smithy-model/src/main/java/software/amazon/smithy/model/selector/AbstractNeighborSelector.java

@@ -32,23 +32,23 @@ abstract class AbstractNeighborSelector implements InternalSelector {
     }
 
     @Override
-    public final boolean push(Context context, Shape shape, Receiver next) {
+    public final Response push(Context context, Shape shape, Receiver next) {
         NeighborProvider resolvedProvider = getNeighborProvider(context, includeTraits);
         for (Relationship rel : resolvedProvider.getNeighbors(shape)) {
             if (matches(rel)) {
-                if (!emitMatchingRel(context, rel, next)) {
+                if (emitMatchingRel(context, rel, next) == Response.STOP) {
                     // Stop pushing shapes upstream and propagate the signal to stop.
-                    return false;
+                    return Response.STOP;
                 }
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     abstract NeighborProvider getNeighborProvider(Context context, boolean includeTraits);
 
-    abstract boolean emitMatchingRel(Context context, Relationship rel, Receiver next);
+    abstract Response emitMatchingRel(Context context, Relationship rel, Receiver next);
 
     private boolean matches(Relationship rel) {
         return rel.getNeighborShape().isPresent()

smithy-model/src/main/java/software/amazon/smithy/model/selector/AndSelector.java

@@ -60,7 +60,7 @@ static final class IntermediateAndSelector implements InternalSelector {
         }
 
         @Override
-        public boolean push(Context ctx, Shape shape, Receiver next) {
+        public Response push(Context ctx, Shape shape, Receiver next) {
             return leftSelector.push(ctx, shape, (c, s) -> rightSelector.push(c, s, next));
         }
 

smithy-model/src/main/java/software/amazon/smithy/model/selector/AttributeSelector.java

@@ -84,11 +84,11 @@ public Collection<? extends Shape> getStartingShapes(Model model) {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         if (matchesAttribute(shape, context)) {
             return next.apply(context, shape);
         } else {
-            return true;
+            return Response.CONTINUE;
         }
     }
 

smithy-model/src/main/java/software/amazon/smithy/model/selector/Context.java

@@ -63,10 +63,10 @@ private static final class Holder implements InternalSelector.Receiver {
         boolean set;
 
         @Override
-        public boolean apply(Context context, Shape shape) {
+        public InternalSelector.Response apply(Context context, Shape shape) {
             set = true;
             // Stop receiving shapes once the first value is seen.
-            return false;
+            return InternalSelector.Response.STOP;
         }
     }
 

smithy-model/src/main/java/software/amazon/smithy/model/selector/ForwardNeighborSelector.java

@@ -37,7 +37,7 @@ NeighborProvider getNeighborProvider(Context context, boolean includeTraits) {
     }
 
     @Override
-    boolean emitMatchingRel(Context context, Relationship rel, Receiver next) {
+    Response emitMatchingRel(Context context, Relationship rel, Receiver next) {
         return next.apply(context, rel.getNeighborShape().get());
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/InSelector.java

@@ -29,13 +29,13 @@ final class InSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         // Some internal selectors provide optimizations for quickly checking if they contain a shape.
         switch (selector.containsShapeOptimization(context, shape)) {
             case YES:
                 return next.apply(context, shape);
             case NO:
-                return true;
+                return Response.CONTINUE;
             case MAYBE:
             default:
                 // Unable to use the optimization, so emit each shape until a match is found.
@@ -46,7 +46,7 @@ public boolean push(Context context, Shape shape, Receiver next) {
                     return next.apply(context, shape);
                 }
 
-                return true;
+                return Response.CONTINUE;
         }
     }
 
@@ -59,13 +59,13 @@ private static final class FilteredHolder implements InternalSelector.Receiver {
         }
 
         @Override
-        public boolean apply(Context context, Shape shape) {
+        public Response apply(Context context, Shape shape) {
             if (shape.equals(shapeToMatch)) {
                 matched = true;
-                return false;
+                return Response.STOP;
             }
 
-            return true;
+            return Response.CONTINUE;
         }
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/InternalSelector.java

