Re: [aspectj-dev] Use of non-statically resolvable pointcut designators

[Adrian Colyer <adrian_colyer@xxxxxxxxxx>]

As a follow-up - Andy & I went searching
all through our docs looking for the place where we say that you can only
use statically evaluable pointcuts in declare eow statements, but I couldn't
find it clearly stated anywhere. (I half recall seeing a list that said
"You can only use the following pcds..." but if it's there, I
couldn't find it).

I think the simplest thing for users
to understand is a compilation error if any of this, target, args, cflow,
cflowbelow or 'if' are used in the pointcut _expression_ associated with
a deow. But, this might break many existing programs that are currently
"getting away with it." 

The next best option seems to me to
be to emit a compiler warning saying that "xxx pcd cannot be used
in declare error or warning statements and will be ignored." (And
then of course, make sure that we really do ignore it). Given our current
position, this is possibly what we should do for 1.2 (leaving us the option
to make it an error in 1.3 once programs have been tidied up perhaps?).

Both of these options have the drawback
of not supporting some deow tests that would have succumbed to full static
evaluation. If that's important enough, we could consider warning only
when a non-statically determinable situation occurs - but what I dislike
about this option is that this can't be determined when compiling the aspect,
but only during shadow matching (which could be at a completely different
time if e.g. you are binary weaving). 

So I think at the moment I'm leaning
towards:=
1) making the docs clearer about exactly
which pcds are supported for deow, and
2) following a warn-and-ignore strategy
for violations of that policy

Open to counter-arguments though...

-- Adrian
Adrian_Colyer@xxxxxxxxxx

Andrew Clement/UK/IBM@IBMGB Sent by: aspectj-dev-admin@xxxxxxxxxxx 23/02/2004 16:16 Please respond to aspectj-dev

To:        aspectj-dev@xxxxxxxxxxx         cc:                 Subject:        [aspectj-dev] Use of non-statically resolvable pointcut designators in declare error/warning.

Hi, 

I'm looking at a bug on this - and I noticed someone else mailed 
the list on a similar topic earlier today.

Eric Bodden reported a problem with using if() in a declare 
warning/error message.  This was a ClassCastException - which of
course I'll fix - but it made me think more about what our 
position is on allowing users to use pointcuts that can't
be wholely resolved at compile time with the declare error/warning
mechanism. 

At the moment, if a pointcut cannot be entirely statically
evaluated then it will behave as if it has matched and the error
or warning message will be produced.  I don't think this is 
quite what we want. 

However, it is not clear whether we should be flagging an 
error if any of the designators that exhibit this behavior 
are used against declare error/warning or if we should be 
flagging an error/warning if it just the case that the entire 
pointcut cannot be completely resolved statically.  There are 
some designators that *could* lead to runtime tests but might 
not if there is enough static info around.  For example 
target()/this() may or may not create an instanceof test for 
execution at runtime depending on what the compiler can 
determine statically. 

So, we have the options: 

Error/Warning if we see a declare error/warning statement whose
pointcut uses any of the designators that *might*
lead to dynamic residue. 

Error/Warning if we see a declare error/warning statement whose
pointcut cannot be completely statically evaluated.

Any comments? 
Andy. 
--- 
Andy Clement 
AJDT/AspectJ Development