[ConstraintSystem] InferSendableFromCaptures: Mark unapplied operator references as @Sendable

Both of these functions are single-apply instance members,
even though their names could be compound the application
is still a regular call with like `next(isolation: ...)`
vs. `next(isolation:)(...)` it would have to be for a "compound"
application.

Operator references don't have a base type and could be found via
unqualified lookup, `adjustFunctionTypeForConcurrency` should handle
them specifically.

Resolves: rdar://131321053

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -1775,8 +1775,11 @@ FunctionType *ConstraintSystem::adjustFunctionTypeForConcurrency(
               adjustedTy->withExtInfo(adjustedTy->getExtInfo().withSendable());
         }
       } else if (isPartialApplication(getConstraintLocator(locator))) {
-        if (baseType &&
-            (baseType->is<AnyMetatypeType>() || baseType->isSendableType())) {
+        // Operators on protocols could be found via unqualified lookup and
+        // won't have a base type.
+        if (decl->isOperator() ||
+            (baseType &&
+             (baseType->is<AnyMetatypeType>() || baseType->isSendableType()))) {
           auto referenceTy = adjustedTy->getResult()->castTo<FunctionType>();
           referenceTy =
               referenceTy->withExtInfo(referenceTy->getExtInfo().withSendable())

test/Concurrency/sendable_methods.swift

@@ -286,3 +286,11 @@ func testPatternMatch(ge: [GenericE<Int>]) {
     _ = a
   }
 }
+
+// rdar://131321053 - cannot pass an operator to parameter that expectes a @Sendable type
+do {
+  func test(_: @Sendable (Int, Int) -> Bool) {
+  }
+
+  test(<) // Ok
+}