zig cc -l example sets the DSO paths incorrectly

[a-khabarov]

Zig Version

0.12.0-dev.3677+22a97cd23

Steps to Reproduce and Observed Behavior

$ mkdir -p /tmp/libtest/mylib
$ cd /tmp/libtest
$ echo 'void f() {}' > mylib/mylib.c
$ echo 'void f();' > mylib/mylib.h
$ echo '#include "mylib/mylib.h"' > main.c
$ echo 'int main() { f(); }' >> main.c
$ zig cc -shared mylib/mylib.c -o mylib/libmylib.so
$ zig cc main.c -Lmylib -lmylib -o main  # Link with name lookup
$ readelf -a main | grep -E 'NEEDED|RUNPATH'
 0x000000000000001d (RUNPATH)            Library runpath: [mylib]
 0x0000000000000001 (NEEDED)             Shared library: [mylib/libmylib.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

Expected Behavior

zig cc with -lmylib (lookup without explicit basename) shouldn't pass the whole resolved path to ld.lld.
Here is what clang (17.0.6) does for cases like this:

$ clang -shared mylib/mylib.c -o mylib/libmylib.so
$ clang main.c -Lmylib -lmylib -o main  # Link with name lookup
$ readelf -a main | grep -E 'NEEDED|RUNPATH'
 0x0000000000000001 (NEEDED)             Shared library: [libmylib.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

Note the absence of mylib/.
gcc (13.2.1 20230801) has the same behavior as clang here:

$ gcc -shared mylib/mylib.c -o mylib/libmylib.so
$ gcc main.c -Lmylib -lmylib -o main  # Link with name lookup
$ readelf -a main | grep -E 'NEEDED|RUNPATH'
 0x0000000000000001 (NEEDED)             Shared library: [libmylib.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

This is essentialy the behavior of zig cc when linking with explicit basename (-l:libmylib.so):

$ zig cc -shared mylib/mylib.c -o mylib/libmylib.so
$ zig cc main.c -Lmylib -l:libmylib.so -o main  # Link with explicit basename via `:`
$ readelf -a main | grep -E 'NEEDED|RUNPATH'
 0x000000000000001d (RUNPATH)            Library runpath: [mylib]
 0x0000000000000001 (NEEDED)             Shared library: [libmylib.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

Related comment: #15743 (comment)
Related issue: #15743

[a-khabarov]

@andrewrk @kubkon This bug is very similar to #15743 and might be a blocker for the 0.12 release.

[JoshuaLeivers]

This issue affects uber/hermetic_cc_toolchain as mentioned here. Linking @motiejus to provide visibility on progress.