Getting the annotation processor working when I'm using kotlin, gradle and kapt.

annotations/processor/src/main/java/run/endive/annotations/processor/WasmModuleProcessor.java

@@ -3,9 +3,14 @@
 import static java.lang.String.format;
 import static javax.tools.Diagnostic.Kind.ERROR;
 import static javax.tools.Diagnostic.Kind.NOTE;
+import static javax.tools.StandardLocation.ANNOTATION_PROCESSOR_PATH;
+import static javax.tools.StandardLocation.CLASS_OUTPUT;
+import static javax.tools.StandardLocation.CLASS_PATH;
+import static javax.tools.StandardLocation.SOURCE_PATH;
 
 import com.github.javaparser.ast.CompilationUnit;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.Writer;
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -22,6 +27,12 @@
 import run.endive.wasm.WasmModule;
 
 public final class WasmModuleProcessor extends AbstractModuleProcessor {
+    private static final StandardLocation[] LOCATIONS = {
+            CLASS_PATH,
+            ANNOTATION_PROCESSOR_PATH,
+            SOURCE_PATH,
+            CLASS_OUTPUT,
+    };
 
     @Override
     public Set<String> getSupportedAnnotationTypes() {
@@ -54,11 +65,7 @@ private void processModule(TypeElement type) throws URISyntaxException, IOExcept
         if (wasmFile.startsWith("file:")) {
             module = Parser.parse(Path.of(new URI(wasmFile)));
         } else {
-            FileObject fileObject =
-                    processingEnv
-                            .getFiler()
-                            .getResource(StandardLocation.CLASS_OUTPUT, "", wasmFile);
-            module = Parser.parse(fileObject.openInputStream());
+            module = Parser.parse(openResource(wasmFile));
         }
 
         var pkg = getPackageName(type);
@@ -76,6 +83,22 @@ private void processModule(TypeElement type) throws URISyntaxException, IOExcept
         writableClasses.forEach((k, v) -> writeCu(k, v, type));
     }
 
+    private InputStream openResource(String wasmFile) throws IOException {
+        var filer = processingEnv.getFiler();
+        IOException lastFailure = null;
+        for (StandardLocation location : LOCATIONS) {
+            try {
+                FileObject fileObject = filer.getResource(location, "", wasmFile);
+                return fileObject.openInputStream();
+            } catch (IOException ioe) {
+                lastFailure = ioe;
+            } catch (IllegalArgumentException iae) {
+                lastFailure = new IOException(iae);
+            }
+        }
+        throw lastFailure;
+    }
+
     private void writeCu(String qualifiedName, CompilationUnit cu, TypeElement type) {
         try (Writer writer = filer().createSourceFile(qualifiedName, type).openWriter()) {
             writer.write(cu.printer(printer()).toString());

annotations/processor/src/test/java/run/endive/annotations/processor/WasmModuleProcessorTest.java

@@ -0,0 +1,35 @@
+package run.endive.annotations.processor;
+
+import static com.google.testing.compile.CompilationSubject.assertThat;
+import static com.google.testing.compile.Compiler.javac;
+
+import com.google.testing.compile.Compilation;
+import com.google.testing.compile.JavaFileObjects;
+import org.junit.jupiter.api.Test;
+
+class WasmModuleProcessorTest {
+
+    @Test
+    void resolvesWasmModuleFromClassPathNotJustClassOutput() {
+        Compilation compilation =
+                javac().withProcessors(new WasmModuleProcessor())
+                        .compile(JavaFileObjects.forResource("IterFactModule.java"));
+
+        assertThat(compilation).succeededWithoutWarnings();
+
+        assertThat(compilation).generatedSourceFile("endive.testing.IterFactModule_ModuleExports");
+    }
+
+    @Test
+    void reportsMissingWasmModule() {
+        Compilation compilation =
+                javac().withProcessors(new WasmModuleProcessor())
+                        .compile(JavaFileObjects.forResource("MissingModule.java"));
+
+        assertThat(compilation).failed();
+
+        assertThat(compilation)
+                .hadErrorContaining("Failed to load wasmFile")
+                .inFile(JavaFileObjects.forResource("MissingModule.java"));
+    }
+}

annotations/processor/src/test/resources/IterFactModule.java

@@ -0,0 +1,6 @@
+package endive.testing;
+
+import run.endive.annotations.WasmModuleInterface;
+
+@WasmModuleInterface("iterfact.wat.wasm")
+public class IterFactModule {}

annotations/processor/src/test/resources/MissingModule.java

@@ -0,0 +1,6 @@
+package endive.testing;
+
+import run.endive.annotations.WasmModuleInterface;
+
+@WasmModuleInterface("does-not-exist.wasm")
+public class MissingModule {}