lix/tests/functional2/repl_characterization/debugger/debug_frames.md

args

args
--debugger

:c at the root repl is not allowed since no debugger is running yet

:c

error: command 'c' can only be used when the debugger is active

:c and other commands become available once a debugger starts

with {}; a

error: undefined variable 'a'
       at «string»:1:10:
            1| with {}; a
             |          ^

:?

The following commands are available:

  <expr>                             Evaluate and print expression
  <x> = <expr>                       Bind expression to variable
  :?, :help                          Print help about all commands (this content)
  :a, :add <expr>                    Add attributes from resulting set to scope
  :b, :build <expr>                  Build a derivation
  :bl, :build-with-gc-roots <expr>   Build a derivation, creating GC roots in the working directory
  :doc <expr>                        Show documentation for the provided function (experimental lambda support)
  :e, :edit <expr>                   Open package or function in $EDITOR
  :env                               Show environment stack
  :i, :build-and-install <expr>      Build derivation, then install result into current profile
  :l, :load <path>                   Load Nix expression and add it to scope
  :log <expr | .drv path>            Show logs for a derivation
  :p, :print <expr>                  Evaluate and print expression recursively
                                     Strings are printed directly, without escaping.
  :q, :quit                          Exit the REPL
  :r, :reload                        Reload all files successfully loaded
  :sh, :shell <expr>                 Build dependencies of derivation, then start nix-shell
  :t, :type <expr>                   Describe result of evaluation
  :te, :trace-enable [bool]          Enable, disable, or toggle showing traces for errors
  :u, :use <expr>                    Build derivation, then start nix-shell

    Debug mode commands

  :bt, :backtrace                    Show trace stack
  :c, :continue                      Go until end of program, exception or builtins.break
  :s, :step                          Go one step
  :st, :show-trace [integer index]   Show current trace. If an integer is provided, this switches to that stack beforehand. If the integer has an explicit + or - sign, it is treated as relative to the current stack index.

    Flakes commands

  :lf, :load-flake <flakeref>        Load Nix flake and add it to the scope

we can now inspect state

:bt

1: error: Fake frame for debugging purposes
«string»:1:10

     1| with {}; a
      |          ^

0: error: undefined variable 'a'
«string»:1:10

     1| with {}; a
      |          ^

and resume execution

:c

error: undefined variable 'a'
       at «string»:1:10:
            1| with {}; a
             |          ^

the debugger is once again disabled

:c

error: command 'c' can only be used when the debugger is active

leaving the debugger from a toplevel error and entering it again doesn't leave old frames visible

with {}; a
:s
with {}; b
:bt

error: undefined variable 'a'
       at «string»:1:10:
            1| with {}; a
             |          ^

error: undefined variable 'a'
       at «string»:1:10:
            1| with {}; a
             |          ^

error: undefined variable 'b'
       at «string»:1:10:
            1| with {}; b
             |          ^


1: error: Fake frame for debugging purposes
«string»:1:10

     1| with {}; b
      |          ^

0: error: undefined variable 'b'
«string»:1:10

     1| with {}; b
      |          ^

exiting from here prints the error

:q

error: undefined variable 'b'
       at «string»:1:10:
            1| with {}; b
             |          ^