Add selective coverage instrumentation for crates

[0xdeafbeef]

This tool already has --exclude-from-report, does it make sense to add black/white lists for toggling instrumentation on and off?
Like --enable-coverage-for crate1 --enable-coverage-for crate2 or --disable coverage-for tokio

[taiki-e]

I guess you can use --dep-coverage (#353).

    --dep-coverage <NAME>
            Show coverage of the specified dependency instead of the crates in the current workspace. (unstable)

[0xdeafbeef]

I guess you can use --dep-coverage (#353).

    --dep-coverage <NAME>
            Show coverage of the specified dependency instead of the crates in the current workspace. (unstable)

Seems not. I want to disable coverage instrumentation for some heavy math libs and tokio, otherwise tests fail because some components time out. It can be done here, if I read code correctly.

cargo-llvm-cov/src/main.rs

Line 177 in 8a8fd85

fn set_env(cx: &Context, env: &mut dyn EnvTarget, IsNextest(is_nextest): IsNextest) -> Result<()> {

I can send a pr if it makes sense

[taiki-e]

My understanding is that excluding the application of -C instrument-coverage in a particular crate, or applying it only to a particular crate, is not yet supported (rust-lang/rfcs#3310), but if there is another way that works, I would like to accept it.

[0xdeafbeef]

I've solved it with this RUSTC_WRAPPER

#!/usr/bin/env python3
import os
import sys


blacklist = ["25519", "tokio"]


def main():
    # The first argument is the path to rustc, followed by its arguments
    args = sys.argv[1:]

    # coverage is necessary only for our project
    crate_name = get_crate_name(args)
    if any(crate in crate_name for crate in blacklist):
        try:
            instrument_coverage_index = args.index("instrument-coverage")
            del args[instrument_coverage_index]
            del args[instrument_coverage_index - 1]
        except ValueError:
            pass

    # Execute rustc with the potentially modified arguments
    os.execvp(args[0], args)


def get_crate_name(args):
    for i, arg in enumerate(args):
        if arg == "--crate-name":
            return args[i + 1]
    return ""

if __name__ == "__main__":
    main()

cargo-llvm-cov can act as a wrapper, but I'm not sure if it's a good idea. Maybe this script can be put to README

[taiki-e]

Ah, RUSTC_WRAPPER is a nice way to go.

Making the cargo-llvm-cov binary act as a RUSTC_WRAPPER only when a specific environment variable is set, making cargo llvm-cov to set RUSTC_WRAPPER=current_exe, and passing information about dependencies from the cargo llvm-cov through the environment variable, etc., would probably be possible to avoid applying instrument-coverage to all dependencies (i.e., emulate rust-lang/rfcs#3310).