This doesn't work for any workingDirectory, though. The working directory must contain the flutter package at package/flutter/lib. Typically we call this directory the flutter root, so I would just call this parameter flutterRoot (or actually make analyzeDirectoryWithRules work on any directory).

I don't understand this sentence...

document what one should do with failures (i.e. this shouldn't throw or anything and just record the failures internally until reportViolations is called)

nit: I would switch the order of these methods around, logically, you need to call applyTo first and then worry about how to get the failures back out.

document: annotated with what?

nit: 'members'

and operators?

Just to have great documentation while this is all loaded into our brains: what about inheritence?

1. If B extends A and A.m is annotated with @debugAssert, can B.m be called outside an assert?
2. If B extends A and A is annotated with @debugAssert, can any of B's members be called outside of an assert?

(I think maybe I don't know what "non-synthetic" members are...)

By "non-synthetic" I guess I just meant the implicit default constructors.

Updated the documentation to talk more about inheritance.

nit: 'Variable'

nit: extensions are not InterfaceElements.

I'm not sure where this sentence starts/stops. Should it be, "), defer to ..."?

I don't think this is correct, even with the quotes. Classes in no way inherit constructors.

If a class doesn't define any constructors then you get class.new(). for free which invokes super() (I think that's the case?) is what I meant. Updated the comment to be more specific.

Hmm, why the first non-synthetic (which I think means "non-default"? Take this example:

class A {
  @debugAssert
  A();
}
class B extends A {
  B();
}
class C extends B {}
void main() {
  C();
}

It seems that the call to C() should be reported even though the first non-default super-constructor called is B() which has no annotation.

I think this case will be caught by the code in visitConstructorDeclaration, since B.new is not debug-only but A.new is, and B.new invokes A.new implicitly.

regarding first non-synthetic, I would like to make this annotation more forgiving, so in this case

class A { 
  @debugAssert
  A();
}
class B1 { 
}
class B2 extends A { 
  B2(); // illegal, implicitly invokes A.new and doesn't have @debugAssert
}

you don't have to add a default constructor to B1 to add the annotation to it.

Might be better performance to just ask if the unnamed constructor is default, instead of walking all of the named ones.

https://pub.dev/documentation/analyzer/latest/dart_element_element/InterfaceElement/unnamedConstructor.html

I'm a bit scared of the TODO(scheglov) Deprecate and remove it. comment on this property, it sounds like unnamedConstructor will be removed soon?

I'm not sure why the synthetic nature makes a difference. Shouldn't this code be reported?

class C {
  @debugAssert
  C();
}

class D extends C {
  D(); // Implicitly calls C().
}

See #130101 (comment)

Also that code will be reported I think? Neither C.new nor D.new is synthetic here?