feat(defaults): "Show Diagnostics" in mouse popupmenu #32122

Problem:
No obvious way to see diagnostics without configuring it first.
Solution:
Add `Show Diagnostics`, `Show All Diagnostics` and `Configure
Diagnostics` buttons to the context menu.

runtime/doc/news.txt

@@ -221,6 +221,8 @@ DEFAULTS
     on a URL.
   • Mouse |popup-menu| includes a "Go to definition" item when LSP is active
     in the buffer.
+  • Mouse |popup-menu| includes "Show Diagnostics", "Show All Diagnostics" and
+    "Configure Diagnostics" items when there are diagnostics in the buffer.
   • |]d-default| and |[d-default| accept a count.
   • |[D-default| and |]D-default| jump to the first and last diagnostic in the
     current buffer, respectively.

runtime/lua/vim/_defaults.lua

@@ -383,9 +383,12 @@ end
 do
   --- Right click popup menu
   vim.cmd([[
-    anoremenu PopUp.Go\ to\ definition      <Cmd>lua vim.lsp.buf.definition()<CR>
     amenu     PopUp.Open\ in\ web\ browser  gx
     anoremenu PopUp.Inspect                 <Cmd>Inspect<CR>
+    anoremenu PopUp.Go\ to\ definition      <Cmd>lua vim.lsp.buf.definition()<CR>
+    anoremenu PopUp.Show\ Diagnostics       <Cmd>lua vim.diagnostic.open_float()<CR>
+    anoremenu PopUp.Show\ All\ Diagnostics  <Cmd>lua vim.diagnostic.setqflist()<CR>
+    anoremenu PopUp.Configure\ Diagnostics  <Cmd>help vim.diagnostic.config()<CR>
     anoremenu PopUp.-1-                     <Nop>
     vnoremenu PopUp.Cut                     "+x
     vnoremenu PopUp.Copy                    "+y
@@ -403,6 +406,9 @@ do
     vim.cmd([[
       amenu disable PopUp.Go\ to\ definition
       amenu disable PopUp.Open\ in\ web\ browser
+      amenu disable PopUp.Show\ Diagnostics
+      amenu disable PopUp.Show\ All\ Diagnostics
+      amenu disable PopUp.Configure\ Diagnostics
     ]])
 
     if ctx == 'url' then
@@ -410,6 +416,20 @@ do
     elseif ctx == 'lsp' then
       vim.cmd([[anoremenu enable PopUp.Go\ to\ definition]])
     end
+
+    local lnum = vim.fn.getcurpos()[2] - 1 ---@type integer
+    local diagnostic = false
+    if next(vim.diagnostic.get(0, { lnum = lnum })) ~= nil then
+      diagnostic = true
+      vim.cmd([[anoremenu enable PopUp.Show\ Diagnostics]])
+    end
+
+    if diagnostic or next(vim.diagnostic.count(0)) ~= nil then
+      vim.cmd([[
+        anoremenu enable PopUp.Show\ All\ Diagnostics
+        anoremenu enable PopUp.Configure\ Diagnostics
+      ]])
+    end
   end
 
   local nvim_popupmenu_augroup = vim.api.nvim_create_augroup('nvim.popupmenu', {})