fix: willRename source path

[luckasRanarison]

Closes #247.
I think getting the relative path is unnecessary because the glob pattern will always match the full path, and it can mess up with some server filters, for example: tsserver uses **/*.js but the relative path omit the parent dir.

[stevearc]

This may fix the immediate problem, but it will introduce more issues. Any pattern that doesn't start with ** will fail to match because we're passing in the absolute path to the file. The root issue here is vim's glob2regpat does not handle ** the way we expect. See:
:echo glob2regpat('*.js') -> \.js$
:echo glob2regpat('**/*.js') -> /.*\.js$
:echo glob2regpat('**/**/*.js') -> /.*/.*\.js$

This is technically correct by some definitions, but does not behave the way LSP expects.

I think the best solution we have available right now is to use the private method vim.lsp._watchfiles._match when it's available, and fall back to glob2regpat when it's not.

https://github.com/neovim/neovim/blob/ca7f8786a0eb578895400e23cd21e25cc0f91800/runtime/lua/vim/lsp/_watchfiles.lua#L83-L89

[luckasRanarison]

Any pattern that doesn't start with ** will fail to match because we're passing in the absolute path to the file.

This is actually not true, try the following:

local pat = vim.fn.glob2regpat("*.js")
local match = vim.fn.match("/dir/file.js", pat)
print(match) -- 9

[stevearc]

Ah, I was overly broad. Yes it's true that a pattern of *.js also works, but if the pattern doesn't start with a * or **, then it will fail. Example:

local pat = vim.fn.glob2regpat("src/*.js")
local match = vim.fn.match("/home/user/project/src/file.js", pat)
print(match) -- -1

[luckasRanarison]

Oh, I see. But I think it's unlikely going to happen, I think FileOperartionPattern is meant to be matched against the absolute path. tsserver, rust_analyzer and php actor which support willRenameFiles all use **/*.filetype.

I'll update this later and use vim.lsp._watchfiles and fallback to both absolute path and relative path as a workaround if you're concerned about it.

[stevearc]

Thanks for the PR!