feat(pack): support `textDocument/documentLink` in confirmation buffer

Problem: In `vim.pack.update()` confirmation buffer it might be useful
  to be able to use `gx` (open link at cursor) when cursor is on
  something like commit or tag.

Solution: Add `textDocument/documentLink` method support for the
  in-process LSP. This may be used by LSP clients and makes `gx`
  automatically work.

  The shortcoming is that this requires tracking how to construct a URL
  from source and commit/tag. Currently only GitHub hosted repositories
  are supported.

2 files changed, 86 insertions, 6 deletions

diff --git a/runtime/lua/vim/pack.lua b/runtime/lua/vim/pack.lua
index ae965c68df..c6dec53d32 100644
--- a/runtime/lua/vim/pack.lua
+++ b/runtime/lua/vim/pack.lua
@@ -1247,6 +1247,9 @@ end
 --- - |]]| and |[[| to navigate through plugin sections.
 ---
 --- Some features are provided via LSP:
+--- - 'textDocument/documentLink' - compute links for plugin paths, sources,
+---   commits, and tags. Use |gx| to open a link to an object at cursor.
+---   Only supports GitHub hosted repositories for commit and tag links.
 --- - 'textDocument/documentSymbol' (`gO` via |lsp-defaults| or |vim.lsp.buf.document_symbol()|) -
 ---   show structure of the buffer.
 --- - 'textDocument/hover' (`K` via |lsp-defaults| or |vim.lsp.buf.hover()|) - show more
diff --git a/runtime/lua/vim/pack/_lsp.lua b/runtime/lua/vim/pack/_lsp.lua
index a3342e9a30..869b0cf73f 100644
--- a/runtime/lua/vim/pack/_lsp.lua
+++ b/runtime/lua/vim/pack/_lsp.lua
@@ -1,7 +1,16 @@
 local M = {}
 
+local git_cmd = function(cmd, cwd, on_exit)
+  cmd = vim.list_extend({ 'git', '-c', 'gc.auto=0' }, cmd)
+  local env = vim.fn.environ() --- @type table<string,string>
+  env.GIT_DIR, env.GIT_WORK_TREE = nil, nil
+  local sys_opts = { cwd = cwd, text = true, env = env, clear_env = true }
+  vim.system(cmd, sys_opts, vim.schedule_wrap(on_exit))
+end
+
 local capabilities = {
   codeActionProvider = true,
+  documentLinkProvider = { resolveProvider = false },
   documentSymbolProvider = true,
   executeCommandProvider = { commands = { 'delete_plugin', 'update_plugin', 'skip_update_plugin' } },
   hoverProvider = true,
@@ -64,6 +73,79 @@ end
 
 --- @alias vim.pack.lsp.Position { line: integer, character: integer }
 --- @alias vim.pack.lsp.Range { start: vim.pack.lsp.Position, end: vim.pack.lsp.Position }
+--- @alias vim.pack.lsp.DocumentLink { range: vim.pack.lsp.Range, target: string }
+
+--- Finds a line range to be linked and computes the LSP style link
+--- @param line string Buffer line to find a link in
+--- @param pattern string Pattern matching link location and contents, like `'^Path: +()(.+)()$'`
+--- @param link_type "commit"|"path"|"src"|"tag"
+--- @param lnum number Line number in a buffer
+--- @param src string Plugin source
+--- @return vim.pack.lsp.DocumentLink? # A link structure according to the LSP specification
+local function match_link(line, pattern, link_type, lnum, src)
+  -- Only support GitHub for now. Maybe other forges in the future.
+  local is_github = vim.startswith(src, 'https://github.com/')
+  if (link_type == 'commit' or link_type == 'tag') and not is_github then
+    return nil
+  end
+
+  --- @type number?, string?, number?
+  local from, match, to = line:match(pattern)
+  if not (from and match and to) then
+    return
+  end
+
+  -- Convert to UTF index used in LSP positions
+  from = vim.str_utfindex(line, 'utf-16', from - 1, false)
+  to = vim.str_utfindex(line, 'utf-16', to - 2, false)
+
+  -- Reference:
+  -- - https://github.com/neovim/nvim-lspconfig/commit/e146efa
+  -- - https://github.com/neovim/nvim-lspconfig/commit/e146efacbafed3789ac568abcc5a981c5decaa58
+  -- - https://github.com/neovim/nvim-lspconfig/releases/tag/v2.8.0
+  local target = match
+  if link_type == 'commit' or link_type == 'tag' then
+    local src_noslash = src:gsub('/+$', '')
+    local middle = link_type == 'commit' and 'commit' or 'releases/tag'
+    target = ('%s/%s/%s'):format(src_noslash, middle, match)
+  elseif link_type == 'path' then
+    target = vim.uri_from_fname(match)
+  end
+
+  return {
+    range = {
+      start = { line = lnum - 1, character = from },
+      ['end'] = { line = lnum - 1, character = to },
+    },
+    target = target,
+  }
+end
+
+--- @param params { textDocument: { uri: string } }
+--- @param callback function
+methods['textDocument/documentLink'] = function(params, callback)
+  local bufnr = get_confirm_bufnr(params.textDocument.uri)
+  if bufnr == nil then
+    return callback(nil, {})
+  end
+
+  --- @type vim.pack.lsp.DocumentLink[]
+  local links = {}
+  local cur_src = ''
+  local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+  for i, l in ipairs(lines) do
+    cur_src = l:match('^Source: +(.+)$') or cur_src
+
+    links[#links + 1] = match_link(l, '^Path: +()(.+)()$', 'path', i, cur_src)
+    links[#links + 1] = match_link(l, '^Source: +()(.+)()$', 'src', i, cur_src)
+    links[#links + 1] = match_link(l, '^Revision[^:]*: +()(%S+)()', 'commit', i, cur_src)
+    -- NOTE: Assume that short revision works in the link
+    links[#links + 1] = match_link(l, '^[><] ()(%S+)()', 'commit', i, cur_src)
+    links[#links + 1] = match_link(l, '^• ()(.+)()$', 'tag', i, cur_src)
+  end
+
+  return callback(nil, links)
+end
 
 --- @param params { textDocument: { uri: string } }
 --- @param callback function
@@ -211,18 +293,13 @@ methods['textDocument/hover'] = function(params, callback)
     return
   end
 
-  local cmd = { 'git', 'show', '--no-color', commit or tag }
   --- @param sys_out vim.SystemCompleted
   local on_exit = function(sys_out)
     local markdown = '```diff\n' .. sys_out.stdout .. '\n```'
     local res = { contents = { kind = vim.lsp.protocol.MarkupKind.Markdown, value = markdown } }
     callback(nil, res)
   end
-
-  -- temporarily clear GIT env vars
-  local env = vim.fn.environ() --- @type table<string,string>
-  env.GIT_DIR, env.GIT_WORK_TREE = nil, nil
-  vim.system(cmd, { cwd = path, env = env, clear_env = true }, vim.schedule_wrap(on_exit))
+  git_cmd({ 'show', '--no-color', commit or tag }, path, on_exit)
 end
 
 local dispatchers = {}