nimpretty --indent:3 can inject syntax errors

[FredTheDino]

I was casually trying out Nim-lang and playing with nimpretty. Ofcourse I decided to mess with a flag called "indent", and nimpretty doesn't seem to handle this.

I don't really have the time to do a full bisect, I just installed it and played around. Felt it was better to report this than to ignore it.

Example run

 ~ :: nim r a.nim
Hint: used config file '/etc/nim/nim.cfg' [Conf]
Hint: used config file '/etc/nim/config.nims' [Conf]
Hint: gc: refc; opt: none (DEBUG BUILD, `-d:release` generates faster code)
9905 lines; 0.010s; 8.645MiB peakmem; proj: /home/ed/a.nim; out: /home/ed/.cache/nim/a_d/a_5220365807561D8E69F6B4EBF89A3C6B14B8A8F3 [SuccessX]
Hint: /home/ed/.cache/nim/a_d/a_5220365807561D8E69F6B4EBF89A3C6B14B8A8F3  [Exec]
 ~ :: nimpretty a.nim --indent:10
 ~ :: nim r a.nim
Hint: used config file '/etc/nim/nim.cfg' [Conf]
Hint: used config file '/etc/nim/config.nims' [Conf]
.........................................................
/home/ed/a.nim(5, 5) Error: invalid indentation

Example

a.nim before

proc x() =
  let
    x = if true: 1
        else: 0
    error = "abc"
  echo x

a.nim after nimpretty --indent:3

proc x() =
   let
      x = if true: 1
        else: 0
    error = "abc"
   echo x

This happens for indent:3 and indent:10. I haven't tested more, I suspect there are some assumptions in the formatter.

Expected Output

proc x() =
   let
      x = if true: 1
          else: 0
      error = "abc"
   echo x

Possible Solution

• Remove the --indent flag, it looks like you
• Fix the implicit assumption in the formatter for 2 spaces as indentation

Additional Information

nim version

Nim Compiler Version 1.6.6 [Linux: amd64]
Compiled at 2022-05-22
Copyright (c) 2006-2021 by Andreas Rumpf

active boot switches: -d:release

nimpretty version

0.2

Disclaimer

Haven't tested with head - nimpretty doesn't seem to have been touched in some time so I saved myself some time there. <3