Feat/Bug: Set the value of `_` (underscore) to the value of the last ruby expression

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#1,069 3 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
ruby
Domain
devtools

Research direction

Start with the irb_integration.rb entry point named in the trace and reproduce the supplied IRB session while comparing normal and debug modes. Done means _ continues to hold the last Ruby expression's value after entering debug mode, without debug commands or errors replacing it.

Written by the indexing model from the issue text.

Description

Your proposal

Pry and IRB have a feature in which _ is always set the the value of the last expression. While I realize it may not make sense to do this with debug commands, it would be nice if the feature was there at least for Ruby expressions. The current behavior seems to be setting _ to the last error, but seemingly only for debug commands like ls. This is kind of a bug in the irb_console since IRB has this feature normally but it stops working after entering debug mode.

Additional context

Shell session: 

irb(#<Foobar:0x000000011efeb9f0>):001> 3+3
=> 6

irb(#<Foobar:0x000000011efeb9f0>):002> puts _
6
=> nil

irb(#<Foobar:0x000000011efeb9f0>):003> 4+4
=> 8

irb(#<Foobar:0x000000011efeb9f0>):004> info
(rdbg:irb) info
%self = #<Foobar:0x000000011efeb9f0 @foo="bar">
@foo = "bar"

irb:rdbg(#<Foobar:0x000000011efeb9f0>):002> puts _

nil

irb:rdbg(#<Foobar:0x000000011efeb9f0>):003> 4+4
8

irb:rdbg(#<Foobar:0x000000011efeb9f0>):004> puts _

nil
irb:rdbg(#<Foobar:0x000000011efeb9f0>):005> 4+4
8

irb:rdbg(#<Foobar:0x000000011efeb9f0>):006> info
%self = #<Foobar:0x000000011efeb9f0 @foo="bar">
_ = nil
@foo = "bar"

irb:rdbg(#<Foobar:0x000000011efeb9f0>):007> ls Bar
Traceback (most recent call last):
	24: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:212:in `block in activate'
	23: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:254:in `session_server_main'
	22: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:365:in `process_event'
	21: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:403:in `wait_command_loop'
	20: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:403:in `loop'
	19: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:404:in `block in wait_command_loop'
	18: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:444:in `wait_command'
	15: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:1981:in `intercept_trap_sigint'
	 4: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/irb_integration.rb:9:in `evaluate'
(irb):7:in `set_foo': uninitialized constant Foobar::Bar (NameError)`

irb:rdbg(#<Foobar:0x000000011efeb9f0>):008> puts _
uninitialized constant Foobar::Bar
nil

irb:rdbg(#<Foobar:0x000000011efeb9f0>):009> ls Bar
Traceback (most recent call last):
	24: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:212:in `block in activate'
	23: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:254:in `session_server_main'
	22: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:365:in `process_event'
	21: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:403:in `wait_command_loop'
	20: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:403:in `loop'
	19: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:404:in `block in wait_command_loop'
	18: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:444:in `wait_command'
	15: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/session.rb:1981:in `intercept_trap_sigint'
	 4: from /Users/joesharp/.asdf/installs/ruby/2.7.8/lib/ruby/gems/2.7.0/gems/debug-1.9.1/lib/debug/irb_integration.rb:9:in `evaluate'
(irb):9:in `set_foo': uninitialized constant Foobar::Bar (NameError)`

irb:rdbg(#<Foobar:0x000000011efeb9f0>):010> info
%self = #<Foobar:0x000000011efeb9f0 @foo="bar">
_ = #<NameError: uninitialized constant Foobar::Bar>
@foo = "bar"

irb:rdbg(#<Foobar:0x000000011efeb9f0>):011> Bar.methods
eval error: uninitialized constant Foobar::Bar
  (rdbg)/scratch.rb:1:in `set_foo'`
nil

irb:rdbg(#<Foobar:0x000000011efeb9f0>):012> info
%self = #<Foobar:0x000000011efeb9f0 @foo="bar">
_ = nil
@foo = "bar"

irb:rdbg(#<Foobar:0x000000011efeb9f0>):013> Bar.methods
eval error: uninitialized constant Foobar::Bar
  (rdbg)/scratch.rb:1:in `set_foo'`
nil

irb:rdbg(#<Foobar:0x000000011efeb9f0>):014> puts _

nil

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