Don't build the `rust-demangler` binary for coverage tests #125816

Zalathar · 2024-05-31T12:21:58Z

The coverage-run tests invoke llvm-cov, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names.

Historically this used src/tools/rust-demangler, which means that we currently build two different command-line tools to help with the coverage tests (rust-demangler and coverage-dump).

However, it occurred to me that if we add a demangler mode to coverage-dump (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build rust-demangler at all.

Note that the rust-demangler binary is separate from the rustc-demangle crate (which both rust-demangler and coverage-dump use as a dependency to do the actual demangling).

So the main benefits/motivations here are:

Slightly faster builds after a fresh checkout or bootstrap bump.
Making it clear that currently no tests actually need the rust-demangler binary, since the coverage tests can use their own tool instead.

The coverage-dump tool already needs `rustc_demangle` for its own purposes, so the amount of extra code needed for a demangle mode is very small.

This avoids the need to build `rust-demangler` when running coverage tests, since we typically need to build `coverage-dump` anyway.

This appears to be the canonical way to build a tool with the stage 0 compiler.

rustbot · 2024-05-31T12:22:06Z

r? @oli-obk

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rustbot · 2024-05-31T12:22:08Z

Some changes occurred in src/tools/compiletest

cc @jieyouxu

jieyouxu · 2024-05-31T12:24:00Z

This looks like mostly a T-bootstrap change
r? bootstrap

Zalathar · 2024-05-31T12:28:11Z

One of the reasons I want to do this is that the rust-demangler binary is pretty obscure, and I haven't seen anything outside of the coverage tests actually use it. There doesn't seem to be much documentation pointing to it, and I'm not sure how users would even get their hands on it.

We might be able to follow up by getting rid of that binary entirely, since the need for demangling seems to be well-served by rustfilt and by the rustc-demangle library.

oli-obk · 2024-05-31T12:37:56Z

Is the rust-demangler something we ship with releases or can we now rip it out?

Zalathar · 2024-05-31T12:43:33Z

Is the rust-demangler something we ship with releases or can we now rip it out?

I honestly don't know, and I was in the middle of trying to figure out who to even ask.

There does seem to be code in bootstrap for including it in source/binary tarballs, but I have no idea where it ends up, and so far I haven't seen any evidence of anyone actually using it.

jieyouxu · 2024-05-31T12:47:11Z

FWIW, the README says

rust-demangler is a Rust “extended tool”, used in Rust compiler tests, and optionally included in Rust distributions that enable coverage profiling. Symbol demangling is implemented using the rustc-demangle crate.

(Note, for Rust developers, the third-party tool rustfilt also supports llvm-cov symbol demangling. rustfilt is a more generalized tool that searches any body of text, using pattern matching, to find and demangle Rust symbols.)

But IDK how accurate that is now.

oli-obk · 2024-05-31T12:47:29Z

It's not shipped by default in nightly (or other releases). It may be in a component I don't have, but I can't think of which one should have it.

oli-obk · 2024-05-31T12:48:20Z

ok

@bors r+

let's MCP removing the tool separately just for visibility (in the hope if anyone still knows a need for it, they'll speak up)

bors · 2024-05-31T12:48:23Z

📌 Commit 54b6849 has been approved by oli-obk

It is now in the queue for this repository.

Don't build the `rust-demangler` binary for coverage tests The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names. Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`). However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all. --- Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling). --- So the main benefits/motivations here are: - Slightly faster builds after a fresh checkout or bootstrap bump. - Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

Rollup of 6 pull requests Successful merges: - rust-lang#125652 (Revert propagation of drop-live information from Polonius) - rust-lang#125730 (Apply `x clippy --fix` and `x fmt` on Rustc) - rust-lang#125752 (run-make: enforce `#[must_use]` and arm command wrappers with drop bombs) - rust-lang#125756 (coverage: Optionally instrument the RHS of lazy logical operators) - rust-lang#125796 (Also InstSimplify `&raw*`) - rust-lang#125816 (Don't build the `rust-demangler` binary for coverage tests) r? `@ghost` `@rustbot` modify labels: rollup

Don't build the `rust-demangler` binary for coverage tests The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names. Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`). However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all. --- Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling). --- So the main benefits/motivations here are: - Slightly faster builds after a fresh checkout or bootstrap bump. - Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#125652 (Revert propagation of drop-live information from Polonius) - rust-lang#125730 (Apply `x clippy --fix` and `x fmt` on Rustc) - rust-lang#125756 (coverage: Optionally instrument the RHS of lazy logical operators) - rust-lang#125776 (Stop using `translate_args` in the new solver) - rust-lang#125796 (Also InstSimplify `&raw*`) - rust-lang#125807 (Also resolve the type of constants, even if we already turned it into an error constant) - rust-lang#125816 (Don't build the `rust-demangler` binary for coverage tests) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#125816 - Zalathar:demangler, r=oli-obk Don't build the `rust-demangler` binary for coverage tests The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names. Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`). However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all. --- Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling). --- So the main benefits/motivations here are: - Slightly faster builds after a fresh checkout or bootstrap bump. - Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

