Sema: De-duplicate defaults in inferTransitiveSupertypeBindings()

This is necessary now that BindingSet::Defaults is a vector and
not a set.

Author: slavapestov

lib/Sema/CSBindings.cpp

@@ -616,6 +616,18 @@ void BindingSet::inferTransitiveKeyPathBindings() {
 }
 
 void BindingSet::inferTransitiveSupertypeBindings() {
+  llvm::SmallDenseSet<ProtocolDecl *> seenLiterals;
+  for (const auto &literal : Literals) {
+    bool inserted = seenLiterals.insert(literal.getProtocol()).second;
+    ASSERT(inserted);
+  }
+
+  llvm::SmallDenseSet<Constraint *> seenDefaults;
+  for (auto *constraint : Defaults) {
+    bool inserted = seenDefaults.insert(constraint).second;
+    ASSERT(inserted);
+  }
+
   for (const auto &entry : Info.SupertypeOf) {
     auto &node = CS.getConstraintGraph()[entry.first];
     if (!node.hasBindingSet())
@@ -648,11 +660,7 @@ void BindingSet::inferTransitiveSupertypeBindings() {
     for (auto literal : bindings.Literals) {
       auto *protocol = literal.getProtocol();
 
-      bool found = llvm::any_of(Literals,
-          [&](const auto &literal) -> bool {
-            return literal.getProtocol() == protocol;
-          });
-      if (found)
+      if (!seenLiterals.insert(protocol).second)
         continue;
 
       literal.setDirectRequirement(false);
@@ -664,6 +672,9 @@ void BindingSet::inferTransitiveSupertypeBindings() {
       if (def->getKind() == ConstraintKind::FallbackType)
         continue;
 
+      if (!seenDefaults.insert(def).second)
+        continue;
+
       addDefault(def);
     }
 

test/Constraints/closures.swift

@@ -1415,3 +1415,17 @@ func test_implicit_result_conversions() {
     return // Ok
   }
 }
+
+// Random example reduced from swift-build which tripped an assert not
+// previously covered by our test suite
+do {
+  struct S {
+    var x: [Int: [String]] = [:]
+  }
+
+  let s = [S]()
+
+  let _: [Int: Set<String>] = s.map(\.x)
+      .reduce([:], { x, y in x.merging(y, uniquingKeysWith: +) })
+      .mapValues { Set($0) }
+}