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Introduce proc_macro_back_compat lint, and emit for time-macros-impl

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Now that future-incompat-report support has landed in nightly Cargo, we
can start to make progress towards removing the various proc-macro
back-compat hacks that have accumulated in the compiler.

This PR introduces a new lint `proc_macro_back_compat`, which results in
a future-incompat-report entry being generated. All proc-macro
back-compat warnings will be grouped under this lint. Note that this
lint will never actually become a hard error - instead, we will remove
the special cases for various macros, which will cause older versions of
those crates to emit some other error.

I've added code to fire this lint for the `time-macros-impl` case. This
is the easiest case out of all of our current back-compat hacks - the
crate was renamed to `time-macros`, so seeing a filename with
`time-macros-impl` guarantees that an older version of the parent `time`
crate is in use.

When Cargo's future-incompat-report feature gets stabilized, affected
users will start to see future-incompat warnings when they build their
crates.
This commit is contained in:
Aaron Hill 2021-03-14 16:55:59 -04:00
parent d6eaea1c88
commit f190bc4f47
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8 changed files with 206 additions and 65 deletions
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53
compiler/rustc_lint_defs/src/builtin.rs
View file

@ -6,7 +6,7 @@
//! compiler code, rather than using their own custom pass. Those
//! lints are all available in `rustc_lint::builtin`.
use crate::{declare_lint, declare_lint_pass};
use crate::{declare_lint, declare_lint_pass, FutureBreakage};
use rustc_span::edition::Edition;
declare_lint! {
@ -2955,6 +2955,7 @@ declare_lint_pass! {
SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
DISJOINT_CAPTURE_DROP_REORDER,
LEGACY_DERIVE_HELPERS,
PROC_MACRO_BACK_COMPAT,
]
}
@ -3082,3 +3083,53 @@ declare_lint! {
edition: None,
};
}
declare_lint! {
/// The `proc_macro_back_compat` lint detects uses of old versions of certain
/// proc-macro crates, which have hardcoded workarounds in the compiler.
///
/// ### Example
///
/// ```rust,ignore (needs-dependency)
///
/// use time_macros_impl::impl_macros;
/// struct Foo;
/// impl_macros!(Foo);
/// ```
///
/// This will produce:
///
/// ```text
/// warning: using an old version of `time-macros-impl`
/// ::: $DIR/group-compat-hack.rs:27:5
/// |
/// LL | impl_macros!(Foo);
/// | ------------------ in this macro invocation
/// |
/// = note: `#[warn(proc_macro_back_compat)]` on by default
/// = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
/// = note: for more information, see issue #83125 <https://github.com/rust-lang/rust/issues/83125>
/// = note: the `time-macros-impl` crate will stop compiling in futures version of Rust. Please update to the latest version of the `time` crate to avoid breakage
/// = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
/// ```
///
/// ### Explanation
///
/// Eventually, the backwards-compatibility hacks present in the compiler will be removed,
/// causing older versions of certain crates to stop compiling.
/// This is a [future-incompatible] lint to ease the transition to an error.
/// See [issue #83125] for more details.
///
/// [issue #83125]: https://github.com/rust-lang/rust/issues/83125
/// [future-incompatible]: ../index.md#future-incompatible-lints
pub PROC_MACRO_BACK_COMPAT,
Warn,
"detects usage of old versions of certain proc-macro crates",
@future_incompatible = FutureIncompatibleInfo {
reference: "issue #83125 <https://github.com/rust-lang/rust/issues/83125>",
edition: None,
future_breakage: Some(FutureBreakage {
date: None
})
};
}