improve settings.yml error messages (#13748)

Changelog: Feature: Improve settings.yml error messages
Docs: Omit

Close #13738

conans/client/cache/cache.py

@@ -256,10 +256,7 @@ def appending_recursive_dict_update(d, u):
 
             appending_recursive_dict_update(settings, settings_user)
 
-        try:
-            return Settings(settings)
-        except AttributeError as e:
-            raise ConanException("Invalid settings.yml format: {}".format(e))
+        return Settings(settings)
 
     def initialize_settings(self):
         # TODO: This is called by ConfigAPI.init(), maybe move everything there?

conans/model/settings.py

@@ -175,6 +175,9 @@ def __init__(self, definition=None, name="settings", parent_value="settings"):
         if parent_value is None and definition:
             raise ConanException("settings.yml: null setting can't have subsettings")
         definition = definition or {}
+        if not isinstance(definition, dict):
+            val = "" if parent_value == "settings" else f"={parent_value}"
+            raise ConanException(f"Invalid settings.yml format: '{name}{val}' is not a dictionary")
         self._name = name  # settings, settings.compiler
         self._parent_value = parent_value  # gcc, x86
         self._data = {k: SettingsItem(v, "%s.%s" % (name, k))

conans/test/integration/configuration/invalid_settings_test.py

@@ -8,10 +8,15 @@
 class TestSettingsLoad:
     def test_invalid_settings(self):
         client = TestClient()
-        client.save({os.path.join(client.cache_folder, 'settings.yml'): """your buggy file""",
+        client.save({os.path.join(client.cache_folder, 'settings.yml'): "your buggy file",
                      "conanfile.txt": ""})
         client.run("install .", assert_error=True)
-        assert "ERROR: Invalid settings.yml format" in client.out
+        assert "ERROR: Invalid settings.yml format: 'settings' is not a dictionary" in client.out
+        client.save({os.path.join(client.cache_folder, 'settings.yml'): "os:\n    Windows: [1, ]",
+                     "conanfile.txt": ""})
+        client.run("install .", assert_error=True)
+        assert "ERROR: Invalid settings.yml format: 'settings.os=Windows' is not a dictionary" \
+               in client.out
 
     def test_invalid_yaml(self):
         client = TestClient()