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Feature #15289

Updated by nobu (Nobuyoshi Nakada) 10 months ago

# Abstract 

 To enable TracePoint for specific location, I propose new keyword argument `target:` to `TracePoint#enable` for specific events (`line`, `call`, `return`, `class`, `end`). 

 Usage: 

 ```ruby ``` 
 line_trace = TracePoint.new(:line){|tp| 
   p tp 
 } 

 def foo 
   p 1 
 end 

 line_trace.enable(target: method(:foo)) do 
   foo 
 end 
 ``` 

 In this case, a line trace is enable only on the method `foo`. 

 `target:` keyword accepts `Method`, `UnboundMethod`, `Proc` and `RubyVM::InstructionSequence` (ISeq for short) . All of objects can pull ISeq objects. 

 Further more, I propose `target_lines:` keyword too, which specify effective line(s). 

 These features can improve "break point" feature and so on. 

 # Background 

 If we want to insert break point in Ruby's source code, we can use `TracePoint` (line event, for example). However, it enables all locations. It hurt performance. 

 This proposal overcomes this performance penalty. 

 # Implementation 

 Now basic design are completed in my mind :p 

 # Discussion 

 ## line or lines 

 For breakpoint purpose, we only need to specify a line. Specifying lines is needed? 

 ## no events on lines 

 It is not clear that if line is specified (for example: 10) and there are no line event (for example, empty line). 

 Possible options: 

 * (1) raise an exception 
 * (2) adjust before/after effective event 
 * (3) ignore 

 I prefer (1). 

 ## no events in Proc 

 Similar to last topic, if we specify `call` event on `Proc` object, there are no `call` event. What happens? 

 ## recursive or not 

 If method `foo` refers other blocks, I think we need to enable recursively.  

 ## how to get File target? 

 Sometimes we want to specify breakponit to the location specified by "file:line". How to get the lines? 

 https://github.com/ko1/iseq_collector provides the feature to collect all of ISeqs. debugger can collects all of them and debugger can filter with path name. 

 Also [Feature #15287] will help to hook not loaded locations. 

 ## `enable` w/ keywords or other method name? 

 I have no strong opinion, but `TracePoint#enable_on(target, lines: ...)` is another idea? 

 # reference 

 Related: https://github.com/ruby/ruby/pull/2000 

 This implementation is based on `trace_` insn. 

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