use `ObligationCtxt` for canonical queries

[lcnr]

Proposal

Canonical queries are currently implemented using an extension trait for InferCtxt and manually create a FulfillmentContext.

Considering that literally all uses of enter_with_canonical create a FulfillmentContext right away, moving all of this to ObligationCtxt seems like a sensible step to me.

Mentors or Reviewers

If you have a reviewer or mentor in mind for this work, mention then here. You can put your own name here if you are planning to mentor the work.

Process

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

• [x] File an issue describing the proposal.
• [x] 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.

[compiler-errors]

seconded, even if rustbot won't do anything yet

[compiler-errors]

I wonder if this works...

@rustbot second

[rustbot]

Error: This issue cannot be seconded; it lacks the major-change label.

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #t-infra on Zulip.

[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

[compiler-errors]

@rustbot second