Re: [Jastadd] Problems with Literals after change to Java 7 frontend

From: Jesper Öqvist <jesper.oqvist_at_cs.lth.se>
Date: Mon, 14 Jan 2013 09:36:56 +0100

Hi Eric,
The numerical literal parsing code in JastAddJ was rebuilt for Java 7.
The reason is that Java 7 added underscores in numeric literals. So,
e.g. the literal 0x1__2 is legal and means the same thing as 0x12.

In order to scan literals with underscores lookahead is required. This
is easy to see: numeric literals may not begin or end with an
underscore, so when the scanner encounters an underscore it can not know
if that is an error, or a legal character - it depends on whether or not
there is a valid digit after this underscore or after any number of
intervening underscores.

We could have changed the scanner to use some form of lookahead, but
that would make the scanner much more complex and remove some of the
advantage of having a generated scanner to boot. So, instead we've made
the scanner simpler - it can now accept illegal numeric literals, the
only requirement for the scanner is that it should be clearly a numeric
literal and not any other type of token. So this inserts invalid
literals in the AST, but they are rewritten to either an object of a
subclass of NumericLiteral representing a valid numeric literal, or
IllegalLiteral if there is a syntax error in the literal.

The only additions to the AST relevant to literals are NumericLiteral
and IllegalLiteral.

The digits field represents the digits of a numeric literal stripped of
underscores and prefixes or suffixes. This field is set during the
parsing of a NumericLiteral. The rewrite rules for NumericLiterals are
all in Java7Frontend/Literals.jrag.

IntegerLiteral.buildIntegerLiteral and friends are used to build literal
objects representing literals that have been parsed from bytecode.

Hope this clears things up

/Jesper

On 2013-01-13 12:09, Eric Bodden wrote:
> Hello.
>
> After changing Soot/abc to the Java7Frontend I am having the problems
> that all numerical constants in processed Java source code get
> interpreted as having the value 0.
>
> The problem seems to be due to the field
> abc.ja.cjp.jrag.NumericLiteral.digits never being assigned a value. It
> is initialized to "" but then never changed afterwards. In particular
> the method IntegerLiteral.buildIntegerLiteral(..) seems never to be
> called. I am afraid I don't quite understand the changes to literals
> between the 1.5 and 7 frontends, so it's hard for me to debug this.
> Does anyone have any idea what could be causing this?
>
> Eric
Received on Mon Jan 14 2013 - 09:36:57 CET