feat(oxlint): Generate markdownDescription fields for oxlint JSON schema. (#15959)

This allows VS Code and other editors to display better descriptions in hover tooltips when editing oxlintrc.json files.

Before:

<img width="676" height="179" alt="Screenshot 2025-11-21 at 9 24 52 PM" src="https://github.com/user-attachments/assets/775cbf62-19cb-44f4-ad48-2a9e3b867900" />

After:

<img width="926" height="164" alt="Screenshot 2025-11-21 at 9 24 41 PM" src="https://github.com/user-attachments/assets/d2e668b2-88a9-4765-9f18-122185fdeb8e" />

This can probably be made more efficient, as I wrote it using GitHub Copilot + Claude Sonnet 4.5. But it's not really ever used outside developers regenerating the schema occasionally, so 🤷. Based heavily on https://github.com/moonrepo/schematic/blob/d3a9422cead2802b940c96f8ab8b188c86ab281f/crates/schematic/src/schema/renderers/json_schema.rs#L84, with permission (via discord).

Part of #15247.

Author: connorshea

crates/oxc_linter/src/config/oxlintrc.rs

@@ -204,6 +204,7 @@ impl Oxlintrc {
     /// Panics if the schema generation fails.
     pub fn generate_schema_json() -> String {
         let mut schema = schema_for!(Oxlintrc);
+
         // Allow comments and trailing commas for vscode-json-languageservice
         // NOTE: This is NOT part of standard JSON Schema specification
         // https://github.com/microsoft/vscode-json-languageservice/blob/fb83547762901f32d8449d57e24666573016b10c/src/jsonLanguageTypes.ts#L151-L159
@@ -212,7 +213,43 @@ impl Oxlintrc {
             .schema
             .extensions
             .insert("allowTrailingCommas".to_string(), serde_json::Value::Bool(true));
-        serde_json::to_string_pretty(&schema).unwrap()
+
+        // Inject markdownDescription fields for better editor support (e.g., VS Code)
+        let mut json = serde_json::to_value(&schema).unwrap();
+        Self::inject_markdown_descriptions(&mut json);
+
+        serde_json::to_string_pretty(&json).unwrap()
+    }
+
+    /// Recursively inject `markdownDescription` fields into the JSON schema.
+    /// This is a non-standard field that some editors (like VS Code) use to render
+    /// markdown in hover tooltips.
+    fn inject_markdown_descriptions(value: &mut serde_json::Value) {
+        match value {
+            serde_json::Value::Object(map) => {
+                // If this object has a `description` field, copy it to `markdownDescription`
+                if let Some(serde_json::Value::String(desc_str)) = map.get("description") {
+                    map.insert(
+                        "markdownDescription".to_string(),
+                        serde_json::Value::String(desc_str.clone()),
+                    );
+                }
+
+                // Recursively process all values in the object
+                for value in map.values_mut() {
+                    Self::inject_markdown_descriptions(value);
+                }
+            }
+            serde_json::Value::Array(items) => {
+                // Recursively process all items in the array
+                for item in items {
+                    Self::inject_markdown_descriptions(item);
+                }
+            }
+            _ => {
+                // Primitive values don't need processing
+            }
+        }
     }
 
     /// Merges two [Oxlintrc] files together