[ConstraintLocator] Generalize pattern decl locator to support "named" and "any"

Author: xedin

include/swift/Sema/ConstraintLocator.h

@@ -1076,6 +1076,39 @@ class LocatorPathElt::PatternBindingElement final
   }
 };
 
+class LocatorPathElt::PatternDecl : public StoredIntegerElement<1> {
+public:
+  PatternDecl(ConstraintLocator::PathElementKind kind)
+      : StoredIntegerElement(kind, /*placeholder=*/0) {
+    assert(classof(this) && "classof needs updating");
+  }
+
+  static bool classof(const LocatorPathElt *elt) {
+    return elt->getKind() == ConstraintLocator::NamedPatternDecl ||
+           elt->getKind() == ConstraintLocator::AnyPatternDecl;
+  }
+};
+
+class LocatorPathElt::NamedPatternDecl final
+    : public LocatorPathElt::PatternDecl {
+public:
+  NamedPatternDecl() : PatternDecl(ConstraintLocator::NamedPatternDecl) {}
+
+  static bool classof(const LocatorPathElt *elt) {
+    return elt->getKind() == ConstraintLocator::NamedPatternDecl;
+  }
+};
+
+class LocatorPathElt::AnyPatternDecl final
+    : public LocatorPathElt::PatternDecl {
+public:
+  AnyPatternDecl() : PatternDecl(ConstraintLocator::AnyPatternDecl) {}
+
+  static bool classof(const LocatorPathElt *elt) {
+    return elt->getKind() == ConstraintLocator::AnyPatternDecl;
+  }
+};
+
 namespace details {
   template <typename CustomPathElement>
   class PathElement {

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -239,8 +239,12 @@ CUSTOM_LOCATOR_PATH_ELT(SyntacticElement)
 /// The element of the pattern binding declaration.
 CUSTOM_LOCATOR_PATH_ELT(PatternBindingElement)
 
-/// The variable declared by a named pattern.
-SIMPLE_LOCATOR_PATH_ELT(NamedPatternDecl)
+/// A declaration introduced by a pattern: name (i.e. `x`) or `_`
+ABSTRACT_LOCATOR_PATH_ELT(PatternDecl)
+  /// The variable declared by a named pattern.
+  CUSTOM_LOCATOR_PATH_ELT(NamedPatternDecl)
+  /// The anonymous variable declared by a `_` pattern.
+  CUSTOM_LOCATOR_PATH_ELT(AnyPatternDecl)
 
 #undef LOCATOR_PATH_ELT
 #undef CUSTOM_LOCATOR_PATH_ELT

lib/Sema/ConstraintLocator.cpp

@@ -98,6 +98,7 @@ unsigned LocatorPathElt::getNewSummaryFlags() const {
   case ConstraintLocator::PackElement:
   case ConstraintLocator::PatternBindingElement:
   case ConstraintLocator::NamedPatternDecl:
+  case ConstraintLocator::AnyPatternDecl:
     return 0;
 
   case ConstraintLocator::FunctionArgument:
@@ -447,6 +448,11 @@ void LocatorPathElt::dump(raw_ostream &out) const {
     out << "named pattern decl";
     break;
   }
+
+  case ConstraintLocator::AnyPatternDecl: {
+    out << "'_' pattern decl";
+    break;
+  }
   }
 }
 

lib/Sema/ConstraintSystem.cpp

@@ -5277,6 +5277,15 @@ void constraints::simplifyLocator(ASTNode &anchor,
       break;
     }
 
+    case ConstraintLocator::AnyPatternDecl: {
+      // This element is just a marker for `_` pattern since it doesn't
+      // have a declaration. We need to make sure that it only appaears
+      // when anchored on `AnyPattern`.
+      assert(getAsPattern<AnyPattern>(anchor));
+      path = path.slice(1);
+      break;
+    }
+
     case ConstraintLocator::ImplicitConversion:
       break;