Make the expr pre check for use commands more fine-grained

We're only interested in ignoring the "guard" part of a use command, but
we still want to go through the arguments to check for any possible
errors during the expr pass. In particular, we're interested in the
NullablePointer constraint check.

src/libponyc/pass/expr.c

@@ -524,10 +524,14 @@ ast_result_t pass_pre_expr(ast_t** astp, pass_opt_t* options)
   switch(ast_id(ast))
   {
     case TK_ARRAY: return expr_pre_array(options, astp);
-    case TK_USE:
-      // Don't look in use commands to avoid false type errors from the guard
-      return AST_IGNORE;
-
+    case TK_IFDEFNOT:
+    case TK_IFDEFAND:
+    case TK_IFDEFOR:
+    case TK_IFDEFFLAG:
+      // Don't look in guards for use commands to avoid false type errors
+      if((ast_parent(ast) != NULL) && (ast_id(ast_parent(ast)) == TK_USE))
+        return AST_IGNORE;
+      break;
     default: {}
   }
 

test/libponyc/ffi.cc

@@ -5,6 +5,11 @@
 // FFI type checking tests
 
 #define TEST_ERROR(src) DO(test_error(src, "expr"))
+
+#define TEST_ERRORS_2(src, err1, err2) \
+  { const char* errs[] = {err1, err2, NULL}; \
+    DO(test_expected_errors(src, "expr", errs)); }
+
 #define TEST_COMPILE(src) DO(test_compile(src, "expr"))
 
 
@@ -201,3 +206,24 @@ TEST_F(FFITest, DeclarationAlias)
 
   TEST_ERROR(src);
 }
+
+TEST_F(FFITest, DeclarationWithNullablePointer)
+{
+  // From issue #3757
+  const char* src =
+    "use @foo[NullablePointer[(U64, U64)]]()\n"
+    "use @bar[NullablePointer[P1]]()\n"
+    "primitive P1\n"
+
+    "actor Main\n"
+    " new create(env: Env) =>\n"
+    "   None";
+
+    TEST_ERRORS_2(src,
+      "NullablePointer[(U64 val, U64 val)] ref is not allowed: "
+        "the type argument to NullablePointer must be a struct",
+
+      "NullablePointer[P1 val] ref is not allowed: "
+        "the type argument to NullablePointer must be a struct");
+
+}