[cfe-dev] Adding balanced parentheses to statements

[Alastair Donaldson]

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 
> <mailto: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?

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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>

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