introduce future-compatibility warning for forbidden lint groups

[rust.git] / compiler / rustc_lint_defs / src / builtin.rs

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 20052ad9bfcbd60ec558becca24683dc8c49e7ab..fdba6b402e662810c5221dfffdb6f164a597b24d 100644 (file)
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -4,10 +4,48 @@
 //! compiler code, rather than using their own custom pass. Those
 //! lints are all available in `rustc_lint::builtin`.
 
+// ignore-tidy-filelength
+
 use crate::{declare_lint, declare_lint_pass};
 use rustc_span::edition::Edition;
 use rustc_span::symbol::sym;
 
+declare_lint! {
+    /// The `forbidden_lint_groups` lint detects violations of
+    /// `forbid` applied to a lint group. Due to a bug in the compiler,
+    /// these used to be overlooked entirely. They now generate a warning.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![forbid(warnings)]
+    /// #![deny(bad_style)]
+    ///
+    /// fn main() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Recommended fix
+    ///
+    /// If your crate is using `#![forbid(warnings)]`,
+    /// we recommend that you change to `#![deny(warnings)]`.
+    ///
+    /// ### Explanation
+    ///
+    /// Due to a compiler bug, applying `forbid` to lint groups
+    /// previously had no effect. The bug is now fixed but instead of
+    /// enforcing `forbid` we issue this future-compatibility warning
+    /// to avoid breaking existing crates.
+    pub FORBIDDEN_LINT_GROUPS,
+    Warn,
+    "applying forbid to lint-groups",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
+        edition: None,
+    };
+}
+
 declare_lint! {
     /// The `ill_formed_attribute_input` lint detects ill-formed attribute
     /// inputs that were previously accepted and used in practice.
@@ -238,41 +276,22 @@
     ///
     /// ```rust,compile_fail
     /// #![allow(unconditional_panic)]
-    /// let x: &'static i32 = &(1 / 0);
+    /// const C: i32 = 1/0;
     /// ```
     ///
     /// {{produces}}
     ///
     /// ### Explanation
     ///
-    /// This lint detects code that is very likely incorrect. If this lint is
-    /// allowed, then the code will not be evaluated at compile-time, and
-    /// instead continue to generate code to evaluate at runtime, which may
-    /// panic during runtime.
-    ///
-    /// Note that this lint may trigger in either inside or outside of a
-    /// [const context]. Outside of a [const context], the compiler can
-    /// sometimes evaluate an expression at compile-time in order to generate
-    /// more efficient code. As the compiler becomes better at doing this, it
-    /// needs to decide what to do when it encounters code that it knows for
-    /// certain will panic or is otherwise incorrect. Making this a hard error
-    /// would prevent existing code that exhibited this behavior from
-    /// compiling, breaking backwards-compatibility. However, this is almost
-    /// certainly incorrect code, so this is a deny-by-default lint. For more
-    /// details, see [RFC 1229] and [issue #28238].
-    ///
-    /// Note that there are several other more specific lints associated with
-    /// compile-time evaluation, such as [`arithmetic_overflow`],
-    /// [`unconditional_panic`].
+    /// This lint detects constants that fail to evaluate. Allowing the lint will accept the
+    /// constant declaration, but any use of this constant will still lead to a hard error. This is
+    /// a future incompatibility lint; the plan is to eventually entirely forbid even declaring
+    /// constants that cannot be evaluated.  See [issue #71800] for more details.
     ///
-    /// [const context]: https://doc.rust-lang.org/reference/const_eval.html#const-context
-    /// [RFC 1229]: https://github.com/rust-lang/rfcs/blob/master/text/1229-compile-time-asserts.md
-    /// [issue #28238]: https://github.com/rust-lang/rust/issues/28238
-    /// [`arithmetic_overflow`]: deny-by-default.html#arithmetic-overflow
-    /// [`unconditional_panic`]: deny-by-default.html#unconditional-panic
+    /// [issue #71800]: https://github.com/rust-lang/rust/issues/71800
     pub CONST_ERR,
     Deny,
-    "constant evaluation detected erroneous expression",
+    "constant evaluation encountered erroneous expression",
     report_in_external_macro
 }
 
@@ -2856,6 +2875,7 @@
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
     HardwiredLints => [
+        FORBIDDEN_LINT_GROUPS,
         ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
         ARITHMETIC_OVERFLOW,
         UNCONDITIONAL_PANIC,