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The ordinary lowering of thir::ExprKind::Let is unreachable

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After desugaring, `let` expressions should only appear inside `if` expressions
or `match` guards, possibly nested within a let-chain. In both cases they are
specifically handled by the lowerings of those expressions, so this case is
currently unreachable.
This commit is contained in:
Zalathar 2024-03-02 17:45:38 +11:00
parent 4cdd20584c
commit 972d8daf47
1 changed files with 6 additions and 32 deletions
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38
compiler/rustc_mir_build/src/build/expr/into.rs
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@ -109,38 +109,12 @@ pub(crate) fn expr_into_dest(
this.cfg.goto(else_blk, source_info, join_block); this.cfg.goto(else_blk, source_info, join_block);
join_block.unit() join_block.unit()
} }
ExprKind::Let { expr, ref pat } => { ExprKind::Let { .. } => {
let scope = this.local_scope(); // After desugaring, `let` expressions should only appear inside `if`
let (true_block, false_block) = this.in_if_then_scope(scope, expr_span, |this| { // expressions or `match` guards, possibly nested within a let-chain.
this.lower_let_expr(block, expr, pat, scope, None, expr_span, true) // In both cases they are specifically handled by the lowerings of
}); // those expressions, so this case is currently unreachable.
span_bug!(expr_span, "unexpected let expression outside of if or match-guard");
this.cfg.push_assign_constant(
true_block,
source_info,
destination,
ConstOperand {
span: expr_span,
user_ty: None,
const_: Const::from_bool(this.tcx, true),
},
);
this.cfg.push_assign_constant(
false_block,
source_info,
destination,
ConstOperand {
span: expr_span,
user_ty: None,
const_: Const::from_bool(this.tcx, false),
},
);
let join_block = this.cfg.start_new_block();
this.cfg.goto(true_block, source_info, join_block);
this.cfg.goto(false_block, source_info, join_block);
join_block.unit()
} }
ExprKind::NeverToAny { source } => { ExprKind::NeverToAny { source } => {
let source_expr = &this.thir[source]; let source_expr = &this.thir[source];