[GSB] Stop warning about 'bare' associated type redeclarations.

Associated type redeclarations occasionally occur to push around
associated type witness inference. Suppress the warning about redeclarations
that add no requirements (i.e., have neither an inheritance nor a
where clause).

lib/AST/GenericSignatureBuilder.cpp

@@ -3497,7 +3497,9 @@ ConstraintResult GenericSignatureBuilder::expandConformanceRequirement(
 
       bool shouldWarnAboutRedeclaration =
         source->kind == RequirementSource::RequirementSignatureSelf &&
-        assocTypeDecl->getDefaultDefinitionLoc().isNull();
+        assocTypeDecl->getDefaultDefinitionLoc().isNull() &&
+        (!assocTypeDecl->getInherited().empty() ||
+         assocTypeDecl->getTrailingWhereClause());
       for (auto inheritedType : knownInherited->second) {
         // If we have inherited associated type...
         if (auto inheritedAssocTypeDecl =

test/Constraints/generic_overload.swift

@@ -1,7 +1,7 @@
 // RUN: %target-typecheck-verify-swift
 
-protocol P1 { associatedtype Assoc } // expected-note{{declared here}}
-protocol P2 : P1 { associatedtype Assoc } // expected-warning{{redeclaration of associated type}}
+protocol P1 { associatedtype Assoc }
+protocol P2 : P1 { associatedtype Assoc }
 protocol P3 { }
 
 struct X1 : P1 { typealias Assoc = X3 }

test/Generics/associated_type_where_clause.swift

@@ -138,16 +138,16 @@ protocol P {
 
 // Lookup of same-named associated types aren't ambiguous in this context.
 protocol P1 {
-  associatedtype A // expected-note 2{{declared here}}
+  associatedtype A
 }
 
 protocol P2: P1 {
-  associatedtype A // expected-warning{{redeclaration of associated type}}
+  associatedtype A
   associatedtype B where A == B
 }
 
 protocol P3: P1 {
-  associatedtype A // expected-warning{{redeclaration of associated type}}
+  associatedtype A
 }
 
 protocol P4 {

test/Generics/canonicalization.swift

@@ -4,11 +4,11 @@
 protocol P0 { }
 
 protocol P {
-  associatedtype A // expected-note{{declared here}}
+  associatedtype A
 }
 
 protocol Q : P {
-  associatedtype A // expected-warning{{redeclaration of associated type 'A' from protocol 'P' is better expressed as a 'where' clause on the protocol}}
+  associatedtype A
 }
 
 func f<T>(t: T) where T : P, T : Q, T.A : P0 { } // expected-note{{'f(t:)' previously declared here}}

test/Generics/protocol_requirement_signatures.swift

@@ -22,7 +22,7 @@ protocol P3 {}
 // CHECK-NEXT: Requirement signature: <Self where Self.X : P1>
 // CHECK-NEXT: Canonical requirement signature: <τ_0_0 where τ_0_0.X : P1>
 protocol Q1 {
-    associatedtype X: P1 // expected-note 2{{declared here}}
+    associatedtype X: P1 // expected-note {{declared here}}
 }
 
 // inheritance
@@ -36,7 +36,7 @@ protocol Q2: Q1 {}
 // CHECK-NEXT: Requirement signature: <Self where Self : Q1>
 // CHECK-NEXT: Canonical requirement signature: <τ_0_0 where τ_0_0 : Q1>
 protocol Q3: Q1 {
-    associatedtype X // expected-warning{{redeclaration of associated type 'X'}}
+    associatedtype X
 }
 
 // inheritance adding a new conformance

test/Generics/requirement_inference.swift

@@ -139,13 +139,13 @@ extension P7 where AssocP6.Element : P6, // expected-note{{conformance constrain
 }
 
 protocol P8 {
-  associatedtype A // expected-note{{'A' declared here}}
-  associatedtype B // expected-note{{'B' declared here}}
+  associatedtype A
+  associatedtype B
 }
 
 protocol P9 : P8 {
-  associatedtype A // expected-warning{{redeclaration of associated type 'A' from protocol 'P8' is better expressed as a 'where' clause on the protocol}}
-  associatedtype B // expected-warning{{redeclaration of associated type 'B' from protocol 'P8' is better expressed as a 'where' clause on the protocol}}
+  associatedtype A
+  associatedtype B
 }
 
 protocol P10 {

test/IDE/complete_associated_types.swift

@@ -32,8 +32,8 @@ protocol FooBaseProtocolWithAssociatedTypes {
   associatedtype FooBaseDefaultedTypeB = Int
   associatedtype FooBaseDefaultedTypeC = Int
 
