Merge pull request #14585 from rudkx/rdar37073401-4.1

[4.1] Fix an issue with the constraint favoring code in the constraint optimizer.

Author: rudkx

include/swift/Basic/LangOptions.h

@@ -152,10 +152,6 @@ namespace swift {
     /// solver should be debugged.
     unsigned DebugConstraintSolverAttempt = 0;
 
-    /// \brief Enable the experimental constraint propagation in the
-    /// type checker.
-    bool EnableConstraintPropagation = false;
-
     /// \brief Enable the iterative type checker.
     bool IterativeTypeChecker = false;
 

include/swift/Option/FrontendOptions.td

@@ -149,9 +149,6 @@ def debug_constraints : Flag<["-"], "debug-constraints">,
 def debug_constraints_attempt : Separate<["-"], "debug-constraints-attempt">,
   HelpText<"Debug the constraint solver at a given attempt">;
 
-def propagate_constraints : Flag<["-"], "propagate-constraints">,
-  HelpText<"Enable constraint propagation in the type checker">;
-
 def iterative_type_checker : Flag<["-"], "iterative-type-checker">,
   HelpText<"Enable the iterative type checker">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -988,7 +988,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableASTScopeLookup |= Args.hasArg(OPT_enable_astscope_lookup);
   Opts.DebugConstraintSolver |= Args.hasArg(OPT_debug_constraints);
-  Opts.EnableConstraintPropagation |= Args.hasArg(OPT_propagate_constraints);
   Opts.IterativeTypeChecker |= Args.hasArg(OPT_iterative_type_checker);
   Opts.NamedLazyMemberLoading &= !Args.hasArg(OPT_disable_named_lazy_member_loading);
   Opts.DebugGenericSignatures |= Args.hasArg(OPT_debug_generic_signatures);

lib/Sema/CMakeLists.txt

@@ -8,7 +8,6 @@ add_swift_library(swiftSema STATIC
   CSBindings.cpp
   CSDiag.cpp
   CSGen.cpp
-  CSPropagate.cpp
   CSRanking.cpp
   CSSimplify.cpp
   CSSolver.cpp

lib/Sema/CSGen.cpp

@@ -828,7 +828,20 @@ namespace {
 
     Type firstArgTy = argTupleTy->getElement(0).getType()->getWithoutParens();
     Type secondArgTy = argTupleTy->getElement(1).getType()->getWithoutParens();
-    
+
+    auto isOptionalWithMatchingObjectType = [](Type optional,
+                                               Type object) -> bool {
+      if (auto objTy = optional->getRValueType()->getAnyOptionalObjectType())
+        return objTy->getRValueType()->isEqual(object->getRValueType());
+
+      return false;
+    };
+
+    auto isPotentialForcingOpportunity = [&](Type first, Type second) -> bool {
+      return isOptionalWithMatchingObjectType(first, second) ||
+             isOptionalWithMatchingObjectType(second, first);
+    };
+
     // Determine whether the given declaration is favored.
     auto isFavoredDecl = [&](ValueDecl *value) -> bool {
       auto valueTy = value->getInterfaceType();
@@ -882,14 +895,14 @@ namespace {
 
       auto resultTy = fnTy->getResult();
       auto contextualTy = CS.getContextualType(expr);
-      
-      return
-        (isFavoredParamAndArg(CS, firstParamTy, firstArg, firstArgTy,
-                              secondArgTy) ||
-         isFavoredParamAndArg(CS, secondParamTy, secondArg, secondArgTy,
-                              firstArgTy)) &&
-         firstParamTy->isEqual(secondParamTy) &&
-        (!contextualTy || contextualTy->isEqual(resultTy));
+
+      return (isFavoredParamAndArg(CS, firstParamTy, firstArg, firstArgTy,
+                                   secondArgTy) ||
+              isFavoredParamAndArg(CS, secondParamTy, secondArg, secondArgTy,
+                                   firstArgTy)) &&
+             firstParamTy->isEqual(secondParamTy) &&
+             !isPotentialForcingOpportunity(firstArgTy, secondArgTy) &&
+             (!contextualTy || contextualTy->isEqual(resultTy));
     };
 
     favorCallOverloads(expr, CS, isFavoredDecl);