probe round 3: builtin headers in system modules vs macro definitions

Author: speak-agent

.github/probe/m27.sh

@@ -1,39 +1,42 @@
 #!/usr/bin/env bash
-# macOS 27: libc++ 22 std.cppm loses INFINITY/NAN. Round 2: mechanism and candidate fixes.
+# macOS 27 round 3: which single flag makes libc++ 22's std module build in strict mode.
 set +e
 r() { echo "READING $*"; }
-L="$LLVM_ROOT"; SDK=$(xcrun --show-sdk-path); S=$L/share/libc++/v1/std.cppm
-r "llvm=$L cfg=$(tr '\n' ' ' < $L/bin/clang++.cfg)"
-r "math.h 55-95:"; sed -n 55,95p $SDK/usr/include/math.h | sed 's/^/READING   math.h| /'
-FH=$($L/bin/clang -print-resource-dir)/include/float.h
-r "clang float.h INFINITY region:"; grep -n -B4 -A3 'define INFINITY' $FH | sed 's/^/READING   float.h| /'
-AF=$(/usr/bin/clang -print-resource-dir)/include/float.h
-r "apple float.h INFINITY region:"; grep -n -B4 -A3 'define INFINITY' $AF | sed 's/^/READING   apple-float.h| /'
+L="$LLVM_ROOT"; SDK=$(xcrun --show-sdk-path); S=$L/share/libc++/v1/std.cppm; SC=$L/share/libc++/v1/std.compat.cppm
 W=$(mktemp -d); cd $W
-BASE=(--no-default-config -nostdinc++ -isystem $L/include/c++/v1 -isysroot $SDK -Wno-reserved-module-identifier)
-try() { name=$1; shift; out=$("$@" 2>&1); rc=$?; r "$name rc=$rc $(printf '%s' "$out" | grep -m1 'error' | cut -c1-200)"; }
-printf 'int main(){ return __has_feature(modules); }\n' > hf.cpp
-try hasfeature-modules-in-precompile-of-plain  $L/bin/clang++ "${BASE[@]}" -std=c++23 -fsyntax-only hf.cpp
-printf 'export module m;\n#if __has_feature(modules)\n#error MODULES_ON\n#endif\n' > hf.cppm
-try hasfeature-modules-in-module-interface $L/bin/clang++ "${BASE[@]}" -std=c++23 --precompile hf.cppm -o hf.pcm
-try c++23            $L/bin/clang++ "${BASE[@]}" -std=c++23   --precompile $S -o a.pcm
-try gnu++23          $L/bin/clang++ "${BASE[@]}" -std=gnu++23 --precompile $S -o b.pcm
-try c++23-U-strict   $L/bin/clang++ "${BASE[@]}" -std=c++23 -U__STRICT_ANSI__ --precompile $S -o c.pcm
-try c++23-inc-math   $L/bin/clang++ "${BASE[@]}" -std=c++23 -include math.h --precompile $S -o d.pcm
-try c++23-fbuiltin-inf $L/bin/clang++ "${BASE[@]}" -std=c++23 "-DINFINITY=__builtin_inff()" "-DNAN=__builtin_nanf(\"\")" --precompile $S -o e.pcm
-try c++26            $L/bin/clang++ "${BASE[@]}" -std=c++26   --precompile $S -o f.pcm
-SDK26=/Library/Developer/CommandLineTools/SDKs/MacOSX26.5.sdk
-BASE26=(--no-default-config -nostdinc++ -isystem $L/include/c++/v1 -isysroot $SDK26 -Wno-reserved-module-identifier)
-try c++23-sdk26.5    $L/bin/clang++ "${BASE26[@]}" -std=c++23 --precompile $S -o g.pcm
-# a program importing std, end to end, with the variant that works
-for std in c++23 gnu++23; do
-  rm -rf p; mkdir p; cd p
-  $L/bin/clang++ "${BASE[@]}" -std=$std --precompile $S -o std.pcm >/dev/null 2>&1
-  $L/bin/clang++ "${BASE[@]}" -std=$std -c std.pcm -o std.o >/dev/null 2>&1
-  printf 'import std;\nint main(){ std::println("inf={} nan={}", std::numeric_limits<double>::infinity(), std::isnan(std::nan(""))); }\n' > m.cpp
-  $L/bin/clang++ "${BASE[@]}" -std=$std -fmodule-file=std=std.pcm -c m.cpp -o m.o >/dev/null 2>&1
-  $L/bin/clang++ --no-default-config -isysroot $SDK -fuse-ld=lld -nostdlib++ m.o std.o $L/lib/libc++.a $L/lib/libc++abi.a -o m >/dev/null 2>&1
-  r "program $std: $(./m 2>&1)"
+BASE=(--no-default-config -nostdinc++ -isystem $L/include/c++/v1 -isysroot $SDK -Wno-reserved-module-identifier -std=c++23)
