMS is at bit 16,
-    # which collides with the 17th language class (CL_Rust).  Shift
+    # which collides with the 17th language class (CL_Rust). Shift
     # every CL_* constant from bit 16 upward by one position.
     File.open(GCC_TREE + 'gcc/opts.h', 'r+') do |opts_h|
       content = opts_h.read.gsub(/\(1U << (\d+)\)/) do |m|
@@ -116,8 +150,8 @@ namespace :gcc do
   end
 
   desc 'Configure the bootstrap compiler'
-  task configure: [HOST_GCC, 'build/host/install'] do |t|
-    build_target = find_build_target
+  task configure: [HOST_GCC, HOST_INSTALL.to_path] do |t|
+    build_target = find_build_target GCC_VERSION
     configure_options = [
       "--prefix=#{File.realpath t.prerequisites.last}",
       '--enable-languages=c,c++,jit,elna',
@@ -125,14 +159,15 @@ namespace :gcc do
       '--disable-multilib',
       '--enable-host-shared',
       '--with-system-zlib',
-      "--target=#{build_target}",
-      "--build=#{build_target}",
-      "--host=#{build_target}"
+      "--target=#{build_target.target}",
+      "--build=#{build_target.target}",
+      "--host=#{build_target.target}",
+      *build_target.configure
     ]
-    mac_os_sdk = '/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk'
-    configure_options << "--with-sysroot=#{mac_os_sdk}" if File.symlink? mac_os_sdk
-
-    env = ENV.slice 'CC', 'CXX'
+    env = {
+      'CC' => ENV['CC'] || build_target.cc,
+      'CXX' => ENV['CXX'] || build_target.cxx
+    }
     env['CFLAGS'] = env['CXXFLAGS'] = '-O0 -g -fPIC -I/opt/homebrew/opt/flex/include'
 
     configure = GCC_TREE.relative_path_from(HOST_GCC) + 'configure'
@@ -163,7 +198,14 @@ namespace :gcc do
       .reject do |file|
         ['/elna1.', '/elna-spec.'].any? { |pattern| file.include? pattern }
       end
-    sh 'clang-tidy', '-p', compile_db.to_path, '--extra-arg=-w', '--warnings-as-errors=*', *sources
+    build_target = find_build_target GCC_VERSION
+    includes = ['.', build_target.target].collect do |inc|
+      HOST_INSTALL + 'include/c++' + GCC_VERSION + inc
+    end
+
+    sh 'clang-tidy', '-p', compile_db.to_path, '--extra-arg=-w', '--warnings-as-errors=*',
+      *includes.collect { |inc| "--extra-arg=-cxx-isystem#{inc.realpath}" },
+      '--extra-arg=-stdlib=libstdc++', *sources
   end
 
   desc 'Build documentation'