Use ControlFlow in HIR Visitor

[Jarcho]

This ended up significantly larger than I originally though it would be. Most changes are trivial signature changes plus code changes to make the function actually return the correct type.

Some visitors were changed to return their result as BreakTy rather than through a field. Most of these are from clippy, which is the main motivation behind this change, but a few are from rustc as well.

There are a few behavior in some diagnostics, but only in the case of unusual spans (e.g. multiple nodes having the same span). This should only cause changes when the diagnostic spans were already questionable in the first place.

[rustbot]

r? @wesleywiser

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[rustbot]

Some changes occurred in need_type_info.rs

cc @lcnr

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

These commits modify the Cargo.lock file. Random changes to Cargo.lock can be introduced when switching branches and rebasing PRs.
This was probably unintentional and should be reverted before this PR is merged.

If this was intentional then you can ignore this comment.

[oli-obk]

Looks like the clippy test suite is having ICEs now

[oli-obk]

Do you have a link to clippy discussions that motivated this change? Not that it's not desirable on its own, but seems good to have some links. You should also open a compiler team MCP, as this is definitely a major change 😆

[Jarcho]

No clippy discussion for this. Just observing how clippy breaks early from most visitors.

[bors]

☔ The latest upstream changes (presumably #108620) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

r? @oli-obk

[pnkfelix]

Discussed in today's T-compiler triage meeting.

Now this did have an MCP which was seconded, that's rust-lang/compiler-team#597

but the MCP second did note that there may be room for adjusting what the actual solution here looks like.

There may be good material to review in the Zulip stream associated with the MCP

[oli-obk]

Kind of blocked on rust-lang/libs-team#187

[Dylan-DPC]

The ACP was closed

[Jarcho]

With the ACP closed that rules out using Try for this. We can still define our own trait e.g.

trait VisitorResult {
  type BreakTy;
  fn continue() -> Self;
  fn from_break_ty(_: Self::BreakTy) -> Self;
}
impl VisitorResult for () {
  type BreakTy = !;
  fn continue() -> Self {
    ()
  }
  fn from_break_ty(_: !) -> Self {
    ()
  }
}
impl<T: Try<Output = ()>> VisitorResult for T {
  type BreakTy = T::Residual;
  fn continue() -> Self {
    Self::from_output(())
  }
  fn from_break_ty(x: Self::BreakTy) -> Self {
    Self::from_residual(x)
  }
}

This does rule out using ? in functions generic over the result type, but those are really only part of the visitor impl and a try-like macro can be made for that.