Rollup merge of #79208 - LeSeulArtichaut:stable-unsafe_op_in_unsafe_fn, r=nikomatsakis

Stabilize `unsafe_op_in_unsafe_fn` lint

This makes it possible to override the level of the `unsafe_op_in_unsafe_fn`, as proposed in https://github.com/rust-lang/rust/issues/71668#issuecomment-729770896.

Tracking issue: #71668
r? ```@nikomatsakis``` cc ```@SimonSapin``` ```@RalfJung```

# Stabilization report

This is a stabilization report for `#![feature(unsafe_block_in_unsafe_fn)]`.

## Summary

Currently, the body of unsafe functions is an unsafe block, i.e. you can perform unsafe operations inside.

The `unsafe_op_in_unsafe_fn` lint, stabilized here, can be used to change this behavior, so performing unsafe operations in unsafe functions requires an unsafe block.

For now, the lint is allow-by-default, which means that this PR does not change anything without overriding the lint level.

For more information, see [RFC 2585](https://github.com/rust-lang/rfcs/blob/master/text/2585-unsafe-block-in-unsafe-fn.md)

### Example

```rust
// An `unsafe fn` for demonstration purposes.
// Calling this is an unsafe operation.
unsafe fn unsf() {}

// #[allow(unsafe_op_in_unsafe_fn)] by default,
// the behavior of `unsafe fn` is unchanged
unsafe fn allowed() {
    // Here, no `unsafe` block is needed to
    // perform unsafe operations...
    unsf();

    // ...and any `unsafe` block is considered
    // unused and is warned on by the compiler.
    unsafe {
        unsf();
    }
}

#[warn(unsafe_op_in_unsafe_fn)]
unsafe fn warned() {
    // Removing this `unsafe` block will
    // cause the compiler to emit a warning.
    // (Also, no "unused unsafe" warning will be emitted here.)
    unsafe {
        unsf();
    }
}

#[deny(unsafe_op_in_unsafe_fn)]
unsafe fn denied() {
    // Removing this `unsafe` block will
    // cause a compilation error.
    // (Also, no "unused unsafe" warning will be emitted here.)
    unsafe {
        unsf();
    }
}
```

compiler/rustc_feature/src/accepted.rs

@@ -275,6 +275,8 @@ declare_features! (
     (accepted, move_ref_pattern, "1.49.0", Some(68354), None),
     /// The smallest useful subset of `const_generics`.
     (accepted, min_const_generics, "1.51.0", Some(74878), None),
+    /// The `unsafe_op_in_unsafe_fn` lint (allowed by default): no longer treat an unsafe function as an unsafe block.
+    (accepted, unsafe_block_in_unsafe_fn, "1.51.0", Some(71668), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features

compiler/rustc_feature/src/active.rs

@@ -557,9 +557,6 @@ declare_features! (
     /// Allows the use of `#[ffi_const]` on foreign functions.
     (active, ffi_const, "1.45.0", Some(58328), None),
 
-    /// No longer treat an unsafe function as an unsafe block.
-    (active, unsafe_block_in_unsafe_fn, "1.45.0", Some(71668), None),
-
     /// Allows `extern "avr-interrupt" fn()` and `extern "avr-non-blocking-interrupt" fn()`.
     (active, abi_avr_interrupt, "1.45.0", Some(69664), None),
 

compiler/rustc_lint_defs/src/builtin.rs

@@ -8,7 +8,6 @@
 
 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
@@ -2489,16 +2488,11 @@ declare_lint! {
 
 declare_lint! {
     /// The `unsafe_op_in_unsafe_fn` lint detects unsafe operations in unsafe
-    /// functions without an explicit unsafe block. This lint only works on
-    /// the [**nightly channel**] with the
-    /// `#![feature(unsafe_block_in_unsafe_fn)]` feature.
-    ///
-    /// [**nightly channel**]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
+    /// functions without an explicit unsafe block.
     ///
     /// ### Example
     ///
     /// ```rust,compile_fail
-    /// #![feature(unsafe_block_in_unsafe_fn)]
     /// #![deny(unsafe_op_in_unsafe_fn)]
     ///
     /// unsafe fn foo() {}
@@ -2536,7 +2530,6 @@ declare_lint! {
     pub UNSAFE_OP_IN_UNSAFE_FN,
     Allow,
     "unsafe operations in unsafe functions without an explicit unsafe block are deprecated",
-    @feature_gate = sym::unsafe_block_in_unsafe_fn;
 }
 
