Clang: Correct member access operator if possible

1 struct Foo { int member; };
 2 void f(Foo *foo)
 3 {
 4     foo.<REQUEST COMPLETION> // correct '.' to '->' and provide results
 5 }

The preferred approach would be to check if "foo" in line 4 is of
pointer type, but there is no suitable cursor (only CompoundStmt) at
that position since the code is usually not yet parsed and thus invalid.

Thus, just run the completion as is. If there are not any results for a
dot completion, re-run the completion with "." exchanged by "->". This
approach is inherently slower than the preferred approach implemented in
the built-in code model.

The following rare cases are not handled:

 1) Requesting completion after white space:
      Works: foo.<COMPLETE HERE>
      Fails: foo. <COMPLETE HERE>

 2) Opening a file and requesting completion (ctrl+space) without prior
    editing. No editing before triggering completion means that no
    unsaved file is generated on the backend side, which is a
    requirement for the correction.

Task-number: QTCREATORBUG-11581
Change-Id: I6bc8e8594778774ab342755fdb01a8a3e5c52ba0
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/tools/clangbackend/ipcsource/codecompleter.cpp

@@ -32,16 +32,33 @@
 
 #include "clangcodecompleteresults.h"
 #include "clangstring.h"
+#include "cursor.h"
 #include "codecompletefailedexception.h"
 #include "codecompletionsextractor.h"
+#include "sourcelocation.h"
+#include "temporarymodifiedunsavedfiles.h"
 #include "clangtranslationunit.h"
+#include "sourcerange.h"
 
 #include <clang-c/Index.h>
 
-#include <QDebug>
-
 namespace ClangBackEnd {
 
+namespace {
+
+CodeCompletions toCodeCompletions(const ClangCodeCompleteResults &results)
+{
+    if (results.isNull())
+        return CodeCompletions();
+
+    CodeCompletionsExtractor extractor(results.data());
+    CodeCompletions codeCompletions = extractor.extractAll();
+
+    return codeCompletions;
+}
+
+} // anonymous namespace
+
 CodeCompleter::CodeCompleter(TranslationUnit translationUnit)
     : translationUnit(std::move(translationUnit))
 {
@@ -49,17 +66,64 @@ CodeCompleter::CodeCompleter(TranslationUnit translationUnit)
 
 CodeCompletions CodeCompleter::complete(uint line, uint column)
 {
-    ClangCodeCompleteResults completeResults(clang_codeCompleteAt(translationUnit.cxTranslationUnitWithoutReparsing(),
-                                                                  translationUnit.filePath().constData(),
-                                                                  line,
-                                                                  column,
-                                                                  translationUnit.cxUnsavedFiles(),
-                                                                  translationUnit.unsavedFilesCount(),
-                                                                  CXCodeComplete_IncludeMacros | CXCodeComplete_IncludeCodePatterns));
+    neededCorrection_ = CompletionCorrection::NoCorrection;
 
-    CodeCompletionsExtractor extractor(completeResults.data());
+    ClangCodeCompleteResults results = complete(line,
+                                                column,
+                                                translationUnit.cxUnsavedFiles(),
+                                                translationUnit.unsavedFilesCount());
 
-    return extractor.extractAll();
+    if (results.hasNoResultsForDotCompletion())
+        results = completeWithArrowInsteadOfDot(line, column);
+
+    return toCodeCompletions(results);
+}
+
+CompletionCorrection CodeCompleter::neededCorrection() const
+{
+    return neededCorrection_;
+}
+
+ClangCodeCompleteResults CodeCompleter::complete(uint line,
+                                                 uint column,
+                                                 CXUnsavedFile *unsavedFiles,
+                                                 unsigned unsavedFileCount)
+{
+    const auto options = CXCodeComplete_IncludeMacros | CXCodeComplete_IncludeCodePatterns;
+
+    return clang_codeCompleteAt(translationUnit.cxTranslationUnitWithoutReparsing(),
+                                translationUnit.filePath().constData(),
+                                line,
+                                column,
+                                unsavedFiles,
+                                unsavedFileCount,
+                                options);
+}
+
+ClangCodeCompleteResults CodeCompleter::completeWithArrowInsteadOfDot(uint line, uint column)
+{
+    TemporaryModifiedUnsavedFiles modifiedUnsavedFiles(translationUnit.cxUnsavedFilesVector());
+    const SourceLocation location = translationUnit.sourceLocationAtWithoutReparsing(line,
+                                                                                     column - 1);
+
+    const bool replaced = modifiedUnsavedFiles.replaceInFile(filePath(),
+                                                             location.offset(),
+                                                             1,
+                                                             Utf8StringLiteral("->"));
+
+    ClangCodeCompleteResults results;
+
+    if (replaced) {
+        results = complete(line,
+                           column + 1,
+                           modifiedUnsavedFiles.cxUnsavedFiles(),
+                           modifiedUnsavedFiles.count());
+
+        if (results.hasResults())
+            neededCorrection_ = CompletionCorrection::DotToArrowCorrection;
+    }
+
+    return results;
 }
 
 Utf8String CodeCompleter::filePath() const