[cfe-dev] Best approach for duplicate case value error

[Sean Silva]

this is what I've been using to dump a SourceRange:

void DumpSourceRange(SourceRange sr, SourceManager& sm) {
  const char* b = sm.getCharacterData(sr.getBegin());
  const char* e = sm.getCharacterData(sr.getEnd())+1; // include last
character
  llvm::errs() << llvm::StringRef(b, e - b) << "\n";
}

I don't think there's a "Right way" to do it. If there were it would
probably be a method on SourceManager though.

--Sean Silva

On Mon, Mar 5, 2012 at 1:35 PM, Philip Reames <listmail at philipreames.com>wrote:

> Over the weekend, I took a look at an easy diagnostic bug.
> (http://llvm.org/bugs/show_bug.cgi?id=9243)  Essentially, the issue
> comes down to how to report duplicate case values when some of the
> values are enums or chars.  As shown today, we show the actual integer
> value of the case value.  This is sometimes confusing.
>
> My proposed syntax for the revised error is:
> CGDecl.cpp:85:8: error: duplicate case for 'Decl::Label' (underlying
> value '6')
>   case Decl::Label:        // __label__ x;
>        ^
> CGDecl.cpp:73:8: note: previous case defined here
>   case Decl::Label:
>
> After some digging around, I couldn't find a way to get the actual text
> of a given source range.  Is there an easy way (within Sema) to get
> this?  I tried playing tricks with looking up enum values from the
> underlying integer, but that has edge cases I wouldn't want to actually
> check in.
>
> The second question I had was whether we should add a warning for the
> use of non-enum labels when switching on an enum value.  While this is
> certainly valid C/C++, it's probably not best practice.  Are best
> practice style warnings something we want to include?  Or is that better
> off in a separate tool?
>
> Yours,
> Philip Reames
>
>
> Here's the c++ test case I've been using.
>
> enum Foo {A=0,B};
>
> int main() {
>   Foo a = A;
>   switch(a) {
>   case A:
>   case A:
>     break;
>   };
>
>   switch(a) {
>   case A:
>   case 0:
>     break;
>   };
>
>   switch(a) {
>   case 0:
>   case 1:
>     break;
>   };
>
>   switch(a) {
>   case A:
>   case '\0':
>     break;
>   };
>
>   char b = '0';
>   switch(b) {
>   case 'a':
>   case 'a':
>     break;
>   };
>
> #define CASE1 case 'a':
>   switch(b) {
>   CASE1
>   CASE1
>     break;
>   };
>
>   return 0;
> }
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