Proposal

• Remove src/tools/rust-demangler, and remove all of its associated code from bootstrap.
  • This is implemented as Remove src/tools/rust-demangler rust#125880.

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/rust#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.

Mentors or Reviewers

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.