Langkit_Support.Generic_API: fix handling of null token kinds

Author: pmderodat

langkit/support/langkit_support-generic_api.adb

@@ -144,6 +144,7 @@ package body Langkit_Support.Generic_API is
 
    function Token_Kind_Name (Kind : Token_Kind_Ref) return Name_Type is
    begin
+      Check_Token_Kind (Kind);
       return Create_Name (Kind.Id.Token_Kinds (Kind.Index).Name.all);
    end Token_Kind_Name;
 

testsuite/tests/ada_api/generic_api/analysis.adb

@@ -90,6 +90,19 @@ begin
    end loop;
    New_Line;
 
+   Put_Line ("Use of null token kind:");
+   declare
+      Dummy : Name_Type;
+   begin
+      Dummy := Token_Kind_Name (No_Token_Kind_Ref);
+      raise Program_Error;
+   exception
+      when Exc : Precondition_Failure =>
+         Put_Line ("Got a Precondition_Failure exception: "
+                   & Exception_Message (Exc));
+   end;
+   New_Line;
+
    Put_Line ("Use of null context:");
    declare
       Dummy : Boolean;

testsuite/tests/ada_api/generic_api/test.out

@@ -51,6 +51,9 @@ Token families:
   Punctuation
   Default_Family
 
+Use of null token kind:
+Got a Precondition_Failure exception: null token kind reference
+
 Use of null context:
 Got a Precondition_Failure exception: null context