Exceptions thrown from before templates should not be added to Preconditions

[Tim te Beek]

What problem are you trying to solve?

When a before template throws a specific exception, that now makes it's way into the preconditions, as seen in openrewrite/rewrite-migrate-java@4bfadd2.
That means the templates will fail to match, since the exception is unlikely to be used in the matched template.

Describe the solution you'd like

Do not add exceptions to preconditions.

Have you considered any alternatives or workarounds?

• Enforce throws Exception from lambdas, rather than specific ones; not ideal, as it loses specificity on the user's side.

Additional context

• openrewrite/rewrite-migrate-java@4bfadd2

[Tim te Beek]

Had some discussions with @knutwannheden around this; excluding the declared thrown exceptions from the lambda seems right, although we might want to double check if that is even an issue still.

We should be able to collect the imports using something like this:

 Set<Symbol> allImports = new HashSet<>(ImportDetector.imports(template.getBody()));
 allImports.addAll(ImportDetector.imports(template.getReturnType()));
 template.getParameters().forEach(p -> allImports.addAll(ImportDetector.imports(p)));
 template.getTypeParameters().forEach(p -> allImports.addAll(ImportDetector.imports(p)));

[Knut Wannheden]

Excluding the method's throws clause is important as it will otherwise add wrong UsesType preconditions. One example would be when the template's throws clause lists runtime exceptions. The code being matched might not have any corresponding catch or throws, so there should not be any corresponding UsesType.