From 4cd38239e786daa0c4a20b94794d2f274b174595 Mon Sep 17 00:00:00 2001
From: Burke Libbey <burke@libbey.me>
Date: Mon, 16 Jan 2017 14:04:39 -0500
Subject: [PATCH] Add a TracePoint for Constant Access

This would be useful for implementing package/module systems.
---
 include/ruby/ruby.h |  1 +
 insns.def           |  1 +
 vm_trace.c          | 27 +++++++++++++++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 06524c1..8074942 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -2064,6 +2064,7 @@ int ruby_native_thread_p(void);
 #define RUBY_EVENT_THREAD_BEGIN      0x0400
 #define RUBY_EVENT_THREAD_END        0x0800
 #define RUBY_EVENT_FIBER_SWITCH      0x1000
+#define RUBY_EVENT_CONSTANT_ACCESS   0x2000
 #define RUBY_EVENT_TRACEPOINT_ALL    0xffff
 
 /* special events */
diff --git a/insns.def b/insns.def
index 4dc4975..973061b 100644
--- a/insns.def
+++ b/insns.def
@@ -1274,6 +1274,7 @@ setinlinecache
 {
     VM_ASSERT(ic->ic_value.value != Qundef);
     ic->ic_value.value = val;
+    EXEC_EVENT_HOOK(GET_THREAD(), RUBY_EVENT_CONSTANT_ACCESS, GET_SELF(), 0, 0, 0, val);
     ic->ic_serial = GET_GLOBAL_CONSTANT_STATE() - ruby_vm_const_missing_count;
     ic->ic_cref = vm_get_const_key_cref(GET_EP());
     ruby_vm_const_missing_count = 0;
diff --git a/vm_trace.c b/vm_trace.c
index 02bf54e..ff1fa06 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -598,6 +598,7 @@ get_event_id(rb_event_flag_t event)
 	C(thread_end, THREAD_END);
 	C(fiber_switch, FIBER_SWITCH);
 	C(specified_line, SPECIFIED_LINE);
+	C(constant_access, CONSTANT_ACCESS);
       case RUBY_EVENT_LINE | RUBY_EVENT_SPECIFIED_LINE: CONST_ID(id, "line"); return id;
 #undef C
       default:
@@ -706,6 +707,7 @@ symbol2event_flag(VALUE v)
     C(specified_line, SPECIFIED_LINE);
     C(a_call, A_CALL);
     C(a_return, A_RETURN);
+    C(constant_access, CONSTANT_ACCESS);
 #undef C
     rb_raise(rb_eArgError, "unknown event: %"PRIsVALUE, rb_sym2str(sym));
 }
@@ -854,6 +856,21 @@ rb_tracearg_return_value(rb_trace_arg_t *trace_arg)
 }
 
 VALUE
+rb_tracearg_constant_value(rb_trace_arg_t *trace_arg)
+{
+    if (trace_arg->event & (RUBY_EVENT_CONSTANT_ACCESS)) {
+	/* ok */
+    }
+    else {
+	rb_raise(rb_eRuntimeError, "not supported by this event");
+    }
+    if (trace_arg->data == Qundef) {
+	rb_bug("tp_attr_constant_value_m: unreachable");
+    }
+    return trace_arg->data;
+}
+
+VALUE
 rb_tracearg_raised_exception(rb_trace_arg_t *trace_arg)
 {
     if (trace_arg->event & (RUBY_EVENT_RAISE)) {
@@ -1001,6 +1018,15 @@ tracepoint_attr_return_value(VALUE tpval)
 }
 
 /*
+ *  Return value from +:constant_access+ event
+ */
+static VALUE
+tracepoint_attr_constant_value(VALUE tpval)
+{
+    return rb_tracearg_constant_value(get_trace_arg());
+}
+
+/*
  * Value from exception raised on the +:raise+ event
  */
 static VALUE
@@ -1501,6 +1527,7 @@ Init_vm_trace(void)
     rb_define_method(rb_cTracePoint, "binding", tracepoint_attr_binding, 0);
     rb_define_method(rb_cTracePoint, "self", tracepoint_attr_self, 0);
     rb_define_method(rb_cTracePoint, "return_value", tracepoint_attr_return_value, 0);
+    rb_define_method(rb_cTracePoint, "constant_value", tracepoint_attr_constant_value, 0);
     rb_define_method(rb_cTracePoint, "raised_exception", tracepoint_attr_raised_exception, 0);
 
     rb_define_singleton_method(rb_cTracePoint, "stat", tracepoint_stat_s, 0);
-- 
2.10.1 (Apple Git-78)