Add --emit= to emit nothing

[clubby789]

Proposal

Currently, if one wishes to ask rustc to perform analysis but not codegen, --emit=metadata can be used. This, however, emits a metadata file which may be unneeded (as well as creating a temporary directory, meaning --emit=metadata=/dev/null fails).

I propose added --emit=, which will cause the compiler to exit early after analysis (using the empty string rather than =nothing because of the reasoning given in rust-lang/rust#52661 (comment)).

Mentors or Reviewers

Process

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

• File an issue describing the proposal.
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• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

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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