qmlls: Fix TextSynchronization

The offset from a given range was incorrectly calculated in
findBlockByNumber because textblocks that are used to obtain that
position were mistakenly ignoring the newline character. This were
leading us to setting a different text than what we actually typed.
Add an extra text block if the text ends with \n.

Add a manual test but exclude it from tst_qmlformat as it is not a valid
qml document.

Fixes: QTBUG-113725
Change-Id: Ifb1b4121fd8af46df7627d986303ae67e170e50c
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 16 insertions, 8 deletions

diff --git a/src/qmlls/qtextdocument.cpp b/src/qmlls/qtextdocument.cpp
index 826deddbb5..54e200274e 100644
--- a/src/qmlls/qtextdocument.cpp
+++ b/src/qmlls/qtextdocument.cpp
@@ -68,22 +68,30 @@ void TextDocument::setPlainText(const QString &text)
     m_content = text;
     m_blocks.clear();
 
-    int blockStart = 0;
-    int blockNumber = 0;
-    while (blockStart < text.size()) {
+    const auto appendToBlocks = [this](int blockNumber, int start, int length) {
         Block block;
-        block.textBlock.setBlockNumber(blockNumber++);
-        block.textBlock.setPosition(blockStart);
+        block.textBlock.setBlockNumber(blockNumber);
+        block.textBlock.setPosition(start);
         block.textBlock.setDocument(this);
+        block.textBlock.setLength(length);
+        m_blocks.append(block);
+    };
 
+    int blockStart = 0;
+    int blockNumber = -1;
+    while (blockStart < text.size()) {
         int blockEnd = text.indexOf(u'\n', blockStart) + 1;
         if (blockEnd == 0)
             blockEnd = text.size();
-
-        block.textBlock.setLength(blockEnd - blockStart);
-        m_blocks.append(block);
+        appendToBlocks(++blockNumber, blockStart, blockEnd - blockStart);
         blockStart = blockEnd;
     }
+    // Add an empty block if the text ends with \n. This is required for retrieving
+    // the actual line of the text editor if requested, for example, in findBlockByNumber.
+    // Consider a case with text aa\nbb\n\n. You are on 4th line of the text editor and even
+    // if it is an empty line, we introduce a text block for it to maybe use later.
+    if (text.endsWith(u'\n'))
+        appendToBlocks(++blockNumber, blockStart, 0);
 }
 
 bool TextDocument::isModified() const