TextEditor: Fix backtab behavior of multi line selection

Check available spaces infront of current column on each line before
removing the text.

Fixes: QTCREATORBUG-16970
Change-Id: Ie6560ce706297f6818a84ca863abc9b106728890
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/textdocument.cpp

@@ -169,35 +169,82 @@ QTextCursor TextDocumentPrivate::indentOrUnindent(const QTextCursor &textCursor,
         cursor.removeSelectedText();
     } else {
         // Indent or unindent at cursor position
+        int maxTargetColumn = -1;
+
+        class BlockIndenter
+        {
+        public:
+            BlockIndenter(const QTextBlock &_block,
+                          const int column,
+                          const TabSettings &_tabSettings)
+                : block(_block)
+                , text(block.text())
+                , tabSettings(_tabSettings)
+            {
+                indentPosition = tabSettings.positionAtColumn(text, column, nullptr, true);
+                spaces = tabSettings.spacesLeftFromPosition(text, indentPosition);
+            }
+
+            void indent(const int targetColumn) const
+            {
+                const int startColumn = tabSettings.columnAt(text, indentPosition - spaces);
+                QTextCursor cursor(block);
+                cursor.setPosition(block.position() + indentPosition);
+                cursor.setPosition(block.position() + indentPosition - spaces, QTextCursor::KeepAnchor);
+                cursor.removeSelectedText();
+                cursor.insertText(tabSettings.indentationString(startColumn, targetColumn, 0, block));
+            }
+
+            int targetColumn(bool doIndent) const
+            {
+                const int optimumTargetColumn
+                    = tabSettings.indentedColumn(tabSettings.columnAt(block.text(), indentPosition),
+                                                 doIndent);
+                const int minimumTargetColumn = tabSettings.columnAt(text, indentPosition - spaces);
+                return std::max(optimumTargetColumn, minimumTargetColumn);
+            }
+
+            const QTextBlock &textBlock() { return block; }
+
+        private:
+            QTextBlock block;
+            const QString text;
+            int indentPosition;
+            int spaces;
+            const TabSettings &tabSettings;
+        };
+
+        std::vector<BlockIndenter> blocks;
+
         for (QTextBlock block = startBlock; block != endBlock; block = block.next()) {
             QString text = block.text();
 
-            int blockColumn = tabSettings.columnAt(text, text.size());
+            const int blockColumn = tabSettings.columnAt(text, text.size());
             if (blockColumn < column) {
                 cursor.setPosition(block.position() + text.size());
                 cursor.insertText(tabSettings.indentationString(blockColumn, column, 0, block));
                 text = block.text();
             }
 
-            int indentPosition = tabSettings.positionAtColumn(text, column, nullptr, true);
+            blocks.emplace_back(BlockIndenter(block, column, tabSettings));
-            int spaces = tabSettings.spacesLeftFromPosition(text, indentPosition);
+            maxTargetColumn = std::max(maxTargetColumn, blocks.back().targetColumn(doIndent));
-            int startColumn = tabSettings.columnAt(text, indentPosition - spaces);
-            int targetColumn = tabSettings.indentedColumn(
-                        tabSettings.columnAt(text, indentPosition), doIndent);
-            cursor.setPosition(block.position() + indentPosition);
-            cursor.setPosition(block.position() + indentPosition - spaces, QTextCursor::KeepAnchor);
-            cursor.removeSelectedText();
-            cursor.insertText(tabSettings.indentationString(startColumn, targetColumn, 0, block));
         }
+        for (const BlockIndenter &blockIndenter : blocks)
+            blockIndenter.indent(maxTargetColumn);
+
         // Preserve initial anchor of block selection
         if (blockSelection) {
-            end = cursor.position();
+            if (offset)
-            if (offset) {
+                *offset = maxTargetColumn - column;
-                *offset = tabSettings.columnAt(cursor.block().text(), cursor.positionInBlock())
+            startBlock = pos < anchor ? blocks.front().textBlock() : blocks.back().textBlock();
-                    - column;
+            start = startBlock.position()
-            }
+                    + tabSettings.positionAtColumn(startBlock.text(), maxTargetColumn);
-            cursor.setPosition(start);
+            endBlock = pos > anchor ? blocks.front().textBlock() : blocks.back().textBlock();
-            cursor.setPosition(end, QTextCursor::KeepAnchor);
+            end = endBlock.position()
+                  + tabSettings.positionAtColumn(endBlock.text(), maxTargetColumn);
+
+            cursor.setPosition(end);
+            cursor.setPosition(start, QTextCursor::KeepAnchor);
         }
     }