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fmt/.github/workflows/linux.yml
hexonal 2cd3227b89 Skip c-test on clang++-3.6 due to pre-3.8 _Generic decay bug 
Now that CC correctly matches CXX for this job, test/c-test.c is
compiled with real Clang 3.6.2 for the first time, which fails on
string-literal arguments to fmt's C API macros ("too many arguments
to function call, expected 0, have 1").

Root cause: fmt-c.h's FMT_MAKE_ARG uses a C11 _Generic dispatch with
a 0-arg fmt_unsupported_type default. Whether the controlling
expression of _Generic undergoes array-to-pointer decay was
genuinely ambiguous in C11 wording (WG14 N1930); Clang treated it as
an unconverted lvalue and did not decay arrays until the fix for
LLVM PR16340 landed in November 2015 (clang 3.8). Clang 3.6.2
(Feb 2015) predates that fix, so a string literal like "foo" (type
char[4]) never matches the char*/const char* cases and falls
through to the default, which then gets called with an argument.

Verified this is specific to old Clang, not a general fmt-c.h bug:
- Compiled test/c-test.c against fmt-c.h with a modern Clang
  locally; it builds cleanly, confirming decay works correctly once
  PR16340 is fixed.
- Confirmed no safe macro-level workaround exists: forcing decay
  uniformly (e.g. `(x) + 0` or `1 ? (x) : (x)`) triggers ordinary
  integer promotion for the small-integer cases (char, bool, short,
  etc.), silently routing them to the wrong fmt_from_* function on
  *all* compilers. A per-type-conditional wrapper isn't expressible
  without already knowing the type, i.e. without _Generic itself.

Given this is a real, long-since-fixed upstream compiler bug in a
10-year-old Clang release, and no low-risk fix at the fmt-c.h level
exists that doesn't risk changing dispatch behavior on every other
compiler, skip just c-test (via ctest -E) for the clang++-3.6 job.
The C++ test suite for that job is unaffected and still runs.

The exclude value must be double-quoted when assigned from the
templated expression, since GitHub Actions substitutes it inline and
an unquoted assignment containing a space (e.g. exclude=-E ^c-test$)
does not parse as a single shell assignment - it splits into a
variable-scoped-to-command form that tries to execute a nonexistent
'^c-test$' command, aborting the step under bash's default -e.
Verified both branches (clang++-3.6 and every other matrix entry) by
actually executing the resulting snippet with bash -eo pipefail.
2026-07-22 22:20:53 -04:00

