[Sema] NFC: Add some unit-tests for solution filtering

Author: xedin

unittests/Sema/CMakeLists.txt

@@ -4,7 +4,8 @@ add_swift_unittest(swiftSemaTests
   BindingInferenceTests.cpp
   ConstraintSimplificationTests.cpp
   UnresolvedMemberLookupTests.cpp
-  PlaceholderTypeInferenceTests.cpp)
+  PlaceholderTypeInferenceTests.cpp
+  SolutionFilteringTests.cpp)
 
 target_link_libraries(swiftSemaTests
   PRIVATE

unittests/Sema/SolutionFilteringTests.cpp

@@ -0,0 +1,138 @@
+//===--- SolutionFilteringTests.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/Sema/ConstraintSystem.h"
+
+using namespace swift;
+using namespace swift::unittest;
+using namespace swift::constraints;
+
+/// Make sure that minimization works as expected
+/// and would remove solutions that score worse
+/// than the best set even in ambiguity cases
+/// (where there is more than one best solution).
+TEST_F(SemaTest, TestFilteringBasedOnSolutionScore) {
+  Score bestScore{};
+
+  Score worseScore1{};
+  Score worseScore2{};
+
+  worseScore1.Data[SK_Unavailable] += 1;
+  worseScore2.Data[SK_Fix] += 1;
+
+  ConstraintSystem CS(DC, ConstraintSystemOptions());
+
+  // Let's test worse solutions in different positions
+  // in the list - beginning, middle, end.
+
+  // To make "best" solutions ambiguous, let's use a single
+  // type variable resolved into multiple distinct types.
+  auto *ambiguousVar = CS.createTypeVariable(
+      CS.getConstraintLocator({}), /*options=*/TVO_PrefersSubtypeBinding);
+
+  auto formSolution = [&](Score score, Type type) -> Solution {
+    Solution solution{CS, score};
+    solution.typeBindings[ambiguousVar] = type;
+    return solution;
+  };
+
+  // Nothing to remove
+  {
+    SmallVector<Solution, 4> solutions;
+
+    solutions.push_back(formSolution(bestScore, getStdlibType("String")));
+    solutions.push_back(formSolution(bestScore, getStdlibType("Int")));
+
+    auto best = CS.findBestSolution(solutions, /*minimize=*/true);
+
+    ASSERT_FALSE(best.hasValue());
+    ASSERT_EQ(solutions.size(), 2u);
+    ASSERT_EQ(solutions[0].getFixedScore(), bestScore);
+    ASSERT_EQ(solutions[1].getFixedScore(), bestScore);
+  }
+
+  // Worst solutions are at the front
+  {
+    SmallVector<Solution, 4> solutions;
+
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore2, getStdlibType("Int")));
+
+    solutions.push_back(formSolution(bestScore, getStdlibType("String")));
+    solutions.push_back(formSolution(bestScore, getStdlibType("Int")));
+
+    auto best = CS.findBestSolution(solutions, /*minimize=*/true);
+
+    ASSERT_FALSE(best.hasValue());
+    ASSERT_EQ(solutions.size(), 2u);
+    ASSERT_EQ(solutions[0].getFixedScore(), bestScore);
+    ASSERT_EQ(solutions[1].getFixedScore(), bestScore);
+  }
+
+  // Worst solutions are in the middle
+  {
+    SmallVector<Solution, 4> solutions;
+
+    solutions.push_back(formSolution(bestScore, getStdlibType("String")));
+
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore2, getStdlibType("Int")));
+
+    solutions.push_back(formSolution(bestScore, getStdlibType("Int")));
+
+    auto best = CS.findBestSolution(solutions, /*minimize=*/true);
+
+    ASSERT_FALSE(best.hasValue());
+    ASSERT_EQ(solutions.size(), 2u);
+    ASSERT_EQ(solutions[0].getFixedScore(), bestScore);
+    ASSERT_EQ(solutions[1].getFixedScore(), bestScore);
+  }
+
+  // Worst solutions are at the end
+  {
+    SmallVector<Solution, 4> solutions;
+
+    solutions.push_back(formSolution(bestScore, getStdlibType("String")));
+    solutions.push_back(formSolution(bestScore, getStdlibType("Int")));
+
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore2, getStdlibType("Int")));
+
+    auto best = CS.findBestSolution(solutions, /*minimize=*/true);
+
+    ASSERT_FALSE(best.hasValue());
+    ASSERT_EQ(solutions.size(), 2u);
+    ASSERT_EQ(solutions[0].getFixedScore(), bestScore);
+    ASSERT_EQ(solutions[1].getFixedScore(), bestScore);
+  }
+
+  // Worst solutions are spread out
+  {
+    SmallVector<Solution, 4> solutions;
+
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(bestScore, getStdlibType("String")));
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore2, getStdlibType("Int")));
+    solutions.push_back(formSolution(bestScore, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore1, getStdlibType("Int")));
+    solutions.push_back(formSolution(worseScore2, getStdlibType("Int")));
+
+    auto best = CS.findBestSolution(solutions, /*minimize=*/true);
+
+    ASSERT_FALSE(best.hasValue());
+    ASSERT_EQ(solutions.size(), 2u);
+    ASSERT_EQ(solutions[0].getFixedScore(), bestScore);
+    ASSERT_EQ(solutions[1].getFixedScore(), bestScore);
+  }
+}