Auto merge of #112887 - WaffleLapkin:become_unuwuable_in_hir, r=compiler-errors,Nilstrieb

`hir`: Add `Become` expression kind (explicit tail calls experiment)

This adds `hir::ExprKind::Become` alongside ast lowering. During hir-thir lowering we currently lower `become` as `return`, so that we can partially test `become` without ICEing.

cc `@scottmcm`
r? `@Nilstrieb`

clippy_lints/src/loops/never_loop.rs

@@ -206,6 +206,12 @@ fn never_loop_expr(expr: &Expr<'_>, ignore_ids: &mut Vec<HirId>, main_loop_id: H
                 NeverLoopResult::AlwaysBreak,
             )
         }),
+        ExprKind::Become(e) => {
+            combine_seq(
+                never_loop_expr(e, ignore_ids, main_loop_id),
+                NeverLoopResult::AlwaysBreak,
+            )
+        }
         ExprKind::InlineAsm(asm) => asm
             .operands
             .iter()

clippy_lints/src/matches/significant_drop_in_scrutinee.rs

@@ -329,6 +329,7 @@ impl<'a, 'tcx> Visitor<'tcx> for SigDropHelper<'a, 'tcx> {
             ExprKind::Field(..) |
             ExprKind::Index(..) |
             ExprKind::Ret(..) |
+            ExprKind::Become(..) |
             ExprKind::Repeat(..) |
             ExprKind::Yield(..) => walk_expr(self, ex),
             ExprKind::AddrOf(_, _, _) |

clippy_lints/src/utils/author.rs

@@ -559,6 +559,11 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
                 kind!("Ret({value})");
                 value.if_some(|e| self.expr(e));
             },
+            ExprKind::Become(value) => {
+                bind!(self, value);
+                kind!("Become({value})");
+                self.expr(value);
+            },
             ExprKind::InlineAsm(_) => {
                 kind!("InlineAsm(_)");
                 out!("// unimplemented: `ExprKind::InlineAsm` is not further destructured at the moment");

clippy_utils/src/eager_or_lazy.rs

@@ -191,6 +191,7 @@ fn expr_eagerness<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> EagernessS
                 ExprKind::Break(..)
                 | ExprKind::Continue(_)
                 | ExprKind::Ret(_)
+                | ExprKind::Become(_)
                 | ExprKind::InlineAsm(_)
                 | ExprKind::Yield(..)
                 | ExprKind::Err(_) => {

clippy_utils/src/hir_utils.rs

@@ -845,6 +845,9 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                     self.hash_expr(e);
                 }
             },
+            ExprKind::Become(f) => {
+                self.hash_expr(f);
+            },
             ExprKind::Path(ref qpath) => {
                 self.hash_qpath(qpath);
             },

clippy_utils/src/sugg.rs

@@ -147,6 +147,7 @@ impl<'a> Sugg<'a> {
             | hir::ExprKind::Path(..)
             | hir::ExprKind::Repeat(..)
             | hir::ExprKind::Ret(..)
+            | hir::ExprKind::Become(..)
             | hir::ExprKind::Struct(..)
             | hir::ExprKind::Tup(..)
             | hir::ExprKind::Err(_) => Sugg::NonParen(get_snippet(expr.span)),

clippy_utils/src/visitors.rs

@@ -651,6 +651,7 @@ pub fn for_each_unconsumed_temporary<'tcx, B>(
             // Either drops temporaries, jumps out of the current expression, or has no sub expression.
             ExprKind::DropTemps(_)
             | ExprKind::Ret(_)
+            | ExprKind::Become(_)
             | ExprKind::Break(..)
             | ExprKind::Yield(..)
             | ExprKind::Block(..)