Make TracePoint#enable with block target current thread by default

If TracePoint#enable is passed a block, it previously started
the trace on all threads.  This changes it to trace only the
current thread by default.  To limit the scope of the change,
the current thread is only used by default if target and
target_line are both nil.  You can pass target_thread: nil
to enable tracing on all threads, to get the previous
default behavior.

Fixes [Bug #16889]

spec/ruby/core/tracepoint/enable_spec.rb

@@ -57,6 +57,30 @@ describe 'TracePoint#enable' do
       end.enable { event_name.should equal(:line) }
     end
 
+    ruby_version_is '3.2' do
+      it 'enables the trace object for any thread' do
+        threads = []
+        trace = TracePoint.new(:line) do |tp|
+          # Runs on purpose on any Thread
+          threads << Thread.current
+        end
+
+        thread = nil
+        trace.enable do
+          line_event = true
+          thread = Thread.new do
+            event_in_other_thread = true
+          end
+          thread.join
+        end
+
+        threads = threads.uniq
+        threads.should.include?(Thread.current)
+        threads.should_not.include?(thread)
+      end
+    end
+
+    ruby_version_is ''...'3.2' do
       it 'enables the trace object for any thread' do
         threads = []
         trace = TracePoint.new(:line) do |tp|
@@ -77,6 +101,7 @@ describe 'TracePoint#enable' do
         threads.should.include?(Thread.current)
         threads.should.include?(thread)
       end
+    end
 
     it 'can accept arguments within a block but it should not yield arguments' do
       event_name = nil

spec/ruby/core/tracepoint/inspect_spec.rb

@@ -98,7 +98,7 @@ describe 'TracePoint#inspect' do
     TracePoint.new(:thread_begin) { |tp|
       next unless Thread.current == thread
       inspect ||= tp.inspect
-    }.enable do
+    }.enable(target_thread: nil) do
       thread = Thread.new {}
       thread_inspection = thread.inspect
       thread.join
@@ -114,7 +114,7 @@ describe 'TracePoint#inspect' do
     TracePoint.new(:thread_end) { |tp|
       next unless Thread.current == thread
       inspect ||= tp.inspect
-    }.enable do
+    }.enable(target_thread: nil) do
       thread = Thread.new {}
       thread_inspection = thread.inspect
       thread.join

test/ruby/test_settracefunc.rb

@@ -727,25 +727,30 @@ CODE
   def test_tracepoint_enable
     ary = []
     args = nil
+    begin
       trace = TracePoint.new(:call){|tp|
         next if !target_thread?
         ary << tp.method_id
       }
       foo
-    trace.enable{|*a|
+      trace.enable(target_thread: nil){|*a|
         args = a
         foo
       }
       foo
       assert_equal([:foo], ary)
       assert_equal([], args)
+    ensure
+      trace&.disable
+    end
 
     trace = TracePoint.new{}
     begin
       assert_equal(false, trace.enable)
       assert_equal(true, trace.enable)
-      trace.enable{}
+      trace.enable(target_thread: nil){}
-      assert_equal(true, trace.enable)
+      trace.disable
+      assert_equal(false, trace.enable)
     ensure
       trace.disable
     end
@@ -977,7 +982,7 @@ CODE
                  tp.defined_class, #=> nil,
                  tp.self.class # tp.self return creating/ending thread
                  ]
-    }.enable{
+    }.enable(target_thread: nil){
       created_thread = Thread.new{thread_self = self}
       created_thread.join
     }
@@ -2239,7 +2244,7 @@ CODE
     # global TP and targeted TP
     ex = assert_raise(ArgumentError) do
       tp = TracePoint.new(:line){}
-      tp.enable{
+      tp.enable(target_thread: nil){
         tp.enable(target: code2){}
       }
     end
@@ -2285,7 +2290,7 @@ CODE
         events << :___
       end
     end
-    assert_equal [:tp1, :tp1, :tp1, :tp1, :tp2, :tp1, :___], events
+    assert_equal [:tp1, :tp1, :tp1, :tp1, :tp1, :tp2, :tp1, :___], events
 
     # success with two tracepoints (targeting/global)
     events = []

trace_point.rb

@@ -153,7 +153,7 @@ class TracePoint
 
   # call-seq:
   #    trace.enable(target: nil, target_line: nil, target_thread: nil)    -> true or false
-  #    trace.enable(target: nil, target_line: nil, target_thread: nil) { block }  -> obj
+  #    trace.enable(target: nil, target_line: nil, target_thread: Thread.current) { block }  -> obj
   #
   # Activates the trace.
   #
@@ -168,14 +168,15 @@ class TracePoint
   #                   #   trace is still enabled
   #
   # If a block is given, the trace will only be enabled within the scope of the
-  # block.
+  # block. If target and target_line are both nil, then target_thread will default
+  # to the current thread if a block is given.
   #
   #    trace.enabled?
   #    #=> false
   #
   #    trace.enable do
   #      trace.enabled?
-  #      # only enabled for this block
+  #      # only enabled for this block and thread
   #    end
   #
   #    trace.enabled?
@@ -208,7 +209,7 @@ class TracePoint
   #    trace.enable { p tp.lineno }
   #    #=> RuntimeError: access from outside
   #
-  def enable(target: nil, target_line: nil, target_thread: nil)
+  def enable(target: nil, target_line: nil, target_thread: (Thread.current if target.nil? && target_line.nil? && defined?(yield)))
     Primitive.tracepoint_enable_m(target, target_line, target_thread)
   end