 declare_lint! {

compiler/rustc_middle/src/mir/query.rs

@@ -28,11 +28,9 @@ pub enum UnsafetyViolationKind {
     BorrowPacked,
     /// Unsafe operation in an `unsafe fn` but outside an `unsafe` block.
     /// Has to be handled as a lint for backwards compatibility.
-    /// Should stay gated under `#![feature(unsafe_block_in_unsafe_fn)]`.
     UnsafeFn,
     /// Borrow of packed field in an `unsafe fn` but outside an `unsafe` block.
     /// Has to be handled as a lint for backwards compatibility.
-    /// Should stay gated under `#![feature(unsafe_block_in_unsafe_fn)]`.
     UnsafeFnBorrowPacked,
 }
 

compiler/rustc_mir/src/transform/check_unsafety.rs

@@ -341,7 +341,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
                 false
             }
             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
-            Safety::FnUnsafe if self.tcx.features().unsafe_block_in_unsafe_fn => {
+            Safety::FnUnsafe => {
                 for violation in violations {
                     let mut violation = *violation;
 
@@ -356,8 +356,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
                 }
                 false
             }
-            // `unsafe` function bodies allow unsafe without additional unsafe blocks (before RFC 2585)
-            Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
+            Safety::BuiltinUnsafe => true,
             Safety::ExplicitUnsafe(hir_id) => {
                 // mark unsafe block as used if there are any unsafe operations inside
                 if !violations.is_empty() {

library/alloc/src/lib.rs

@@ -133,7 +133,7 @@
 #![feature(trusted_len)]
 #![feature(unboxed_closures)]
 #![feature(unicode_internals)]
-#![feature(unsafe_block_in_unsafe_fn)]
+#![cfg_attr(bootstrap, feature(unsafe_block_in_unsafe_fn))]
 #![feature(unsize)]
 #![feature(unsized_fn_params)]
 #![feature(allocator_internals)]

library/core/src/lib.rs

@@ -164,8 +164,8 @@
 #![feature(const_caller_location)]
 #![feature(slice_ptr_get)]
 #![feature(no_niche)] // rust-lang/rust#68303
-#![feature(unsafe_block_in_unsafe_fn)]
 #![feature(int_error_matching)]
+#![cfg_attr(bootstrap, feature(unsafe_block_in_unsafe_fn))]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 #[prelude_import]

library/core/tests/lib.rs

@@ -72,7 +72,6 @@
 #![feature(peekable_peek_mut)]
 #![cfg_attr(not(bootstrap), feature(ptr_metadata))]
 #![feature(once_cell)]
-#![feature(unsafe_block_in_unsafe_fn)]
 #![feature(unsized_tuple_coercion)]
 #![feature(int_bits_const)]
 #![feature(nonzero_leading_trailing_zeros)]
@@ -80,8 +79,9 @@
 #![feature(integer_atomics)]
 #![feature(slice_group_by)]
 #![feature(trusted_random_access)]
-#![deny(unsafe_op_in_unsafe_fn)]
+#![cfg_attr(bootstrap, feature(unsafe_block_in_unsafe_fn))]
 #![cfg_attr(not(bootstrap), feature(unsize))]
+#![deny(unsafe_op_in_unsafe_fn)]
 
 extern crate test;
 

library/std/src/lib.rs

@@ -327,7 +327,7 @@
 #![feature(try_blocks)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
-#![feature(unsafe_block_in_unsafe_fn)]
+#![cfg_attr(bootstrap, feature(unsafe_block_in_unsafe_fn))]
 #![feature(unsafe_cell_raw_get)]
 #![feature(unwind_attributes)]
 #![feature(vec_into_raw_parts)]

src/test/ui/feature-gates/feature-gate-unsafe_block_in_unsafe_fn.rs

@@ -1,6 +0,0 @@
-#![deny(unsafe_op_in_unsafe_fn)]
-//~^ ERROR the `unsafe_op_in_unsafe_fn` lint is unstable
-//~| ERROR the `unsafe_op_in_unsafe_fn` lint is unstable
-//~| ERROR the `unsafe_op_in_unsafe_fn` lint is unstable
-
-fn main() {}

