fix(Message::appendText): QRegularExpression whitespace bug

Unlike QRegExp, when a QRegularExpression starts with \s,
it may match whitespace *including newlines*.

So when looking for the start of a section, we might match
"\n\n == January 2025 ==" instead of " == January 2025 =="

Then the logic that tries to skip past the header, would instead
skip past the first \n, which is still _before_ the header.
Then we would think the target header is the start of the next section,
and we would end up inserting a message just before the section
it was intended to be appended to.

QRegularExpression is available since Qt 5.0 and is recommended.
Let's get rid of the old QRegExp and fix the QRegularExpression usage.

src/huggle_core/message.cpp

@@ -22,6 +22,7 @@
 #include "wikisite.hpp"
 #include "wikiutil.hpp"
 #include "wikiuser.hpp"
+#include <QRegularExpression>
 #include <QUrl>
 
 using namespace Huggle;
@@ -205,7 +206,7 @@ void Message::processNextStep()
                 this->Error = MessageError_ArticleExist;
             } else
             {
-                this->Fail(_l("error-unknown-code",ec));
+                this->Fail(_l("error-unknown-code", ec));
                 this->Error = MessageError_Unknown;
             }
             return;
@@ -319,17 +320,15 @@ void Message::processSend()
         if (this->SectionKeep)
         {
             this->Text = this->appendText(this->Text, this->originalUnmodifiedPageText, this->Title);
-        } else
-        {
+        } else {
             // original page needs to be included in new value
             if (!this->originalUnmodifiedPageText.isEmpty())
                 this->Text = this->originalUnmodifiedPageText + "\n\n" + this->Text;
         }
         this->query->Parameters = "title=" + QUrl::toPercentEncoding(User->GetTalk()) + "&summary=" + QUrl::toPercentEncoding(summary)
                 + "&text=" + QUrl::toPercentEncoding(this->Text) + parameters
                 + "&token=" + QUrl::toPercentEncoding(this->User->GetSite()->GetProjectConfig()->Token_Csrf);
-    }else
-    {
+    } else {
         this->query->Parameters = "title=" + QUrl::toPercentEncoding(User->GetTalk()) + "&section=new&sectiontitle="
                 + QUrl::toPercentEncoding(this->Title) + "&summary=" + QUrl::toPercentEncoding(summary)
                 + "&text=" + QUrl::toPercentEncoding(this->Text) + parameters + "&token="
@@ -357,8 +356,7 @@ void Message::processTalkPageRetrieval()
         this->originalUnmodifiedPageText = page->Value;
         this->previousTalkPageRetrieved = true;
         return;
-    } else
-    {
+    } else {
         if (!missing)
         {
             Huggle::Syslog::HuggleLogs->DebugLog(this->query->Result->Data);
@@ -375,12 +373,10 @@ QString Message::appendText(QString text, QString original_text, QString section
         // there is nothing to insert this to
         return original_text += "\n\n" + text + "\n\n";
     }
-#ifdef QT6_BUILD
+
     QRegularExpression regex("\\s*==\\s*" + QRegularExpression::escape(section_name) + "\\s*==");
-#else
-    QRegExp regex("\\s*==\\s*" + QRegExp::escape(section_name) + "\\s*==");
-#endif
-    if (!original_text.contains(regex))
+    QRegularExpressionMatch regex_match;
+    if (!original_text.contains(regex, &regex_match))
     {
         // there is no section to append to
         if (!original_text.isEmpty())
@@ -390,32 +386,21 @@ QString Message::appendText(QString text, QString original_text, QString section
         original_text += "== " + section_name + " ==\n\n" + text;
         return original_text;
     }
-#ifdef QT6_BUILD
-    QRegularExpression header("\\s*==.*==\\s*");
-#else
-    QRegExp header("\\s*==.*==\\s*");
-#endif
-    int start_of_desired_section = original_text.lastIndexOf(regex);
+
     // we need to check if there is any other section after this one
+    int start_of_desired_section = original_text.lastIndexOf(regex) + regex_match.capturedView().length();
     QString section = original_text.mid(start_of_desired_section);
-    if (section.contains("\n"))
-    {
-        // cut the header text
-        int Diff = section.indexOf("\n") + 1;
-        start_of_desired_section += Diff;
-        section = section.mid(Diff);
-    }
+    QRegularExpression next_header("\\s*==.*==\\s*");
     int start_point = start_of_desired_section;
-    if (section.contains(header))
+    if (section.contains(next_header))
     {
         // yes there is some other section, so we need to know where it is, so that we know where current
         // section ends (we want to append text to bottom of current section)
-        start_point += section.indexOf(header);
+        start_point += section.indexOf(next_header);
     } else
     {
         start_point += section.length();
     }
     // write the text exactly after the start point, but leave some space after it
-    original_text = original_text.insert(start_point, "\n\n" + text + "\n");
-    return original_text;
+    return original_text.insert(start_point, "\n\n" + text + "\n");
 }