SIL: Handle ProtocolCompositionType in SubstFunctionTypePatternVisitor

Fixes #62061.

Author: slavapestov

include/swift/SIL/AbstractionPattern.h

@@ -1516,6 +1516,10 @@ class AbstractionPattern {
   /// the abstraction pattern for its self type.
   AbstractionPattern getDynamicSelfSelfType() const;
 
+  /// Given that the value being abstracted is a protocol composition
+  /// type, return the abstraction pattern for one of its member types.
+  AbstractionPattern getProtocolCompositionMemberType(unsigned i) const;
+
   /// Given that the value being abstracted is a parameterized protocol
   /// type, return the abstraction pattern for one of its argument types.
   AbstractionPattern getParameterizedProtocolArgType(unsigned i) const;

lib/SIL/IR/AbstractionPattern.cpp

@@ -1022,6 +1022,14 @@ AbstractionPattern AbstractionPattern::getDynamicSelfSelfType() const {
                             cast<DynamicSelfType>(getType()).getSelfType());
 }
 
+AbstractionPattern
+AbstractionPattern::getProtocolCompositionMemberType(unsigned argIndex) const {
+  assert(getKind() == Kind::Type);
+  return AbstractionPattern(getGenericSubstitutions(),
+                            getGenericSignature(),
+            cast<ProtocolCompositionType>(getType()).getMembers()[argIndex]);
+}
+
 AbstractionPattern
 AbstractionPattern::getParameterizedProtocolArgType(unsigned argIndex) const {
   assert(getKind() == Kind::Type);
@@ -2699,22 +2707,44 @@ class SubstFunctionTypePatternVisitor
   CanType visitParameterizedProtocolType(CanParameterizedProtocolType ppt,
                                          AbstractionPattern pattern) {
     // Recurse into the arguments of the parameterized protocol.
-    SmallVector<Type, 4> substArgs;
     auto origPPT = pattern.getAs<ParameterizedProtocolType>();
     if (!origPPT)
       return ppt;
 
+    SmallVector<Type, 4> substArgs;
     for (unsigned i = 0; i < ppt->getArgs().size(); ++i) {
       auto argTy = ppt.getArgs()[i];
       auto origArgTy = pattern.getParameterizedProtocolArgType(i);
-      auto substEltTy = visit(argTy, origArgTy);
-      substArgs.push_back(substEltTy);
+      auto substArgTy = visit(argTy, origArgTy);
+      substArgs.push_back(substArgTy);
     }
 
     return CanType(ParameterizedProtocolType::get(
         TC.Context, ppt->getBaseType(), substArgs));
   }
 
+  CanType visitProtocolCompositionType(CanProtocolCompositionType pct,
+                                       AbstractionPattern pattern) {
+    // Recurse into the arguments of the protocol composition.
+    auto origPCT = pattern.getAs<ProtocolCompositionType>();
+    if (!origPCT)
+      return pct;
+    
+    SmallVector<Type, 4> substMembers;
+    for (unsigned i = 0; i < pct->getMembers().size(); ++i) {
+      auto memberTy = CanType(pct->getMembers()[i]);
+      auto origMemberTy = pattern.getProtocolCompositionMemberType(i);
+      auto substMemberTy = visit(memberTy, origMemberTy);
+      substMembers.push_back(substMemberTy);
+    }
+
+    return CanType(ProtocolCompositionType::get(
+        TC.Context,
+        substMembers,
+        pct->getInverses(),
+        pct->hasExplicitAnyObject()));
+  }
+
   /// Visit a tuple pattern.  Note that, because of vanishing tuples,
   /// we can't handle this case by matching a tuple type in the
   /// substituted type; we have to check for a tuple pattern in the

test/SILGen/subst_function_type_existential.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-emit-silgen %s
+
+// https://github.com/swiftlang/swift/issues/62061
+
+protocol P {}
+
+class C<T> {}
+
+protocol Q {
+  associatedtype A
+}
+
+func foo1<T>(t: T) {
+  let _: (any P & C<T>) -> T = { x in t }
+}
+
+func foo2<T: Q>(t: T) {
+  let _: (any P & C<(T.A) -> ()>) -> T = { x in t }
+}
+