Remove `src/tools/rust-demangler` `rust-demangler` is a small binary that reads a list of mangled symbols from stdin, demangles them (using the `rustc-demangle` library crate), and prints the demangled symbols to stdout. It was added as part of the initial implementation of coverage instrumentation in 2020/2021, so that coverage tests could pass it to `llvm-cov --Xdemangler` when generating coverage reports. It has been largely untouched since then. As of rust-lang#125816 it is no longer used by coverage tests, and has no remaining in-tree uses. There is code in bootstrap to build and package the demangler, but it's unclear where the resulting binaries actually end up, or whether there's any reasonable way for `rustup` users to obtain them. --- For users needing a command-line demangler, `rustfilt` exists and is more actively maintained. It's also quite easy to use the `rustc-demangle` library to build a custom command-line demangler if necessary, with only a few lines of code. The tool's name (`rust-demangler`) is easily confused with the name of the library crate `rustc-demangle`, so removing the tool will eliminate that confusion. There also doesn't appear to be much reason to use `rust-demangler` over `rustfilt`. --- This PR therefore removes the tool, and removes all of its associated code from bootstrap. MCP filed: rust-lang/compiler-team#754

Rollup merge of rust-lang#125880 - Zalathar:demangler, r=oli-obk Remove `src/tools/rust-demangler` `rust-demangler` is a small binary that reads a list of mangled symbols from stdin, demangles them (using the `rustc-demangle` library crate), and prints the demangled symbols to stdout. It was added as part of the initial implementation of coverage instrumentation in 2020/2021, so that coverage tests could pass it to `llvm-cov --Xdemangler` when generating coverage reports. It has been largely untouched since then. As of rust-lang#125816 it is no longer used by coverage tests, and has no remaining in-tree uses. There is code in bootstrap to build and package the demangler, but it's unclear where the resulting binaries actually end up, or whether there's any reasonable way for `rustup` users to obtain them. --- For users needing a command-line demangler, `rustfilt` exists and is more actively maintained. It's also quite easy to use the `rustc-demangle` library to build a custom command-line demangler if necessary, with only a few lines of code. The tool's name (`rust-demangler`) is easily confused with the name of the library crate `rustc-demangle`, so removing the tool will eliminate that confusion. There also doesn't appear to be much reason to use `rust-demangler` over `rustfilt`. --- This PR therefore removes the tool, and removes all of its associated code from bootstrap. MCP filed: rust-lang/compiler-team#754

Zalathar added 4 commits May 31, 2024 21:52

Add an alternate --demangle mode to coverage-dump

9abfebd

The coverage-dump tool already needs `rustc_demangle` for its own purposes, so the amount of extra code needed for a demangle mode is very small.

Use coverage-dump --demangle as the demangler for coverage-run tests

10ffc22

This avoids the need to build `rust-demangler` when running coverage tests, since we typically need to build `coverage-dump` anyway.

Use Builder::tool_exe to build the coverage-dump tool

feb8f3c

This appears to be the canonical way to build a tool with the stage 0 compiler.

Remove unused rust-demangler support from compiletest

54b6849

rustbot assigned oli-obk May 31, 2024

rustbot added A-testsuite Area: The testsuite used to check the correctness of rustc S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels May 31, 2024

rustbot assigned albertlarsan68 and unassigned oli-obk May 31, 2024

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 31, 2024

jieyouxu mentioned this pull request May 31, 2024

Rollup of 6 pull requests #125817

Closed

jieyouxu mentioned this pull request May 31, 2024

Rollup of 9 pull requests #125820

Closed

matthiaskrgr mentioned this pull request May 31, 2024

Rollup of 7 pull requests #125824

Merged

bors merged commit df9cd17 into rust-lang:master May 31, 2024
6 checks passed

rustbot added this to the 1.80.0 milestone May 31, 2024

Zalathar deleted the demangler branch June 1, 2024 01:19

Zalathar mentioned this pull request Jun 2, 2024

Remove src/tools/rust-demangler #125880

Merged

fmease mentioned this pull request Jun 2, 2024

Remove src/tools/rust-demangler rust-lang/compiler-team#754

Closed

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