From c719e24a45e159526dc9a81e264692942fbf36d4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tu=E1=BA=A5n-Anh=20Nguy=E1=BB=85n?= <ubolonton@gmail.com>
Date: Thu, 27 Feb 2020 21:09:20 +0700
Subject: [PATCH] Make ts_language_field_name_for_id return NULL for
 out-of-bound id

---
 lib/binding_rust/lib.rs | 11 +++++++----
 lib/src/language.c      |  2 +-
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/lib/binding_rust/lib.rs b/lib/binding_rust/lib.rs
index a222dbf7..9da94510 100644
--- a/lib/binding_rust/lib.rs
+++ b/lib/binding_rust/lib.rs
@@ -212,10 +212,13 @@ impl Language {
     }
 
     /// Get the field names for the given numerical id.
-    pub fn field_name_for_id(&self, field_id: u16) -> &'static str {
-        unsafe { CStr::from_ptr(ffi::ts_language_field_name_for_id(self.0, field_id)) }
-            .to_str()
-            .unwrap()
+    pub fn field_name_for_id(&self, field_id: u16) -> Option<&'static str> {
+        let ptr = unsafe { ffi::ts_language_field_name_for_id(self.0, field_id) };
+        if ptr.is_null() {
+            None
+        } else {
+            Some(unsafe { CStr::from_ptr(ptr) }.to_str().unwrap())
+        }
     }
 
     /// Get the numerical id for the given field name.
diff --git a/lib/src/language.c b/lib/src/language.c
index e240ef2a..05b189c6 100644
--- a/lib/src/language.c
+++ b/lib/src/language.c
@@ -119,7 +119,7 @@ const char *ts_language_field_name_for_id(
   TSFieldId id
 ) {
   uint32_t count = ts_language_field_count(self);
-  if (count) {
+  if (count && id <= count) {
     return self->field_names[id];
   } else {
     return NULL;