[CodeComplete] Fix completion in the middle of idents in macro calls

Summary:
This patch removes IdentifierInfo from completion token after remembering
the identifier in the preprocessor.

Prior to this patch, completion token had the IdentifierInfo set to null when
completing at the start of identifier and to the II for completion prefix
when in the middle of identifier.

This patch unifies how code completion token is handled when it is insterted
before the identifier and in the middle of the identifier.

The actual IdentifierInfo can still be obtained from the Preprocessor.

Reviewers: bkramer, arphaman

Reviewed By: bkramer

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D42241

llvm-svn: 323133

clang/lib/Lex/Preprocessor.cpp

@@ -773,8 +773,13 @@ void Preprocessor::Lex(Token &Result) {
     }
   } while (!ReturnedToken);
 
-  if (Result.is(tok::code_completion))
+  if (Result.is(tok::code_completion) && Result.getIdentifierInfo()) {
+    // Remember the identifier before code completion token.
     setCodeCompletionIdentifierInfo(Result.getIdentifierInfo());
+    // Set IdenfitierInfo to null to avoid confusing code that handles both
+    // identifiers and completion tokens.
+    Result.setIdentifierInfo(nullptr);
+  }
 
   LastTokenWasAt = Result.is(tok::at);
 }

clang/test/CodeCompletion/inside-macros.cpp

@@ -0,0 +1,13 @@
+#define ID(X) X
+
+void test(bool input_var) {
+  ID(input_var) = true;
+  // Check that input_var shows up when completing at the start, in the middle
+  // and at the end of the identifier.
+  //
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:4:6 %s -o - | FileCheck %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:4:8 %s -o - | FileCheck %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:4:15 %s -o - | FileCheck %s
+
+  // CHECK: input_var
+}