From: "hurricup (Alexandr Evstigneev)" <noreply@...>
Date: 2022-04-27T06:24:20+00:00
Subject: [ruby-core:108409] [Ruby master Bug#18740] Use of rightward assignment changes line number needed for line-targeted TracePoint

Issue #18740 has been updated by hurricup (Alexandr Evstigneev).


jeremyevans0 (Jeremy Evans) wrote in #note-1:
> You can set a tracepoint, rightward assignment just moves the line you need to target.  In your example, you have to use `target_line: 6` instead of `target_line: 2`.  I'm not sure if this is considered a bug or not.

Yes, I can see that. But his is not intuitive for the debugger user and too big difference for the case without `=> lines`, where you can use line 2. This is not a bug (like segfault or smth) but more like usability issue. 

Feels like you should be able to debug full expression, not only assigning part.

----------------------------------------
Bug #18740: Use of rightward assignment changes line number needed for line-targeted TracePoint
https://bugs.ruby-lang.org/issues/18740#change-97444

* Author: hurricup (Alexandr Evstigneev)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Affected ruby 3.1.1

Sample illustrating the problem (`test.rb`):

```
def foo
  File.read("test.rb")
      .split("\n")
      .map(&:strip)
      .reject(&:empty?)
      .first(10) => lines

  puts lines
end

TracePoint.new(:line){ puts 'Hi' }.enable(target: RubyVM::InstructionSequence.of(method :foo), target_line: 2)
foo
```

produces

```
<internal:trace_point>:212:in `enable': can not enable any hooks (ArgumentError)
```

iseq for method:
```
== disasm: #<ISeq:foo@/home/hurricup/test.rb:1 (1,0)-(9,3)> (catch: FALSE)
local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
[ 1] lines@0
0000 putnil                                                           (   6)[LiCa]
0001 putnil
0002 putobject                              false
0004 putnil
0005 putnil
0006 opt_getinlinecache                     15, <is:0>                (   2)
0009 putobject                              true
0011 getconstant                            :File
0013 opt_setinlinecache                     <is:0>
0015 putstring                              "test.rb"
0017 opt_send_without_block                 <calldata!mid:read, argc:1, ARGS_SIMPLE>
0019 putstring                              "\n"                      (   3)
0021 opt_send_without_block                 <calldata!mid:split, argc:1, ARGS_SIMPLE>
0023 putobject                              :strip                    (   4)
0025 send                                   <calldata!mid:map, argc:0, ARGS_BLOCKARG>, nil
0028 putobject                              :empty?                   (   5)
0030 send                                   <calldata!mid:reject, argc:0, ARGS_BLOCKARG>, nil
0033 putobject                              10                        (   6)
0035 opt_send_without_block                 <calldata!mid:first, argc:1, ARGS_SIMPLE>
0037 dup
0038 setlocal_WC_0                          lines@0
0040 jump                                   88
0042 putspecialobject                       1                         (   2)
0044 topn                                   4
0046 branchif                               64
0048 putobject                              NoMatchingPatternError
0050 putspecialobject                       1
0052 putobject                              "%p: %s"
0054 topn                                   4
0056 topn                                   7
0058 opt_send_without_block                 <calldata!mid:core#sprintf, argc:3, ARGS_SIMPLE>
0060 opt_send_without_block                 <calldata!mid:core#raise, argc:2, ARGS_SIMPLE>
0062 jump                                   84
0064 putobject                              NoMatchingPatternKeyError
0066 putspecialobject                       1
0068 putobject                              "%p: %s"
0070 topn                                   4
0072 topn                                   7
0074 opt_send_without_block                 <calldata!mid:core#sprintf, argc:3, ARGS_SIMPLE>
0076 topn                                   7
0078 topn                                   9
0080 opt_send_without_block                 <calldata!mid:new, argc:3, kw:[matchee,key], KWARG>
0082 opt_send_without_block                 <calldata!mid:core#raise, argc:1, ARGS_SIMPLE>
0084 adjuststack                            7
0086 jump                                   90
0088 adjuststack                            6                         (   6)
0090 putself                                                          (   8)[Li]
0091 getlocal_WC_0                          lines@0
0093 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
0095 leave                                                            (   9)[Re]
```

Works like a charm without `=> lines`



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