ClangFormat: Fix iteration through text blocks

Document might be edited between consecutive currentBlock.next()
calls which is unsafe. Let's instead operate with block numbers.

Fixes: QTCREATORBUG-21521
Change-Id: I6863a77a32f5583269e1c796f38afb45cc9e7f77
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangformat/clangformatindenter.cpp

@@ -69,6 +69,13 @@ void adjustFormatStyleForLineBreak(format::FormatStyle &style)
     style.SortUsingDeclarations = false;
 }
 
+StringRef clearExtraNewline(StringRef text)
+{
+    while (text.startswith("\n\n"))
+        text = text.drop_front();
+    return text;
+}
+
 Replacements filteredReplacements(const Replacements &replacements,
                                   int offset,
                                   int extraOffsetToAdd,
@@ -83,10 +90,13 @@ Replacements filteredReplacements(const Replacements &replacements,
         if (replacementOffset + 1 >= offset)
             replacementOffset += extraOffsetToAdd;
 
+        StringRef text = onlyIndention ? clearExtraNewline(replacement.getReplacementText())
+                                       : replacement.getReplacementText();
+
         Error error = filtered.add(Replacement(replacement.getFilePath(),
                                                static_cast<unsigned int>(replacementOffset),
                                                replacement.getLength(),
-                                               replacement.getReplacementText()));
+                                               text));
         // Throws if error is not checked.
         if (error)
             break;
@@ -335,10 +345,19 @@ void ClangFormatIndenter::indent(QTextDocument *doc,
                                  bool /*autoTriggered*/)
 {
     if (cursor.hasSelection()) {
-        QTextBlock currentBlock = doc->findBlock(cursor.selectionStart());
+        // Calling currentBlock.next() might be unsafe because we change the document.
-        while (currentBlock.isValid() && currentBlock.position() < cursor.selectionEnd()) {
+        // Let's operate with block numbers instead.
+        const int startNumber = doc->findBlock(cursor.selectionStart()).blockNumber();
+        const int endNumber = doc->findBlock(cursor.selectionEnd()).blockNumber();
+        for (int currentBlockNumber = startNumber; currentBlockNumber <= endNumber;
+             ++currentBlockNumber) {
+            const QTextBlock currentBlock = doc->findBlockByNumber(currentBlockNumber);
+            if (currentBlock.isValid()) {
+                const int blocksAmount = doc->blockCount();
                 indentBlock(doc, currentBlock, typedChar, tabSettings);
-            currentBlock = currentBlock.next();
+                QTC_CHECK(blocksAmount == doc->blockCount()
+                          && "ClangFormat plugin indentation changed the amount of blocks.");
+            }
         }
     } else {
         indentBlock(doc, cursor.block(), typedChar, tabSettings);