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Fix cargo kcov crashing/generating incorrect reports for proc-macros #3207

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Fix cargo kcov crashing/generating incorrect reports for proc-macros #3207

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8 changes: 8 additions & 0 deletions tests/integration_tests/build/test_coverage.py
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,14 @@ def test_coverage(test_fc_session_root_path, test_session_tmp_path):
exclude_region = "'mod tests {'"
target = "{}-unknown-linux-musl".format(platform.machine())

# Temporarily modify PATH so that "rustc" resolved to our wrapper script
# This is required as cargo kcov parses cargo's verbose output, and looking for lines starting
# with "Running `rustc":
# https://github.com/kennytm/cargo-kcov/blob/master/src/target_finder.rs#L44
# However, if we use the RUSTC_WRAPPER environment variable to make cargo run out script, the
# output will contain the lines "Running /firecracker/tests/rustc", and thus cargo kcov will
# fail to resolve the paths of the binaries compiled.
os.environ["PATH"] = "/firecracker/tests" + os.pathsep + os.environ["PATH"]
cmd = (
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Did you try using CARGO_TARGET_x86_64_unknown_linux_musl_RUSTFLAGS=-Clink-dead-code as an alternative?

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Yes, those flags only affect the code that is actually compiled to run on the specified target, and thus also excludes proc macros and build scripts

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Actually it should be CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=-Clink-dead-code (uppercased), but if it's not going to apply by design then probably not worth trying again.

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I did try both! (if you use the lowercase option then cargo will tell you to use the uppercase one instead)

'CARGO_WRAPPER="kcov" RUSTFLAGS="{}" CARGO_TARGET_DIR={} '
"cargo kcov --all "
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9 changes: 9 additions & 0 deletions tests/rustc
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@@ -0,0 +1,9 @@
#!/bin/bash

# We have to fully qualify the path to rustc here, as we modified $PATH in a way that this script is founds before
# the actual rust executable.
# Then we invoke normal rustc, but force the 'link-dead-code' codegen option. This option is required for gathering
# coverage reports on proc-macros during cross-compilation, as the 'RUSTFLAGS' environment variable is ignored by cargo
# for build-scripts, plugins and proc-macros in this case.
# See also https://doc.rust-lang.org/cargo/reference/config.html#buildrustflags
/usr/local/rust/bin/rustc $@ -Clink-dead-code