[Constraint solver] Migrate ConstraintGraph::gatherConstraints() off adjacencies list.

Use the adjacencies implied by the constraints of a node rather than looking
at the "adjacency" list, and try to simplify this code path a bit. The
diagnostic change is because we are now uniformly recording the
members of the equivalence class.

(cherry picked from commit 54bdd7b)

Author: DougGregor

lib/Sema/ConstraintGraph.cpp

@@ -486,51 +486,43 @@ void ConstraintGraph::gatherConstraints(
   auto &reprNode = (*this)[CS.getRepresentative(typeVar)];
   auto equivClass = reprNode.getEquivalenceClass();
   llvm::SmallPtrSet<TypeVariableType *, 4> typeVars;
-  for (auto typeVar : equivClass) {
-    if (!typeVars.insert(typeVar).second)
-      continue;
-
-    for (auto constraint : (*this)[typeVar].getConstraints()) {
-      if (acceptConstraint(constraint))
-        constraints.insert(constraint);
-    }
-
-    auto &node = (*this)[typeVar];
 
-    // Retrieve the constraints from adjacent bindings.
-    for (auto adjTypeVar : node.getAdjacencies()) {
-      switch (kind) {
-      case GatheringKind::EquivalenceClass:
-        if (!node.getAdjacency(adjTypeVar).FixedBinding)
-          continue;
-        break;
-
-      case GatheringKind::AllMentions:
-        break;
-      }
 
-      ArrayRef<TypeVariableType *> adjTypeVarsToVisit;
-      switch (kind) {
-      case GatheringKind::EquivalenceClass:
-        adjTypeVarsToVisit = adjTypeVar;
-        break;
+  /// Add constraints for the given adjacent type variable.
+  auto addAdjacentConstraints = [&](TypeVariableType *adjTypeVar) {
+    auto adjTypeVarsToVisit =
+        (*this)[CS.getRepresentative(adjTypeVar)].getEquivalenceClass();
+    for (auto adjTypeVarEquiv : adjTypeVarsToVisit) {
+      if (!typeVars.insert(adjTypeVarEquiv).second)
+        continue;
 
-      case GatheringKind::AllMentions:
-        adjTypeVarsToVisit
-          = (*this)[CS.getRepresentative(adjTypeVar)].getEquivalenceClass();
-        break;
+      for (auto constraint : (*this)[adjTypeVarEquiv].getConstraints()) {
+        if (acceptConstraint(constraint))
+          constraints.insert(constraint);
       }
+    }
+  };
 
-      for (auto adjTypeVarEquiv : adjTypeVarsToVisit) {
-        if (!typeVars.insert(adjTypeVarEquiv).second)
-          continue;
+  for (auto typeVar : equivClass) {
+    auto &node = (*this)[typeVar];
+    for (auto constraint : node.getConstraints()) {
+      if (acceptConstraint(constraint))
+        constraints.insert(constraint);
 
-        for (auto constraint : (*this)[adjTypeVarEquiv].getConstraints()) {
-          if (acceptConstraint(constraint))
-            constraints.insert(constraint);
+      // If we want all mentions, visit type variables within each of our
+      // constraints.
+      if (kind == GatheringKind::AllMentions) {
+        for (auto adjTypeVar : constraint->getTypeVariables()) {
+          addAdjacentConstraints(adjTypeVar);
         }
       }
     }
+
+    // For any type variable mentioned in a fixed binding, add adjacent
+    // constraints.
+    for (auto adjTypeVar : node.getFixedAdjacencies()) {
+      addAdjacentConstraints(adjTypeVar);
+    }
   }
 }
 

test/Constraints/generics.swift

@@ -646,7 +646,7 @@ let arr = [BottleLayout]()
 let layout = BottleLayout(count:1)
 let ix = arr.firstIndex(of:layout) // expected-error {{argument type 'BottleLayout' does not conform to expected type 'Equatable'}}
 
-let _: () -> UInt8 = { .init("a" as Unicode.Scalar) } // expected-error {{initializer 'init(_:)' requires that 'Unicode.Scalar' conform to 'BinaryInteger'}}
+let _: () -> UInt8 = { .init("a" as Unicode.Scalar) } // expected-error {{missing argument label 'ascii:' in call}}
 
 // https://bugs.swift.org/browse/SR-9068
 func compare<C: Collection, Key: Hashable, Value: Equatable>(c: C)

test/Constraints/patterns.swift

@@ -291,9 +291,7 @@ switch staticMembers {
   case .init(0): break
   case .init(_): break // expected-error{{'_' can only appear in a pattern}}
   case .init(let x): break // expected-error{{cannot appear in an expression}}
-case .init(opt: 0): break // expected-error{{value of optional type 'StaticMembers?' must be unwrapped to a value of type 'StaticMembers'}}
-  // expected-note@-1{{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}
-  // expected-note@-2{{coalesce using '??' to provide a default when the optional value contains 'nil'}}
+  case .init(opt: 0): break // expected-error{{pattern cannot match values of type 'StaticMembers'}}
 
   case .prop: break
   // TODO: repeated error message