Previously using the `counted_by` or `counted_by_or_null` attribute on a
pointer with an incomplete pointee type was forbidden. Unfortunately
this prevented a situation like the following from being allowed.
Header file:
```
struct EltTy; // Incomplete type
struct Buffer {
size_t count;
struct EltTy* __counted_by(count) buffer; // error before this patch
};
```
Implementation file:
```
struct EltTy {
// definition
};
void allocBuffer(struct Buffer* b) {
b->buffer = malloc(sizeof(EltTy)* b->count);
}
```
To allow code like the above but still enforce that the pointee
type size is known in locations where `-fbounds-safety` needs to
emit bounds checks the following scheme is used.
* For incomplete pointee types that can never be completed (e.g. `void`)
these are treated as error where the attribute is written (just like
before this patch).
* For incomplete pointee types that might be completable later on
(struct, union, and enum forward declarations)
in the translation unit, writing the attribute on the incomplete
pointee type is allowed on the FieldDecl declaration but "uses" of the
declared pointer are forbidden if at the point of "use" the pointee
type is still incomplete.
For this patch a "use" of a FieldDecl covers:
* Explicit and Implicit initialization (note see **Tentative Definition
Initialization** for an exception to this)
* Assignment
* Conversion to an lvalue (e.g. for use in an expression)
In the swift lang fork of Clang the `counted_by` and
`counted_by_or_null` attribute are allowed in many more contexts. That
isn't the case for upstream Clang so the "use" checks for the attribute
on VarDecl, ParamVarDecl, and function return type have been omitted
from this patch because they can't be tested. However, the
`BoundsSafetyCheckAssignmentToCountAttrPtrWithIncompletePointeeTy` and
`BoundsSafetyCheckUseOfCountAttrPtrWithIncompletePointeeTy` functions
retain the ability to emit diagnostics for these other contexts to avoid
unnecessary divergence between upstream Clang and Apple's internal fork.
Support for checking "uses" will be upstreamed when upstream Clang
allows the `counted_by` and `counted_by_or_null` attribute in additional
contexts.
This patch has a few limitations:
** 1. Tentative Defition Initialization **
This patch currently allows something like:
```
struct IncompleteTy;
struct Buffer {
int count;
struct IncompleteTy* __counted_by(count) buf;
};
// Tentative definition
struct Buffer GlobalBuf;
```
The Tentative definition in this example becomes an actual definition
whose initialization **should be checked** but it currently isn't.
Addressing this problem will be done in a subseqent patch.
** 2. When the incomplete pointee type is a typedef diagnostics are slightly misleading **
For this situation:
```
struct IncompleteTy;
typedef struct IncompleteTy Incomplete_t;
struct Buffer {
int count;
struct IncompleteTy* __counted_by(count) buf;
};
void use(struct Buffer b) {
b.buf = 0x0;
}
```
This code emits `note: forward declaration of 'Incomplete_t' (aka
'struct IncompleteTy')` but the location is on the `struct
IncompleteTy;` forward declaration. This is misleading because
`Incomplete_t` isn't actually forward declared there (instead the
underlying type is). This could be resolved by additional diagnostics
that walk the chain of typedefs and explain each step of the walk.
However, that would be very verbose and didn't seem like a direction
worth pursuing.
rdar://133600117
Previously we weren't properly checking that using
`-fexperimental-late-parse-attributes` worked on source code that didn't
need late parsing.
For example we weren't testing that the attribute appearing in the type
position generated the right AST with
`-fexperimental-late-parse-attributes` off.
This patch adds additional `RUN` lines to re-run the relevant test cases
with `-fexperimental-late-parse-attributes` enabled.
rdar://133325597
The attributes `sized_by`, `counted_by_or_null` and `sized_by_or_null`
have been added as variants on `counted_by`, each with slightly
different semantics. `sized_by` takes a byte size parameter instead of
an element count, allowing pointees with unknown size. The
`counted_by_or_null` and `sized_by_or_null` variants are equivalent to
their base variants, except the pointer can be null regardless of
count/size value. If the pointer is null the size is effectively 0.
rdar://125400354
