structs as errors in fallibles

compiler/checker/checker.odin

@@ -3976,19 +3976,20 @@ validate_declarations :: proc(checker: ^Checker) {
 		}
 		if types.is_valid(function.error) && !signature_poisoned {
 			error_type := type_from_syntax(checker, function.error, function.pkg, function.file)
-			error_sum := types.is_enum(error_type, &checker.module.types) ||
-			             types.is_tagged_union(error_type, &checker.module.types)
+			error_channel := types.is_enum(error_type, &checker.module.types) ||
+			                 types.is_struct(error_type, &checker.module.types) ||
+			                 types.is_tagged_union(error_type, &checker.module.types)
 			if function.c_abi {
 				checker.template_diagnostics[function_id] = source.add(
 					checker.diagnostics,
 					function.span,
 					"fallible functions must use 'func', not 'c_func'",
 				)
-			} else if !error_sum {
+			} else if !error_channel {
 				checker.template_diagnostics[function_id] = source.add(
 					checker.diagnostics,
 					function.span,
-					"fallible function error type must be a native enum or tagged union",
+					"fallible function error type must be a native enum, struct, or tagged union",
 				)
 			}
 		}

compiler/checker/comptime.odin

@@ -4487,6 +4487,19 @@ ct_return_value :: proc(state: ^Ct_State, expr_id: ast.Expr_Id, span: source.Spa
 		if expr.kind == .Enum_Literal && types.sum_has_name(&checker.module.types, error_type, u32(expr.name)) {
 			error_path = true
 			expected = error_type
+		} else if expr.kind == .Struct_Literal {
+			target_pkg, available := expr_package(checker, expr, state.pkg, state.file, true)
+			named := types.find_named(
+				&checker.module.types,
+				u32(target_pkg),
+				u32(expr.name),
+				file=u32(expr_lookup_file(expr, state.file)),
+			) if available else types.INVALID
+			named = types.resolve_alias(named, &checker.module.types)
+			if can_implicitly_convert_type(checker, named, error_type) {
+				error_path = true
+				expected = error_type
+			}
 		} else if expr.kind == .Name && !symbol.is_valid(expr.qualifier) {
 			if index, found := ct_find_binding_index(state, expr.name); found {
 				actual := state.bindings[index].type