Properly report default argument inference errors (ponylang#2504)

* Properly report default argument inference errors

errors for default arguments could leave the AST in an illegal state
which was causing assertions when evaluating default args during TK_CALL evaluation in the expr pass.

This PR makes those errors stop compilation immediately, so they are properly reported.

* use ast_passes_subtree instead of expr_seq for default arguments

as this does not result in double error messages when evaluating default args for function definitions and function calls

src/libponyc/expr/call.c

@@ -186,7 +186,7 @@ static bool apply_default_arg(pass_opt_t* opt, ast_t* param, ast_t** argp)
     ast_replace(argp, def_arg);
   }
 
-  if(!expr_seq(opt, *argp))
+  if(!ast_passes_subtree(argp, opt, PASS_EXPR))
     return false;
 
   return true;

test/libponyc/literal_inference.cc

@@ -6,6 +6,9 @@
 #define TEST_ERROR(src) DO(test_error(src, "expr"))
 #define TEST_COMPILE(src) DO(test_compile(src, "expr"))
 
+#define TEST_ERRORS_1(src, err1) \
+  { const char* errs[] = {err1, NULL}; \
+    DO(test_expected_errors(src, "expr", errs)); }
 
 class LiteralTest : public PassTest
 {
@@ -243,7 +246,21 @@ TEST_F(LiteralTest, CantInfer_Let_InsufficientlySpecifiedGeneric)
     "  new create() =>\n"
     "    let x: A = 17";
 
-  TEST_ERROR(src);
+  TEST_ERRORS_1(src, "could not infer literal type, no valid types found");
+}
+
+TEST_F(LiteralTest, CantInfer_DefaultArg_InsufficientlySpecifiedGeneric)
+{
+  const char* src =
+    "class Foo[A]\n"
+    "  new create(field: A = 0) =>\n"
+    "    None\n"
+    "\n"
+    "class Bar\n"
+    "  new create() =>\n"
+    "    let foo = Foo[U16]()";
+
+  TEST_ERRORS_1(src, "could not infer literal type, no valid types found");
 }