Per review

crates/ruff/src/args.rs

@@ -975,10 +975,11 @@ The path `{value}` does not point to a configuration file"
 
             match Options::metadata().find(key) {
                 Some(OptionEntry::Set(set)) if !value.starts_with('{') => {
-                    let prefixed_subkeys = format!("{set}")
-                        .trim_ascii()
-                        .split('\n')
-                        .map(|child| format!("- `{key}.{child}`"))
+                    let prefixed_subfields = set.collect_entries()
+                        .iter()
+                        .filter_map(|(name, entry)| {
+                            entry.is_field().then(|| format!("- `{key}.{name}`"))
+                        })
                         .join("\n");
 
                     tip.push_str(&format!(
@@ -989,7 +990,7 @@ Did you want to override one of the table's subkeys?
 
 Possible choices:
 
-{prefixed_subkeys}"
+{prefixed_subfields}"
                     ));
                 }
                 _ => {

crates/ruff/tests/lint.rs

@@ -781,7 +781,7 @@ fn each_toml_option_requires_a_new_flag_2() {
 }
 
 #[test]
-fn value_given_to_table_key_is_not_inline_table() {
+fn value_given_to_table_key_is_not_inline_table_1() {
     // https://github.com/astral-sh/ruff/issues/13995
     assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
         .args(STDIN_BASE_OPTIONS)
@@ -817,6 +817,57 @@ fn value_given_to_table_key_is_not_inline_table() {
     "#);
 }
 
+#[test]
+fn value_given_to_table_key_is_not_inline_table_2() {
+    // https://github.com/astral-sh/ruff/issues/13995
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        // spaces *also* can't be used to delimit different config overrides;
+        // you need a new --config flag for each override
+        .args([".", "--config", r#"lint=123"#]),
+        @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: invalid value 'lint=123' for '--config <CONFIG_OPTION>'
+
+      tip: A `--config` flag must either be a path to a `.toml` configuration file
+           or a TOML `<KEY> = <VALUE>` pair overriding a specific configuration
+           option
+
+    `lint` is a table of configuration options.
+    Did you want to override one of the table's subkeys?
+
+    Possible choices:
+
+    - `lint.allowed-confusables`
+    - `lint.dummy-variable-rgx`
+    - `lint.extend-ignore`
+    - `lint.extend-select`
+    - `lint.extend-fixable`
+    - `lint.external`
+    - `lint.fixable`
+    - `lint.ignore`
+    - `lint.extend-safe-fixes`
+    - `lint.extend-unsafe-fixes`
+    - `lint.ignore-init-module-imports`
+    - `lint.logger-objects`
+    - `lint.select`
+    - `lint.explicit-preview-rules`
+    - `lint.task-tags`
+    - `lint.typing-modules`
+    - `lint.unfixable`
+    - `lint.per-file-ignores`
+    - `lint.extend-per-file-ignores`
+    - `lint.exclude`
+    - `lint.preview`
+
+    For more information, try '--help'.
+    ");
+}
+
 #[test]
 fn config_doubly_overridden_via_cli() -> Result<()> {
     let tempdir = TempDir::new()?;

crates/ruff_workspace/src/options_base.rs

@@ -42,7 +42,7 @@ where
 }
 
 /// Metadata of an option that can either be a [`OptionField`] or [`OptionSet`].
-#[derive(Clone, PartialEq, Eq, Debug, Serialize)]
+#[derive(Clone, PartialEq, Eq, Debug, Serialize, is_macro::Is)]
 #[serde(untagged)]
 pub enum OptionEntry {
     /// A single option.
@@ -285,6 +285,24 @@ impl OptionSet {
             None
         }
     }
+
+    pub fn collect_entries(&self) -> Vec<(String, OptionEntry)> {
+        struct EntryCollector(pub Vec<(String, OptionEntry)>);
+
+        impl Visit for EntryCollector {
+            fn record_field(&mut self, name: &str, field: OptionField) {
+                self.0.push((name.to_string(), OptionEntry::Field(field)));
+            }
+
+            fn record_set(&mut self, name: &str, group: OptionSet) {
+                self.0.push((name.to_string(), OptionEntry::Set(group)));
+            }
+        }
+
+        let mut visitor = EntryCollector(vec![]);
+        self.record(&mut visitor);
+        visitor.0
+    }
 }
 
 /// Visitor that writes out the names of all fields and sets.