lib/addoninfo.cpp: When loading a JSON addon, test 'script' key. (#5797)

In case a user accidentally uses a wrong JSON file (e.g. naming.json,
which is the config file for namingng.py), the code could give a
confusing exception. This happens when the key 'script' is not defined
as a string.

This is solved by testing the key for existence and type. In case
'script' is not a key or refers to a type other than a string, a clear
error is given, stating for example: 'Loading naming.json failed. script
must be set to a string value.'

The message is kept in line with other messages. Maybe it can be
clarified further, e.g. 'Loading naming.json failed. A key "script" must
be set with a string value referring to a Python script.' - in which
case the errors relating to other keys may also be clarified.

lib/addoninfo.cpp

@@ -87,6 +87,11 @@ static std::string parseAddonInfo(AddonInfo& addoninfo, const picojson::value &j
         return "";
     }
 
+    if (!obj.count("script") || !obj["script"].is<std::string>())
+    {
+        return "Loading " + fileName + " failed. script must be set to a string value.";
+    }
+
     return addoninfo.getAddonInfo(obj["script"].get<std::string>(), exename);
 }
 

test/cli/test-other.py

@@ -278,6 +278,22 @@ extern const char* f()
     assert stderr == '{}:4:12: warning: strerror is MT-unsafe [threadsafety-unsafe-call]\n'.format(test_file)
 
 
+def test_addon_invalidjson(tmpdir):
+    addon_file = os.path.join(tmpdir, 'invalid.json')
+    with open(addon_file, 'wt') as f:
+        f.write("""
+{
+    "Script": "addons/something.py"
+}
+                """)
+
+    args = ['--addon={}'.format(addon_file), '--enable=all', 'nonexistent.cpp']
+
+    exitcode, stdout, stderr = cppcheck(args)
+    assert exitcode != 0
+    assert stdout == 'Loading {} failed. script must be set to a string value.\n'.format(addon_file)
+
+
 def test_addon_naming(tmpdir):
     # the addon does nothing without a config
     addon_file = os.path.join(tmpdir, 'naming1.json')