vim9-conversion-aid

A little help for upgrading to Vim9 by converting legacy Vim to Vim 9 script. No miracles, nor bullet proof, but giving a head start in the conversion process by a :Vim9Convert (that operates either on the current or supplied buffer) command to

• replace all occurrences of func, function, etc. with def and enddef,
• replace comment string " with #,
• replace v:true, v:false with true, false,
• add leading/trailing space to = and to comparison signs as needed,
• remove line continuation symbol \,
• ... and so much more.

Caveats

The let commands won't be converted automatically unless you set g:vim9_conversion_aid_fix_let = true, though rather fix the variables definitions, but not their usage.

For example, if at script level you have the following statement:

let newdict = CreateDict()
call PrintDictContent(newdict)

then it will be converted to the following:

g:newdict = CreateDict()
PrintDictContent(newdict)

That is, the argument to the function call shall be manually fixed.

Finally, in a similar vein, neither are a:, l: and s: removed automatically.

This way, you can better inspect if your script semantic is still valid. Once done inspecting, run a simple :%s/\v(a:|s:|l:)//g.

Or, if you still prefer that to happen automatically, you can set g:vim9_conversion_aid_fix_asl = true.

Usage

The converted file will most likely have errors, but the error messages should tell you what shall be fixed and how. Also, mind that :h vim9 can be a great support for fixing the remaining errors if you really don't know how.

You can line-by-line compare the old and converted script by opening them next to each other and running windo setlocal scrollbind diffthis.

Testing

To see how the tool perform the upgrade you can take a look at the ./test/test_script.vim and ./test/expected_script.vim scripts.

As you will see, some manual work is still required, but the starting point is rather favorable compared to starting from scratch. Note that ./test/test_script.vim does not do anything special, it has been written with the sole purpose of hitting a reasonable amount of corners.

Limitations

The tool works better if the original script is not written in a fancy way. As said, don't expect miracles and consider the following limitations:

• no inline comments, e.g. the following won't be fixed:

let s:a = 3 " This is a comment

The following will be fixed:

" This is a comment
let s:a = 3

• it won't fix string concatenation if the concatenation operator . does not have a leading and a trailer white-space,
• functions with variable number of arguments won't be fixed,
• it won't remove eval,
• lambda expressions will not be converted in the new format,
• Vim9 syntax/semantics updates and datatypes shall be handled manually.

... but there is certainly more that you will need to fix manually. If you find bugs or have improvements suggestions, please open an issue or send a PR. In the latter case, don't forget to update the tests.

To circumnavigate some of the above limitations, prepare your script to don't hit the above limitations. Plus, avoid using script-local variable names that shadow vim builtin keywords (e.g. avoid to call a variable let s:vertical because vertical is a builtin keyword.