Set evaluation result to `_` local variable #1159

HeyNonster · 2025-10-15T12:50:34Z

This resolves #1069.

This PR makes a change to the thread client to set the _ local variable to the result of the last evaluation similar to the behavior in irb¹.

The reason _ doesn't work even when using the irb console is because we leave the irb evaluation early if the input should be handled by the debugger². Otherwise, we would end up in IRB::Context#evaluate and we would call set_last_value³.

There's a bit of a quirk here when using the irb console. I was hoping in thread_client to evaluate the result then set the _ local variable and the @last_value ivar all in the same method, similar to how irb does it¹. However, because we're using the irb console we use a new irb Workspace which nils out _ when initialized⁴. To get around that, we set the local variable just before evaluating.

This PR makes a change to the thread client to set the `_` local variable to the result of the last evaluation similar to the behavior in irb[^1]. The reason `_` doesn't work even when using the `irb` console is because we leave the `irb` evaluation early if the input should be handled by the debugger[^2]. Otherwise, we would end up in IRB::Context#evaluate` and we would call `set_last_value`[^3]. There's a bit of a quirk here when using the `irb` console. I was hoping in `thread_client` to evaluate the result then set the `_` local variable and the `@last_value` ivar all in the same method, similar to how `irb` does it[^1]. However, because we're using the `irb` console we use a new `irb` `Workspace` which nils out `_` when initialized[^4]. To get around that, we set the local variable just before evaluating. [^1]:(https://github.com/ruby/irb/blob/d43c3d764ae439706aa1b26a3ec299cc45eaed5b/lib/irb/context.rb#L460-L465) [^2]:(https://github.com/ruby/irb/blob/d43c3d764ae439706aa1b26a3ec299cc45eaed5b/lib/irb.rb#L195-L198) [^3]:(https://github.com/ruby/irb/blob/d43c3d764ae439706aa1b26a3ec299cc45eaed5b/lib/irb/context.rb#L550-L558) [^4]:(https://github.com/ruby/irb/blob/d43c3d764ae439706aa1b26a3ec299cc45eaed5b/lib/irb/workspace.rb#L81) This PR was created by Zendesk's Ruby infrastructure team: Co-authored-by: Benjamin Quorning <bquorning@zendesk.com> Co-authored-by: Edyta Rozczypała <edyta.rozczypala@zendesk.com> Co-authored-by: Jury Razumau <jury.razumau@zendesk.com> Co-authored-by: Leonid Batizhevskii <leonid.batizhevskii@zendesk.com> Co-authored-by: Luis Manotas <lgerman@gmail.com> Co-authored-by: Thomas Countz <thomascountz@gmail.com>

launchable-app · 2025-10-15T12:53:42Z

❌ 1/689 Tests Failed

/home/runner/work/debug/debug/test/protocol/catch_raw_dap_test.rb#test_catching_any_exception_works_correctly

