CppEditor: Consider selection when requesting quickfixes

If the user has a token selected, prefer that to the actual cursor
position.

Fixes: QTCREATORBUG-27886
Change-Id: Ib32e24676510bff42292fe23e4962720fcbac4ed
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/3rdparty/cplusplus/TranslationUnit.cpp

@@ -26,6 +26,9 @@
 #include "AST.h"
 #include "Literals.h"
 #include "DiagnosticClient.h"
+
+#include <utils/textutils.h>
+
 #include <stack>
 #include <vector>
 #include <cstdarg>
@@ -382,6 +385,13 @@ void TranslationUnit::getTokenPosition(int index,
                                        const StringLiteral **fileName) const
 { return getPosition(tokenAt(index).utf16charsBegin(), line, column, fileName); }
 
+int TranslationUnit::getTokenPositionInDocument(int index, const QTextDocument *doc) const
+{
+    int line, column;
+    getTokenPosition(index, &line, &column);
+    return Utils::Text::positionInText(doc, line, column);
+}
+
 void TranslationUnit::getTokenStartPosition(int index, int *line,
                                             int *column,
                                             const StringLiteral **fileName) const

src/libs/3rdparty/cplusplus/TranslationUnit.h

@@ -28,6 +28,10 @@
 #include <unordered_map>
 #include <vector>
 
+QT_BEGIN_NAMESPACE
+class QTextDocument;
+QT_END_NAMESPACE
+
 namespace CPlusPlus {
 
 class CPLUSPLUS_EXPORT TranslationUnit
@@ -124,6 +128,8 @@ public:
                           int *column = nullptr,
                           const StringLiteral **fileName = nullptr) const;
 
+    int getTokenPositionInDocument(int index, const QTextDocument *doc) const;
+
     void pushLineOffset(int offset);
     void pushPreprocessorLine(int utf16charOffset,
                               int line,

src/plugins/cppeditor/cppquickfixassistant.cpp

@@ -86,7 +86,7 @@ CppQuickFixInterface::CppQuickFixInterface(CppEditorWidget *editor, AssistReason
     QTC_CHECK(m_semanticInfo.doc->translationUnit());
     QTC_CHECK(m_semanticInfo.doc->translationUnit()->ast());
     ASTPath astPath(m_semanticInfo.doc);
-    m_path = astPath(editor->textCursor());
+    m_path = astPath(adjustedCursor());
 }
 
 const QList<AST *> &CppQuickFixInterface::path() const
@@ -129,6 +129,50 @@ bool CppQuickFixInterface::isCursorOn(const AST *ast) const
     return currentFile()->isCursorOn(ast);
 }
 
+// Some users like to select identifiers and expect the quickfix to apply to the selection.
+// However, as the cursor position is at the end of the selection, it can happen that
+// the quickfix is applied to the following token instead; see e.g. QTCREATORBUG-27886.
+// We try to detect this condition: If there is a selection *and* this selection
+// corresponds to a C++ token, we move the cursor to that token's position.
+QTextCursor CppQuickFixInterface::adjustedCursor()
+{
+    QTextCursor cursor = this->cursor();
+    if (!cursor.hasSelection())
+        return cursor;
+
+    const TranslationUnit * const tu = m_semanticInfo.doc->translationUnit();
+    const int selStart = cursor.selectionStart();
+    const int selEnd = cursor.selectionEnd();
+    const QTextDocument * const doc = m_editor->textDocument()->document();
+
+    // Binary search for matching token.
+    for (int l = 0, u = tu->tokenCount() - 1; l <= u; ) {
+        const int i = (l + u) / 2;
+        const int tokenPos = tu->getTokenPositionInDocument(i, doc);
+        if (selStart < tokenPos) {
+            u = i - 1;
+            continue;
+        }
+        if (selStart > tokenPos) {
+            l = i + 1;
+            continue;
+        }
+
+        // Selection does not end at token end.
+        if (tokenPos + tu->tokenAt(i).utf16chars() != selEnd)
+            break;
+
+        cursor.setPosition(selStart);
+
+        // Try not to have the cursor "at the edge", in order to prevent potential ambiguities.
+        if (selEnd - selStart > 1)
+            cursor.setPosition(cursor.position() + 1);
+
+        return cursor;
+    }
+    return cursor;
+}
+
 QuickFixOperations quickFixOperations(const TextEditor::AssistInterface *interface)
 {
     const auto cppInterface = dynamic_cast<const CppQuickFixInterface *>(interface);

src/plugins/cppeditor/cppquickfixassistant.h

@@ -33,7 +33,6 @@
 
 #include <cplusplus/LookupContext.h>
 
-
 namespace CppEditor {
 class CppEditorWidget;
 class CppRefactoringFile;
@@ -59,6 +58,8 @@ public:
     bool isBaseObject() const override { return false; }
 
 private:
+    QTextCursor adjustedCursor();
+
     CppEditorWidget *m_editor;
     SemanticInfo m_semanticInfo;
     CPlusPlus::Snapshot m_snapshot;