[gcc/devel/rust/master] typecheck: Fix casting error behind generics

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:193c21c85b4b3f603b1b6280779c758d35570446

commit 193c21c85b4b3f603b1b6280779c758d35570446
Author: bl7awy <mahadelr19@gmail.com>
Date:   Tue Feb 28 20:53:01 2023 +0300

    typecheck: Fix casting error behind generics
    
    gcc/rust/ChangeLog:
            * typecheck/rust-casts.cc (TypeCastRules::cast_rules): Perform destructure on `from` type.
    
    gcc/testsuite/ChangeLog:
            * rust/compile/cast_generics.rs: New test.
    
    Signed-off-by: Mahmoud Mohamed  <mahadelr19@gmail.com>

Diff:
---
 gcc/rust/typecheck/rust-casts.cc            | 11 ++++++-----
 gcc/testsuite/rust/compile/cast_generics.rs |  8 ++++++++
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/gcc/rust/typecheck/rust-casts.cc b/gcc/rust/typecheck/rust-casts.cc
index 0ecb50f7d1d..f41c7134a75 100644
--- a/gcc/rust/typecheck/rust-casts.cc
+++ b/gcc/rust/typecheck/rust-casts.cc
@@ -60,15 +60,16 @@ TypeCastRules::cast_rules ()
   // https://github.com/rust-lang/rust/blob/7eac88abb2e57e752f3302f02be5f3ce3d7adfb4/compiler/rustc_typeck/src/check/cast.rs#L596
   // https://github.com/rust-lang/rust/blob/7eac88abb2e57e752f3302f02be5f3ce3d7adfb4/compiler/rustc_typeck/src/check/cast.rs#L654
 
-  rust_debug ("cast_rules from={%s} to={%s}",
-	      from.get_ty ()->debug_str ().c_str (),
+  TyTy::BaseType *from_type = from.get_ty ()->destructure ();
+
+  rust_debug ("cast_rules from={%s} to={%s}", from_type->debug_str ().c_str (),
 	      to.get_ty ()->debug_str ().c_str ());
 
-  switch (from.get_ty ()->get_kind ())
+  switch (from_type->get_kind ())
     {
       case TyTy::TypeKind::INFER: {
 	TyTy::InferType *from_infer
-	  = static_cast<TyTy::InferType *> (from.get_ty ());
+	  = static_cast<TyTy::InferType *> (from_type);
 	switch (from_infer->get_infer_kind ())
 	  {
 	  case TyTy::InferType::InferTypeKind::GENERAL:
@@ -290,4 +291,4 @@ TypeCastRules::emit_cast_error () const
 }
 
 } // namespace Resolver
-} // namespace Rust
+} // namespace Rust
\ No newline at end of file
diff --git a/gcc/testsuite/rust/compile/cast_generics.rs b/gcc/testsuite/rust/compile/cast_generics.rs
new file mode 100644
index 00000000000..7d185964e50
--- /dev/null
+++ b/gcc/testsuite/rust/compile/cast_generics.rs
@@ -0,0 +1,8 @@
+fn test<T>(a: T) -> T {
+  a
+}
+
+fn main() {
+  let t: i32 = test(123 as i32) as i32;
+  // { dg-warning "unused name" "" { target *-*-* } .-1 }
+}