zdm/event-bus
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event-bus
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Fix several edge cases in EventProcessor 

When encountering an event handler with an invalid signature, the
processor doesn't crash anymore. Also, event parameters that aren't
objects are now reported as errors.
This commit is contained in:
Kai S. K. Engelbart 2021-02-17 08:22:48 +01:00
parent 1dd9e05c38
commit ff35e7f37d
Signed by: kske
GPG Key ID: 8BEB13EC5DF7EF13
2 changed files with 36 additions and 22 deletions
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4
README.md
View File

@ -157,9 +157,9 @@ If you intend to use event handlers that are inaccessible to Event Bus by means
opens my.module to dev.kske.eventbus.core;
```
## Compile-Time Error Checking with Event Bus AP
## Compile-Time Error Checking with Event Bus Proc
To assist you with writing event listeners, the Event Bus AP (Annotation Processor) module enforces correct usage of the `@Event` annotation during compile time.
To assist you with writing event listeners, the Event Bus Proc (Annotation Processor) module enforces correct usage of the `@Event` annotation during compile time.
This reduces difficult-to-debug bugs that occur during runtime to compile-time errors which can be easily fixed.
The event annotation processor detects invalid event handlers and event type issues with more to come in future versions.

54
event-bus-proc/src/main/java/dev/kske/eventbus/proc/EventProcessor.java
View File

@ -34,9 +34,10 @@ public class EventProcessor extends AbstractProcessor {
private void processRound(Set<ExecutableElement> eventHandlers) {
for (ExecutableElement eventHandler : eventHandlers) {
Event eventAnnotation = eventHandler.getAnnotation(Event.class);
Event eventAnnotation = eventHandler.getAnnotation(Event.class);
TypeMirror eventType;
// Determine how the event type is defined
// Determine the event type and how it is defined
boolean useParameter;
try {
eventAnnotation.value();
@ -45,36 +46,49 @@ public class EventProcessor extends AbstractProcessor {
} catch (MirroredTypeException e) {
// Task failed successfully
useParameter = processingEnv.getTypeUtils().isSameType(e.getTypeMirror(),
eventType = e.getTypeMirror();
useParameter = processingEnv.getTypeUtils().isSameType(eventType,
getTypeMirror(Event.USE_PARAMETER.class));
}
// Check for correct method signature and return type
if (eventHandler.getParameters().size() == 0 && useParameter)
// Check handler signature
boolean pass = false;
if (useParameter && eventHandler.getParameters().size() == 0)
error(eventHandler, "The method or the annotation must define the event type");
if (eventHandler.getParameters().size() == 1 && !useParameter)
else if (!useParameter && eventHandler.getParameters().size() == 1)
error(eventHandler,
"Either the method or the annotation must define the event type");
if (eventHandler.getParameters().size() > 1)
else if (eventHandler.getParameters().size() > 1)
error(eventHandler, "Method must not have more than one parameter");
if (eventHandler.getReturnType().getKind() != TypeKind.VOID)
else if (eventHandler.getReturnType().getKind() != TypeKind.VOID)
error(eventHandler, "Method must return void");
else
pass = true;
// Get first parameter as type and element
var paramElement = eventHandler.getParameters().get(0);
var paramType = paramElement.asType();
// Abort checking if the handler signature is incorrect
if (!pass)
continue;
// Additional checks if parameter is used
if (useParameter) {
VariableElement paramElement = eventHandler.getParameters().get(0);
eventType = paramElement.asType();
// Check if parameter is object
// Abort checking otherwise
if (eventType.getKind() != TypeKind.DECLARED) {
error(paramElement, "Event must be an object");
continue;
}
}
// Check for handlers for abstract types that aren't polymorphic
Element eventElement = ((DeclaredType) eventType).asElement();
if (eventHandler.getAnnotation(Polymorphic.class) == null
&& paramType.getKind() == TypeKind.DECLARED) {
var declaredElement = ((DeclaredType) paramType).asElement();
if (declaredElement.getKind() == ElementKind.INTERFACE
|| declaredElement.getModifiers().contains(Modifier.ABSTRACT))
warning(paramElement,
"Parameter should be instantiable or handler should use @Polymorphic");
&& (eventElement.getKind() == ElementKind.INTERFACE
|| eventElement.getModifiers().contains(Modifier.ABSTRACT))) {
warning(eventHandler,
"Parameter should be instantiable or handler should use @Polymorphic");
}
}
}