Confused about the priority of BytecodeTransformerBuildItem application.

[skku-daniilkim]

Hello,

I am writing an extension, in which I want my bytecode transformer to always run the first - it does some type substitution (something like pre-processing), so I want it to run before any hibernate, panache, or other extensions. Looking at the ClassTransformingBuildStep, BytecodeTransformerBuildItem are sorted by getPriority, so I assumed the lower the priority, the earlier the transformer is applied, but the javadoc for the said method confused me a little bit

quarkus/core/deployment/src/main/java/io/quarkus/deployment/builditem/BytecodeTransformerBuildItem.java

Lines 137 to 157 in b38e9e3

	/**
	* Bytecode transformers are applied in ascending priority order. That is, lower priority
	* value means the transformer is applied sooner, and higher priority value means
	* the transformer is applied later.
	* <p>
	* This applies directly to {@link #inputTransformer} functions: an input transformer
	* function with lower priority is applied first and its result is passed to the transformer
	* function with higher priority.
	* <p>
	* It is a bit counter-intuitive when it comes to the {@link #visitorFunction}. The visitor
	* function doesn't directly transform bytecode; instead, it constructs an ASM
	* {@link ClassVisitor} from an earlier class visitor. This means that the priority order
	* is effectively turned around: the later a bytecode transformer is called,
	* the <em>higher</em> in the class visitor chain it ends up, and the <em>sooner</em>
	* is the visitor eventually called.
	* <p>
	* The priority value defaults to {@code 0}.
	*/
	public int getPriority() {
	return priority;
	}

Since the visitors are chained (if I understood it correctly), it means that the earlier they are applied, the later they are run, therefore does it mean that the lower priority of the transformer, will actually cause it to be run later?

[skku-daniilkim]

After further testing, it seems like the higher the priority, the earlier the transformer will be applied.