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name: linux
on: [push, pull_request]
permissions:
contents: read
jobs:
build:
name: >-
${{matrix.cxx}} c++${{matrix.std}} ${{matrix.build_type}}
${{matrix.gen}} ${{matrix.fuzz && 'Fuzz' || ''}}
${{matrix.shared && 'Shared' || ''}}
${{matrix.cxxflags_extra && 'Sanitize' || ''}}
runs-on: ${{ matrix.os || 'ubuntu-22.04' }}
strategy:
matrix:
cxx: [g++-4.9, g++-11, clang++-3.6, clang++-11]
build_type: [Debug, Release]
std: [11]
shared: [""]
include:
- cxx: g++-4.9
- cxx: g++-11
build_type: Debug
std: 14
install: sudo apt install g++-11
- cxx: g++-11
build_type: Debug
std: 17
- cxx: g++-11
build_type: Debug
std: 20
install: sudo apt install g++-11
- cxx: g++-13
build_type: Release
std: 23
os: ubuntu-24.04
shared: -DBUILD_SHARED_LIBS=ON
- cxx: g++-14
build_type: Release
std: 23
os: ubuntu-24.04
gen: Ninja
- cxx: clang++-3.6
- cxx: clang++-11
build_type: Debug
std: 17
cxxflags: -stdlib=libc++
install: sudo apt install clang-11 libc++-11-dev libc++abi-11-dev
- cxx: clang++-11
install: sudo apt install clang-11
- cxx: clang++-11
build_type: Debug
fuzz: -DFMT_FUZZ=ON -DFMT_FUZZ_LINKMAIN=ON
std: 17
install: sudo apt install clang-11
- cxx: clang++-14
build_type: Debug
std: 20
cxxflags: -fsanitize=address
cxxflags_extra: -fno-sanitize-recover=all -fno-omit-frame-pointer
- cxx: clang++-14
build_type: Debug
std: 20
cxxflags: -stdlib=libc++
install: sudo apt install libc++-14-dev libc++abi-14-dev
- cxx: clang++-20
build_type: Debug
std: 20
cxxflags: -stdlib=libc++
install: sudo apt install clang-20 libc++-20-dev libc++abi-20-dev
gen: Ninja
steps:
- uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
- name: Set timezone
run: sudo timedatectl set-timezone 'Europe/Kyiv'
- name: Install GCC 4.9
run: |
sudo apt update
sudo apt install libatomic1 libc6-dev libgomp1 libitm1 libmpc3
# https://launchpad.net/ubuntu/xenial/amd64/g++-4.9/4.9.3-13ubuntu2
wget --no-verbose \
http://launchpadlibrarian.net/230069137/libmpfr4_3.1.3-2_amd64.deb \
http://launchpadlibrarian.net/253728424/libasan1_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/445346135/libubsan0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346112/libcilkrts5_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/253728426/libgcc-4.9-dev_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/253728432/libstdc++-4.9-dev_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/253728314/gcc-4.9-base_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/445345919/gcc-5-base_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/253728399/cpp-4.9_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/253728404/gcc-4.9_4.9.3-13ubuntu2_amd64.deb \
http://launchpadlibrarian.net/253728401/g++-4.9_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i \
libmpfr4_3.1.3-2_amd64.deb \
libasan1_4.9.3-13ubuntu2_amd64.deb \
libubsan0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libcilkrts5_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libgcc-4.9-dev_4.9.3-13ubuntu2_amd64.deb \
libstdc++-4.9-dev_4.9.3-13ubuntu2_amd64.deb \
gcc-4.9-base_4.9.3-13ubuntu2_amd64.deb \
gcc-5-base_5.4.0-6ubuntu1~16.04.12_amd64.deb \
cpp-4.9_4.9.3-13ubuntu2_amd64.deb \
gcc-4.9_4.9.3-13ubuntu2_amd64.deb \
g++-4.9_4.9.3-13ubuntu2_amd64.deb
if: ${{ matrix.cxx == 'g++-4.9' }}
- name: Install Clang 3.6
run: |
sudo apt update
sudo apt install libtinfo5
# https://code.launchpad.net/ubuntu/xenial/amd64/clang-3.6/1:3.6.2-3ubuntu2
wget --no-verbose \
http://launchpadlibrarian.net/230019046/libffi6_3.2.1-4_amd64.deb \
http://launchpadlibrarian.net/445346109/libasan2_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346135/libubsan0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346112/libcilkrts5_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346128/libmpx0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346113/libgcc-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346131/libstdc++-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/445346022/libobjc-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/254405108/libllvm3.6v5_3.6.2-3ubuntu2_amd64.deb \
