rjmccall added inline comments.
================
Comment at: lib/Sema/SemaExprObjC.cpp:534
+ NSStringPointer, NSStringPointer);
+ return new (Context) ObjCBoxedExpr(SL, BoxedType, nullptr, SR);
+ }
----------------
ahatanak wrote:
> rjmccall wrote:
> > You're implicitly dropping sugar from the source expression here; I really
> > think you should preserve that, and if it means you end up having to look
> > through array-decay expressions, that's not the end of the world.
> >
> > The need for a special case here is just to allow us to compile these even
> > if there isn't a boxing method available?
> >
> > Do you need to restrict the type of the string literal so that it doesn't
> > apply to e.g. wide strings?
> Line 516 checks that the pointee type has the same unqualified type as
> 'char'. If the string literal inside the parentheses is of a wider type
> (e.g., `@(u"abc")`), this piece of code won't be executed, and a diagnostic
> is emitted later ("illegal type 'const char16_t *' used in a boxed
> expression").
>
> The original motivation for special-casing string literals inside boxed
> expressions was to silence the `-Wnullable-to-nonnull-conversion` warning
> mentioned here: https://oleb.net/2018/@keypath/. The warning is issued
> because the return type of `stringWithUTF8String` is nullable.
>
> ```
> ...
> + (nullable instancetype)stringWithUTF8String:(const char
> *)nullTerminatedCString;
> ...
>
> NSString * _Nonnull ptr = @("abc"); // expected-error {{implicit conversion
> from nullable pointer 'NSString * _Nullable' to non-nullable pointer type
> 'NSString * _Nonnull'}}
> ```
I see. So in addition to guaranteeing to skip the boxing call, you'd like to
adjust the type to report the result as non-null, which we can do because we're
unconditionally making a constant string. Makes sense.
However, I think you need to check that the string is valid UTF-8 or else this
is semantics-changing, since such strings are rejected by
`+stringWithUTF8String:` (which is why it returns a nullable pointer at all).
It should be alright to warn about strings that are statically known to be
invalid UTF-8, but you'll then need to emit them using the normal boxing method.
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D58729/new/
https://reviews.llvm.org/D58729
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