`EarlyBinder` as default

[lcnr]

Proposal

Change all queries which currently have a bound_X variant to return EarlyBinder<T> by default and remove the bound_X version. Add a method fn EarlyBinder::<T>::subst_identity(self) -> T if these queries are used in the identity context and don't need to actually substitute anything.

Not having EarlyBinder be the default can very easily result in incorrect uses of these queries, e.g. https://github.com/rust-lang/rust/blob/736c675d2ab65bcde6554e1b73340c2dbc27c85a/compiler/rustc_hir_analysis/src/astconv/mod.rs#L2720 which I found while reviewing https://github.com/rust-lang/rust/pull/101947. The normalize_ty normalizes type_of(def_id) in the wrong environment as we only call subst afterwards.

Mentors or Reviewers

I am available to mentor and review this work.

Process

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

• [x] File an issue describing the proposal.
• [ ] A types 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.
  • Types 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.

cc @rust-lang/types

[oli-obk]

@rustbot second

[lcnr]

closing as accepted