[cfe-dev] Template parameters for out-of-line definitions of class template methods.

[John McCall]

On Jun 3, 2010, at 11:32 PM, Abramo Bagnara wrote:

> Il 03/06/2010 08:52, Enea Zaffanella ha scritto:
>> Douglas Gregor wrote:
>>> On Apr 21, 2010, at 12:20 PM, Enea Zaffanella wrote:
>>> 
>>>> Hello.
>>>> 
>>>> We have a somewhat naive question regarding the AST generated for the 
>>>> following program fragment:
>>>> ======================================
>>>> template <typename T>
>>>> struct S {
>>>>  void foo();
>>>> };
>>>> 
>>>> template <class W>
>>>> void S<W>::foo() {}
>>>> ======================================
>>>> 
>>>> We would like to retrieve the template parameter list for the 
>>>> out-of-line definition of method foo(), that is
>>>>  template <class W>
>>>> but we cannot see if and how this could be achieved.
>>> 
>>> Clang's AST doesn't actually store the template parameter list that was used in the out-of-line definition. It should.
>> 
>> Hello.
>> 
>> Reconsidering the point above, we would like to propose a solution.
>> 
>> The template parameter lists we are interested in are simply thrown away 
>> after calls to method
>> 
>>   TemplateParameterList*
>>   Sema::MatchTemplateParametersToScopeSpecifier
>>     (SourceLocation DeclStartLoc, const CXXScopeSpec &SS,
>>      TemplateParameterList **ParamLists, unsigned NumParamLists,
>>      bool IsFriend, bool &IsExplicitSpecialization);
>> 
>> Hence, we simply have to store somewhere the lists of parameters that 
>> have been matched against the CXXScopeSpec: either all of the lists in 
>> ParamLists, or all but the last one (which would be the one returned as 
>> result).
>> 
>> As far as we can see, the best place for this info is in the ExtInfo 
>> struct inside DeclaratorDecl, so that the space overhead will be paid 
>> only in the uncommon case of an out-of-line declaration:
>> 
>> 00369 class DeclaratorDecl : public ValueDecl {
>> 00370   // A struct representing both a TInfo and a syntactic qualifier,
>> 00371   // to be used for the (uncommon) case of out-of-line declarations.
>> 00372   struct ExtInfo {
>> 00373     TypeSourceInfo *TInfo;
>> 00374     NestedNameSpecifier *NNS;
>> 00375     SourceRange NNSRange;
>> 00376   };
>> 
>> A similar chnage will be done for the ExtInfo struct inside TagDecl nodes.
>> 
>> Would this be OK?
> 
> The attached patch shows better and implement the proposal of Enea for
> your review/approval.

If NNSInfo is going to be used in multiple places, which I think is the intent, please
lift it out of DeclaratorDecl and give it a better name.  QualifierInfo, maybe?
OutOfLineInfo?

+  unsigned getNumTemplateParameterLists() const {
+    return hasExtInfo() ? DeclInfo.get<ExtInfo*>()->NumTemplParamLists : 0;
+  }

Please use getExtInfo() consistently.

Otherwise looks good!

John.