[gcc r15-8512] gccrs: fix bad type inference on local patterns

[Arthur Cohen]

https://gcc.gnu.org/g:389756b2ac97beeb72cd160eeefee5ea381e55e9

commit r15-8512-g389756b2ac97beeb72cd160eeefee5ea381e55e9
Author: Philip Herron <herron.philip@googlemail.com>
Date:   Mon Nov 4 14:43:25 2024 +0000

    gccrs: fix bad type inference on local patterns
    
    We do not need to inject inference variables on generic patterns
    with generic blocks. This will just cause unconstrained inference
    variables as they may not unify against something.
    
    Fixes Rust-GCC#2323
    
    gcc/rust/ChangeLog:
    
            * typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_root_path): dont infer here
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/nr2/exclude: nr2 cant handle this
            * rust/compile/issue-2323.rs: New test.
    
    Signed-off-by: Philip Herron <herron.philip@googlemail.com>

Diff:
---
 gcc/rust/typecheck/rust-hir-type-check-path.cc | 3 ++-
 gcc/testsuite/rust/compile/issue-2323.rs       | 9 +++++++++
 gcc/testsuite/rust/compile/nr2/exclude         | 1 +
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/typecheck/rust-hir-type-check-path.cc b/gcc/rust/typecheck/rust-hir-type-check-path.cc
index 231ddd604db2..7b934b38eb37 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-path.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-path.cc
@@ -245,6 +245,7 @@ TypeCheckExpr::resolve_root_path (HIR::PathInExpression &expr, size_t *offset,
 
       auto seg_is_module = mappings.lookup_module (ref).has_value ();
       auto seg_is_crate = mappings.is_local_hirid_crate (ref);
+      auto seg_is_pattern = mappings.lookup_hir_pattern (ref).has_value ();
       if (seg_is_module || seg_is_crate)
 	{
 	  // A::B::C::this_is_a_module::D::E::F
@@ -321,7 +322,7 @@ TypeCheckExpr::resolve_root_path (HIR::PathInExpression &expr, size_t *offset,
 	  if (lookup->get_kind () == TyTy::TypeKind::ERROR)
 	    return new TyTy::ErrorType (expr.get_mappings ().get_hirid ());
 	}
-      else if (lookup->needs_generic_substitutions ())
+      else if (lookup->needs_generic_substitutions () && !seg_is_pattern)
 	{
 	  lookup = SubstMapper::InferSubst (lookup, expr.get_locus ());
 	}
diff --git a/gcc/testsuite/rust/compile/issue-2323.rs b/gcc/testsuite/rust/compile/issue-2323.rs
new file mode 100644
index 000000000000..02a3f90b4d81
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-2323.rs
@@ -0,0 +1,9 @@
+#[lang = "sized"]
+trait Sized {}
+
+pub struct S<T>(T);
+
+pub fn foo<T>(x: T) {
+    let y = S(x);
+    y.0;
+}
diff --git a/gcc/testsuite/rust/compile/nr2/exclude b/gcc/testsuite/rust/compile/nr2/exclude
index 4ba27d31f88b..eaa2a1e0d0bc 100644
--- a/gcc/testsuite/rust/compile/nr2/exclude
+++ b/gcc/testsuite/rust/compile/nr2/exclude
@@ -222,4 +222,5 @@ if_let_expr_simple.rs
 iflet.rs
 issue-3033.rs
 issue-3009.rs
+issue-2323.rs
 # please don't delete the trailing newline