[CSSimplify] Fix key path to function conversion to check key path re…

lib/Sema/CSDiagnostics.cpp

@@ -411,6 +411,14 @@ ValueDecl *RequirementFailure::getDeclRef() const {
     }
   }
 
+  // If this is a key path to function conversion, the requirements come
+  // from a key path type implicitly formed by the solver.
+  if (isExpr<KeyPathExpr>(getRawAnchor()) &&
+      getLocator()->isFirstElement<LocatorPathElt::KeyPathType>() &&
+      getOwnerType()->is<FunctionType>()) {
+    return getASTContext().getKeyPathDecl();
+  }
+
   return getAffectedDeclFromType(getOwnerType());
 }
 

lib/Sema/CSSimplify.cpp

@@ -12982,8 +12982,29 @@ ConstraintSystem::simplifyKeyPathConstraint(
       auto paramFnTy = FunctionType::get(paramParam, fnTy->getResult(),
                                          fnTy->getExtInfo());
 
+      // Form a key path type as well to make sure that root and value
+      // types satisfy all of its requirements.
+      // Note that `KeyPath` types used to have no requirements but now
+      // they do require `Root` and `Value` to be `Copyable` and `Escapable`.
+      {
+        auto keyPathTy =
+            openUnboundGenericType(
+                getASTContext().getKeyPathDecl(),
+                /*parent=*/Type(),
+                locator.withPathElement(LocatorPathElt::KeyPathType()),
+                /*isTypeResolution=*/false)
+                ->castTo<BoundGenericType>();
+        addConstraint(ConstraintKind::Bind, keyPathTy->getGenericArgs()[0],
+                      rootTy,
+                      locator.withPathElement(LocatorPathElt::KeyPathRoot()));
+        addConstraint(ConstraintKind::Bind, keyPathTy->getGenericArgs()[1],
+                      valueTy,
+                      locator.withPathElement(LocatorPathElt::KeyPathValue()));
+      }
+
       return !matchTypes(kpFnTy, paramFnTy, ConstraintKind::Conversion,
-                         subflags, locator).isFailure();
+                         subflags, locator)
+                  .isFailure();
     }
 
     assert(contextualRootTy && contextualValueTy);

test/Sema/keypaths_noncopyable.swift

@@ -53,9 +53,9 @@ public func testKeypath<V: ~Copyable>(m: consuming M<V>) {
   // expected-error@-1 {{key path cannot refer to noncopyable type 'M<V>'}}
 
   let b = Box(NC())
-  _ = b.with(\.data)
-  _ = b.with(\.next)
-  _ = b.with(\.next?.wrapped) // expected-error {{key path cannot refer to noncopyable type 'NC'}}
+  _ = b.with(\.data) // expected-error {{key path cannot refer to noncopyable type 'NC'}}
+  _ = b.with(\.next) // expected-error {{key path cannot refer to noncopyable type 'NC'}}
+  _ = b.with(\.next?.wrapped) // expected-error 2 {{key path cannot refer to noncopyable type 'NC'}}
   _ = b.with(\.next!.wrapped.data) // expected-error {{key path cannot refer to noncopyable type 'NC'}}
 }
 
@@ -68,3 +68,16 @@ func testAsFunc(_ someA: A) -> Int {
   let fn: (A) -> Int = \A.b.c.d // expected-error {{key path cannot refer to noncopyable type 'B'}}
   return fn(someA)
 }
+
+// https://github.com/swiftlang/swift/issues/84150
+func testKeyPathToFunctionConversion() {
+  struct HasID: ~Copyable {
+    let id: Int
+  }
+
+  func map(_ operation: (consuming HasID) -> Int) {}
+
+  map(\.id) // expected-error {{key path cannot refer to noncopyable type 'HasID'}}
+
+  let _: (consuming HasID) -> Int = \.id // expected-error {{key path cannot refer to noncopyable type 'HasID'}}
+}