{C,CXX}FLAGS envs are ignored when {c,cpp}_link_args are specified since Meson 1.8.0

[kleisauke]

Describe the bug
Similar to #14533, it seems the CFLAGS / CXXFLAGS environment variables are ignored when c_link_args / cpp_link_args are specified via the CLI since Meson 1.8.0. PR #14566 (included in Meson 1.8.1) does not appear to fix this.

To Reproduce

$ export CFLAGS="-fsanitize=address"
$ export CXXFLAGS="$CFLAGS"
$ export LDFLAGS="-I."
$ export CC=clang
$ export CXX=clang++
$ meson init
$ meson setup build -Dc_link_args="$LDFLAGS -Wl,-rpath=\$ORIGIN/lib"
The Meson build system
Version: 1.8.1
Source dir: /home/kleisauke/regression
Build dir: /home/kleisauke/regression/build
Build type: native build
Project name: regression
Project version: 0.1
C compiler for the host machine: clang (clang 20.1.3 "clang version 20.1.3 (Fedora 20.1.3-1.fc42)")
C linker for the host machine: clang ld.bfd 2.44-3
Host machine cpu family: x86_64
Host machine cpu: x86_64
Build targets in project: 1

regression 0.1

  User defined options
    c_link_args: -I. -Wl,-rpath=$ORIGIN/lib

Found ninja-1.12.1 at /usr/bin/ninja
$ meson compile -vC build
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/kleisauke/regression/build -v
ninja: Entering directory `/home/kleisauke/regression/build'
[1/2] clang -Iregression.p -I. -I.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -O0 -g -fsanitize=address -MD -MQ regression.p/regression.c.o -MF regression.p/regression.c.o.d -o regression.p/regression.c.o -c ../regression.c
[2/2] clang  -o regression regression.p/regression.c.o -I. -Wl,--as-needed -Wl,--no-undefined '-Wl,-rpath=$ORIGIN/lib'
FAILED: regression 
clang  -o regression regression.p/regression.c.o -I. -Wl,--as-needed -Wl,--no-undefined '-Wl,-rpath=$ORIGIN/lib'
/usr/bin/ld: /usr/bin/ld: DWARF error: mangled line number section (bad file number)
regression.p/regression.c.o: in function `main':
/home/kleisauke/regression/build/../regression.c:7:(.text+0x36): undefined reference to `__asan_report_load8'
/usr/bin/ld: regression.p/regression.c.o: in function `asan.module_ctor':
regression.c:(.text.asan.module_ctor[asan.module_ctor]+0x5): undefined reference to `__asan_init'
/usr/bin/ld: regression.c:(.text.asan.module_ctor[asan.module_ctor]+0xa): undefined reference to `__asan_version_mismatch_check_v8'
/usr/bin/ld: regression.c:(.text.asan.module_ctor[asan.module_ctor]+0x27): undefined reference to `__asan_register_elf_globals'
/usr/bin/ld: regression.p/regression.c.o: in function `asan.module_dtor':
regression.c:(.text.asan.module_dtor[asan.module_dtor]+0x1d): undefined reference to `__asan_unregister_elf_globals'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.

Expected behavior

$ meson setup build -Dc_link_args="$LDFLAGS -Wl,-rpath=\$ORIGIN/lib"
The Meson build system
Version: 1.7.2
Source dir: /home/kleisauke/regression
Build dir: /home/kleisauke/regression/build
Build type: native build
Project name: regression
Project version: 0.1
C compiler for the host machine: clang (clang 20.1.3 "clang version 20.1.3 (Fedora 20.1.3-1.fc42)")
C linker for the host machine: clang ld.bfd 2.44-3
Host machine cpu family: x86_64
Host machine cpu: x86_64
Build targets in project: 1

regression 0.1

  User defined options
    c_link_args: -I. -Wl,-rpath=$ORIGIN/lib

Found ninja-1.12.1 at /usr/bin/ninja
$ meson compile -vC build
INFO: autodetecting backend as ninja
INFO: calculating backend command to run: /usr/bin/ninja -C /home/kleisauke/regression/build -v
ninja: Entering directory `/home/kleisauke/regression/build'
[1/2] clang -Iregression.p -I. -I.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -O0 -g -fsanitize=address -MD -MQ regression.p/regression.c.o -MF regression.p/regression.c.o.d -o regression.p/regression.c.o -c ../regression.c
[2/2] clang  -o regression regression.p/regression.c.o -I. -Wl,--as-needed -Wl,--no-undefined '-Wl,-rpath=$ORIGIN/lib' -fsanitize=address

Additional information
Diff between the successful and failed clang invocation:

@@ -2,5 +2,5 @@ INFO: autodetecting backend as ninja
 INFO: calculating backend command to run: /usr/bin/ninja -C /home/kleisauke/regression/build -v
 ninja: Entering directory `/home/kleisauke/regression/build'
 [1/2] clang -Iregression.p -I. -I.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -O0 -g -fsanitize=address -MD -MQ regression.p/regression.c.o -MF regression.p/regression.c.o.d -o regression.p/regression.c.o -c ../regression.c
-[2/2] clang  -o regression regression.p/regression.c.o -I. -Wl,--as-needed -Wl,--no-undefined '-Wl,-rpath=$ORIGIN/lib' -fsanitize=address
+[2/2] clang  -o regression regression.p/regression.c.o -I. -Wl,--as-needed -Wl,--no-undefined '-Wl,-rpath=$ORIGIN/lib'
 

(notice the missing -fsanitize=address)

We could workaround this by avoiding cpp_link_args and just use the LDFLAGS environment variable instead, see:
libvips/libvips#4535

System parameters

• Plain native build
• Fedora 42
• Python 3.13.3
• Meson 1.8.1 (bf17c66)
• Ninja 1.12.1