On May 15, 2012, at 3:28 PM, Terry Long <[email protected]> wrote:
>
> Am 15.05.2012 um 16:09 schrieb Douglas Gregor
>>
>>
>> I'm a bit uncomfortable with the textual approach here. Why not analyze the
>> expressions to check whether they are references to named declarations, and
>> use those names in the diagnostic? It won't catch some macro cases, but it's
>> far simpler.
>
> I was also uncomfortable with the textual approach, and in fact I first tried
> seeing if the case expression was a DeclRefExpr that refers to a valid
> NamedDecl. The problem I found with that approach was that it was not
> catching very many situations. Doing it that way only works for enums as far
> as I can tell. Macros, const ints, case overflows, casting, and more
> complicated expressions (like "case 2+2") are not DeclRefExprs, and I don't
> see any obvious way to grab the necessary diagnostic info without using a
> textual approach.
You can look through implicit conversions (e.g., promotions) and parentheses to
find the underlying expression. We'll get a DeclRefExpr for enumerators and
variables that are constant ("const int x = 17;"), which are presumably the
common cases. We won't get macros, of course, but we might not want to: it's
probably more useful to show the value we get when the macro is expanded, and
let the macro-substitution backtrace show how we got there.
- Doug
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