Requirement Machine: Fix an issue with pack expansion + tuple type crashes

Support pack expansion types in term rewriting, maintaining shape invariants and not
throwing assertions unnecessarily.

Additional tests added for an inifinite case and a concrete case.

Author: kathygray-pl

lib/AST/RequirementMachine/InterfaceType.cpp

@@ -424,7 +424,12 @@ RewriteContext::getRelativeTermForType(CanType typeWitness,
   // Get the substitution S corresponding to τ_0_n.
   unsigned index = getGenericParamIndex(typeWitness->getRootGenericParam());
   result = MutableTerm(substitutions[index]);
-  ASSERT(!result.hasShape());
+  bool hasShape = false;
+
+  if (result.hasShape()) {
+    hasShape = true;
+    result.removeShape();
+  }
 
   // If the substitution is a term consisting of a single protocol symbol
   // [P], save P for later.
@@ -463,6 +468,9 @@ RewriteContext::getRelativeTermForType(CanType typeWitness,
   for (auto iter = symbols.rbegin(), end = symbols.rend(); iter != end; ++iter)
     result.add(*iter);
 
+  if (hasShape)
+    result.add(Symbol::forShape(*this));
+
   return result;
 }
 
@@ -571,8 +579,6 @@ RewriteContext::getRelativeSubstitutionSchemaFromType(
         //
         // τ_0_0 := T
         // τ_0_1 := U.[shape]
-        ASSERT(pos != TypePosition::Shape && "Not implemented");
-
         unsigned index = result.size();
 
         result.push_back(Term::get(term, *this));

test/Generics/infinite_concrete_type.swift

@@ -55,4 +55,14 @@ protocol TooManyDifferences {
   associatedtype A2
   associatedtype B
   associatedtype C
-}
+}
+
+struct G2<T> {
+    func f2<each A>()
+// expected-error@-1 {{cannot build rewrite system for generic signature; concrete type nesting limit exceeded}}
+// expected-note@-2 {{failed rewrite rule is }}
+// expected-error@-3 {{generic parameter 'A' is not used in function signature}}
+  where (repeat each A, T) == T {}
+// expected-error@-1 {{tuple with noncopyable element type 'repeat each A' is not supported}}
+
+}

test/Generics/parameter-pack-requirements.swift

@@ -126,3 +126,9 @@ func sameTypeMatch1<T: PP, each U: PP, each V: PP>(t: T, u: repeat each U, v: re
 // CHECK-NEXT: <T, each U, each V where T : PP, repeat each U : PP, (repeat (each U, each V)) : Any, repeat each V : PP, T.[PP]A == (/* shape: each U */ repeat ())>
 func sameTypeMatch2<T: PP, each U: PP, each V: PP>(t: T, u: repeat each U, v: repeat each V)
   where T.A == Shape<repeat each U>, T.A == Shape<repeat each V> {}
+
+// CHECK-LABEL: PackTupleNesting
+// CHECK-NEXT: <T, U, V, each W where T == ((repeat each W), (repeat each W)), U == (repeat each W), V == (repeat each W)>
+struct PackTupleNesting<T, U, V, each W>
+  where T == ((repeat each W), U),
+        T == (V, (repeat each W)) {} // expected-warning 3{{same-type requirement makes generic parameter}}

validation-test/compiler_crashers/RewriteContext-getRelativeTermForType-5e95d5.swift

@@ -0,0 +1,4 @@
+// RUN: not %target-swift-frontend -typecheck %s
+extension Result {
+  func a<each b>() where Success == (Result) -> (repeat each b)> {}
+}

validation-test/compiler_crashers/RewriteContext-getRelativeTermForType-6235b4.swift

@@ -0,0 +1,6 @@
+// RUN: not %target-swift-frontend -typecheck %s
+// https://github.com/swiftlang/swift/issues/84490
+struct a < b > {
+  func
+    c < each d where (repeat each d , b) == b>()
+}