GSB: Remove unsound cycle-breaking hack

Author: slavapestov

lib/AST/GenericSignatureBuilder.cpp

@@ -5209,12 +5209,6 @@ class GenericSignatureBuilder::InferRequirementsWalker : public TypeWalker {
     // Infer from generic nominal types.
     auto decl = ty->getAnyNominal();
     if (!decl) return Action::Continue;
-
-    // FIXME: The GSB and the request evaluator both detect a cycle here if we
-    // force a recursive generic signature.  We should look into moving cycle
-    // detection into the generic signature request(s) - see rdar://55263708
-    if (!decl->hasComputedGenericSignature())
-      return Action::Continue;
 
     auto genericSig = decl->getGenericSignature();
     if (!genericSig)

test/Generics/generic_types.swift

@@ -230,7 +230,7 @@ class Top {}
 class Bottom<T : Bottom<Top>> {}
 // expected-error@-1 {{'Bottom' requires that 'Top' inherit from 'Bottom<Top>'}}
 // expected-note@-2 {{requirement specified as 'T' : 'Bottom<Top>' [with T = Top]}}
-// expected-error@-3 {{generic class 'Bottom' has self-referential generic requirements}}
+// expected-error@-3 4{{generic class 'Bottom' has self-referential generic requirements}}
 // expected-note@-4 {{while resolving type 'Bottom<Top>'}}
 // expected-note@-5 {{through reference here}}
 

test/decl/protocol/req/recursion.swift

@@ -10,6 +10,7 @@ extension SomeProtocol where T == Optional<T> { } // expected-error{{same-type c
 
 class X<T> where T == X { // expected-error{{same-type constraint 'T' == 'X<T>' is recursive}}
 // expected-error@-1{{same-type requirement makes generic parameter 'T' non-generic}}
+// expected-error@-2 3{{generic class 'X' has self-referential generic requirements}}
     var type: T { return Swift.type(of: self) } // expected-error{{cannot convert return expression of type 'X<T>.Type' to return type 'T'}}
 }
 
@@ -44,7 +45,7 @@ public protocol P {
 }
 
 public struct S<A: P> where A.T == S<A> {
-// expected-error@-1 {{generic struct 'S' has self-referential generic requirements}}
+// expected-error@-1 4{{generic struct 'S' has self-referential generic requirements}}
 // expected-note@-2 {{while resolving type 'S<A>'}}
   func f(a: A.T) {
     g(a: id(t: a)) // `a` has error type which is diagnosed as circular reference
@@ -70,7 +71,7 @@ protocol PI {
 }
 
 struct SI<A: PI> : I where A : I, A.T == SI<A> {
-// expected-error@-1 {{generic struct 'SI' has self-referential generic requirements}}
+// expected-error@-1 4{{generic struct 'SI' has self-referential generic requirements}}
 // expected-note@-2 {{while resolving type 'SI<A>'}}
   func ggg<T : I>(t: T.Type) -> T {
     return T()
@@ -98,7 +99,9 @@ struct S5<A: PI> : I where A : I, A.T == S4<A> { }
 
 // Used to hit ArchetypeBuilder assertions
 struct SU<A: P> where A.T == SU {
+// expected-error@-1 3{{generic struct 'SU' has self-referential generic requirements}}
 }
 
 struct SIU<A: PI> : I where A : I, A.T == SIU {
+// expected-error@-1 3{{generic struct 'SIU' has self-referential generic requirements}}
 }

validation-test/compiler_crashers_2_fixed/0064-rdar27627862.swift

@@ -1,6 +1,7 @@
-// RUN: %target-swift-frontend %s -emit-ir
+// RUN: %target-typecheck-verify-swift
 
 enum Term<S> where S: Sequence, S.Iterator.Element == Term {
+// expected-error@-1 3{{generic enum 'Term' has self-referential generic requirements}}
     case Cons(head: String, tail: S)
 }