FakeVim: Merge comments when joining lines with 'J'

This is the default behavior in vim as well

Change-Id: Ia4d56e3cfc7f91fc353078daefaabeada9a86bed
Reviewed-by: hjk <hjk@qt.io>

doc/qtcreator/src/editors/creator-only/creator-fakevim.qdoc

@@ -108,6 +108,8 @@
         \li \c :undo, \c :redo
         \li \c :normal
         \li \c :<, \c :>
+        \li \c{set formatoptions=}, see \c{:h fo-table} in the Vim documentation.
+            Currently supported letters: \c fo-j
     \endlist
 
     \section2 Plugin Emulation

src/plugins/fakevim/fakevim_test.cpp

@@ -4071,6 +4071,17 @@ void FakeVimPlugin::test_vim_command_J()
     KEYS("3J", lmid(0, 5) + " " + lmid(5, 1) + " " + lmid(6, 1).mid(4) + "| " + lmid(7));
     KEYS("uu", lmid(0, 4) + "\nint |main(int argc, char *argv[])\n" + lmid(5));
     COMMAND("redo", lmid(0, 4) + "\nint |main(int argc, char *argv[]) " + lmid(5));
+
+    // Joining comments
+    data.doCommand("set formatoptions=f");
+    data.setText("// abc" N "// def");
+    KEYS("J", "// abc def");
+
+    data.setText("/*" N X "* abc" N "* def" N "*/");
+    KEYS("J", "/*" N "* abc def" N "*/");
+
+    data.setText("# abc" N "# def");
+    KEYS("J", "# abc def");
 }
 
 void FakeVimPlugin::test_vim_command_put_at_eol()

src/plugins/fakevim/fakevimactions.cpp

@@ -113,6 +113,7 @@ FakeVimSettings::FakeVimSettings()
     createAction(ConfigBackspace,      QString("indent,eol,start"), "ConfigBackspace", "bs");
     createAction(ConfigIsKeyword,      QString("@,48-57,_,192-255,a-z,A-Z"), "IsKeyword", "isk");
     createAction(ConfigClipboard,      QString(), "Clipboard", "cb");
+    createAction(ConfigFormatOptions,  QString(), "formatoptions", "fo");
 
     // Emulated plugins
     createAction(ConfigEmulateVimCommentary, false, "commentary");

src/plugins/fakevim/fakevimactions.h

@@ -107,6 +107,7 @@ enum FakeVimSettingsCode
     ConfigShowCmd,
     ConfigScrollOff,
     ConfigRelativeNumber,
+    ConfigFormatOptions,
 
     // Plugin emulation
     ConfigEmulateVimCommentary,

src/plugins/fakevim/fakevimhandler.cpp

@@ -7615,6 +7615,13 @@ void FakeVimHandler::Private::joinLines(int count, bool preserveSpace)
 {
     int pos = position();
     const int blockNumber = m_cursor.blockNumber();
+
+    const QString currentLine = lineContents(blockNumber + 1);
+    const bool startingLineIsComment
+            = currentLine.contains(QRegularExpression("^\\s*\\/\\/")) // Cpp-style
+              || currentLine.contains(QRegularExpression("^\\s*\\/?\\*")) // C-style
+              || currentLine.contains(QRegularExpression("^\\s*#")); // Python/Shell-style
+
     for (int i = qMax(count - 2, 0); i >= 0 && blockNumber < document()->blockCount(); --i) {
         moveBehindEndOfLine();
         pos = position();
@@ -7625,6 +7632,18 @@ void FakeVimHandler::Private::joinLines(int count, bool preserveSpace)
         } else {
             while (characterAtCursor() == ' ' || characterAtCursor() == '\t')
                 moveRight();
+
+            // If the line we started from is a comment, remove the comment string from the next line
+            if (startingLineIsComment && config(ConfigFormatOptions).toString().contains('f')) {
+                if (characterAtCursor() == '/' && characterAt(position() + 1) == '/')
+                    moveRight(2);
+                else if (characterAtCursor() == '*' || characterAtCursor() == '#')
+                    moveRight(1);
+
+                if (characterAtCursor() == ' ')
+                    moveRight();
+            }
+
             m_cursor.insertText(QString(' '));
         }
     }