[cfe-commits] [patch] Better diagnostics in for-range expressions.

[Sam Panzer]

Hi,

Richard Smith suggested that I try to improve the diagnostic emitted when
Clang encounters certain kinds of invalid C+11 ranged-based for loops.

When a pointer to a container is used as the range in a range-based for,
> Clang's diagnostic is not awesome:
>
> struct S { int *begin(); int *end(); };
>> void f(S *p) {
>>  for (auto i : p) {}
>> }
>> tmp.cpp:3:15: error: use of undeclared identifier 'begin'
>>  for (auto i : p) {} }
>>              ^
>> tmp.cpp:3:15: note: range has type 'S *'
>
>
> We should do better than that, and suggest inserting the missing '*'.
>

This patch replaces the errors complaining about undeclared identifiers
with an error specific to ranged-for loops, along with an explanatory note.
I also updated the existing test cases to reflect the change. For example,
the above code now generates this:

test.cpp:3:15: error: invalid range expression of type 'S *'
>  for (auto i : p) {}
>              ^ ~
> test.cpp:3:16: note: range expression is of type 'S *'; did you
>       mean to dereference it with '*'?
>  for (auto i : p) {}
>                ^
>                *
> test.cpp:3:14: note: no viable 'end' function for range of type
>       'S *'
>  for (auto i : p) {}


I hope that this is helpful, and comments are always welcome.

-Sam
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