I encountered a surprising error when working with a custom compiler recently. It looks like the compiler is expecting headers for libzstd to be in a directory that might change when the lib is updated. I don't now if this is the expected behaviour, but it feels wrong to have to re-configure and re-build the compiler after such an update.

Environment:

• Platform: Mac M1
• Compiler version: a branch based on 5.1
• libzstd installed with brew

Steps to reproduce:

• Configure and build the compiler
• Update the zstd library with brew (in my case from 1.5.2 to 1.5.5)
• Link an executable with the compiler

$ echo "print_int 42" > main.ml
$ ocamlopt.opt main.ml
ld: warning: directory not found for option '-L/opt/homebrew/Cellar/zstd/1.5.2/lib'
ld: library not found for -lzstd
clang: error: linker command failed with exit code 1 (use -v to see invocation)
File "caml_startup", line 1:
Error: Error during linking (exit code 1)

Output of ocamlc -config:

bytecomp_c_libraries:  -L/opt/homebrew/Cellar/zstd/1.5.2/lib -lzstd -lm  -lpthread
native_c_libraries:  -L/opt/homebrew/Cellar/zstd/1.5.2/lib -lzstd -lm  -lpthread

Output of otool -L _opam/bin/ocamlopt.opt (otoolis a ldd equivalent)

_opam/bin/ocamlopt.opt:
        /opt/homebrew/opt/zstd/lib/libzstd.1.dylib (compatibility version 1.0.0, current version 1.5.2)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1319.100.3)