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When invoking `syn::Spanned::span`, it attempts to return a > overall span that covers the whole expression. If the `join` function is > unavailable, however, only the span of the first token is generated. > > This causes worse diagnostics quality for all macros, notably pin-init, > when compared to the pin-init's own diagnostics test suite with the featu= re > enabled. > > For example, this diagnostic refers to only a fragment of path and not th= e > full one: > > error: The field index `1` of type `PhantomPinned` only has an effect= if it has the `#[pin]` attribute > --> tests/ui/compile-fail/pin_data/tuple_struct_missing_pin_phantom.= rs:6:20 > | > 6 | struct Tuple(T, core::marker::PhantomPinned); > | ^^^^ > > The special "<-" syntax gets parsed as two tokens, so they are only > partially marked in diagnostics: > > error: `<-` is not supported in tuple constructor syntax; name the fi= elds by index instead, e.g. `Type { 0 <- initializer, 1: value }` > --> tests/ui/compile-fail/init/no_tuple_paren_arrow.rs:7:29 > | > 7 | let _ =3D pin_init!(Tuple(<- 1, 2)); > | ^ > > In the upcoming pin-init self-reference series, there are also custom > diagnostics that wish to use the span of the full type instead of its fir= st > token. > > Thus, enable the `proc_macro_span` feature. This does make use of the > unstable `Span::join` function, but this is for producing diagnostics onl= y, > so we do not have a hard reliance on the feature. A very small tweak of > proc-macro2 vendored code is needed to make the code compile for 1.85. > > Signed-off-by: Gary Guo Applied to pin-init-next. Thanks all! Best, Gary > --- > Miguel, please let me know if you're okay with the proc-macro2 > modification. > > I'd like to take this via pin-init-next if possible. > --- > rust/Makefile | 1 + > rust/proc-macro2/README.md | 3 ++- > rust/proc-macro2/probe/proc_macro_span.rs | 8 -------- > 3 files changed, 3 insertions(+), 9 deletions(-)