Proposal

A lot of types in the compiler are wrapped in Boxes. To make matching on them more ergonomic, the box_patterns (tracking issue) feature is used at the moment. The current plan for this feature is that it will not be stabilized; instead, deref_patterns (tracking issue) supersedes it.

I propose to replace the usage of box_patterns in the compiler with deref_patterns. This has several advantages:

• It makes it possible to remove box_patterns entirely in the future
• It removes the need for using the weird box keyword in the compiler, making the code slightly easier to read
• We might find possible bugs in the deref_patterns implementation by using it in practice

The feature was previously moved from incomplete to unstable in rust-lang/rust#153053.

Mentors or Reviewers

I am willing to create the PRs that update the affected compiler crates to use the newer feature.

Process

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

• File an issue describing the proposal.
• A compiler team member who is knowledgeable in the area can second by writing @rustbot second or kickoff a team FCP with @rfcbot fcp $RESOLUTION.
  • Refer to Proposals, Approvals and Stabilization docs for when a second is sufficient, or when a full team FCP is required.
• Once an MCP is seconded, the Final Comment Period begins.
  • Final Comment Period lasts for 10 days after all outstanding concerns are solved.
  • Outstanding concerns will block the Final Comment Period from finishing. Once all concerns are resolved, the 10 day countdown is restarted.
  • If no concerns are raised after 10 days since the resolution of the last outstanding concern, the MCP is considered approved.

You can read more about Major Change Proposals on forge.