Change $HOME before it gets accessed

Question

I'm using vim 8.1 on windows. The IT department has set $HOME to a slow network drive. Every time a file gets written to $HOME vim slows down.

I have $VIM/vimrc with the following content.

let $HOME = $USERPROFILE

This used to work, but now netrw still creates files on the network drive.

How do I change $HOME so that no slowdown occurs?

Answer 1

After you answered the question yourself, the focus shifted. It seems the Question is now "How can I prevent Vim from checking for $HOME/_vimrc?".

Try the following:

• Create the file $USERPROFILE/vimrc with all your configuration.
• Create the environment variable VIMINIT with the value source $USERPROFILE/vimrc.

On startup the variable VIMINIT is checked first. If it is set, the value of $VIMINIT is used as an Ex command line.

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Update (I know that the questioner is not interested anymore):

You should also check your runtimepath. Most likely it still points to $HOME/vimfiles (on Windows). So you should create the directory $USERPROFILE/vimfiles to store extended configuration and plugins etc.

At the beginning of $USERPROFILE/vimrc you have to fix the runtimepath. I would try it like this:

set runtimepath-=~/vimfiles
set runtimepath^=$USERPROFILE/vimfiles
set runtimepath-=~/vimfiles/after
set runtimepath+=$USERPROFILE/vimfiles/after

After that you should still change $HOME, as others (like netrw) still uses it.

let $HOME=$USERPROFILE

I'm on Linux, so someone should test this on Windows.

Answer 2

_{Running without major issues for a week now so I'm adding this as an alternative answer.}

I tried all suggestions made here and wherever I could find and the only thing that effectively worked in skipping accessing my networked homefolder was using gvim --clean.

• Although the help states that --clean is equivalent to -u DEFAULTS -U NONE -i NONE, it is not. Using procmon, it was clear that vim was still accessing my network drive.
• It's not a solution. It's good to troubleshoot but I don't want to work with a clean vim.

I ended up patching the executable to skip the HOME* environment variables all together.
_{It did require me to change my $HOME references in my vimrc.local to an absolute path}

Tested on vim 8.1.282.0
_{if the byte sequence is present in your version of vim, I assume it will work as well. You might just as well crash vim but there's little/no harm in trying}

search for following bytes

CB 65 00 E8 D1 9B F1 FF 8B E8 83 C4 04 85 ED 74 06 80 7D 00 00 75 7F
68 04 CC 65 00 E8 B8 9B F1 FF 83 C4 04 8B F8

and replace with

CB 65 00 E8 D1 9B F1 FF 8B E8 83 C4 04 85 ED 74 04 80 7D 00 00 EB 7F
68 04 CC 65 00 E8 B8 9B F1 FF 83 C4 04 8B F8 

• Original vim's MD5 E6BBB217EAAB09FE6E2C380D4DF09BD3
• Patched vim's MD5 BDAAAC3FA3F6796825A51EF1C0E5B3FD

Description of the patch

Using Ghidra to reverse engineer vim, you can find where references to the HOME* environment variables get checked. I have relabeled the autogenerated labels in below screenshots as to show what the block of code does in the context of following/skipping the home folders.

I found two code paths that lead to executing the Cullprit code depending on whether or not the HOME* environment variables are set. The plan of attack then was to patch the code to always flow to SkipHome

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Patch two instructions

1. Changed the 74 06 JZ instruction to 74 04 JZ so instead of jumping 6 bytes into the Cullprit code when the $HOME environment variable is not set, jump to our unconditional JMP
2. Changed the 75 7f JNZ conditional jump to a eb 7f JMP unconditional jump.

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Addendum

That said, vim first checks for a $HOME variable and only checks for $HOMEDRIVE and $HOMEPATH if $HOME is empty. Windows, afaik, does not set a $HOME variable out of the box so I assume that is simply a cross platform check.

If you don't want to mess with your existing HOME* variables and don't want to patch, it looks like you can abuse that fact by setting a $HOME variable to whatever you like and skip the HOME* code.

for example setx home <path to your _vimrc> might just work.

Answer 3

You can use the -u option to give an alternate .vimrc file of your choice when starting vim. As stated here, you can also use the $MYVIMRC variable to automate this (this takes precedence over $HOME), which should answer your question.

Answer 4

Turns out the culprit was

source $VIMRUNTIME/vimrc_example.vim

in my $HOME/_vimrc. After removing it no files were created anymore.

Never mind. After more testing it didn't work.

Solution

Create a vimrc in $VIM with following content

let $HOME = $USERPROFILE

This however is not a perfect solution.

According to the documentation it first searches $HOME and then $VIM. This means there is a slow access to the network drive to check if there exists a vimrc. This is quite noticeable. To fix that you either have to somehow undo the work of the IT guys or open Vim with -u everywhere. Or just keep Vim open forever.

Or you use an editor with manners that saves its configuration in %appdata% like it's supposed to. I'm out.