When parsing settings as JSON, check the types we get back

emcc.py

@@ -275,7 +275,7 @@ def apply_user_settings():
       try:
         value = parse_value(value, expected_type)
       except Exception as e:
-        exit_with_error('a problem occurred in evaluating the content after a "-s", specifically "%s=%s": %s', key, value, str(e))
+        exit_with_error(f'error parsing "-s" setting "{key}={value}": {e}')
 
     setattr(settings, user_key, value)
 
@@ -1506,10 +1506,20 @@ def parse_string_list(text):
     # if json parsing fails, we fall back to our own parser, which can handle a few
     # simpler syntaxes
     try:
-      return json.loads(text)
+      parsed = json.loads(text)
     except ValueError:
       return parse_string_list(text)
 
+    # if we succeeded in parsing as json, check some properties of it before returning
+    if type(parsed) not in (str, list):
+      raise ValueError(f'settings must be strings or lists (not ${type(parsed)})')
+    if type(parsed) is list:
+      for elem in parsed:
+        if type(elem) is not str:
+          raise ValueError(f'list members in settings must be strings (not ${type(elem)})')
+
+    return parsed
+
   if expected_type == float:
     try:
       return float(text)

test/test_other.py

@@ -7660,7 +7660,7 @@ def test_dash_s_unclosed_list(self):
 
   def test_dash_s_valid_list(self):
     err = self.expect_fail([EMCC, test_file('hello_world.cpp'), "-sTEST_KEY=[Value1, \"Value2\"]"])
-    self.assertNotContained('a problem occurred in evaluating the content after a "-s", specifically', err)
+    self.assertNotContained('error parsing "-s" setting', err)
 
   def test_dash_s_wrong_type(self):
     err = self.expect_fail([EMCC, test_file('hello_world.cpp'), '-sEXIT_RUNTIME=[foo,bar]'])
@@ -7692,6 +7692,15 @@ def test_dash_s_hex(self):
     # Ensure that 0x0 is parsed as a zero and not as the string '0x0'.
     self.run_process([EMCC, test_file('hello_world.c'), '-nostdlib', '-sERROR_ON_UNDEFINED_SYMBOLS=0x0'])
 
+  def test_dash_s_bad_json_types(self):
+    # Dict rather than string/list
+    err = self.expect_fail([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS={"a":1}'])
+    self.assertContained("settings must be strings or lists (not $<class 'dict'>", err)
+
+    # List element is not a string
+    err = self.expect_fail([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS=[{"a":1}]'])
+    self.assertContained("list members in settings must be strings (not $<class 'dict'>)", err)
+
   def test_zeroinit(self):
     create_file('src.c', r'''
 #include <stdio.h>