Separate incremental crate identity

[Zoxc]

Proposal

This proposes changing crate identity used for matching previous incremental compilation sessions to not depend on the crate name in the source code. Crate identity for incremental compilation would instead only be based on information in command line arguments.

The current scheme is problematic since we need to parse the crate before loading the previous compilation session. This is not ideal for performance and it also prevents moving of parsing into the query system.

This does not change the other uses of crate identity in the compiler.

This change would not affect the behavior of Cargo as it uses a separate incremental compilation directory per crate and thus has its own separate concept of crate identity. It may however affect non-Cargo users of incremental compilation.

#115693 is a related PR.

Mentors or Reviewers

Process

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

• [x] 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.

[rustbot]

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.

Concerns or objections to the proposal should be discussed on Zulip and formally registered here by adding a comment with the following syntax:

 @rustbot concern reason-for-concern 
 <description of the concern> 

Concerns can be lifted with:

 @rustbot resolve reason-for-concern 

See documentation at https://forge.rust-lang.org

cc @rust-lang/compiler @rust-lang/compiler-contributors

[oli-obk]

@rustbot second