[Parse] Don't tell CodeCompletion nonsense about protocol/AT where clauses.

This doesn't give particularly useful information yet (i.e. Self isn't
listed, see rdar://problem/31981641 ), but it does stop the completion
code from just directly crashing.

Fixes rdar://problem/31981486.

Author: huonw

lib/Parse/ParseGeneric.cpp

@@ -390,12 +390,7 @@ ParserStatus Parser::parseProtocolOrAssociatedTypeWhereClause(
     trailingWhere =
         TrailingWhereClause::create(Context, whereLoc, requirements);
   } else if (whereStatus.hasCodeCompletion()) {
-    // FIXME: this is completely (hah) cargo culted.
-    if (CodeCompletion && firstTypeInComplete) {
-      CodeCompletion->completeGenericParams(nullptr);
-    } else {
-      return makeParserCodeCompletionStatus();
-    }
+    return whereStatus;
   }
 
   return ParserStatus();

test/IDE/complete_crashes.swift

@@ -196,3 +196,9 @@ struct S_RDAR_28991372 {
 
 S_RDAR_28991372(x: #^RDAR_28991372^#, y: <#T##Int#>)
 // RDAR_28991372: Begin completions
+
+// rdar://problem/31981486
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=RDAR_31981486 | %FileCheck %s -check-prefix=RDAR_31981486
+
+protocol P where #^RDAR_31981486^#
+// RDAR_31981486: Begin completions

validation-test/IDE/crashers_2/0012-protocol-where-clause.swift

@@ -0,0 +1,4 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+// REQUIRES: asserts
+
+protocol a where #^A^#