Create empty manifest when no source models

build.gradle

@@ -107,6 +107,7 @@ subprojects {
         test {
             testLogging {
                 events = ["passed", "skipped", "failed"]
+                exceptionFormat = "full"
             }
         }
     }

docs/source/1.0/guides/building-models/build-config.rst

@@ -1134,7 +1134,8 @@ The ``sources`` plugin copies the source models and creates a manifest.
 When building the ``source`` projection, the models that were used to build the
 model are copied over literally. When a JAR is used as a source model, the
 Smithy models contained within the JAR are copied as a source model while the
-JAR itself is not copied.
+JAR itself is not copied. If there are no source models, an empty manifest is
+created.
 
 When applying a projection, a new model file is created that contains only
 the shapes, trait definitions, and metadata that were defined in a source

smithy-build/src/main/java/software/amazon/smithy/build/plugins/SourcesPlugin.java

@@ -88,14 +88,15 @@ public void execute(PluginContext context) {
             projectSources(context);
         }
 
+        String manifest = "";
         if (names.isEmpty()) {
-            LOGGER.info(String.format("Skipping `%s` manifest because no Smithy sources found", projectionName));
+            LOGGER.info(String.format("Writing empty `%s` manifest because no Smithy sources found", projectionName));
         } else {
             LOGGER.fine(() -> String.format("Writing `%s` manifest", projectionName));
             // Normalize filenames to Unix style.
-            String manifest = names.stream().map(name -> name.replace("\\", "/")).collect(Collectors.joining("\n"));
-            context.getFileManifest().writeFile("manifest", manifest + "\n");
+            manifest = names.stream().map(name -> name.replace("\\", "/")).collect(Collectors.joining("\n"));
         }
+        context.getFileManifest().writeFile("manifest", manifest + "\n");
     }
 
     private static List<String> copySources(PluginContext context) {

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

@@ -19,6 +19,7 @@
 import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -133,6 +134,26 @@ public void buildsModels() throws Exception {
         assertThat(Files.isRegularFile(outputDirectory.resolve("b/model/model.json")), is(true));
     }
 
+    @Test
+    public void createsEmptyManifest() throws Exception {
+        SmithyBuildConfig config = SmithyBuildConfig.builder()
+                .load(Paths.get(getClass().getResource("empty-config.json").toURI()))
+                .outputDirectory(outputDirectory.toString())
+                .build();
+        Model model = Model.assembler()
+                .assemble()
+                .unwrap();
+        SmithyBuild builder = new SmithyBuild().config(config).model(model);
+        SmithyBuildResult results = builder.build();
+        List<Path> files = results.allArtifacts().collect(Collectors.toList());
+
+        assertThat(files, hasItem(outputDirectory.resolve("source/sources/manifest")));
+        assertThat("\n", equalTo(IoUtils.readUtf8File(results.allArtifacts()
+                .filter(path -> path.toString().endsWith("/manifest"))
+                .findFirst()
+                .get())));
+    }
+
     @Test
     public void doesNotCopyErroneousModelsToBuildOutput() throws Exception {
         SmithyBuildConfig config = SmithyBuildConfig.builder()
@@ -377,6 +398,7 @@ public void buildCanOverrideConfigOutputDirectory() throws Exception {
         List<Path> files = results.allArtifacts().collect(Collectors.toList());
 
         assertThat(files, containsInAnyOrder(
+                outputDirectory.resolve("source/sources/manifest"),
                 outputDirectory.resolve("source/model/model.json"),
                 outputDirectory.resolve("source/build-info/smithy-build-info.json"),
                 outputDirectory.resolve("a/sources/manifest"),