From f742ecbabd8e9408ad27dd7f39d2a30a1e641ecf Mon Sep 17 00:00:00 2001
From: Enrico Maria De Angelis <enricomaria.dean6elis@gmail.com>
Date: Sat, 22 Jul 2023 07:24:53 +0100
Subject: [PATCH] Address #4165: provide a highlight group for the detailed
 diagnostic popup

This seems to work, but I have a few questions

  - What tests should I look at to understand how to write one for this
    change?
  - Are you happy with the name `YcmErrorPopup`?
  - What should I set as `'priority'`, `'combine'`, `'override'`?
---
 README.md                   | 4 ++++
 autoload/youcompleteme.vim  | 4 ++++
 doc/youcompleteme.txt       | 4 ++++
 python/ycm/youcompleteme.py | 2 +-
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index b4bd2b11de..9d60804fd8 100644
--- a/README.md
+++ b/README.md
@@ -1770,6 +1770,10 @@ You can also style the line that has the warning/error with these groups:
 - `YcmWarningLine`, which falls back to group `SyntasticWarningLine` if it
   exists
 
+Finally, you can also style the popup for the detailed diagnostics (it is shown
+if `g:ycm_show_detailed_diag_in_popup` is set) using the group `YcmErrorPopup`,
+which falls back to `ErrorMsg`.
+
 Note that the line highlighting groups only work when the
 [`g:ycm_enable_diagnostic_signs`](#the-gycm_enable_diagnostic_signs-option)
 option is set. If you want highlighted lines but no signs in the Vim gutter,
diff --git a/autoload/youcompleteme.vim b/autoload/youcompleteme.vim
index f525316dcb..aacbf6e95c 100644
--- a/autoload/youcompleteme.vim
+++ b/autoload/youcompleteme.vim
@@ -512,6 +512,10 @@ function! s:SetUpSyntaxHighlighting()
           \ 'combine': 0,
           \ 'override': 1 } )
   endif
+
+  if !hlexists( 'YcmErrorPopup' )
+    highlight default link YcmErrorPopup ErrorMsg
+  endif
 endfunction
 
 
diff --git a/doc/youcompleteme.txt b/doc/youcompleteme.txt
index decfa99ae4..c16c100e2c 100644
--- a/doc/youcompleteme.txt
+++ b/doc/youcompleteme.txt
@@ -2017,6 +2017,10 @@ You can also style the line that has the warning/error with these groups:
 - 'YcmWarningLine', which falls back to group 'SyntasticWarningLine' if it
   exists
 
+Finally, you can also style the popup for the detailed diagnostics (it is shown
+if |g:ycm_show_detailed_diag_in_popup| is set) using the group 'YcmErrorPopup',
+which falls back to |ErrorMsg|.
+
 Note that the line highlighting groups only work when the
 |g:ycm_enable_diagnostic_signs| option is set. If you want highlighted lines
 but no signs in the Vim gutter, set the 'signcolumn' option to 'no' in your
diff --git a/python/ycm/youcompleteme.py b/python/ycm/youcompleteme.py
index 5d9ac6cd15..d7eb18862b 100644
--- a/python/ycm/youcompleteme.py
+++ b/python/ycm/youcompleteme.py
@@ -849,7 +849,7 @@ def ShowDetailedDiagnostic( self, message_in_popup ):
           'maxwidth': available_columns,
           'close': 'click',
           'fixed': 0,
-          'highlight': 'ErrorMsg',
+          'highlight': 'YcmErrorPopup',
           'border': [ 1, 1, 1, 1 ],
           # Close when moving cursor
           'moved': 'expr',