@@ -52,7 +52,13 @@ interface InternalSelector {
      * @param next Receiver to call 0 or more times.
      * @return Returns true to continue sending shapes to the selector.
      */
-    boolean push(Context ctx, Shape shape, Receiver next);
+    Response push(Context ctx, Shape shape, Receiver next);
+
+    /** Tells shape emitters whether to continue to send shapes to an InternalSelector or Receiver. */
+    enum Response {
+        CONTINUE,
+        STOP
+    }
 
     /**
      * Pushes {@code shape} through the selector and adds all results to {@code captures}.
@@ -71,7 +77,7 @@ interface InternalSelector {
     default <C extends Collection<Shape>> C pushResultsToCollection(Context context, Shape shape, C captures) {
         push(context, shape, (c, s) -> {
             captures.add(s);
-            return true;
+            return Response.CONTINUE;
         });
         return captures;
     }
@@ -127,6 +133,6 @@ interface Receiver {
          * @param shape Shape that is received.
          * @return Returns true to continue receiving shapes.
          */
-        boolean apply(Context context, Shape shape);
+        Response apply(Context context, Shape shape);
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/IsSelector.java

@@ -33,13 +33,13 @@ static InternalSelector of(List<InternalSelector> predicates) {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         for (InternalSelector selector : selectors) {
-            if (!selector.push(context, shape, next)) {
-                return false;
+            if (selector.push(context, shape, next) == Response.STOP) {
+                return Response.STOP;
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/NotSelector.java

@@ -29,11 +29,11 @@ final class NotSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         if (!context.receivedShapes(shape, selector)) {
             return next.apply(context, shape);
         } else {
-            return true;
+            return Response.CONTINUE;
         }
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/RecursiveNeighborSelector.java

@@ -25,21 +25,21 @@
  */
 final class RecursiveNeighborSelector implements InternalSelector {
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         Walker walker = new Walker(context.neighborIndex.getProvider());
         Iterator<Shape> shapeIterator = walker.iterateShapes(shape);
 
         while (shapeIterator.hasNext()) {
             Shape nextShape = shapeIterator.next();
             // Don't include the shape being visited.
             if (!nextShape.equals(shape)) {
-                if (!next.apply(context, nextShape)) {
+                if (next.apply(context, nextShape) == Response.STOP) {
                     // Stop sending recursive neighbors when told to stop and propagate.
-                    return false;
+                    return Response.STOP;
                 }
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/ReverseNeighborSelector.java

@@ -37,7 +37,7 @@ NeighborProvider getNeighborProvider(Context context, boolean includeTraits) {
     }
 
     @Override
-    boolean emitMatchingRel(Context context, Relationship rel, Receiver next) {
+    Response emitMatchingRel(Context context, Relationship rel, Receiver next) {
         return next.apply(context, rel.getShape());
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/RootSelector.java

@@ -36,14 +36,14 @@ final class RootSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         for (Shape v : context.getRootResult(id)) {
-            if (!next.apply(context, v)) {
-                return false;
+            if (next.apply(context, v) == Response.STOP) {
+                return Response.STOP;
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     @Override

smithy-model/src/main/java/software/amazon/smithy/model/selector/ScopedAttributeSelector.java

@@ -64,11 +64,11 @@ interface ScopedFactory {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         if (matchesAssertions(shape, context.getVars())) {
             return next.apply(context, shape);
         } else {
-            return true;
+            return Response.CONTINUE;
         }
     }
 

smithy-model/src/main/java/software/amazon/smithy/model/selector/SelectorParser.java

@@ -259,7 +259,7 @@ private InternalSelector parseSelectorFunction() {
             default:
                 LOGGER.warning(String.format("Unknown function name `%s` found in selector: %s",
                                              name, expression()));
-                return (context, shape, next) -> true;
+                return (context, shape, next) -> InternalSelector.Response.CONTINUE;
         }
     }
 

smithy-model/src/main/java/software/amazon/smithy/model/selector/ShapeTypeCategorySelector.java

@@ -27,12 +27,12 @@ final class ShapeTypeCategorySelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context ctx, Shape shape, Receiver next) {
+    public Response push(Context ctx, Shape shape, Receiver next) {
         if (shapeCategory.isInstance(shape)) {
             return next.apply(ctx, shape);
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     @Override

smithy-model/src/main/java/software/amazon/smithy/model/selector/ShapeTypeSelector.java

