From 3c6a0033e3dc7da2898232a2efc7367ae6fc536a Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Mon, 27 Dec 2021 14:08:59 -0800
Subject: Avoid trace events in implementation of TracePoint#enable

This is more backwards compatible, and should fix issues with
power_assert.

Unfortunately, it requires using a sentinel value as the default
value of target_thread, instead of the more natural expression
used in the original approach.
---
 vm_trace.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'vm_trace.c')

diff --git a/vm_trace.c b/vm_trace.c
index b9ba6de73e..a9074c338e 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -34,6 +34,8 @@
 
 #include "builtin.h"
 
+static VALUE sym_default;
+
 /* (1) trace mechanisms */
 
 typedef struct rb_event_hook_struct {
@@ -1334,6 +1336,15 @@ tracepoint_enable_m(rb_execution_context_t *ec, VALUE tpval, VALUE target, VALUE
     rb_tp_t *tp = tpptr(tpval);
     int previous_tracing = tp->tracing;
 
+    if (target_thread == sym_default) {
+        if (rb_block_given_p() && NIL_P(target) && NIL_P(target_line)) {
+            target_thread = rb_thread_current();
+        }
+        else {
+            target_thread = Qnil;
+        }
+    }
+
     /* check target_thread */
     if (RTEST(target_thread)) {
         if (tp->target_th) {
@@ -1563,6 +1574,8 @@ tracepoint_allow_reentry(rb_execution_context_t *ec, VALUE self)
 void
 Init_vm_trace(void)
 {
+    sym_default = ID2SYM(rb_intern_const("default"));
+
     /* trace_func */
     rb_define_global_function("set_trace_func", set_trace_func, 1);
     rb_define_method(rb_cThread, "set_trace_func", thread_set_trace_func_m, 1);
-- 
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