[Sema] Don't assume member refs have base types

- Add a precondition on `doesDeclRefApplyCurriedSelf` to expect
a member decl, and rename it to make the precondition explicit.

- Don't assume that not having a base type means this isn't a member
reference, as member references to static operators don't have base
types.

Resolves SR-10843.

lib/Sema/CSSimplify.cpp

@@ -100,17 +100,18 @@ static Optional<unsigned> scoreParamAndArgNameTypo(StringRef paramName,
   return dist;
 }
 
-bool constraints::doesDeclRefApplyCurriedSelf(Type baseTy,
+bool constraints::doesMemberRefApplyCurriedSelf(Type baseTy,
                                                 const ValueDecl *decl) {
-  // If this isn't a member reference, there's nothing to apply.
-  if (!baseTy || baseTy->is<ModuleType>())
-    return false;
+  assert(decl->getDeclContext()->isTypeContext() &&
+         "Expected a member reference");
 
   // For a reference to an instance method on a metatype, we want to keep the
   // curried self.
-  if (auto *afd = dyn_cast<AbstractFunctionDecl>(decl))
-    if (afd->isInstanceMember() && baseTy->is<AnyMetatypeType>())
+  if (decl->isInstanceMember()) {
+    assert(baseTy);
+    if (isa<AbstractFunctionDecl>(decl) && baseTy->is<AnyMetatypeType>())
       return false;
+  }
 
   // Otherwise the reference applies self.
   return true;
@@ -157,7 +158,7 @@ bool constraints::areConservativelyCompatibleArgumentLabels(
   // the member lookup applying the curried self at the first level. But there
   // are cases where we can get an unapplied declaration reference back.
   auto hasAppliedSelf =
-      decl->hasCurriedSelf() && doesDeclRefApplyCurriedSelf(baseType, decl);
+      decl->hasCurriedSelf() && doesMemberRefApplyCurriedSelf(baseType, decl);
 
   auto *fnType = decl->getInterfaceType()->castTo<AnyFunctionType>();
   if (hasAppliedSelf) {
@@ -860,7 +861,7 @@ getCalleeDeclAndArgs(ConstraintSystem &cs,
     // In most cases where we reference a declaration with a curried self
     // parameter, it gets dropped from the type of the reference.
     bool hasAppliedSelf =
-        decl->hasCurriedSelf() && doesDeclRefApplyCurriedSelf(baseType, decl);
+        decl->hasCurriedSelf() && doesMemberRefApplyCurriedSelf(baseType, decl);
     return std::make_tuple(decl, hasAppliedSelf, argLabels, hasTrailingClosure);
   }
 

lib/Sema/ConstraintSystem.cpp

@@ -1222,7 +1222,7 @@ ConstraintSystem::getTypeOfMemberReference(
 
   // Check to see if the self parameter is applied, in which case we'll want to
   // strip it off later.
-  auto hasAppliedSelf = doesDeclRefApplyCurriedSelf(baseObjTy, value);
+  auto hasAppliedSelf = doesMemberRefApplyCurriedSelf(baseObjTy, value);
 
   baseObjTy = baseObjTy->getMetatypeInstanceType();
   FunctionType::Param baseObjParam(baseObjTy);

lib/Sema/ConstraintSystem.h

@@ -3738,13 +3738,13 @@ matchCallArguments(ConstraintSystem &cs,
 /// subscript, etc.), find the underlying target expression.
 Expr *getArgumentLabelTargetExpr(Expr *fn);
 
-/// Returns true if a reference to a declaration on a given base type will
-/// apply its curried self parameter, assuming it has one.
+/// Returns true if a reference to a member on a given base type will apply its
+/// curried self parameter, assuming it has one.
 ///
 /// This is true for most member references, however isn't true for things like
 /// an instance member being referenced on a metatype, where the curried self
 /// parameter remains unapplied.
-bool doesDeclRefApplyCurriedSelf(Type baseTy, const ValueDecl *decl);
+bool doesMemberRefApplyCurriedSelf(Type baseTy, const ValueDecl *decl);
 
 /// Attempt to prove that arguments with the given labels at the
 /// given parameter depth cannot be used with the given value.

test/Constraints/operator.swift

@@ -223,3 +223,17 @@ func rdar46459603() {
   _ = [arr.values] == [[e]]
   // expected-error@-1 {{protocol type 'Any' cannot conform to 'Equatable' because only concrete types can conform to protocols}}
 }
+
+// SR-10843
+infix operator ^^^
+func ^^^ (lhs: String, rhs: String) {}
+
+struct SR10843 {
+  static func ^^^ (lhs: SR10843, rhs: SR10843) {}
+}
+
+func sr10843() {
+  let s = SR10843()
+  (^^^)(s, s)
+  _ = (==)(0, 0)
+}