[unittests/Sema] Add a simple integer literal type inference test

include/swift/Sema/ConstraintSystem.h

@@ -4942,6 +4942,7 @@ class ConstraintSystem {
   Optional<Type> checkTypeOfBinding(TypeVariableType *typeVar, Type type) const;
   Optional<PotentialBindings> determineBestBindings();
 
+public:
   /// Infer bindings for the given type variable based on current
   /// state of the constraint system.
   PotentialBindings inferBindingsFor(TypeVariableType *typeVar,

unittests/Sema/BindingInferenceTests.cpp

@@ -0,0 +1,46 @@
+//===--- BindingInferenceTests.cpp ----------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "SemaFixture.h"
+#include "swift/AST/Expr.h"
+#include "swift/Sema/ConstraintSystem.h"
+
+using namespace swift;
+using namespace swift::unittest;
+using namespace swift::constraints;
+
+TEST_F(SemaTest, TestIntLiteralBindingInference) {
+  ConstraintSystemOptions options;
+  options |= ConstraintSystemFlags::AllowUnresolvedTypeVariables;
+
+  ConstraintSystem cs(DC, options);
+
+  auto *intLiteral = IntegerLiteralExpr::createFromUnsigned(Context, 42);
+
+  auto *literalTy = cs.createTypeVariable(cs.getConstraintLocator(intLiteral),
+                                          /*options=*/0);
+
+  cs.addConstraint(
+      ConstraintKind::LiteralConformsTo, literalTy,
+      Context.getProtocol(KnownProtocolKind::ExpressibleByIntegerLiteral)
+          ->getDeclaredInterfaceType(),
+      cs.getConstraintLocator(intLiteral));
+
+  auto bindings = cs.inferBindingsFor(literalTy);
+
+  ASSERT_EQ(bindings.Bindings.size(), (unsigned)1);
+
+  const auto &binding = bindings.Bindings.front();
+
+  ASSERT_TRUE(binding.BindingType->isEqual(getStdlibType("Int")));
+  ASSERT_TRUE(binding.hasDefaultedLiteralProtocol());
+}

unittests/Sema/CMakeLists.txt

@@ -1,6 +1,7 @@
 
 add_swift_unittest(swiftSemaTests
-  SemaFixture.cpp)
+  SemaFixture.cpp
+  BindingInferenceTests.cpp)
 
 target_link_libraries(swiftSemaTests
   PRIVATE