JEP 447 improve error message for constructor calls occurring nested in some control structure

[stephan-herrmann]

public class TestFlow {
	TestFlow(boolean f) {
		if (f)
			super();
		else
			this();
	}
}

This reports "Constructor call must be the first statement in a constructor", despite the preview being enabled.

In JLS this is managed by grammar rules admitting constructor calls only as a top level statement in the constructor body. When this feature enabled, should we say smth like "must be a top-level statement in a constructor body"? Would that be clear, or do we need to explicitly mention what is not allowed: wrapping the constructor call in some control structure or block?

[stephan-herrmann]

Found this comment in a recent spec draft:

The grammar makes it impossible, for example, to place explicit constructor invocations in different branches of an if statement.

[stephan-herrmann]

should we say smth like "must be a top-level statement in a constructor body"? Would that be clear, or do we need to explicitly mention what is not allowed: wrapping the constructor call in some control structure or block?

In #2685 I opted for a simply "Constructor call is not allowed here" (javac says "Explicit onstructor call is not allowed here")

[stephan-herrmann]

Resolved via #2685