AST: WhereClauseOwner never visit the obsolete 'where' clause inside a GenericParamList

Otherwise, we'll end up visiting it twice in InferredGenericSignatureRequest.
The GSB uniques requirements seen this way, whereas the Requirement Machine
does not, leading to redundant requirement diagnostics.

Author: slavapestov

lib/AST/TypeCheckRequests.cpp

@@ -340,28 +340,26 @@ void RequirementSignatureRequest::cacheResult(RequirementSignature value) const
 // Requirement computation.
 //----------------------------------------------------------------------------//
 
-WhereClauseOwner::WhereClauseOwner(GenericContext *genCtx): dc(genCtx) {
-  if (const auto whereClause = genCtx->getTrailingWhereClause())
-    source = whereClause;
-  else
-    source = genCtx->getGenericParams();
-}
+WhereClauseOwner::WhereClauseOwner(GenericContext *genCtx)
+    : dc(genCtx),
+      source(genCtx->getTrailingWhereClause()) {}
 
 WhereClauseOwner::WhereClauseOwner(AssociatedTypeDecl *atd)
     : dc(atd->getInnermostDeclContext()),
       source(atd->getTrailingWhereClause()) {}
 
 SourceLoc WhereClauseOwner::getLoc() const {
-  if (auto where = source.dyn_cast<TrailingWhereClause *>())
-    return where->getWhereLoc();
-
-  if (auto attr = source.dyn_cast<SpecializeAttr *>())
+  if (auto genericParams = source.dyn_cast<GenericParamList *>()) {
+    return genericParams->getWhereLoc();
+  } else if (auto attr = source.dyn_cast<SpecializeAttr *>()) {
     return attr->getLocation();
-
-  if (auto attr = source.dyn_cast<DifferentiableAttr *>())
+  } else if (auto attr = source.dyn_cast<DifferentiableAttr *>()) {
     return attr->getLocation();
+  } else if (auto where = source.dyn_cast<TrailingWhereClause *>()) {
+    return where->getWhereLoc();
+  }
 
-  return source.get<GenericParamList *>()->getWhereLoc();
+  return SourceLoc();
 }
 
 void swift::simple_display(llvm::raw_ostream &out,

test/IDE/annotation.swift

@@ -81,8 +81,8 @@ class SubCls : MyCls, Prot {
   var protocolProperty2 = 0
 }
 
-// CHECK: func <Func>genFn</Func><<GenericTypeParam>T</GenericTypeParam> : <Protocol@64:10>Prot</Protocol> where <GenericTypeParam@85:12>T</GenericTypeParam>.<AssociatedType@65:18>Blarg</AssociatedType> : <Protocol@71:10>Prot2</Protocol>>(_ <Param>p</Param> : <GenericTypeParam@85:12>T</GenericTypeParam>) -> <iStruct@>Int</iStruct> {}{{$}}
-func genFn<T : Prot where T.Blarg : Prot2>(_ p : T) -> Int {}
+// CHECK: func <Func>genFn</Func><<GenericTypeParam>T</GenericTypeParam> : <Protocol@64:10>Prot</Protocol>>(_ <Param>p</Param> : <GenericTypeParam@85:12>T</GenericTypeParam>) -> <iStruct@>Int</iStruct> where <GenericTypeParam@85:12>T</GenericTypeParam>.<AssociatedType@65:18>Blarg</AssociatedType> : <Protocol@71:10>Prot2</Protocol> {}{{$}}
+func genFn<T : Prot>(_ p : T) -> Int where T.Blarg : Prot2 {}
 
 func test(_ x: Int) {
   // CHECK: <Func@[[@LINE-3]]:6>genFn</Func>(<Class@[[@LINE-11]]:7>SubCls</Class>())

test/Parse/deprecated_where.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -swift-version 4
+// RUN: %target-typecheck-verify-swift -swift-version 4 -requirement-machine-protocol-signatures=on -requirement-machine-inferred-signatures=on
 
 protocol Mashable { }
 protocol Womparable { }

test/type/protocol_composition.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -swift-version 4 -requirement-machine-protocol-signatures=verify -requirement-machine-inferred-signatures=verify
+// RUN: %target-typecheck-verify-swift -swift-version 4 -requirement-machine-protocol-signatures=on -requirement-machine-inferred-signatures=on
 
 func canonical_empty_protocol() -> Any {
   return 1