[cfe-dev] K&R style argument lists and the type system

[Eli Friedman]

Consider the following testcase:
int a() {return 0;}
int b() {return a(1);}

Calling b has undefined behavior per C99, but no diagnostics are required.

Consider the following testcase:
int a(int);
int a() {return 0;}
This is a constraint violation per C99.

We currently map a() to FunctionTypeNoProto, and this has roughly the
right behavior when we don't merge types.  However, by adding merge
types, we conclude that a() has type a(int), which is clearly wrong,
and leads to crashes trying to access non-existent parameter
declarations.  But if we instead map a() to a FunctionTypeProto with
no parameters, we incorrectly error out on the first example.

And actually, we already have this problem for cases like the
following, which are less common:
int a(x,y) int x,y; {return x+y;}
int b() {return a(1,2,3);}

Any ideas for how to solve this?  We could always map definitions
identifier-lists to FunctionTypeNoProto, but that means a good chunk
of additional code to check type-merging doesn't do bad stuff to a
definition and allow CodeGen to synthesize the type of such a function
definition properly.  Another possibility would be to  add a flag to
FunctionTypeProto which signifies whether the type comes from an
identifier list; however, I have no idea where to add such a flag.

-Eli