fix(util): add and use forge link computation

Problem: There are many Git forges each with a different way of
  constructing permanent links to like commits and tags.

Solution: Add a private utility function that computes these special
  links on the best effort basis.

runtime/lua/vim/_core/util.lua

@@ -129,4 +129,41 @@ function M.term_exitcode()
   return ''
 end
 
+--- Compute a link to a target on a forge host
+--- @param repo string URL of repo, usually "https://<domain>/<user>/<name>"
+--- @param target string Identifier of a target, like commit hash or tag name
+--- @param target_type "commit"|"tag"
+--- @return string? # Example: <repo>/releases/tag/<target>
+function M.get_forge_url(repo, target, target_type)
+  -- The structure <host>/<middle>/<target> works for most forges. Like:
+  -- - https://github.com/neovim/nvim-lspconfig/commit/e146efa
+  -- - https://github.com/neovim/nvim-lspconfig/releases/tag/v2.8.0
+  local ref_middles = {
+    { pattern = '^https://github%.com/', commit = 'commit', tag = 'releases/tag' },
+    { pattern = '^https://gitlab%.com/', commit = '-/commit', tag = '-/tags' },
+    { pattern = '^https://git%.sr%.ht/', commit = 'commit', tag = 'refs' },
+    { pattern = '^https://tangled%.org/', commit = 'commit', tag = 'tags' },
+    { pattern = '^https://bitbucket%.org/', commit = 'commits', tag = 'src' },
+
+    -- Fall back to Forgejo style since there is no fixed host
+    { pattern = '^https://', commit = 'commit', tag = 'src/tag' },
+  }
+
+  local middle = ''
+  for _, mid in ipairs(ref_middles) do
+    if repo:match(mid.pattern) then
+      middle = mid[target_type]
+      if middle ~= '' then
+        break
+      end
+    end
+  end
+
+  if middle == '' then
+    return nil
+  end
+  repo = repo:gsub('/+$', '')
+  return ('%s/%s/%s'):format(repo, middle, target)
+end
+
 return M

runtime/lua/vim/pack.lua

@@ -1248,8 +1248,8 @@ end
 ---
 --- 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.
+---   commits, and tags. Makes a best effort educated guess about a link structure.
+---   Use |gx| to open a link to an object at cursor.
 --- - '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

runtime/lua/vim/pack/_lsp.lua

@@ -83,42 +83,32 @@ end
 --- @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
+    return nil
   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
+  --- @type string?
   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)
+    ---@diagnostic disable-next-line: param-type-mismatch
+    target = require('vim._core.util').get_forge_url(src, match, link_type)
   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,
-  }
+  if target == nil then
+    return nil
+  end
+
+  local start = { line = lnum - 1, character = from }
+  local end_ = { line = lnum - 1, character = to }
+  return { range = { start = start, ['end'] = end_ }, target = target }
 end
 
 --- @param params { textDocument: { uri: string } }