[CodeCompletion] No crash on a terribly wrong code completion position. rdar://21796881

Swift SVN r30706

Author: nkcsgexi

include/swift/Parse/PersistentParserState.h

@@ -128,6 +128,8 @@ class PersistentParserState {
   std::unique_ptr<FunctionBodyState>
   takeFunctionBodyState(AbstractFunctionDecl *AFD);
 
+  bool hasFunctionBodyState(AbstractFunctionDecl *AFD);
+
   void delayAccessorBodyParsing(AbstractFunctionDecl *AFD,
                                 SourceRange BodyRange,
                                 SourceLoc PreviousLoc,

lib/Parse/Parser.cpp

@@ -89,7 +89,7 @@ class ParseDelayedFunctionBodies : public ASTWalker {
         Parsed = true;
       }
     }
-    if (!Parsed)
+    if (!Parsed && ParserState.hasFunctionBodyState(AFD))
       TheParser.parseAbstractFunctionBodyDelayed(AFD);
     if (CodeCompletion)
       CodeCompletion->doneParsing();

lib/Parse/PersistentParserState.cpp

@@ -41,6 +41,10 @@ PersistentParserState::takeFunctionBodyState(AbstractFunctionDecl *AFD) {
   return State;
 }
 
+bool PersistentParserState::hasFunctionBodyState(AbstractFunctionDecl *AFD) {
+  return DelayedFunctionBodies.find(AFD) != DelayedFunctionBodies.end();
+}
+
 void PersistentParserState::delayAccessorBodyParsing(AbstractFunctionDecl *AFD,
                                                      SourceRange BodyRange,
                                                      SourceLoc PreviousLoc,

test/IDE/complete_crashes.swift

@@ -67,3 +67,8 @@ struct CustomGenericCollection<Key> : DictionaryLiteralConvertible {
   var count: Int { #^GENERIC_PARAM_AND_ASSOC_TYPE^# }
 }
 
+// rdar://problem/21796881
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=RDAR_21796881
+extension NilLiteralConvertible {
+   var nil: Self { #^RDAR_21796881^#
+}