@@ -29,12 +29,12 @@ final class ShapeTypeSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context ctx, Shape shape, Receiver next) {
+    public Response push(Context ctx, Shape shape, Receiver next) {
         if (shape.getType().isShapeType(shapeType)) {
             return next.apply(ctx, shape);
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     @Override

smithy-model/src/main/java/software/amazon/smithy/model/selector/TestSelector.java

@@ -32,16 +32,15 @@ final class TestSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         for (InternalSelector predicate : selectors) {
             if (context.receivedShapes(shape, predicate)) {
                 // The instant something matches, stop testing selectors.
                 return next.apply(context, shape);
             }
         }
 
-        // Note that this does not return false when there is not a match,
-        // since it should to continue to receive shapes to test.
-        return true;
+        // Continue to receive shapes because other shapes could match.
+        return Response.CONTINUE;
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/TopDownSelector.java

@@ -33,22 +33,22 @@ final class TopDownSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         if (shape.isServiceShape() || shape.isResourceShape() || shape.isOperationShape()) {
             return pushMatch(false, context, shape, next, new HashSet<>());
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     // While a model can't contain recursive resource references, a custom
     // validator might use the :topdown selector function on a model with
     // recursive references. Custom validators are applied before resource
     // cycles are detected, meaning this function needs to protect against
     // recursion.
-    private boolean pushMatch(boolean qualified, Context context, Shape shape, Receiver next, Set<ShapeId> visited) {
+    private Response pushMatch(boolean qualified, Context context, Shape shape, Receiver next, Set<ShapeId> visited) {
         if (visited.contains(shape.getId())) {
-            return true;
+            return Response.CONTINUE;
         }
 
         visited.add(shape.getId());
@@ -64,22 +64,22 @@ private boolean pushMatch(boolean qualified, Context context, Shape shape, Recei
         }
 
         // If the shape is matched, then it's sent to the next receiver.
-        if (qualified && !next.apply(context, shape)) {
-            return false; // fast-fail if the receiver fast-fails.
+        if (qualified && next.apply(context, shape) == Response.STOP) {
+            return Response.STOP; // fast-fail if the receiver fast-fails.
         }
 
         // Recursively check each nested resource/operation.
         for (Relationship rel : context.neighborIndex.getProvider().getNeighbors(shape)) {
             if (rel.getNeighborShape().isPresent() && !rel.getNeighborShapeId().equals(shape.getId())) {
                 if (rel.getRelationshipType() == RelationshipType.RESOURCE
                         || rel.getRelationshipType() == RelationshipType.OPERATION) {
-                    if (!pushMatch(qualified, context, rel.getNeighborShape().get(), next, visited)) {
-                        return false;
+                    if (pushMatch(qualified, context, rel.getNeighborShape().get(), next, visited) == Response.STOP) {
+                        return Response.STOP;
                     }
                 }
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 }

smithy-model/src/main/java/software/amazon/smithy/model/selector/VariableGetSelector.java

@@ -30,16 +30,16 @@ final class VariableGetSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
-        // Do not fail on an invalid variable access.
+    public Response push(Context context, Shape shape, Receiver next) {
+        // Do not fail on invalid variable access.
         for (Shape v : getShapes(context)) {
-            if (!next.apply(context, v)) {
+            if (next.apply(context, v) == Response.STOP) {
                 // Propagate the signal to stop upstream.
-                return false;
+                return Response.STOP;
             }
         }
 
-        return true;
+        return Response.CONTINUE;
     }
 
     private Set<Shape> getShapes(Context context) {

smithy-model/src/main/java/software/amazon/smithy/model/selector/VariableStoreSelector.java

@@ -38,7 +38,7 @@ final class VariableStoreSelector implements InternalSelector {
     }
 
     @Override
-    public boolean push(Context context, Shape shape, Receiver next) {
+    public Response push(Context context, Shape shape, Receiver next) {
         // Buffer the result of piping the shape through the selector
         // so that it can be retrieved through context vars.
         Set<Shape> captures = selector.pushResultsToCollection(context, shape, new HashSet<>());