Bash autocompletion causes slow interactive login times

[ElvishJerricco]

When I set programs.bash.enableCompletion = true;, it adds 0.8s to my login time, regardless of whether the shell is interactive or not. Annoying enough that now I just disable it.

[LnL7]

I recall something about this related to the fact that the default version of bash on macOS is really old. Using the nix version of bash as your login shell might resolve this if that's the case.

[ElvishJerricco]

@LnL7 I have:

{ pkgs, ... }: {
  users.users.will = {
    description = "Will Fancher";
    home = "/Users/will";
    shell = "/run/current-system/sw/bin/bash";
  };
  environment.shells = [ pkgs.bashInteractive ];
}

So I thought I had that set up right. And in fact:

$ echo $BASH
/run/current-system/sw/bin/bash
$ echo $BASH_VERSION
4.4.12(1)-release

However, oddly enough, if I do these things directly from SSH then I get different results:

$ ssh hostname 'echo $BASH'
/bin/bash
$ ssh hostname 'echo $BASH_VERSION'
4.4.12(1)-release

It's using /bin/bash, though it does appear to be a recent version.

EDIT: Weird:

$ ssh hostname /bin/bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin16)
Copyright (C) 2007 Free Software Foundation, Inc.

[LnL7]

With #109 non-interactive cases shouldn't suffer from this anymore, but unless that was the cause somehow there's not much that can be done about it I think.

[ElvishJerricco]

@LnL7 though it's definitely less of a problem for only interactive logins to be slow, I think it's still a problem. The issue should probably remain open and be renamed.

[LnL7]

Oh, I confused this with #98.

[ElvishJerricco]

but unless that was the cause somehow there's not much that can be done about it I think.

@LnL7 How does NixOS avoid this problem? I remember reading somewhere that Bash can lazily load completions. Maybe we need to do that?

[LnL7]

Not sure, that's why my initial suspicion was the default bash 3.2.

[Kaali]

Pushed a fix for this which speeds up the interactive bash startup time significantly. Bash loads the completions from /share/ on demand, so they don't have to be preloaded. NixOS also fixed this in the same way in NixOS/nixpkgs#32534