TextEditor: fix finding whole words

'_' was handled as a word separator, in contrast the global search did
not. So the user received different results when using find toolbar or
the advanced search while searching with the same option and pattern.

Fixes: QTCREATORBUG-10276
Change-Id: Ie07303fbaa35475bb98bdb813358169474c3ba1d
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/texteditor/texteditor.cpp

@@ -4154,10 +4154,17 @@ void TextEditorWidgetPrivate::highlightSearchResults(const QTextBlock &block, co
         l = match.capturedLength();
         if (l == 0)
             break;
-        if ((m_findFlags & FindWholeWords)
-            && ((idx && text.at(idx-1).isLetterOrNumber())
-                || (idx + l < text.length() && text.at(idx + l).isLetterOrNumber())))
-            continue;
+        if (m_findFlags & FindWholeWords) {
+            auto posAtWordSeparator = [](const QString &text, int idx) {
+                if (idx < 0 || idx >= text.length())
+                    return false;
+                const QChar c = text.at(idx);
+                return !c.isLetterOrNumber() && c != QLatin1Char('_');
+            };
+            if (!posAtWordSeparator(text, idx - 1) || !posAtWordSeparator(text, idx + l))
+                continue;
+        }
+
 
         const int start = blockPosition + idx;
         const int end = start + l;