Warn about unknown fields when editing settings json (#33678)

Closes #30017

* While generating the settings JSON schema, defaults all schema
definitions to reject unknown fields via `additionalProperties: false`.

* Uses `unevaluatedProperties: false` at the top level to check fields
that remain after the settings field names + release stage override
field names.

* Changes json schema version from `draft07` to `draft_2019_09` to have
support for `unevaluatedProperties`.

Release Notes:

- Added warnings for unknown fields when editing `settings.json`.

crates/settings/src/settings_json.rs

@@ -1,17 +1,19 @@
 use anyhow::Result;
 use gpui::App;
-use schemars::{JsonSchema, Schema};
+use schemars::{JsonSchema, Schema, transform::transform_subschemas};
 use serde::{Serialize, de::DeserializeOwned};
 use serde_json::Value;
 use std::{ops::Range, sync::LazyLock};
 use tree_sitter::{Query, StreamingIterator as _};
 use util::RangeExt;
 
+/// Parameters that are used when generating some JSON schemas at runtime.
 pub struct SettingsJsonSchemaParams<'a> {
     pub language_names: &'a [String],
     pub font_names: &'a [String],
 }
 
+/// Value registered which specifies JSON schemas that are generated at runtime.
 pub struct ParameterizedJsonSchema {
     pub add_and_get_ref:
         fn(&mut schemars::SchemaGenerator, &SettingsJsonSchemaParams, &App) -> schemars::Schema,
@@ -19,24 +21,26 @@ pub struct ParameterizedJsonSchema {
 
 inventory::collect!(ParameterizedJsonSchema);
 
+const DEFS_PATH: &str = "#/$defs/";
+
+/// Replaces the JSON schema definition for some type, and returns a reference to it.
 pub fn replace_subschema<T: JsonSchema>(
     generator: &mut schemars::SchemaGenerator,
     schema: schemars::Schema,
 ) -> schemars::Schema {
-    const DEFINITIONS_PATH: &str = "#/definitions/";
     // The key in definitions may not match T::schema_name() if multiple types have the same name.
     // This is a workaround for there being no straightforward way to get the key used for a type -
     // see https://github.com/GREsau/schemars/issues/449
     let ref_schema = generator.subschema_for::<T>();
     if let Some(serde_json::Value::String(definition_pointer)) = ref_schema.get("$ref") {
-        if let Some(definition_name) = definition_pointer.strip_prefix(DEFINITIONS_PATH) {
+        if let Some(definition_name) = definition_pointer.strip_prefix(DEFS_PATH) {
             generator
                 .definitions_mut()
                 .insert(definition_name.to_string(), schema.to_value());
             return ref_schema;
         } else {
             log::error!(
-                "bug: expected `$ref` field to start with {DEFINITIONS_PATH}, \
+                "bug: expected `$ref` field to start with {DEFS_PATH}, \
                 got {definition_pointer}"
             );
         }
@@ -48,7 +52,39 @@ pub fn replace_subschema<T: JsonSchema>(
     generator
         .definitions_mut()
         .insert(schema_name.to_string(), schema.to_value());
-    Schema::new_ref(format!("{DEFINITIONS_PATH}{schema_name}"))
+    Schema::new_ref(format!("{DEFS_PATH}{schema_name}"))
+}
+
+/// Adds a new JSON schema definition and returns a reference to it. **Panics** if the name is
+/// already in use.
+pub fn add_new_subschema(
+    generator: &mut schemars::SchemaGenerator,
+    name: &str,
+    schema: Value,
+) -> Schema {
+    let old_definition = generator.definitions_mut().insert(name.to_string(), schema);
+    assert_eq!(old_definition, None);
+    schemars::Schema::new_ref(format!("{DEFS_PATH}{name}"))
+}
+
+/// Defaults `additionalProperties` to `true`, as if `#[schemars(deny_unknown_fields)]` was on every
+/// struct. Skips structs that have `additionalProperties` set (such as if #[serde(flatten)] is used
+/// on a map).
+#[derive(Clone)]
+pub struct DefaultDenyUnknownFields;
+
+impl schemars::transform::Transform for DefaultDenyUnknownFields {
+    fn transform(&mut self, schema: &mut schemars::Schema) {
+        if let Some(object) = schema.as_object_mut() {
+            if object.contains_key("properties")
+                && !object.contains_key("additionalProperties")
+                && !object.contains_key("unevaluatedProperties")
+            {
+                object.insert("additionalProperties".to_string(), false.into());
+            }
+        }
+        transform_subschemas(self, schema);
+    }
 }
 
 pub fn update_value_in_json_text<'a>(