Clang: Add commentary about column convertion

... to/from utf8 byte offset used by Clang.

Change-Id: I294d6cd61b416e5f2d64206ee2f3f1b4a91fb1d3
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/clangcodemodel/clangcompletionassistprocessor.cpp

@@ -558,9 +558,9 @@ ClangCompletionAssistProcessor::extractLineColumn(int position)
 
     int line = -1, column = -1;
     ::Utils::Text::convertPosition(m_interface->textDocument(), position, &line, &column);
+
     const QTextBlock block = m_interface->textDocument()->findBlock(position);
-    const QString stringOnTheLeft = block.text().left(column);
-    column = stringOnTheLeft.toUtf8().size() + 1; // '+ 1' is for 1-based columns
+    column = Utils::clangColumn(block.text(), column);
     return {line, column};
 }
 

src/plugins/clangcodemodel/clangdiagnosticmanager.cpp

@@ -64,6 +64,9 @@ int positionInText(QTextDocument *textDocument,
 {
     auto textBlock = textDocument->findBlockByNumber(
                 static_cast<int>(sourceLocationContainer.line()) - 1);
+    // 'sourceLocationContainer' already has the CppEditor column converted from
+    // the utf8 byte offset from the beginning of the line provided by clang.
+    // - 1 is required for 0-based columns.
     const int column = static_cast<int>(sourceLocationContainer.column()) - 1;
     return textBlock.position() + column;
 }

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -348,8 +348,7 @@ ClangEditorDocumentProcessor::cursorInfo(const CppTools::CursorInfoParams &param
         return defaultCursorInfoFuture();
 
     const QTextBlock block = params.textCursor.document()->findBlockByNumber(line - 1);
-    const QString stringOnTheLeft = block.text().left(column);
-    column = stringOnTheLeft.toUtf8().size() + 1; // '+ 1' is for 1-based columns
+    column = Utils::clangColumn(block.text(), column);
     const CppTools::SemanticInfo::LocalUseMap localUses
         = CppTools::BuiltinCursorInfo::findLocalUses(params.semanticInfo.doc, line, column);
 

src/plugins/clangcodemodel/clangutils.cpp

@@ -190,5 +190,15 @@ void setLastSentDocumentRevision(const QString &filePath, uint revision)
         document->sendTracker().setLastSentRevision(int(revision));
 }
 
+int clangColumn(const QString &lineText, int cppEditorColumn)
+{
+    // (1) cppEditorColumn is the actual column shown by CppEditor.
+    // (2) The return value is the column in Clang which is the utf8 byte offset from the beginning
+    //     of the line.
+    // Here we convert column from (1) to (2).
+    // '+ 1' is for 1-based columns
+    return lineText.left(cppEditorColumn).toUtf8().size() + 1;
+}
+
 } // namespace Utils
 } // namespace Clang

src/plugins/clangcodemodel/clangutils.h

@@ -46,6 +46,7 @@ CppTools::ProjectPart::Ptr projectPartForFile(const QString &filePath);
 CppTools::ProjectPart::Ptr projectPartForFileBasedOnProcessor(const QString &filePath);
 bool isProjectPartLoaded(const CppTools::ProjectPart::Ptr projectPart);
 QString projectPartIdForFile(const QString &filePath);
+int clangColumn(const QString &lineText, int cppEditorColumn);
 
 } // namespace Utils
 } // namespace Clang

src/tools/clangbackend/source/sourcelocation.cpp

@@ -100,6 +100,9 @@ SourceLocation::SourceLocation(CXTranslationUnit cxTranslationUnit,
         const char *contents = clang_getFileContents(cxTranslationUnit, cxFile, nullptr);
         if (!contents)
             return;
+        // (1) column in SourceLocation is the actual column shown by CppEditor.
+        // (2) column in Clang is the utf8 byte offset from the beginning of the line.
+        // Here we convert column from (2) to (1).
         column_ = static_cast<uint>(QString::fromUtf8(&contents[lineStart],
                                                       static_cast<int>(column_)).size());
     }