gccrs: Add size checking to SlicePattern

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc(TypeCheckPattern::visit(SlicePattern)):
		Implement size checking for SlicePattern when type checking against array parent

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

Author: Polygonalr

gcc/rust/typecheck/rust-hir-type-check-pattern.cc

@@ -652,11 +652,24 @@ TypeCheckPattern::visit (HIR::SlicePattern &pattern)
     {
     case TyTy::ARRAY:
       {
-	// FIXME: implement compile-time size checks when ArrayType's capacity
-	// is updated to be evaluated in compile-time
-	// https://github.com/Rust-GCC/gccrs/issues/3882
 	auto &array_ty_ty = static_cast<TyTy::ArrayType &> (*parent);
 	parent_element_ty = array_ty_ty.get_element_type ();
+	tree cap = array_ty_ty.get_capacity ();
+	if (error_operand_p (cap))
+	  {
+	    rust_error_at (parent->get_locus (),
+			   "capacity of array %qs is not known at compile time",
+			   array_ty_ty.get_name ().c_str ());
+	    break;
+	  }
+	auto cap_wi = wi::to_wide (cap).to_uhwi ();
+	if (cap_wi != pattern.get_items ().size ())
+	  {
+	    rust_error_at (pattern.get_locus (), ErrorCode::E0527,
+			   "pattern requires %zu elements but array has %llu",
+			   pattern.get_items ().size (), cap_wi);
+	    break;
+	  }
 	break;
       }
     case TyTy::SLICE:

gcc/testsuite/rust/compile/slicepattern-size-mismatch.rs

@@ -0,0 +1,8 @@
+fn main() {
+    let arr = [0, 1];
+
+    match arr {
+        [0, 1, 2] => {} // { dg-error "pattern requires 3 elements but array has 2 .E0527." }
+        _ => {}
+    }
+}