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Prefer /usr/bin/clang as default CC on darwin #10823

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Prefer /usr/bin/clang as default CC on darwin #10823

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46 changes: 44 additions & 2 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -185,6 +185,24 @@ AS_CASE(["${build_os}"],
# Clang on Solaris is largely untested.
# https://bugs.ruby-lang.org/issues/17949
AC_CHECK_TOOLS([CC], [cc gcc])
],
[darwin*], [
# /usr/bin/clang is always available as long as Command Line Tools or Xcode is installed.
# Prefer absolute path to avoid PATH lookup, which may lead to unaligned tool selection.
rb_darwin_default_CC=/usr/bin/clang
AC_MSG_CHECKING([for darwin default CC $rb_darwin_default_CC])
AS_IF([test -z "$CC" -a -x "$rb_darwin_default_CC"],
[
AC_MSG_RESULT([yes])
CC=$rb_darwin_default_CC
],
[
AC_MSG_RESULT([no])
# Fall back to PATH lookup just in case the /usr/bin/clang is not
# available for some reason.
AC_CHECK_TOOLS([CC], [clang cc gcc c99])
]
)
Comment on lines +189 to +205
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What about expand rb_CC absolute path, only if the found CC is Xcode?

    AS_IF([$rb_CC -E -dM -xc - < /dev/null | grep -F __apple_build_version__ > /dev/null],
          [llvm_prefix= rb_CC=`command -v $rb_CC`], [llvm_prefix=llvm-])

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@kateinoigakukun kateinoigakukun May 23, 2024 •
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What we are trying to solve is unaligned toolset selection in the situation where PATH contains mixed toolchains (e.g. LLVM from Homebrew, Conda toolchain?, and Xcode).

e.g.

$ ls /path/to/conda/bin
clang # but no nm
$ ls /usr/bin
clang nm ...
$ export PATH=/path/to/conda:/usr/bin

If we continue looking up CC from PATH and align toolset only when CC comes from Xcode, the problem won't be mitigated for the above situation.
That's why I prefer fixed /usr/bin/clang as the default decision.

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@rubyFeedback rubyFeedback May 23, 2024 •
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Not disagreeing with you as such, but it should be pointed out that at the least on Linux, the default assumption is that the entries in $PATH coming first, have higher precedence. So, for instance, if a user would have a PATH that first has /opt/bin/, and /usr/bin/ as second entry, then /opt/bin/ should be searched first. This will probably happen only very, very rarely, so it does not invalidate your statement, but I wanted to mention it in regards to (possible) user's expectations.

If we continue looking up CC from PATH and align toolset only when CC comes from Xcode, the problem won't be mitigated for the above situation.

Right, but it should also pointed out that this appears to be an incorrect assumption by conda then, if it assumes that the bin/ it searches for must be in the same directory (e. g. assuming /usr/bin/). My clang binary, for instance, is under /home/Programs/Llvm/18.1.2/bin/, for instance. (I follow a symlink-version approach similar to GoboLinux, but I also only use /usr/bin/ and just update the current symlink in use, for all programs on my linux machine, just as info; obviously darwin follows another scheme.)

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I think we should abort in that case, if not [test -x "${rb_prog}"], rather than searching from $PATH.

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It makes sense to me. It sounds well consistent behavior.

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I think rb_darwin_default_CC is not needed anymore.

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Sorry, do you mean we should find CC from PATH instead of having the default value?

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Yes, only for Xcode clang, as commented above.

], [
# OpenBSD wants to prefer cc over gcc.
# See https://github.com/ruby/ruby/pull/2443
Expand All @@ -207,7 +225,31 @@ set rb_dummy ${CC}
rb_CC=$2
AC_DEFUN([RUBY_CHECK_PROG_FOR_CC], [
rb_prog=`echo "${rb_CC}" | sed "$2"`
AC_CHECK_PROG([$1], [$rb_prog], [$rb_prog])
rb_prog_optional="$3"
rb_prog_found=no
# If the tool is not explicitly specified and the compiler
# is absolute, check the one next to the compiler.
AS_IF([test -z "$$1"], [
AS_CASE(["${rb_prog}"],
[/*], [
AC_MSG_CHECKING([for ${rb_prog}])
AS_IF([test -x "${rb_prog}"], [
rb_prog_found=yes
$1=${rb_prog}
], [
# Abort if the tool is required and expected to be next
# to the compiler but not found.
AS_IF([test "x${rb_prog_optional}" != xyes], [
AC_MSG_ERROR("executable ${rb_prog} is not found")
])
])
AC_MSG_RESULT([$rb_prog_found])
], [
# Otherwise, try to find it in PATH with given program name
rb_prog=`echo "${rb_prog}" | sed 's,.*/,,'`
AC_CHECK_PROG([$1], [$rb_prog], [$rb_prog])
])
])
])
AS_CASE(["/${rb_CC} "],
[*@<:@\ /@:>@"cc "*], [
Expand Down Expand Up @@ -245,7 +287,7 @@ AS_CASE(["/${rb_CC} "],
# RUBY_CHECK_PROG_FOR_CC([AS], [s/clang/${llvm_prefix}as/])
RUBY_CHECK_PROG_FOR_CC([CXX], [s/clang/clang++/])
RUBY_CHECK_PROG_FOR_CC([NM], [s/clang/${llvm_prefix}nm/])
RUBY_CHECK_PROG_FOR_CC([OBJCOPY], [s/clang/${llvm_prefix}objcopy/])
RUBY_CHECK_PROG_FOR_CC([OBJCOPY], [s/clang/${llvm_prefix}objcopy/], [yes]) # optional
RUBY_CHECK_PROG_FOR_CC([OBJDUMP], [s/clang/${llvm_prefix}objdump/])
RUBY_CHECK_PROG_FOR_CC([RANLIB], [s/clang/${llvm_prefix}ranlib/])
RUBY_CHECK_PROG_FOR_CC([STRIP], [s/clang/${llvm_prefix}strip/])
Expand Down
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