Add Better error message for lists in config file (#6200)

Add Better error message for lists in config file

Author: humitos

readthedocs/config/config.py

@@ -114,12 +114,19 @@ def __init__(self, key, code, error_message, source_file=None):
         self.code = code
         self.source_file = source_file
         message = self.message_template.format(
-            key=key,
+            key=self._get_display_key(),
             code=code,
             error=error_message,
         )
         super().__init__(message, code=code)
 
+    def _get_display_key(self):
+        # Checks for patterns similar to `python.install.0.requirements`
+        # if matched change to `python.install[0].requirements` using backreference.
+        return re.sub(
+            r'^(python\.install)(\.)(\d+)(\.\w+)$', r'\1[\3]\4', self.key
+        )
+
 
 class BuildConfigBase:
 

readthedocs/config/tests/test_config.py

@@ -1098,6 +1098,23 @@ def test_python_install_requirements_does_not_allow_null(self, tmpdir):
             build.validate()
         assert excinfo.value.key == 'python.install.0.requirements'
 
+    def test_python_install_requirements_error_msg(self, tmpdir):
+        build = self.get_build_config(
+            {
+                'python': {
+                    'install': [{
+                        'path': '.',
+                        'requirements': None,
+                    }],
+                },
+            },
+            source_file=str(tmpdir.join('readthedocs.yml')),
+        )
+        with raises(InvalidConfig) as excinfo:
+            build.validate()
+
+        assert str(excinfo.value) == 'Invalid "python.install[0].requirements": expected string'
+
     def test_python_install_requirements_does_not_allow_empty_string(self, tmpdir):
         build = self.get_build_config(
             {