Error rebugging function when cursor is not positioned over the first character.

[roberthoenig]

julia> abs(2)

To rebug this, the cursor currently must be positioned on the a.
If it's on e.g. the b, an error is thrown:

julia> a┌ Error: Error in the keymap
│   exception =
│    UndefVarError: abegin not defined
│    Stacktrace:
│     [1] top-level scope
│     [2] eval(::Module, ::Any) at ./boot.jl:319
│     [3] stepin(::Base.GenericIOBuffer{Array{UInt8,1}}) at /home/robert/.julia/packages/Rebugger/QDOWe/src/debug.jl:110
│     [4] stepin(::REPL.LineEdit.MIState) at /home/robert/.julia/packages/Rebugger/QDOWe/src/ui.jl:91
│     [5] (::getfield(Rebugger, Symbol("##16#18")))(::REPL.LineEdit.MIState, ::REPL.LineEditREPL, ::Vararg{Any,N} where N) at /home/robert/.julia/packages/Rebugger/QDOWe/src/ui.jl:217
│     [6] #invokelatest#1 at ./essentials.jl:686 [inlined]
│     [7] invokelatest at ./essentials.jl:685 [inlined]
│     [8] (::getfield(REPL.LineEdit, Symbol("##27#28")){getfield(Rebugger, Symbol("##16#18")),String})(::Any, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/REPL/src/LineEdit.jl:1319
│     [9] prompt!(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/REPL/src/LineEdit.jl:2353
│     [10] run_interface(::REPL.Terminals.TextTerminal, ::REPL.LineEdit.ModalInterface, ::REPL.LineEdit.MIState) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/REPL/src/LineEdit.jl:2256
│     [11] run_frontend(::REPL.LineEditREPL, ::REPL.REPLBackendRef) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:1029
│     [12] run_repl(::REPL.AbstractREPL, ::Any) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/REPL/src/REPL.jl:191
│     [13] (::getfield(Base, Symbol("##720#722")){Bool,Bool,Bool,Bool})(::Module) at ./logging.jl:311
│     [14] #invokelatest#1 at ./essentials.jl:686 [inlined]
│     [15] invokelatest at ./essentials.jl:685 [inlined]
│     [16] macro expansion at ./logging.jl:308 [inlined]
│     [17] run_main_repl(::Bool, ::Bool, ::Bool, ::Bool, ::Bool) at ./client.jl:330
│     [18] exec_options(::Base.JLOptions) at ./client.jl:242
│     [19] _start() at ./client.jl:421

It'd be great if rebugger worked with the cursor positined at any character of the function name.

[timholy]

I think this is a good idea. However, I worry a bit about distinguishing things like this (imagine your cursor is positioned on the l in float):

julia> x = 1.2
1.2

julia> 2float(x)    # means the same thing as 2*float(x)
2.4

julia> int2float(x)   # references a method 
ERROR: UndefVarError: int2float not defined
Stacktrace:
 [1] top-level scope at none:0

So while you're backing up do you include the 2 or not?

Worst-case scenario I can throw a nicer error. Not quite sure what's best here.

[roberthoenig]

Hmm, I see. I'm not familiar with the internals of Rebugger, but I thought that it'd work with Expr objects of the actual code? Your comments seems to suggest that rather, it does string-parsing. If that's the case, I think parsing the actual expression would be a more robust approach that'd allow Rebugger too see in the case of 2float(x) that it should rebug only the float, and in the case of int2float, that it should rebug the whole int2float, if that makes sense.

[oxinabox]

It would be nice if rebugger did something sensible rather than throw this error.
Even if it was just throw a more descriptive error

[timholy]

The best way to solve this would be to parse the complete input line. But because parsing doesn't provide any mechanism to then match expressions/symbols/whatever to the position in the input string, it's not entirely obvious how you go about aligning the two.

[oxinabox]

CSTParser.jl should provide that information, but it's docs are sparse (and it is a big dep).
Maybe just tokenize the line with Tokenizer.jl?

Or as a quick hack use a regex to go backward til you hit a non-letter