A repeated -p keeps only the last value: mcpp test -p a -p b tests b alone, and says nothing #750

-p/--package selects one workspace member. When it is given twice, the first value is dropped without a word: mcpp test -p a -p b builds and tests only b, and mcpp build -p a -p b builds only b. The exit status is 0 and the summary line counts only b's tests, so a script or CI step that lists members this way looks as if it tested both.

The cause is in the argument parser rather than in mcpp itself. -p is declared with takes_value() and without multiple() on build, run, test, pack and emit build-database (cli.cppm L390, L436, L538, L660, L707), and the selection it feeds is a single string (prepare.cppm L635). In mcpplibs.cmdline 0.0.1, an option without multiple() that appears again simply replaces the value it had (cmdline.cppm L206-L207). That holds for every single-valued option, --profile included, but -p is the one where repeating it reads like a reasonable request.

Either of two behaviors would be fine: accept several -p values and act on each named member, the way --workspace acts on all of them, or refuse a repeated -p with an error that mentions --workspace. Keeping the last value silently is the one outcome that hides the mistake.

Reproduction

mcpp 2026.9.30.1, llvm@22.1.8, Linux x86_64 (host target). The declarations above are unchanged at main (8e00a18, 2026.9.30.2).

mcpp.toml:

[workspace]
members = ["a", "b"]

[toolchain]
default = "llvm@22.1.8"

a/mcpp.toml (b is the same with b in place of a, here and in the two files below):

[package]
name    = "a"
version = "0.1.0"

[targets.a]
kind = "lib"

a/src/a.cppm:

export module a;
export int a_value() { return 1; }

a/tests/test_a.cpp:

import a;
int main() { return a_value() == 1 ? 0 : 1; }

$ mcpp test -p a -p b
   Workspace building member 'b'
   Resolving toolchain
    Resolved llvm@22.1.8 → @mcpp/registry/data/xpkgs/xim-x-llvm/22.1.8/bin/clang++
      Target x86_64-unknown-linux-gnu
   Compiling workspace v0.0.0 (.)
   Compiling b (path)
   Compiling b v0.1.0 (b)
   Compiling test_b (test)
     Running bin/test_b
test_b ... ok (0.02s)

 test result ok. 1 passed; 0 failed; finished in 0.39s (build 0.20s + run 0.02s)

The exit status is 0. Swapping the order, mcpp test -p b -p a tests only a, and mcpp build -p a -p b builds only b.