Merge pull request swiftlang#31104 from xedin/compute-diag-anchors-on-demand

[Diagnostics] Refactor `FailureDiagnostic` to operate on `TypedNode`

Author: xedin

include/swift/AST/Expr.h

@@ -3759,7 +3759,12 @@ class ClosureExpr : public AbstractClosureExpr {
     assert(hasExplicitResultType() && "No explicit result type");
     return ExplicitResultType;
   }
-  
+
+  TypeRepr *getExplicitResultTypeRepr() const {
+    assert(hasExplicitResultType() && "No explicit result type");
+    return ExplicitResultType.getTypeRepr();
+  }
+
   void setExplicitResultType(SourceLoc arrowLoc, TypeLoc resultType) {
     ArrowLoc = arrowLoc;
     ExplicitResultType = resultType;

lib/Sema/CSApply.cpp

@@ -166,10 +166,17 @@ ConstraintLocator *Solution::getCalleeLocator(ConstraintLocator *locator,
 }
 
 ConstraintLocator *
-Solution::getConstraintLocator(Expr *anchor,
+Solution::getConstraintLocator(const Expr *anchor,
                                ArrayRef<LocatorPathElt> path) const {
   auto &cs = getConstraintSystem();
-  return cs.getConstraintLocator(anchor, path);
+  return cs.getConstraintLocator(const_cast<Expr *>(anchor), path);
+}
+
+ConstraintLocator *
+Solution::getConstraintLocator(ConstraintLocator *base,
+                               ArrayRef<LocatorPathElt> path) const {
+  auto &cs = getConstraintSystem();
+  return cs.getConstraintLocator(base, path);
 }
 
 /// Return the implicit access kind for a MemberRefExpr with the