Typecheck else expression of let-else to ensure it diverges
#3469
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CohenArthur
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Mar 5, 2025
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| // FIXME: Is that enough? Do we need to do something like | ||
| // `append_reference` here as well? |
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@philberty I'm not sure if there's anything else we need to do here. I was trying to use something like coercion_site(...) but obviously it doesn't work because any type is coercible to !, which is not the behavior we actually want here
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! should be coercible to any other type, but not the other way around
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gcc/rust/ChangeLog: * ast/rust-stmt.h (class LetStmt): Add optional expression for diverging else. * ast/rust-ast-builder.cc (Builder::let): Use new API.
gcc/rust/ChangeLog: * parse/rust-parse-impl.h (Parser::parse_let_stmt): Add new parsing in case of `else` token.
gcc/rust/ChangeLog: * ast/rust-ast-collector.cc (TokenCollector::visit): Add handling for diverging else expression.
gcc/rust/ChangeLog: * resolve/rust-ast-resolve-stmt.h: Add handling for diverging else. * resolve/rust-late-name-resolver-2.0.cc (Late::visit): Likewise.
gcc/rust/ChangeLog: * hir/tree/rust-hir-stmt.h (class LetStmt): Add optional diverging else expression. * hir/tree/rust-hir-stmt.cc: Likewise. * hir/rust-ast-lower-stmt.cc (ASTLoweringStmt::visit): Add handling for lowering diverging else.
CohenArthur
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Make sure the `else` expression resolves to the never type. gcc/rust/ChangeLog: * typecheck/rust-hir-type-check-stmt.cc (TypeCheckStmt::visit): Check diverging else against `!`. gcc/testsuite/ChangeLog: * rust/compile/let-else-invalid-type.rs: New test.
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The
elseexpression of alet-elsemust always diverge, which we enforce during typecheck. Needs #3468