Throw CycleException when cycles are detected

This changes the DependencyGraph's topological sort to throw a
dedicated exception class so that it can be better handled.

Author: JordonPhillips

smithy-build/src/main/java/software/amazon/smithy/build/SmithyBuildImpl.java

@@ -33,6 +33,7 @@
 import software.amazon.smithy.model.node.ObjectNode;
 import software.amazon.smithy.model.transform.ModelTransformer;
 import software.amazon.smithy.model.validation.ValidatedResult;
+import software.amazon.smithy.utils.CycleException;
 import software.amazon.smithy.utils.DependencyGraph;
 import software.amazon.smithy.utils.Pair;
 import software.amazon.smithy.utils.SmithyBuilder;
@@ -242,7 +243,7 @@ private List<ResolvedPlugin> resolvePlugins(String projectionName, ProjectionCon
         List<PluginId> sorted;
         try {
             sorted = dependencyGraph.toSortedList();
-        } catch (IllegalStateException e) {
+        } catch (CycleException e) {
             throw new SmithyBuildException(e.getMessage(), e);
         }
 

smithy-build/src/test/java/software/amazon/smithy/build/SmithyBuildTest.java

@@ -624,7 +624,7 @@ public void detectsPluginCycles() throws Exception {
                 .build());
 
         SmithyBuildException e = assertThrows(SmithyBuildException.class, builder::build);
-        assertThat(e.getMessage(), containsString("Cycle(s) detected in dependency graph"));
+        assertThat(e.getMessage(), containsString("Cycle(s) detected"));
     }
 
     @Test

smithy-build/src/test/java/software/amazon/smithy/build/TimestampPlugin1.java

@@ -20,6 +20,9 @@ public void execute(PluginContext context) {
         } catch (InterruptedException ignored) {}
     }
 
+    // This is made serial to protect against test failures if we decide later to
+    // have plugins run in parallel. These plugins MUST run serially with respect
+    // to each other to function.
     @Override
     public boolean isSerial() {
         return true;

smithy-build/src/test/java/software/amazon/smithy/build/TimestampPlugin2.java

@@ -27,6 +27,9 @@ public List<String> runBefore() {
         return ListUtils.of("timestampPlugin1");
     }
 
+    // This is made serial to protect against test failures if we decide later to
+    // have plugins run in parallel. These plugins MUST run serially with respect
+    // to each other to function.
     @Override
     public boolean isSerial() {
         return true;

smithy-build/src/test/java/software/amazon/smithy/build/TimestampPlugin3.java

@@ -27,6 +27,9 @@ public List<String> runAfter() {
         return ListUtils.of("timestampPlugin1");
     }
 
+    // This is made serial to protect against test failures if we decide later to
+    // have plugins run in parallel. These plugins MUST run serially with respect
+    // to each other to function.
     @Override
     public boolean isSerial() {
         return true;

smithy-codegen-core/src/main/java/software/amazon/smithy/codegen/core/IntegrationTopologicalSort.java

@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.logging.Logger;
+import software.amazon.smithy.utils.CycleException;
 import software.amazon.smithy.utils.DependencyGraph;
 
 final class IntegrationTopologicalSort<I extends SmithyIntegration<?, ?, ?>> {
@@ -46,7 +47,7 @@ List<I> sort() {
         List<String> sorted;
         try {
             sorted = dependencyGraph.toSortedList(this::compareIntegrations);
-        } catch (IllegalStateException e) {
+        } catch (CycleException e) {
             throw new IllegalArgumentException(e);
         }
         for (String name : sorted) {

smithy-utils/src/main/java/software/amazon/smithy/utils/CycleException.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package software.amazon.smithy.utils;
+
+import java.util.Collection;
+import java.util.stream.Collectors;
+
+public class CycleException extends RuntimeException {
+    public CycleException(Collection<?> cyclicNodes) {
+        super(String.format("Cycle(s) detected amongst: [%s]",
+                cyclicNodes.stream().map(Object::toString).collect(Collectors.joining(", "))));
+    }
+}

smithy-utils/src/main/java/software/amazon/smithy/utils/DependencyGraph.java

@@ -349,15 +349,13 @@ private List<T> toSortedList(Queue<T> satisfied) {
 
         // Check for cycles.
         if (result.size() != reverseDependencies.size()) {
-            List<String> remaining = new ArrayList<>(reverseDependencies.size() - result.size());
+            List<T> remaining = new ArrayList<>(reverseDependencies.size() - result.size());
             for (T node : reverseDependencies.keySet()) {
                 if (!result.contains(node)) {
-                    remaining.add(node.toString());
+                    remaining.add(node);
                 }
             }
-            throw new IllegalStateException(
-                    String.format("Cycle(s) detected in dependency graph while attempting to sort among [%s]",
-                            String.join(", ", remaining)));
+            throw new CycleException(remaining);
         }
 
         return result;

smithy-utils/src/test/java/software/amazon/smithy/utils/DependencyGraphTest.java

@@ -233,7 +233,7 @@ public void sortedListThrowsErrorOnCycle() {
         graph.addDependency("spam", "eggs");
         graph.addDependency("eggs", "spam");
 
-        assertThrows(IllegalStateException.class, graph::toSortedList);
+        assertThrows(CycleException.class, graph::toSortedList);
     }
 
     @Test