gccrs: Fix ICE in path pattern refutability - #4808
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PathPattern::is_refutable looked up the final path segment's HirId in the HIR item map, where it is never a key, so every path pattern in a let or function parameter hit rust_internal_error_at. Resolve path patterns before looking up their HIR items, checking both namespaces. Handle non-enum ADTs as irrefutable to avoid rust_unreachable. Update path pattern tests to assert the expected E0005 diagnostics. Fixes Rust-GCC#4732 gcc/rust/ChangeLog: * hir/tree/rust-hir-pattern-abstract.cc (PathPattern::is_refutable): Resolve the path before looking up its HIR item, and treat non-enum ADTs as irrefutable. gcc/testsuite/ChangeLog: * rust/compile/refutable-path.rs: Replace dg-ice with the expected E0005 diagnostics. Signed-off-by: Utkarsh Bahuguna <utkarshbahuguna10@gmail.com>
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Fixes #4732
PathPattern::is_refutable looked up the final path segment's HirId in the HIR item map. That map is keyed on each item's own HirId, and a path segment never carries one, so lookup_hir_item always failed and every path pattern in a let binding or a function parameter reached rust_internal_error_at. The enum check below it was consequently unreachable dead code.
The fix resolves the path before looking it up. Late::visit (AST::PathInExpression&) maps usage on the path expression's NodeId rather than on any segment, so the lookup now uses get_mappings ().get_nodeid () and maps the resolved definition back through lookup_node_to_hir to reach the HIR item. It covers both Values and Types because resolve_path is called with both namespaces and records whichever one matched.
Enum variants are registered with insert_hir_enumitem rather than insert_hir_item, so lookup_hir_item legitimately fails for them and the code falls through to the scrutinee check by design. That check also needed a non-enum ADT case: unit struct path patterns reach it too, and without returning false for them, struct S; let S: S; would hit rust_unreachable, trading one ICE for another on a case no test currently covers.
This requires including rust-finalized-name-resolution-context.h from hir/tree. No file under gcc/rust/hir currently includes anything from gcc/rust/resolve, so this would be the first such dependency. I am open to moving the lookup somewhere else if that layering is unwanted.
refutable-path.rs loses its dg-ice and now asserts the four expected E0005 diagnostics, covering both the let bindings and the function parameters. irrefutable-path.rs keeps its dg-ice but reports a different ICE: with a single-variant enum the parameter is irrefutable, so compilation proceeds into the backend and hits the pre-existing function_set_parameters assert from #4553, which irrefutable-slice.rs already XFAILs on.
Validation passes increased from 11,450 to 11,458 with zero unexpected failures, measured against a baseline taken at e56b411. Four of the new PASS lines are refutable-path.rs. The other four are empty_path2.rs and empty_path3.rs, which arrived upstream in #4799 after that baseline was taken and are unrelated to this change.