Don't track `--emit=` options as part of crate SVH

[chbaker0]

Proposal

The list of artifact types passed to --emit= does not affect the contents of those artifacts (with one exception). If foo.rlib depends on bar.rlib which was generated with --emit=link, then overwritten with e.g. --emit=link,dep-info, a downstream rustc invocation should still be able to use the newer bar.rlib.

The one exception is with --emit=metadata,...: if metadata is passed alone the .rmeta output does not contain MIR, so it is not suitable for building .rlib dependents. However, this results in an obvious compile error like error: missing optimized MIR for an item in the crate foo, and cannot cause the incorrectness that the SVH check prevents.

Excluding the --emit list from the SVH allows more flexibility when building Rust code in third-party build systems.

Mentors or Reviewers

TBD

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

[cjgillot]

From the zulip discussion and my own reflexion, this should go ahead provided the questions around --emit metadata get answered. @rustbot second

[apiraino]

@rustbot label -final-comment-period +major-change-accepted