-------------------------
| All Protocol Messages |
-------------------------

V>D {"seq":1,"command":"initialize","arguments":{"clientID":"vscode","clientName":"Visual Studio Code","adapterID":"rdbg","pathFormat":"path","linesStartAt1":true,"columnsStartAt1":true,"supportsVariableType":true,"supportsVariablePaging":true,"supportsRunInTerminalRequest":true,"locale":"en-us","supportsProgressReporting":true,"supportsInvalidatedEvent":true,"supportsMemoryReferences":true},"type":"request"}
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V>D {"seq":3,"command":"setFunctionBreakpoints","arguments":{"breakpoints":[]},"type":"request"}
V>D {"seq":4,"command":"setExceptionBreakpoints","arguments":{"filters":[],"filterOptions":[{"filterId":"RuntimeError"}]},"type":"request"}
V>D {"seq":5,"command":"configurationDone","type":"request"}
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V<D {"type":"event","event":"initialized","seq":2}
V<D {"type":"event","event":"output","body":{"category":"console","output":"Ruby REPL: You can run any Ruby expression here.\nNote that output to the STDOUT/ERR printed on the TERMINAL.\n[experimental]\n  `,COMMAND` runs `COMMAND` debug command (ex: `,info`).\n  `,help` to list all debug commands.\n"},"seq":3}
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V<D {"type":"response","command":"configurationDone","request_seq":5,"success":true,"message":"Success","seq":7}
V<D {"type":"event","event":"stopped","body":{"reason":"pause","threadId":1,"allThreadsStopped":true},"seq":8}
V>D {"seq":6,"command":"threads","type":"request"}
V<D {"type":"response","command":"threads","request_seq":6,"success":true,"message":"Success","body":{"threads":[{"id":1,"name":"#1 /tmp/debug-20251015-2727-y0wy3o.rb:1:in '<main>'"}]},"seq":9}
V>D {"seq":7,"command":"threads","type":"request"}
V<D {"type":"response","command":"threads","request_seq":7,"success":true,"message":"Success","body":{"threads":[{"id":1,"name":"#1 /tmp/debug-20251015-2727-y0wy3o.rb:1:in '<main>'"}]},"seq":10}
V>D {"seq":8,"command":"stackTrace","arguments":{"threadId":1,"startFrame":0,"levels":20},"type":"request"}
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V>D {"seq":13,"command":"threads","type":"request"}
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--------------------------
| Last Protocol Messages |
--------------------------

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{
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  "seq": 17
}
{
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  "command": "stackTrace",
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{
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--------------------
| Debuggee Session |
--------------------

> DEBUGGER: Debugger can attach via UNIX domain socket (/run/user/1001/rdbg-2727-17)
> DEBUGGER: wait for debugger connection...
> DEBUGGER: Connected.


-------------------
| Failure Message |
-------------------

expected:
{
  "type": "response",
  "command": "stackTrace",
  "request_seq": 14,
  "success": true,
  "message": "Success",
  "body": {
    "stackFrames": [
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          "path": "(?-mix:\\/tmp\\/debug-20251015-2727-y0wy3o.rb)",
          "sourceReference": 0
        },
        "id": 2
      },
      {
        "name": "Foo::Bar.a",
        "line": 4,
        "column": 1,
        "source": {
          "name": "(?-mix:debug-20251015-2727-y0wy3o.rb)",
          "path": "(?-mix:\\/tmp\\/debug-20251015-2727-y0wy3o.rb)",
          "sourceReference": 0
        },
        "id": 3
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        "column": 1,
        "source": {
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          "sourceReference": 0
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        "id": 4
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          "sourceReference": 0
        },
        "id": 5
      }
    ]
  }
}

result:
{
  "type": "response",
  "command": "stackTrace",
  "request_seq": 14,
  "success": true,
  "message": "Success",
  "body": {
    "stackFrames": [
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        "name": "Foo::Bar.a",
        "line": 4,
        "column": 1,
        "source": {
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          "path": "/tmp/debug-20251015-2727-y0wy3o.rb",
          "sourceReference": 0
        }
      },
      {
        "id": 3,
        "name": "<module:Foo>",
        "line": 7,
        "column": 1,
        "source": {
          "name": "debug-20251015-2727-y0wy3o.rb",
          "path": "/tmp/debug-20251015-2727-y0wy3o.rb",
          "sourceReference": 0
        }
      },
      {
        "id": 4,
        "name": "<main>",
        "line": 1,
        "column": 1,
        "source": {
          "name": "debug-20251015-2727-y0wy3o.rb",
          "path": "/tmp/debug-20251015-2727-y0wy3o.rb",
          "sourceReference": 0
        }
      }
    ],
    "totalFrames": 4
  },
  "seq": 18
}.
<"[C] Integer#/"> expected but was
<"Foo::Bar.a">.

[-> View Test suite health in main branch]

HeyNonster mentioned this pull request Oct 15, 2025

After entering debug, _ (underscore) stops working ruby/irb#891

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Set evaluation result to `_` local variable #1159

Set evaluation result to `_` local variable #1159

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❌ 1/689 Tests Failed

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Set evaluation result to `_` local variable #1159

Set evaluation result to `_` local variable #1159

HeyNonster commented Oct 15, 2025 •

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