gccrs: Fix ICE for repr attribute malformation

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-base.cc (parse_repr_options): Changed TOKEN_TREE
	assert into error, update malformed repr attribute error message to be inline
	with other attribute error messages.

Signed-off-by: Yap Zhi Heng <[email protected]>

Author: Polygonalr

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

@@ -412,7 +412,7 @@ TypeCheckBase::parse_repr_options (const AST::AttrVec &attrs, location_t locus)
       bool is_repr = attr.get_path ().as_string () == Values::Attributes::REPR;
       if (is_repr && !attr.has_attr_input ())
 	{
-	  rust_error_at (attr.get_locus (), "malformed %qs attribute", "repr");
+	  rust_error_at (attr.get_locus (), "malformed %<repr%> attribute");
 	  continue;
 	}
 
@@ -421,7 +421,11 @@ TypeCheckBase::parse_repr_options (const AST::AttrVec &attrs, location_t locus)
 	  const AST::AttrInput &input = attr.get_attr_input ();
 	  bool is_token_tree = input.get_attr_input_type ()
 			       == AST::AttrInput::AttrInputType::TOKEN_TREE;
-	  rust_assert (is_token_tree);
+	  if (!is_token_tree)
+	    {
+	      rust_error_at (attr.get_locus (), "malformed %<repr%> attribute");
+	      continue;
+	    }
 	  const auto &option = static_cast<const AST::DelimTokenTree &> (input);
 	  AST::AttrInputMetaItemContainer *meta_items
 	    = option.parse_to_meta_item ();

gcc/testsuite/rust/compile/issue-4231.rs

@@ -0,0 +1,6 @@
+#[repr = ""] // { dg-error "malformed .repr. attribute" }
+struct ThreeInts {
+    first: i16,
+    second: i8,
+    third: i32
+}