fix(diagnostic): allow virtual_{lines,text} cursor exclusivity #33517

Problem:
virtual_text diagnostics are great when skimming a file, and
virtual_lines are great when "zooming in" on a particular problem.
Having both enabled results in duplicate diagnostics on-screen.

Solution:
This PR expands the behavior of `current_line` for virtual_text and
virtual_lines by making `virtual_text.current_line = false` distinct
from `nil`.  If you set:

    vim.diagnostic.config({
      virtual_text = { current_line = false },
      virtual_lines = { current_line = true },
    })

With this configuration, virtual_text will be used to display
diagnostics until the cursor reaches the same line, at which point they
will be hidden and virtual_lines will take its place.

runtime/doc/diagnostic.txt

@@ -624,8 +624,12 @@ Lua module: vim.diagnostic                                    *diagnostic-api*
       • {severity}?           (`vim.diagnostic.SeverityFilter`) Only show
                               virtual text for diagnostics matching the given
                               severity |diagnostic-severity|
-      • {current_line}?       (`boolean`) Only show diagnostics for the
-                              current line. (default `false`)
+      • {current_line}?       (`boolean`) Show or hide diagnostics based on
+                              the current cursor line. If `true`, only
+                              diagnostics on the current cursor line are
+                              shown. If `false`, all diagnostics are shown
+                              except on the current cursor line. If `nil`, all
+                              diagnostics are shown. (default `nil`)
       • {source}?             (`boolean|"if_many"`) Include the diagnostic
                               source in virtual text. Use `'if_many'` to only
                               show sources if there is more than one

runtime/lua/vim/diagnostic.lua

@@ -190,8 +190,10 @@ end
 --- severity |diagnostic-severity|
 --- @field severity? vim.diagnostic.SeverityFilter
 ---
---- Only show diagnostics for the current line.
---- (default `false`)
+--- Show or hide diagnostics based on the current cursor line.  If `true`, only diagnostics on the
+--- current cursor line are shown.  If `false`, all diagnostics are shown except on the current
+--- cursor line.  If `nil`, all diagnostics are shown.
+--- (default `nil`)
 --- @field current_line? boolean
 ---
 --- Include the diagnostic source in virtual text. Use `'if_many'` to only
@@ -1562,12 +1564,15 @@ M.handlers.underline = {
 --- @param diagnostics table<integer, vim.Diagnostic[]>
 --- @param opts vim.diagnostic.Opts.VirtualText
 local function render_virtual_text(namespace, bufnr, diagnostics, opts)
+  local lnum = api.nvim_win_get_cursor(0)[1] - 1
   api.nvim_buf_clear_namespace(bufnr, namespace, 0, -1)
 
   for line, line_diagnostics in pairs(diagnostics) do
     local virt_texts = M._get_virt_text_chunks(line_diagnostics, opts)
+    local skip = (opts.current_line == true and line ~= lnum)
+      or (opts.current_line == false and line == lnum)
 
-    if virt_texts then
+    if virt_texts and not skip then
       api.nvim_buf_set_extmark(bufnr, namespace, line, 0, {
         hl_mode = opts.hl_mode or 'combine',
         virt_text = virt_texts,
@@ -1621,32 +1626,18 @@ M.handlers.virtual_text = {
 
     local line_diagnostics = diagnostic_lines(diagnostics)
 
-    if opts.virtual_text.current_line == true then
+    if opts.virtual_text.current_line ~= nil then
       api.nvim_create_autocmd('CursorMoved', {
         buffer = bufnr,
         group = ns.user_data.virt_text_augroup,
         callback = function()
-          local lnum = api.nvim_win_get_cursor(0)[1] - 1
-          render_virtual_text(
-            ns.user_data.virt_text_ns,
-            bufnr,
-            { [lnum] = diagnostics_at_cursor(line_diagnostics) },
-            opts.virtual_text
-          )
+          render_virtual_text(ns.user_data.virt_text_ns, bufnr, line_diagnostics, opts.virtual_text)
         end,
       })
-      -- Also show diagnostics for the current line before the first CursorMoved event.
-      local lnum = api.nvim_win_get_cursor(0)[1] - 1
-      render_virtual_text(
-        ns.user_data.virt_text_ns,
-        bufnr,
-        { [lnum] = diagnostics_at_cursor(line_diagnostics) },
-        opts.virtual_text
-      )
-    else
-      render_virtual_text(ns.user_data.virt_text_ns, bufnr, line_diagnostics, opts.virtual_text)
     end
 
+    render_virtual_text(ns.user_data.virt_text_ns, bufnr, line_diagnostics, opts.virtual_text)
+
     save_extmarks(ns.user_data.virt_text_ns, bufnr)
   end,
   hide = function(namespace, bufnr)

test/functional/lua/diagnostic_spec.lua

@@ -2144,6 +2144,25 @@ describe('vim.diagnostic', function()
       eq(1, #result)
       eq(' Error here!', result[1][4].virt_text[3][1])
     end)
+
+    it('can hide virtual_text for the current line', function()
+      local result = exec_lua(function()
+        vim.api.nvim_win_set_cursor(0, { 1, 0 })
+
+        vim.diagnostic.config({ virtual_text = { current_line = false } })
+
+        vim.diagnostic.set(_G.diagnostic_ns, _G.diagnostic_bufnr, {
+          _G.make_error('Error here!', 0, 0, 0, 0, 'foo_server'),
+          _G.make_error('Another error there!', 1, 0, 1, 0, 'foo_server'),
+        })
+
+        local extmarks = _G.get_virt_text_extmarks(_G.diagnostic_ns)
+        return extmarks
+      end)
+
+      eq(1, #result)
+      eq(' Another error there!', result[1][4].virt_text[3][1])
+    end)
   end)
 
   describe('handlers.virtual_lines', function()