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Bazel Coverage failing to generate lcov with --@rules_rust//rust/settings:experimental_use_cc_common_link=true #2729

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Ryang20718 opened this issue Jul 6, 2024 · 1 comment · May be fixed by #2836
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Bazel Coverage failing to generate lcov with --@rules_rust//rust/settings:experimental_use_cc_common_link=true #2729

Ryang20718 opened this issue Jul 6, 2024 · 1 comment · May be fixed by #2836
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@Ryang20718
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Ryang20718 commented Jul 6, 2024 •
edited
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bazel coverage with the following additional build setting leads to .dat files not getting generated

build --@rules_rust//rust/settings:experimental_use_cc_common_link=true

To repro, first see code cov is generated on main.

git clone https://github.com/bazelbuild/rules_rust.git
bazelisk coverage //test/inline_test_with_deps/... 
cat bazel-out/_coverage/_coverage_report.dat

With this newly added flag, code coverage fails

bazelisk coverage //test/inline_test_with_deps/... --@rules_rust//rust/settings:experimental_use_cc_common_link=true
cat bazel-out/_coverage/_coverage_report.dat

reproable on bazel 7.2.1 and 6.5
@Ryang20718
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Ryang20718 commented Aug 31, 2024 •
edited by UebelAndre
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I’m attempting to debug why --@rules_rust//rust/settings:experimental_use_cc_common_link=true causes coverage instrumentation to fail to generate on rules_rust (0.49.3)

leveraging bazel’s -s --sandbox_debug, I’m seeing the main diff is --codegen=link-arg=--coverage (i think 😓 )

i.e, for a running bazel coverage on a rust_test without this flag --@rules_rust//rust/settings:experimental_use_cc_common_link=true enabled

bazel-out/k8-opt-exec-2B5CBBC6/bin/external/rules_rust/util/process_wrapper/process_wrapper
--arg-file
bazel-out/k8-opt/bin/external/crate_index__serde-1.0.204/serde_build_script.linksearchpaths
<snip>'--codegen=linker=/usr/bin/gcc'
'--codegen=link-arg=--coverage'
'--codegen=link-arg=-fuse-ld=gold'
'--codegen=link-arg=-Wl,-no-as-needed'
'--codegen=link-arg=-Wl,-z,relro,-z,now'
'--codegen=link-arg=-B/usr/bin'
'--codegen=link-arg=-pass-exit-codes'
'--codegen=link-arg=-lstdc++'
'--codegen=link-arg=-lm'
'--codegen=link-arg=-Wl,--gc-sections'
'--extern=serde=bazel-out/k8-opt/bin/external/crate_index__serde-1.0.204/libserde-1107839584.rlib'
'--extern=thiserror=bazel-out/k8-opt/bin/external/crate_index__thiserror-1.0.63/libthiserror-1171055757.rlib'
'-Ldependency=bazel-out/k8-opt-exec-2B5CBBC6/bin/external/crate_index__serde_derive-1.0.204'
'-Ldependency=bazel-out/k8-opt/bin/external/crate_index__serde-1.0.204'
'-Ldependency=bazel-out/k8-opt-exec-2B5CBBC6/bin/external/crate_index__thiserror-impl-1.0.63'
'-Ldependency=bazel-out/k8-opt/bin/external/crate_index__thiserror-1.0.63'
'--codegen=instrument-coverage'
'-Ctarget-cpu=x86-64-v3'
'-Cforce-frame-pointers=y'
'-Cforce-unwind-tables=y')

With this flag enabled, we don’t see codegen=link-arg=--coverage at all

I think it has to do with this:

rules_rust/rust/private/rustc.bzl

Lines 1317 to 1333 in ef8ac18

if ctx.executable._process_wrapper:
# Run as normal
ctx.actions.run(
executable = ctx.executable._process_wrapper,
inputs = compile_inputs,
outputs = action_outputs,
env = env,
arguments = args.all,
mnemonic = "Rustc",
progress_message = "Compiling Rust {} {}{} ({} files)".format(
crate_info.type,
ctx.label.name,
formatted_version,
len(crate_info.srcs.to_list()),
),
toolchain = "@rules_rust//rust:toolchain_type",
)

I think we need to build and link these artifacts

rules_rust/rust/private/rustc.bzl

Lines 1283 to 1286 in ef8ac18

if experimental_use_cc_common_link:
obj_ext = ".o"
output_o = ctx.actions.declare_file(crate_info.name + obj_ext, sibling = crate_info.output)
outputs = [output_o]

with --coverage flags, but I’m not entirely sure where those should be added? Wondering if I’m heading down the right direction?

@UebelAndre UebelAndre added the bug label Aug 31, 2024
@Ryang20718 Ryang20718 linked a pull request Sep 5, 2024 that will close this issue
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[bug] fix coverage linker flags when using --@rules_rust//rust/settin… Ryang20718/rules_rust
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@UebelAndre @Ryang20718