company-mode off-by-one error regarding prefix length in dap-ui-repl

[doeblerh]

When using dap-ui-repl-mode for python debugging with debugpy, the last character entered is ignored in filtering the completion candidates. For example, when debugging

class C:
    def __init__(self):
        self.abcdx = 1
        self.abcex = 2

c = C()
# breakpoint here!

and entering dap-ui-repl, I get

>> c.abcd[CURSOR HERE]
    |abcdx field|
    |abcex field|

but

>> c.abcdE[CURSOR HERE]
    |abcdx field|

So it seems as if the prefix that is extracted and used for completion candidate computation is missing the last character entered.

To reproduce, install emacs 27.1, a plain spacemacs (select vim style keybindings, i.e. evil), add layers

     dap
     (python :variables
             python-backend 'lsp
             python-lsp-server 'pyright
             python-formatter 'black
             python-format-on-save t
             )

and debug the above python code using M-x dap-debug -> "Python :: Run file (buffer)"

I am currently using as workaround a patched version of dap-ui-repl--calculate-candidates, where I add 1 to the column specified in dap-ui.el, i.e., i replaced the corresponding line with

  :column (1+ (- (length text) (- (point-at-eol) (point))))))

which fixes completion to behave as expected.

However, since this is the only scenario in which I use dap-ui-repl, I cannot check or tell if this change breaks completion under different conditions. Maybe, it is evil-related?