+try() { name=$1; shift; out=$("$@" 2>&1); rc=$?; r "$name rc=$rc $(printf '%s' "$out" | grep -m1 -E 'error|warning' | cut -c1-220)"; }
+r "modulemap infinity_nan: $(grep -n -A3 'infinity_nan' $($L/bin/clang -print-resource-dir)/include/module.modulemap | tr '\n' ' ')"
+r "driver cc1 builtin-headers: $($L/bin/clang++ "${BASE[@]}" -### -fsyntax-only -x c++ /dev/null 2>&1 | tr ' ' '\n' | grep -i 'builtin-headers\|fmodules' | tr '\n' ' ')"
+try baseline               $L/bin/clang++ "${BASE[@]}" --precompile $S -o a.pcm
+try builtin-in-sysmodules  $L/bin/clang++ "${BASE[@]}" -Xclang -fbuiltin-headers-in-system-modules --precompile $S -o b.pcm
+try no-modulemaps          $L/bin/clang++ "${BASE[@]}" -fno-implicit-module-maps --precompile $S -o c.pcm
+try need-inf-nan           $L/bin/clang++ "${BASE[@]}" -D__need_infinity_nan --precompile $S -o d.pcm
+try defs-sdk-spelling      $L/bin/clang++ "${BASE[@]}" "-DINFINITY=HUGE_VALF" "-DNAN=__builtin_nanf(\"0x7fc00000\")" --precompile $S -o e.pcm
+# the winner must also give std.compat and a working program, and must not warn in plain TUs
+printf '#include <cmath>\n#include <cfloat>\n#include <math.h>\n#include <float.h>\nint main(){ return INFINITY > 0 && NAN != NAN ? 0 : 1; }\n' > p.cpp
+printf '#include <math.h>\n#include <float.h>\nint main(void){ return INFINITY > 0 && NAN != NAN ? 0 : 1; }\n' > p.c
+for v in "builtin-in-sysmodules:-Xclang -fbuiltin-headers-in-system-modules" "defs-sdk-spelling:-DINFINITY=HUGE_VALF -DNAN=__builtin_nanf(\"0x7fc00000\")"; do
+  name=${v%%:*}; flags=${v#*:}
+  eval "F=($flags)"
+  try "$name plain-c++ -Werror" $L/bin/clang++ "${BASE[@]}" "${F[@]}" -Werror -Wall p.cpp -o pcpp
+  try "$name plain-c -Werror"   $L/bin/clang --no-default-config -isysroot $SDK "${F[@]}" -std=c17 -Werror -Wall p.c -o pc
+  try "$name std.compat"        $L/bin/clang++ "${BASE[@]}" "${F[@]}" -fmodule-file=std=a.pcm --precompile $SC -o sc.pcm
+  rm -rf prog; mkdir prog; cd prog
+  $L/bin/clang++ "${BASE[@]}" "${F[@]}" --precompile $S -o std.pcm >/dev/null 2>&1
+  $L/bin/clang++ "${BASE[@]}" "${F[@]}" -c std.pcm -o std.o >/dev/null 2>&1
+  printf 'export module mm;\nimport std;\n#include <cmath>\nexport double inf() { return INFINITY; }\n' > mm.cppm
+  $L/bin/clang++ "${BASE[@]}" "${F[@]}" -fmodule-file=std=std.pcm --precompile mm.cppm -o mm.pcm 2> mm.err
+  $L/bin/clang++ "${BASE[@]}" "${F[@]}" -c mm.pcm -o mm.o >/dev/null 2>&1
+  printf 'import std;\nimport mm;\nint main(){ std::println("inf={} nan={}", inf(), std::isnan(std::nan(""))); }\n' > m.cpp
+  $L/bin/clang++ "${BASE[@]}" "${F[@]}" -fmodule-file=std=std.pcm -fmodule-file=mm=mm.pcm -c m.cpp -o m.o 2> m.err
+  $L/bin/clang++ --no-default-config -isysroot $SDK -fuse-ld=lld -nostdlib++ m.o mm.o std.o $L/lib/libc++.a $L/lib/libc++abi.a -o m 2> l.err
+  r "$name program: $(./m 2>&1) | $(head -1 mm.err) $(head -1 m.err) $(head -1 l.err)"
   cd ..
 done
+# same flags on the macOS 26.5 SDK: must stay green
+SDK26=/Library/Developer/CommandLineTools/SDKs/MacOSX26.5.sdk
+B26=(--no-default-config -nostdinc++ -isystem $L/include/c++/v1 -isysroot $SDK26 -Wno-reserved-module-identifier -std=c++23)
+try sdk26-builtin-in-sysmodules $L/bin/clang++ "${B26[@]}" -Xclang -fbuiltin-headers-in-system-modules --precompile $S -o f.pcm
+try sdk26-plain-c++-Werror      $L/bin/clang++ "${B26[@]}" -Xclang -fbuiltin-headers-in-system-modules -Werror -Wall p.cpp -o p26
 exit 0