From 62d3a2110df4999b39e25026ad85628551b5e80c Mon Sep 17 00:00:00 2001
From: Yochem van Rosmalen <git@yochem.nl>
Date: Mon, 13 Oct 2025 00:08:18 +0200
Subject: [PATCH] fix(help): wrong tag url in third-party help docs #36115

fix(help): only set url for nvim-owned tags

Problem:
1. gx on |nonexistingtag| opens
https://neovim.io/doc/user/helptag.html?nonexistingtag.
2. b:undo_ftplugin doesn't remove url extmarks.

Solution:
1. Check if the tag is defined in a help file in $VIMRUNTIME.
2. Solution: clear namespace for buffer in b:undo_ftplugin.
---
 runtime/ftplugin/help.lua       | 24 ++++++++++++++++++------
 test/functional/lua/ui_spec.lua |  9 +++++++++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/runtime/ftplugin/help.lua b/runtime/ftplugin/help.lua
index 34a477ad62..0379bd0c97 100644
--- a/runtime/ftplugin/help.lua
+++ b/runtime/ftplugin/help.lua
@@ -115,8 +115,8 @@ do
   end, { buffer = true })
 end
 
+local url_ns = vim.api.nvim_create_namespace('nvim.help.urls')
 do
-  local ns = vim.api.nvim_create_namespace('nvim.help.urls')
   local base = 'https://neovim.io/doc/user/helptag.html?tag='
   local query = vim.treesitter.query.parse(
     'vimdoc',
@@ -129,17 +129,28 @@ do
   ]]
   )
 
+  local function is_nvim_tag(tag)
+    local tagsfile = vim.fs.joinpath(vim.env.VIMRUNTIME, 'doc', 'tags')
+    local candidates = vim.fn.taglist('^' .. tag .. '$', tagsfile)
+    if #candidates == 0 then
+      return false
+    end
+    return vim.fs.relpath(vim.env.VIMRUNTIME, candidates[1].filename) ~= nil
+  end
+
   for _, match, _ in query:iter_matches(root, 0, 0, -1) do
     for id, nodes in pairs(match) do
       if query.captures[id] == 'helplink' then
         for _, node in ipairs(nodes) do
           local start_line, start_col, end_line, end_col = node:range()
           local tag = vim.treesitter.get_node_text(node, 0)
-          vim.api.nvim_buf_set_extmark(0, ns, start_line, start_col, {
-            end_line = end_line,
-            end_col = end_col,
-            url = base .. vim.uri_encode(tag),
-          })
+          if is_nvim_tag(tag) then
+            vim.api.nvim_buf_set_extmark(0, url_ns, start_line, start_col, {
+              end_line = end_line,
+              end_col = end_col,
+              url = base .. vim.uri_encode(tag),
+            })
+          end
         end
       end
     end
@@ -149,4 +160,5 @@ end
 vim.b.undo_ftplugin = (vim.b.undo_ftplugin or '')
   .. '\n sil! exe "nunmap <buffer> gO" | sil! exe "nunmap <buffer> g=="'
   .. '\n sil! exe "nunmap <buffer> ]]" | sil! exe "nunmap <buffer> [["'
+  .. ('\n call v:lua.vim.api.nvim_buf_clear_namespace(0, %d, 0, -1)'):format(url_ns)
 vim.b.undo_ftplugin = vim.b.undo_ftplugin .. ' | call v:lua.vim.treesitter.stop()'
diff --git a/test/functional/lua/ui_spec.lua b/test/functional/lua/ui_spec.lua
index 572df3ee26..5fe4257a3d 100644
--- a/test/functional/lua/ui_spec.lua
+++ b/test/functional/lua/ui_spec.lua
@@ -202,6 +202,15 @@ describe('vim.ui', function()
       local tagname =
         n.api.nvim_buf_get_text(0, tag[2], tag[3], tag[4].end_row, tag[4].end_col, {})[1]
       eq(vim.uri_encode(tagname), param)
+
+      -- non-nvim tags are ignored
+      local buf = n.api.nvim_create_buf(false, false)
+      n.api.nvim_buf_set_lines(buf, 0, 0, false, {
+        '|nonexisting|',
+      })
+      n.api.nvim_set_option_value('filetype', 'help', { buf = buf, scope = 'local' })
+      local tags = n.api.nvim_buf_get_extmarks(buf, link_ns, 0, -1, {})
+      eq(#tags, 0)
     end)
   end)
 end)