-  associatedtype DeducedTypeCommonA // expected-note{{declared here}}
-  associatedtype DeducedTypeCommonB // expected-note{{declared here}}
+  associatedtype DeducedTypeCommonA
+  associatedtype DeducedTypeCommonB
   associatedtype DeducedTypeCommonC
   associatedtype DeducedTypeCommonD
   func deduceCommonA() -> DeducedTypeCommonA
@@ -57,8 +57,8 @@ protocol FooProtocolWithAssociatedTypes : FooBaseProtocolWithAssociatedTypes {
 
   associatedtype FooBaseDefaultedTypeB = Double
 
-  associatedtype DeducedTypeCommonA // expected-warning{{redeclaration of associated type}}
-  associatedtype DeducedTypeCommonB // expected-warning{{redeclaration of associated type}}
+  associatedtype DeducedTypeCommonA
+  associatedtype DeducedTypeCommonB
   func deduceCommonA() -> DeducedTypeCommonA
   func deduceCommonB() -> DeducedTypeCommonB
 
@@ -79,7 +79,7 @@ protocol BarBaseProtocolWithAssociatedTypes {
   associatedtype DefaultedTypeCommonA = Int
   associatedtype DefaultedTypeCommonC = Int
 
-  associatedtype DeducedTypeCommonA // expected-note{{'DeducedTypeCommonA' declared here}}
+  associatedtype DeducedTypeCommonA
   associatedtype DeducedTypeCommonC
   func deduceCommonA() -> DeducedTypeCommonA
   func deduceCommonC() -> DeducedTypeCommonC
@@ -102,7 +102,7 @@ protocol BarProtocolWithAssociatedTypes : BarBaseProtocolWithAssociatedTypes {
   associatedtype DefaultedTypeCommonA = Int
   associatedtype DefaultedTypeCommonD = Int
 
-  associatedtype DeducedTypeCommonA // expected-warning{{redeclaration of associated type}}
+  associatedtype DeducedTypeCommonA
   associatedtype DeducedTypeCommonD
   func deduceCommonA() -> DeducedTypeCommonA
   func deduceCommonD() -> DeducedTypeCommonD

test/attr/attr_autoclosure.swift

@@ -42,10 +42,10 @@ class DerivedClass {
 }
 
 protocol P1 {
-  associatedtype Element // expected-note{{declared here}}
+  associatedtype Element
 }
 protocol P2 : P1 {
-  associatedtype Element // expected-warning{{redeclaration of associated type 'Element'}}
+  associatedtype Element
 }
 
 func overloadedEach<O: P1>(_ source: O, _ closure: @escaping () -> ()) {

test/attr/attr_noescape.swift

@@ -183,10 +183,10 @@ func redundant(_ fn : @noescape  // expected-error @+1 {{@noescape is implied by
 
 
 protocol P1 {
-  associatedtype Element // expected-note{{declared here}}
+  associatedtype Element
 }
 protocol P2 : P1 {
-  associatedtype Element // expected-warning{{redeclaration of associated type 'Element'}}
+  associatedtype Element
 }
 
 func overloadedEach<O: P1, T>(_ source: O, _ transform: @escaping (O.Element) -> (), _: T) {}

test/decl/protocol/indirectly_recursive_requirement.swift

@@ -5,7 +5,7 @@ protocol Incrementable  {
 }
 
 protocol _ForwardIndex  {
-  associatedtype Distance  = MyInt // expected-note{{declared here}}
+  associatedtype Distance  = MyInt
 }
 
 protocol ForwardIndex : _ForwardIndex {
@@ -19,7 +19,7 @@ protocol BidirectionalIndex : ForwardIndex, _BidirectionalIndex {
 }
 
 protocol _RandomAccessIndex : _BidirectionalIndex {
-  associatedtype Distance // expected-warning{{redeclaration of associated type 'Distance}}
+  associatedtype Distance
 }
 
 protocol RandomAccessIndex