Debugging utilities (#860)

* add debug printing for Ast and DocumentScope

* add optional failing allocator

build.zig

@@ -49,6 +49,18 @@ pub fn build(b: *std.build.Builder) !void {
         "enable_tracy_callstack",
         b.option(bool, "enable_tracy_callstack", "Enable callstack graphs.") orelse false,
     );
+    
+    exe_options.addOption(
+        bool,
+        "enable_failing_allocator",
+        b.option(bool, "enable_failing_allocator", "Whether to use a randomly failing allocator.") orelse false,
+    );
+
+    exe_options.addOption(
+        u32,
+        "enable_failing_allocator_likelihood",
+        b.option(u32, "enable_failing_allocator_likelihood", "The chance that an allocation will fail is `1/likelihood`") orelse 256,
+    );
 
     const version = v: {
         const version_string = b.fmt("{d}.{d}.{d}", .{ zls_version.major, zls_version.minor, zls_version.patch });