According to c3c --list-manifest-properties both cflags and cflags-override belong among target properties.

But it seems that target cflags are ignored. I created a library somelib.c3l with a single C file lib.c

#ifndef OPT_A
#error "Missing option A"
#endif

#ifndef OPT_B
#error "Missing option B"
#endif

and following manifest.json

{
  "provides": "somelib",
  "cflags": "-DOPT_A",
  "c-sources": ["lib.c"],
  "targets": {
    "macos-aarch64": {
      "cflags": "-DOPT_B",
      "linked-libraries": ["c"]
    }
  }
}

When using it it I get the error which confirms that cflags in a target has no effect:

./somelib.c3l/lib.c:6:2: error: "Missing option B"
    6 | #error "Missing option B"
      |  ^
1 error generated.
Failed to compile c sources using command 'cc -fPIC -c -DOPT_A ./somelib.c3l/lib.c -o .build/obj/macos-aarch64/somelib/lib.o'.

Experiment with cflags-override

Using cflags-override

{
  "provides": "somelib",
  "cflags": "-DOPT_A",
  "c-sources": ["lib.c"],
  "targets": {
    "macos-aarch64": {
      "cflags-override": "-DOPT_B",
      "linked-libraries": ["c"]
    }
  }
}

overrides existing cflags so with the code above it results in

./somelib.c3l/lib.c:2:2: error: "Missing option A"
    2 | #error "Missing option A"
      |  ^
1 error generated.
Failed to compile c sources using command 'cc -fPIC -c -DOPT_B ./somelib.c3l/lib.c -o .build/obj/macos-aarch64/somelib/lib.o'.

which works as expected.

Ideas how to fix this

I think either c3c --list-manifest-properties should be updated to not show cflags under Target properties section.

Or parse_library_target in src/build/libraries.c shall be updated to read cflags of a target and merge them with manifest cflags.

My C3 version

C3 Compiler Version:       0.7.3 (Pre-release, Jun 10 2025 14:55:09)
Git Hash:                  bbd9f6dc9695c9627bd4b69cd44492ed5833c3a4
Backends:                  LLVM
LLVM version:              20.1.6
LLVM default target:       arm64-apple-darwin24.4.0