Unit testing (running) a Rule[I, O] which requires something on the value-stack

[Ian Hummel]

Hi folks,

Really enjoying Parboiled2 so far, but have a question about how to unit test a rule which relies on the presence of an item in the value stack.

I'm trying to parse some XML-like messages with nested tags.  Take something like this for instance

<foo><bar>this is a bar</bar><baz>bazzz</baz></foo>

Foo is actually an Avro specific record and when I encounter a <bar> or <baz> tag (they can appear in any order) I want to be able to set the relevant properties on the Foo object.  Here's a slightly simplified example to illustrate how my parser is written:

def foo= rule {

  tagBegin("foo") ~ push(Foo.newBuilder()) ~ ws ~ zeroOrMore(bar | baz) ~ tagEnd("foo") ~>((f: Foo.Builder) => f.build())

}

def bar = rule { leafTag("bar") ~>((f: Foo.Builder, s: String) => f.setBar(s)) }

def baz = rule { leafTag("baz") ~>((f: Foo.Builder, s: String) => f.setBaz(s)) }

I can easily unit test my "foo" rule with:

it should "parse a Foo" in {

  val p = new FooParser("<foo><bar>this is a bar</bar><baz>bazzz</baz></foo>")

  p.foo.run() match {

    case Success(x) => println(x)

    case Failure(e: ParseError) => println(p.formatError(e))

    case Failure(e) => throw e

  }

}

But how do I unit test my "bar" or "baz" rules?  They rely on the presence of an existing value on the value-stack...  This fails to compile:

it should "parse a Foo" in {

  val p = new FooParser("<bar>this is a bar</bar>")

  p.bar.run() match {

    case Success(x) => println(x)

    case Failure(e: ParseError) => println(p.formatError(e))

    case Failure(e) => throw e

  }

}

I get

Error:(43, 11) value run is not a member of org.parboiled2.Rule[shapeless.::[com.example.Foo.Builder,shapeless.HNil],shapeless.::[com.example.Foo.Builder,shapeless.HNil]]

    p.bar.run() match {

          ^

How can I prepare the value-stack and then run the parser to get the output?  Is there a different pattern I should be following for setting properties of an object conditional on what was parsed?

Advice appreciated, thanks!

[Mathias Doenitz]

Hi Ian,

one thing you could do is extend your `FooParser` class in your tests and give it two more rule methods:

def barWithBuilder(b: Foo.Builder) = rule { push(b) ~ bar }
def bazWithBuilder(b: Foo.Builder) = rule { push(b) ~ baz }

Then you can simply call the `...WithBuilder` methods in your test.

Cheers,
Mathias

---
mat...@parboiled.org
http://www.parboiled.org

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