[cfe-dev] Start of source range for Decl nodes.

[Enea Zaffanella]

Hello.

In our application we are facing a problem related to the quality of
source location information for Decl nodes. When using method
    Decl::getSourceRange()
we noticed a few cases where we obtain not so accurate location info for
the start of the range.
Here are a few examples.

For DeclaratorDecl nodes:
  const int a;
  static int b;
  inline int foo() { return 5; }
the range starts from "int", rather than "const" or "static" or "inline".

For a NamespaceDecl node such as
  namespace N { }
the range starts from the identifier N, rather than from the "namespace"
keyword. Similarly for a linkage specification such as
  extern "C" { ... }

All of these minor problems can be easily fixed as soon as there will be
a place where the start for the range can be recorded. For instance,
when creating a new VarDecl node in SemaDecl.cpp:2956

    NewVD = VarDecl::Create(Context, DC, D.getIdentifierLoc(),
                            II, R, TInfo, SC, SCAsWritten);

the Declarator object D could provide accurate source range info, but
the VarDecl constructor has no parameter accepting the start of such a
range: it has a SourceLocation for the identifier loc and a
TypeSourceInfo, which does not take into account syntactic elements such
as storage classes, CVR qualifiers, inline specifiers, etc.
As a result, we obtain strange-looking differences whereby declaration
    int const a;
has an accurate source range, whereas
    const int a;
is skipping the const keyword.

Assuming that the goal of obtaining precise source location info should
be achieved by all means, now the question is: which is best place where
this additional source location (the start of the range) for the Decl
hierarchy should be stored?
Would it be OK to store them at the top of the hierarchy?
Are there better places?

Regards,
Enea.