src/test/ui/feature-gates/feature-gate-unsafe_block_in_unsafe_fn.stderr

@@ -1,30 +0,0 @@
-error[E0658]: the `unsafe_op_in_unsafe_fn` lint is unstable
-  --> $DIR/feature-gate-unsafe_block_in_unsafe_fn.rs:1:1
-   |
-LL | #![deny(unsafe_op_in_unsafe_fn)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #71668 <https://github.com/rust-lang/rust/issues/71668> for more information
-   = help: add `#![feature(unsafe_block_in_unsafe_fn)]` to the crate attributes to enable
-
-error[E0658]: the `unsafe_op_in_unsafe_fn` lint is unstable
-  --> $DIR/feature-gate-unsafe_block_in_unsafe_fn.rs:1:1
-   |
-LL | #![deny(unsafe_op_in_unsafe_fn)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #71668 <https://github.com/rust-lang/rust/issues/71668> for more information
-   = help: add `#![feature(unsafe_block_in_unsafe_fn)]` to the crate attributes to enable
-
-error[E0658]: the `unsafe_op_in_unsafe_fn` lint is unstable
-  --> $DIR/feature-gate-unsafe_block_in_unsafe_fn.rs:1:1
-   |
-LL | #![deny(unsafe_op_in_unsafe_fn)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #71668 <https://github.com/rust-lang/rust/issues/71668> for more information
-   = help: add `#![feature(unsafe_block_in_unsafe_fn)]` to the crate attributes to enable
-
-error: aborting due to 3 previous errors
-
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/unsafe/rfc-2585-unsafe_op_in_unsafe_fn.rs

@@ -1,4 +1,3 @@
-#![feature(unsafe_block_in_unsafe_fn)]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![deny(unused_unsafe)]
 

src/test/ui/unsafe/rfc-2585-unsafe_op_in_unsafe_fn.stderr

@@ -1,18 +1,18 @@
 error: call to unsafe function is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:10:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:9:5
    |
 LL |     unsf();
    |     ^^^^^^ call to unsafe function
    |
 note: the lint level is defined here
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:2:9
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:1:9
    |
 LL | #![deny(unsafe_op_in_unsafe_fn)]
    |         ^^^^^^^^^^^^^^^^^^^^^^
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
 error: dereference of raw pointer is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:12:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:11:5
    |
 LL |     *PTR;
    |     ^^^^ dereference of raw pointer
@@ -20,7 +20,7 @@ LL |     *PTR;
    = note: raw pointers may be NULL, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
 
 error: use of mutable static is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:14:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:13:5
    |
 LL |     VOID = ();
    |     ^^^^^^^^^ use of mutable static
@@ -28,25 +28,25 @@ LL |     VOID = ();
    = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
 
 error: unnecessary `unsafe` block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:17:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:16:5
    |
 LL |     unsafe {}
    |     ^^^^^^ unnecessary `unsafe` block
    |
 note: the lint level is defined here
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:3:9
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:2:9
    |
 LL | #![deny(unused_unsafe)]
    |         ^^^^^^^^^^^^^
 
 error: call to unsafe function is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:25:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:24:5
    |
 LL |     unsf();
    |     ^^^^^^ call to unsafe function
    |
 note: the lint level is defined here
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:23:8
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:22:8
    |
 LL | #[deny(warnings)]
    |        ^^^^^^^^
@@ -54,7 +54,7 @@ LL | #[deny(warnings)]
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
 error: dereference of raw pointer is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:27:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:26:5
    |
 LL |     *PTR;
    |     ^^^^ dereference of raw pointer
@@ -62,7 +62,7 @@ LL |     *PTR;
    = note: raw pointers may be NULL, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
 
 error: use of mutable static is unsafe and requires unsafe block (error E0133)
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:29:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:28:5
    |
 LL |     VOID = ();
    |     ^^^^^^^^^ use of mutable static
@@ -70,13 +70,13 @@ LL |     VOID = ();
    = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
 
 error: unnecessary `unsafe` block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:31:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:30:5
    |
 LL |     unsafe {}
    |     ^^^^^^ unnecessary `unsafe` block
 
 error: unnecessary `unsafe` block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:45:14
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:44:14
    |
 LL |     unsafe { unsafe { unsf() } }
    |     ------   ^^^^^^ unnecessary `unsafe` block
@@ -84,7 +84,7 @@ LL |     unsafe { unsafe { unsf() } }
    |     because it's nested under this `unsafe` block
 
 error: unnecessary `unsafe` block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:56:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:55:5
    |
 LL | unsafe fn allow_level() {
    | ----------------------- because it's nested under this `unsafe` fn
@@ -93,7 +93,7 @@ LL |     unsafe { unsf() }
    |     ^^^^^^ unnecessary `unsafe` block
 
 error: unnecessary `unsafe` block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:68:9
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:67:9
    |
 LL | unsafe fn nested_allow_level() {
    | ------------------------------ because it's nested under this `unsafe` fn
@@ -102,7 +102,7 @@ LL |         unsafe { unsf() }
    |         ^^^^^^ unnecessary `unsafe` block
 
 error[E0133]: call to unsafe function is unsafe and requires unsafe block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:74:5
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:73:5
    |
 LL |     unsf();
    |     ^^^^^^ call to unsafe function
@@ -110,7 +110,7 @@ LL |     unsf();
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
 error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
-  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:78:9
+  --> $DIR/rfc-2585-unsafe_op_in_unsafe_fn.rs:77:9
    |
 LL |         unsf();
    |         ^^^^^^ call to unsafe function