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These functions are currently covered by both the `proc_macro_span_file` and the `proc_macro_span` probe. These APIs are redesigned and stabilized in the same release cycle (1.88); this means that the API only exists under `proc_macro_span` for a very short duration of time, between nightly 2025-04-16 to 2025-05-08. For earlier nightly compiler, the probe will cause the probe to fail because the API is yet redesigned; for later compilers the probe isn't useful because the feature is already stable. Drop the probes, and instead check rustc version instead; this is the same approach used by other features. Signed-off-by: Gary Guo <gary@garyguo.net>
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proc_macro_span_file featureproc_macro_span_file feature
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The `Span::join` function is very important in generating useful
diagnostics. When invoking `syn::Spanned::span`, it attempts to return an
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 feature
enabled.
For example, this diagnostic covers only part of the text where replacement
is suggested:
error: expected nothing or `..Zeroable::init_zeroed()`.
--> tests/ui/compile-fail/zeroable/invalid_spread.rs:15:11
|
15 | ..MyZeroable::init_zeroed()
| ^^^^^^^^^^
In the upcoming pin-init self-reference series, spans of full types or
expressions are used quite heavily to make diagnostics not confusing.
Thus, enable the `proc_macro_span` feature. This does make use of the
unstable `Span::join` function, but this is for producing diagnostics only,
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.
Link: rust-lang/rust#54725
Link: dtolnay/proc-macro2#542
Signed-off-by: Gary Guo <gary@garyguo.net>
nbdd0121
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Sep 30, 2026
The `Span::join` function is very important in generating useful
diagnostics. When invoking `syn::Spanned::span`, it attempts to return an
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 feature
enabled.
For example, this diagnostic covers only part of the text where replacement
is suggested:
error: expected nothing or `..Zeroable::init_zeroed()`.
--> tests/ui/compile-fail/zeroable/invalid_spread.rs:15:11
|
15 | ..MyZeroable::init_zeroed()
| ^^^^^^^^^^
In the upcoming pin-init self-reference series, spans of full types or
expressions are used quite heavily to make diagnostics not confusing.
Thus, enable the `proc_macro_span` feature. This does make use of the
unstable `Span::join` function, but this is for producing diagnostics only,
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.
Link: rust-lang/rust#54725
Link: dtolnay/proc-macro2#542
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Link: https://patch.msgid.link/20260921115708.4009754-1-gary@kernel.org/
[ Updated example diagnostics, removed unused PathBuf import. - Gary ]
Signed-off-by: Gary Guo <gary@garyguo.net>
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Fix #522
These functions are currently covered by both the
proc_macro_span_fileand theproc_macro_spanprobe. These APIs are redesigned and stabilized in the same release cycle (1.88); this means that the API only exists underproc_macro_spanfor a very short duration of time, between nightly 2025-04-16 to 2025-05-08.For earlier nightly compiler, the probe will cause the probe to fail because the API is yet redesigned; for later compilers the probe isn't useful because the feature is already stable.
Drop the probes, and instead check rustc version instead; this is the same approach used by other features.
The motivation of this change is that in Linux kernel we support 1.85 with RUSTC_BOOTSTRAP=1 as minimum; and we want to enable
proc_macro_spanso.join()works properly and produce better diagnostics. Currently we cannot enableproc_macro_spanbecause thelocal_fileandfilefunction do not exist before nightly-2025-04-16. That said, I think this change is a useful cleanup on its own.