bug: Crash in SniperJavaPrettyPrinter.calculate if the printer is set after building the model

[slarse]

Hi,

As the title says, SniperJavaPrettyPrinter.calculate crashes if the printer is set with Environment.setPrettyPrinterCreator after one builds the model. The reason for this is that when building the model, this happens:

spoon/src/main/java/spoon/support/compiler/jdt/JDTBasedSpoonCompiler.java

Lines 128 to 131 in 55bdd96

	if (factory.getEnvironment().createPrettyPrinter() instanceof SniperJavaPrettyPrinter) {
	//setup a model change collector
	new SourceFragmentCreator().attachTo(factory.getEnvironment());
	}

And in the call to calculate, the sniper tries to access that change collector (with getChangeCollector():

spoon/src/main/java/spoon/support/sniper/SniperJavaPrettyPrinter.java

Line 138 in 55bdd96

new ChangeResolver(getChangeCollector(), compilationUnit)),

I have a use case where I need to collect some information from the model to feed to a printer preprocessor, which one typically sets in the supplier passed to setPrettyPrinterCreator. That's how I encountered this problem. It's easy enough to work around (e.g. by setting a "dummy" sniper printer before building the model), but the crash isn't easy to understand if you don't know too much about Spoon.

Any ideas on a solution? The easy solution would of course be to always attach the change collector, but I don't know what kinds of overhead that would impose on non-sniper use cases.

[slarse]

#3694 has a test case that reproduces the issue

[slarse]

Quick-link to error: https://travis-ci.com/github/INRIA/spoon/jobs/439064234#L1059-L1061