[cfe-dev] Stmt.getEndLoc() vs semicolon

[Yitzhak Mandelbaum via cfe-dev]

Alexander,

I agree that this behavior is rather confusing, especially to first-time
users. The cause of the issue is that Expr derives from Stmt so that Exprs
can appear directly in, for example, compound statements, rather than being
wrapped in an explicit node to represent statements that consist only of an
expression.  As far as I understand, this choice to avoid an explicit node
had some (positive) performance implications for the AST when it was
originally designed.  While I'd love to see this choice revisited, I think
it would be a significant effort and don't expect it to happen.

Instead, we tend to work around the issue.  For getting proper ranges of
statements, you might find clang::tooling::getExtendedText/getExtendedRange
meet your needs:
https://github.com/llvm/llvm-project/blob/master/clang/include/clang/Tooling/Transformer/SourceCode.h#L56

For declarations, the (just added!) getAssociatedRange might be even
better:
https://github.com/llvm/llvm-project/blob/master/clang/include/clang/Tooling/Transformer/SourceCode.h#L39

Cheers,
Yitzhak

On Tue, Feb 25, 2020 at 5:15 PM Alexander Lanin via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello,
>
>
>
> I’m having trouble with the locations returned by Stmt
> getEndLoc()/getSourceRange() and am wondering whether this is a bug/flaw:
>
> the returned location sometimes includes and sometimes excludes the
> semicolon in the end.
>
> This gets even more interesting when there are (multiple) comments before
> the semicolon, simply because the difference between the returned values
> gets even bigger.
>
> Here is an example showing how DeclStmt includes the semicolon, while
> CallExpr and BinaryOperator exclude the semicolon
> http://ce.steveire.com/z/TW3IAG.
>
>
>
> So Stmt behaves “completely differently” depending on it’s type, which is
> no way suggested by it’s interface.
>
> Wouldn’t it be better for Stmt-Users if it would always be the same?
>
> (Not sure whether it should always be included or excluded. It’s not even
> always a semicolon as in that 3rd foo() in the example)
>
> https://en.wikipedia.org/wiki/Liskov_substitution_principle
>
>
>
> Here is one of the effects of this complexity for users of Stmt as they
> struggle to find that semicolon:
>
> https://bugs.llvm.org/show_bug.cgi?id=25970 /
> https://reviews.llvm.org/D16267
>
> Of course it’s fixable there, but that would imply working around the
> issue in multiple places.
>
>
>
> Regards,
>
> Alexander Lanin
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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