Add PatKind::Err to AST/HIR

[ShE3py]

#116715 added thir::PatKind::Error; this PR adds hir::PatKind::Err and ast::PatKind::Err (see #118625 (comment).)

---

@rustbot label +A-patterns
r? WaffleLapkin

[rustbot]

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

Some changes might have occurred in exhaustiveness checking

cc @Nadrieril

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[fmease]

Btw, if you'd like to have another small side project, you can equip ast::ExprKind::Err with ErrorGuaranteed, too 😉
In a separate PR ofc.

[compiler-errors]

Btw, if you'd like to have another small side project, you can equip ast::ExprKind::Err with ErrorGuaranteed, too

We use ast::ExprKind::Err as the "null" value for some places in the AST, so this is probably not possible without some work:

rust/compiler/rustc_ast/src/ast.rs

Lines 1294 to 1305 in 2730354

	pub fn take(&mut self) -> Self {
	mem::replace(
	self,
	Expr {
	id: DUMMY_NODE_ID,
	kind: ExprKind::Err,
	span: DUMMY_SP,
	attrs: AttrVec::new(),
	tokens: None,
	},
	)
	}

[WaffleLapkin]

r=me with the comment removed

[WaffleLapkin]

Not related to this PR, but I find this weird... Wild can match only a single thing if it's for a type like (), similarly 1..=1, similarly []....

[WaffleLapkin]

@bors delegate+

[bors]

✌️ @ShE3py, you can now approve this pull request!

If @WaffleLapkin told you to "r=me" after making some further change, please make that change, then do @bors r=@WaffleLapkin

[fmease]

Might be worth mentioning that the impls of DummyAstNode for Expr, Ty and so on use Err but Wild for ast::Pat:

rust/compiler/rustc_ast/src/mut_visit.rs

Lines 1635 to 1667 in aa5f781

	impl DummyAstNode for Expr {
	fn dummy() -> Self {
	Expr {
	id: DUMMY_NODE_ID,
	kind: ExprKind::Err,
	span: Default::default(),
	attrs: Default::default(),
	tokens: Default::default(),
	}
	}
	}
	impl DummyAstNode for Ty {
	fn dummy() -> Self {
	Ty {
	id: DUMMY_NODE_ID,
	kind: TyKind::Err,
	span: Default::default(),
	tokens: Default::default(),
	}
	}
	}
	impl DummyAstNode for Pat {
	fn dummy() -> Self {
	Pat {
	id: DUMMY_NODE_ID,
	kind: PatKind::Wild,
	span: Default::default(),
	tokens: Default::default(),
	}
	}
	}

[ShE3py]

Ty!
@bors r=WaffleLapkin

---

Btw, if you'd like to have another small side project, you can equip ast::ExprKind::Err with ErrorGuaranteed, too

We use ast::ExprKind::Err as the "null" value for some places in the AST, so this is probably not possible without some work

I looked a bit and at first glance it may be possible to add something like ast::ExprKind::Dummy and to lower it as:

ast::ExprKind::Err(guar) => hir::ExprKind::Err(*guar),
ast::ExprKind::Dummy => hir::ExprKind::Err(self.dcx().span_delayed_bug(e.span, "lowered ExprKind::Dummy")),

I might give it a try next week.

[bors]

📌 Commit 7889e99 has been approved by WaffleLapkin

It is now in the queue for this repository.

[compiler-errors]

@ShE3py: Yeah, general approach of splitting it and adding a dummy variant for "ast::Expr::take" is probably the best one. Even better, you could make it span_bug!() if Dummy gets lowered. That should never happen, I think.

[fmease]

ast::Expr::take isn't actually used. I can compile rustc successfully without it (rustfmt and clippy don't seem to use it either). However, DummyAstNode would be really hard to get rid of. +1 to ast::ExprKind::Dummy.