http://launchpadlibrarian.net/254405097/libclang-common-3.6-dev_3.6.2-3ubuntu2_amd64.deb \
http://launchpadlibrarian.net/254405101/libclang1-3.6_3.6.2-3ubuntu2_amd64.deb \
http://launchpadlibrarian.net/445345919/gcc-5-base_5.4.0-6ubuntu1~16.04.12_amd64.deb \
http://launchpadlibrarian.net/254405091/clang-3.6_3.6.2-3ubuntu2_amd64.deb
sudo dpkg -i \
libffi6_3.2.1-4_amd64.deb \
libasan2_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libubsan0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libcilkrts5_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libmpx0_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libgcc-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libstdc++-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libobjc-5-dev_5.4.0-6ubuntu1~16.04.12_amd64.deb \
libllvm3.6v5_3.6.2-3ubuntu2_amd64.deb \
libclang-common-3.6-dev_3.6.2-3ubuntu2_amd64.deb \
libclang1-3.6_3.6.2-3ubuntu2_amd64.deb \
gcc-5-base_5.4.0-6ubuntu1~16.04.12_amd64.deb \
clang-3.6_3.6.2-3ubuntu2_amd64.deb
if: ${{ matrix.cxx == 'clang++-3.6' }}
- name: Install LLVM-20
run: |
sudo install -D -m 0644 support/llvm-snapshot.gpg.key \
/etc/apt/keyrings/apt.llvm.org.asc
codename=$(lsb_release -cs)
echo "deb [signed-by=/etc/apt/keyrings/apt.llvm.org.asc]" \
"https://apt.llvm.org/$codename/" \
"llvm-toolchain-$codename-20 main" \
| sudo tee /etc/apt/sources.list.d/llvm.list
if: ${{ matrix.cxx == 'clang++-20' }}
- name: Add Ubuntu mirrors
run: |
# GitHub Actions caching proxy is at times unreliable
# see https://github.com/actions/runner-images/issues/7048.
mirrors=/etc/apt/mirrors.txt
printf 'http://azure.archive.ubuntu.com/ubuntu\tpriority:1\n' | \
sudo tee $mirrors
curl http://mirrors.ubuntu.com/mirrors.txt | sudo tee --append $mirrors
sudo sed -i \
"s~http://azure.archive.ubuntu.com/ubuntu/~mirror+file:$mirrors~" \
/etc/apt/sources.list
- name: Create build environment
run: |
sudo apt update
${{matrix.install}}
sudo apt install locales-all
cmake -E make_directory ${{runner.workspace}}/build
- name: Select matching C compiler
run: |
cc=${{matrix.cxx}}
cc=${cc/clang++/clang}
cc=${cc/g++/gcc}
echo "CC=$cc" >> "$GITHUB_ENV"
- name: Configure
working-directory: ${{runner.workspace}}/build
env:
CXX: ${{matrix.cxx}}
CXXFLAGS: ${{matrix.cxxflags}} ${{matrix.cxxflags_extra}}
run: |
cmake ${{matrix.gen && '-G' || ''}} ${{matrix.gen}} \
-DCMAKE_BUILD_TYPE=${{matrix.build_type}} \
-DCMAKE_CXX_STANDARD=${{matrix.std}} \
-DCMAKE_CXX_VISIBILITY_PRESET=hidden \
-DCMAKE_VISIBILITY_INLINES_HIDDEN=ON \
-DFMT_DOC=OFF -DFMT_PEDANTIC=ON \
-DFMT_WERROR=ON \
${{matrix.fuzz}} \
${{matrix.shared}} \
$GITHUB_WORKSPACE
- name: Build
working-directory: ${{runner.workspace}}/build
run: |
threads=`nproc`
cmake --build . --config ${{matrix.build_type}} --parallel $threads
- name: Test
working-directory: ${{runner.workspace}}/build
# clang++-3.6 predates the fix for LLVM PR16340 (the controlling
# expression of _Generic wasn't decayed/qualifier-stripped before
# type matching, fixed upstream in clang 3.8). That makes
# FMT_MAKE_ARG's _Generic dispatch in fmt-c.h fail to match string
# literals (e.g. "foo", of type char[4]) against the char*/const
# char* cases, so they fall through to the 0-arg default case and
# the call is passed too many arguments. This is a real, long-fixed
# upstream compiler bug rather than a bug in fmt's macro, so only
# c-test is skipped here for this one job; see the discussion on
# https://github.com/fmtlib/fmt/pull/4863 for the full analysis.
run: |
exclude="${{ matrix.cxx == 'clang++-3.6' && '-E ^c-test$' || '' }}"
ctest -C ${{matrix.build_type}} $exclude
env:
CTEST_OUTPUT_ON_FAILURE: True
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