[cfe-commits] Patch for review: Parenthesis range in CXXConstructExprs

[John McCall]

On Jul 10, 2012, at 10:23 PM, Richard Smith wrote:
> On Tue, Jul 10, 2012 at 10:05 PM, Daniel Jasper <djasper at google.com> wrote:
> On Wed, Jul 11, 2012 at 12:33 AM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Tue, Jul 10, 2012 at 3:07 PM, Daniel Jasper <djasper at google.com> wrote:
> I don't think this is fully what I am trying to fix with this patch. This patch addresses the inconsistency that the CXXConstructExpr contains the correct ParenRange for Stmts like:
> 
> X value(7);
> 
> But an incorrect range if the constructor is called like a function, e.g.:
> 
> X(7);
> 
> Right. My point is we don't have rules for what a correct range would be, and we need such rules before we can say whether your patch is right. My proposed rule means that the source range is wrong in both cases, and shouldn't include the parens (and that we should drop the ParenRange from CXXConstructExpr entirely). The fix for that is completely different from what you're proposing :-)
> 
> As for printing, I don't know whether the SourceRange of the CXXConstructExpr should include the parentheses. However, for refactoring, it is definitely highly beneficial to know it (and in fact I think we'll have to go and add it to other nodes as well). So, as CXXConstructExpr already contains a member for that, we should definitely populate it as best we can.
> 
> That presumes that the parens are somehow logically part of the CXXConstructExpr, which I think is really the relevant question here. CXXConstructExpr is used in various cases where the parens are either part of some other construct, or where there are no parens, so I don't think it makes much sense to include the parens in the source range. I would imagine that for refactoring, what's really desired is a consistent and rational set of rules for what the source range of an expression means, which, as my examples demonstrate, we're *really really far* from having.
> 
> Consider these two cases:
> 
> X value(7);
> int value(7);
> 
> In the first case, the source range for the initializer covers 'value' and the parentheses. For the second case, it covers only the '7'. The right fix for the second case seems naturally to be that we should store the source locations of the parentheses on the VarDecl. And that would remove any need for storing them on the CXXConstructExpr in the first case.
> 
> Likewise in these expressions:
> 
> X(7)
> int(7)
> 
> Here, the CXXFunctionalCastExpr already contains the source locations of the parentheses. In the 'int' case, we don't store them anywhere else (and nor do we need to). In the 'X' case, we include the 'X' and the '(' in the source range of the CXXConstructExpr. That is inconsistent and unnecessary.
> 
> Why do we not need the parenthesis for int(7)? Because there are no diagnostics that can trigger on a range including them?
> 
> Because they can be derived from the CXXFunctionalCastExpr (also, there's no other AST node where they could reasonably go).

CXXConstructExpr generally doesn't imply a particular syntactic form.
Instead of putting the parens range for a direct-initialization there, why
don't we introduce a CXXDirectInitExpr expression instead?  That way
we'd still store the parens for scalars and conversion operators.

John.
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