[cfe-dev] Adding balanced parentheses to statements

[Richard Smith]

On Tue, Jun 23, 2015 at 2:09 PM, Alastair Donaldson <
alastair.donaldson at imperial.ac.uk> wrote:

>  Dear Richard
>
> On 23/06/2015 21:55, Richard Smith wrote:
>
>  On Tue, Jun 23, 2015 at 1:05 PM, Alastair Donaldson <
> alastair.donaldson at imperial.ac.uk> wrote:
>
>> Dear all
>>
>> I am trying to use the Rewriter class to do something conceptually pretty
>> straightforward to a source file.  What I actually want to do is pretty
>> specific, but if I could work out how to do the following it would be
>> obvious how to solve my problem:
>>
>> - for every Stmt node in the AST, replace the source code associated with
>> the Stmt with:
>>
>>     open(x) original_source_code_for_Stmt close(x)
>>
>> where x is a number chosen uniquely for the Stmt node.
>>
>> For instance, if the Stmt is the expression:
>>
>> x + y
>>
>> then I would like to end up with something like:
>>
>> open(2) open(0) x close(0) + open(1) y close(1) close(2)
>>
>> I hope my objective makes sense.
>>
>> What I've tried to do is write a class that extends RecursiveASTVisitor,
>> equipped with a Rewriter field, "TheRewriter", and an int field,
>> "counter".  The Rewriter should allow me to rewrite the source code.  The
>> counter is used to give each open and close a unique x.  I'm assuming for
>> now that all my code is in one source file.
>>
>> I've tried two things:
>>
>>   bool TraverseStmt(Stmt *s) {
>>     bool result = RecursiveASTVisitor::TraverseStmt(s);
>>     std::stringstream ss_start;
>>     ss_start << "open(" << counter << ")";
>>     TheRewriter.InsertTextAfter(s->getLocStart(), ss_start.str());
>>     std::stringstream ss_end;
>>     ss_end << "close(" << counter << ")";
>>     TheRewriter.InsertTextAfterToken(s->getLocEnd(), ss_end.str());
>>
>
>  InsertTextAfter and InsertTextAfterToken return a bool indicating
> whether the insertion was possible (false on success, true on failure). You
> could use that to isolate which particular call is failing.
>
>
> Thanks for this suggestion.  However, the calls do not fail: all the
> "open" and "close" strings are emitted.  They are just not balanced.  For
> example, I see this:
>
>     open(8)(open(0)open(1)open(7)d close(1)close(0)+
> open(6)(open(2)open(3)open(5)d close(3)close(2)/
> open(4)2)close(5)close(4))close(7)close(6);close(8)
>
> for the expression:
>
>    (d + (d / 2))
>
> So you can see that all the opens have matching closes.  It's just that
> they are not balanced.
>
> Does this bring anything else to mind?
>

Oh, I see what you mean now. The problem seems to be that you're adding the
"open" string for the outer statement after the open string for its first
substatement. Try this:

InsertTextAfter(s->getLocStart(), ...);
TraverseStmt(s);
InsertTextAfterToken(s->getLocEnd(), ...);

(or change your first InsertTextAfter to InsertTextBefore).


> Many thanks
>
> Ally
>
>
>
>
>  That said, the only cases where the above calls would currently fail are
> if they're given a location for which TheRewriter.isRewritable returns
> false. That only happens if the location provided is within a macro
> expansion. Could that be the case in your failing examples?
>
>
>>     counter++;
>>     return result;
>>   }
>>
>> (This is what seemed natural to me from the clang APIs)
>>
>> and also:
>>
>>   bool TraverseStmt(Stmt *s) {
>>     bool result = RecursiveASTVisitor::TraverseStmt(s);
>>     std::stringstream ss_start;
>>     ss_start << "open(" << counter << ")";
>>     TheRewriter.InsertTextAfter(s->getLocStart(), ss_start.str());
>>     int offset = Lexer::MeasureTokenLength(s->getLocEnd(),
>> TheRewriter.getSourceMgr(), TheRewriter.getLangOpts()) + 1;
>>     auto END1 = s->getLocEnd().getLocWithOffset(offset);
>>     std::stringstream ss_end;
>>     ss_end << "close(" << counter << ")";
>>     TheRewriter.InsertTextBefore(END1, ss_end.str());
>>     counter++;
>>     return result;
>>   }
>>
>> (I came up with this after reading this source code from Robert Ankeney:
>> https://github.com/loarabia/Clang-tutorial/blob/master/CIrewriter.cpp)
>>
>> However, neither work - my parentheses end up being unbalanced.
>>
>> I think the problem may be that in an expression such as:
>>
>> x + y
>>
>> the sub-expressions "y" and "x + y" have the same end source location.
>> But I cannot figure out how to get around this.
>>
>> I'd be really grateful if anyone can give me a pointer here.
>>
>> Best wishes
>>
>> Ally Donaldson
>>
>> _______________________________________________
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>> cfe-dev at cs.uiuc.edu
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>>
>
>
>
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