Clang: Fix/silence some coverty issues

clangcompletionassistprocessor.cpp: 136
CID 1475671:  Possible Control flow issues  (DEADCODE)
  Execution cannot reach the expression "codeCompletion.completionKind
  != ClangBackEnd::CodeCompletion::SlotCompletionKind" inside this
  statement: "if (slotCompletion && codeC...".

clangbackendcommunicator.cpp: 272
CID 1475649:  Null pointer dereferences  (NULL_RETURNS)
  Dereferencing a pointer that might be null "document" when calling
  "contents". (The dereference happens because this is a virtual
  function call.)

clangutils.cpp: 335
CID 1475678:  Error handling issues  (CHECKED_RETURN)
  Calling "open" without checking return value (as is done elsewhere 144
  out of 158 times).

codecompletionsextractor.cpp: 48
CID 1475676:  Uninitialized members  (UNINIT_CTOR)
  Non-static class member field
  "currentCxCodeCompleteResult.CompletionString" is not initialized in
  this constructor nor in any functions that it calls.

Change-Id: I4c8767ee6e824ba1c42d2f8914ad66dc95ac6717
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/clangbackendcommunicator.cpp

@@ -261,14 +261,14 @@ void BackendCommunicator::unsavedFilesUpdatedForUiHeaders()
 void BackendCommunicator::documentsChangedFromCppEditorDocument(const QString &filePath)
 {
     const CppTools::CppEditorDocumentHandle *document = ClangCodeModel::Utils::cppDocument(filePath);
-
+    QTC_ASSERT(document, return);
     documentsChanged(filePath, document->contents(), document->revision());
 }
 
 void BackendCommunicator::unsavedFielsUpdatedFromCppEditorDocument(const QString &filePath)
 {
     const CppTools::CppEditorDocumentHandle *document = ClangCodeModel::Utils::cppDocument(filePath);
-
+    QTC_ASSERT(document, return);
     unsavedFilesUpdated(filePath, document->contents(), document->revision());
 }
 

src/plugins/clangcodemodel/clangcompletionassistprocessor.cpp

@@ -122,8 +122,9 @@ static QList<AssistProposalItemInterface *> toAssistProposalItems(
         const CodeCompletions &completions,
         const ClangCompletionAssistInterface *interface)
 {
-    bool signalCompletion = false; // TODO
-    bool slotCompletion = false; // TODO
+    // TODO: Handle Qt4's SIGNAL/SLOT
+    //   Possibly check for m_completionOperator == T_SIGNAL
+    //   Possibly check for codeCompletion.completionKind == CodeCompletion::SignalCompletionKind
 
     QList<AssistProposalItemInterface *> items;
     items.reserve(completions.size());
@@ -131,11 +132,6 @@ static QList<AssistProposalItemInterface *> toAssistProposalItems(
         if (codeCompletion.text.isEmpty())
             continue; // It's an OverloadCandidate which has text but no typedText.
 
-        if (signalCompletion && codeCompletion.completionKind != CodeCompletion::SignalCompletionKind)
-            continue;
-        if (slotCompletion && codeCompletion.completionKind != CodeCompletion::SlotCompletionKind)
-            continue;
-
         const QString name = codeCompletion.completionKind == CodeCompletion::KeywordCompletionKind
                 ? CompletionChunksToTextConverter::convertToName(codeCompletion.chunks)
                 : codeCompletion.text.toString();

src/plugins/clangcodemodel/clangutils.cpp

@@ -332,7 +332,9 @@ void generateCompilationDB(::Utils::FileName projectDir, CppTools::ProjectInfo p
 {
     QFile compileCommandsFile(projectDir.toString() + "/compile_commands.json");
 
-    compileCommandsFile.open(QIODevice::WriteOnly | QIODevice::Truncate);
+    const bool fileOpened = compileCommandsFile.open(QIODevice::WriteOnly | QIODevice::Truncate);
+    if (!fileOpened)
+        return;
     compileCommandsFile.write("[");
     for (ProjectPart::Ptr projectPart : projectInfo.projectParts()) {
         const ::Utils::FileName buildDir = buildDirectory(*projectPart);

src/tools/clangbackend/source/codecompletionsextractor.h

@@ -82,8 +82,8 @@ private:
 private:
     CodeCompletion currentCodeCompletion_;
     const UnsavedFile &unsavedFile;
-    CXCompletionResult currentCxCodeCompleteResult;
-    CXCodeCompleteResults *cxCodeCompleteResults;
+    CXCompletionResult currentCxCodeCompleteResult{CXCursor_UnexposedDecl, nullptr};
+    CXCodeCompleteResults *cxCodeCompleteResults = nullptr;
     uint cxCodeCompleteResultIndex = 0;
 };