Make the new line its own entry in the history buffer. (#4389)

* Make the new line its own entry in the history buffer.

Placing the new (empty) line in its own entry in the history buffer
changes functionality by fixing two issues:

 - when mHighlightHistory is false, it is annoying to clear the
   history after scrolling through it: after pressing up followed by
   down does not clear the line, and it's challenging to clear it.

 - when mAutoClearCommandLineAfterSend is false, if you go up in
   history, then clear that by starting to type, if you press up again
   you get the _second_ to last command you sent.

There are other ways you could fix these issues, but this method is
clean and will be convenient for allowing editing of history, which is
my next pull request.

* response to code review

src/TCommandLine.cpp

@@ -81,11 +81,7 @@ void TCommandLine::processNormalKey(QEvent* event)
     QPlainTextEdit::event(event);
     adjustHeight();
 
-    if (mpHost->mAutoClearCommandLineAfterSend) {
-        mHistoryBuffer = -1;
-    } else {
-        mHistoryBuffer = 0;
-    }
+    mHistoryBuffer = 0;
     if (mTabCompletionOld != toPlainText()) {
         mUserKeptOnTyping = true;
         mAutoCompletionCount = -1;
@@ -136,11 +132,7 @@ bool TCommandLine::event(QEvent* event)
                 mTabCompletionCount = -1;
                 mAutoCompletionCount = -1;
                 mTabCompletionTyped.clear();
-                if (mpHost->mAutoClearCommandLineAfterSend) {
-                    mHistoryBuffer = -1;
-                } else {
-                    mHistoryBuffer = 0;
-                }
+                mHistoryBuffer = 0;
                 mLastCompletion.clear();
                 break;
 
@@ -222,11 +214,7 @@ bool TCommandLine::event(QEvent* event)
         case Qt::Key_Backspace:
             if ((ke->modifiers() & (allModifiers & ~(Qt::ControlModifier|Qt::ShiftModifier))) == Qt::NoModifier) {
                 // Ignore state of <CTRL> and <SHIFT> keys
-                if (mpHost->mAutoClearCommandLineAfterSend) {
-                    mHistoryBuffer = -1;
-                } else {
-                    mHistoryBuffer = 0;
-                }
+                mHistoryBuffer = 0;
 
                 if (mTabCompletionTyped.size() >= 1) {
                     mTabCompletionTyped.chop(1);
@@ -249,11 +237,7 @@ bool TCommandLine::event(QEvent* event)
 
         case Qt::Key_Delete:
             if ((ke->modifiers() & allModifiers) == Qt::NoModifier) {
-                if (mpHost->mAutoClearCommandLineAfterSend) {
-                    mHistoryBuffer = -1;
-                } else {
-                    mHistoryBuffer = 0;
-                }
+                mHistoryBuffer = 0;
 
                 if (mTabCompletionTyped.size() >= 1) {
                     mTabCompletionTyped.chop(1);
@@ -405,11 +389,7 @@ bool TCommandLine::event(QEvent* event)
                 mTabCompletionCount = -1;
                 mAutoCompletionCount = -1;
                 setPalette(mRegularPalette);
-                if (mpHost->mAutoClearCommandLineAfterSend) {
-                    mHistoryBuffer = -1;
-                } else {
-                    mHistoryBuffer = 0;
-                }
+                mHistoryBuffer = 0;
                 ke->accept();
                 return true;
 
@@ -862,17 +842,24 @@ void TCommandLine::enterCommand(QKeyEvent* event)
     }
 
     if (!toPlainText().isEmpty()) {
-        mHistoryBuffer = 0;
+        if (mpHost->mAutoClearCommandLineAfterSend) {
+            mHistoryBuffer = 0;
+        } else {
+            mHistoryBuffer = 1;
+        }
         setPalette(mRegularPalette);
 
         mHistoryList.removeAll(toPlainText());
-        mHistoryList.push_front(toPlainText());
+        if (!mHistoryList.isEmpty()) {
+            mHistoryList[0] = toPlainText();
+        } else {
+            mHistoryList.push_front(toPlainText());
+        }
+        mHistoryList.push_front(QString());
     }
     if (mpHost->mAutoClearCommandLineAfterSend) {
-        mHistoryBuffer = -1;
         clear();
     } else {
-        mHistoryBuffer = 0;
         selectAll();
     }
     adjustHeight();
@@ -1006,9 +993,7 @@ void TCommandLine::historyMove(MoveDirection direction)
     }
     int shift = (direction == MOVE_UP ? 1 : -1);
     if ((textCursor().selectedText().size() == toPlainText().size()) || (toPlainText().size() == 0) || !mpHost->mHighlightHistory) {
-        if (toPlainText().size() != 0) {
-            mHistoryBuffer += shift;
-        }
+        mHistoryBuffer += shift;
         if (mHistoryBuffer >= mHistoryList.size()) {
             mHistoryBuffer = mHistoryList.size() - 1;
         }