Rollup merge of #56706 - oli-obk:const_unsafe_fn, r=Centril

Make `const unsafe fn` bodies `unsafe`

r? @Centril

Updated for tracking issue discussion https://github.com/rust-lang/rust/issues/55607#issuecomment-445882296

8 files changed, 33 insertions, 131 deletions

diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 4acf3a15ebf..fd74e713416 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -70,7 +70,7 @@ assert_eq!(size_of::<Option<std::num::", stringify!($Ty), ">>(), size_of::<", st
                 #[stable(feature = "nonzero", since = "1.28.0")]
                 #[inline]
                 pub const unsafe fn new_unchecked(n: $Int) -> Self {
-                    $Ty(unsafe { NonZero(n) })
+                    $Ty(NonZero(n))
                 }
 
                 /// Create a non-zero if the given value is not zero.
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index 79ca600b4a5..b3c93ae1fa7 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -2928,7 +2928,7 @@ impl<T: ?Sized> NonNull<T> {
     #[stable(feature = "nonnull", since = "1.25.0")]
     #[inline]
     pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
-        NonNull { pointer: unsafe { NonZero(ptr as _) } }
+        NonNull { pointer: NonZero(ptr as _) }
     }
 
     /// Creates a new `NonNull` if `ptr` is non-null.
diff --git a/src/librustc_mir/build/mod.rs b/src/librustc_mir/build/mod.rs
index ab52d9be6b8..451034fd153 100644
--- a/src/librustc_mir/build/mod.rs
+++ b/src/librustc_mir/build/mod.rs
@@ -111,13 +111,6 @@ pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'t
 
             let safety = match fn_sig.unsafety {
                 hir::Unsafety::Normal => Safety::Safe,
-                hir::Unsafety::Unsafe if tcx.is_min_const_fn(fn_def_id) => {
-                    // As specified in #55607, a `const unsafe fn` differs
-                    // from an `unsafe fn` in that its body is still considered
-                    // safe code by default.
-                    assert!(implicit_argument.is_none());
-                    Safety::Safe
-                },
                 hir::Unsafety::Unsafe => Safety::FnUnsafe,
             };
 
diff --git a/src/librustc_mir/transform/check_unsafety.rs b/src/librustc_mir/transform/check_unsafety.rs
index 6af29b74c1c..36078693840 100644
--- a/src/librustc_mir/transform/check_unsafety.rs
+++ b/src/librustc_mir/transform/check_unsafety.rs
@@ -311,13 +311,9 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
                            violations: &[UnsafetyViolation],
                            unsafe_blocks: &[(ast::NodeId, bool)]) {
         let safety = self.source_scope_local_data[self.source_info.scope].safety;
-        let within_unsafe = match (safety, self.min_const_fn) {
-            // Erring on the safe side, pun intended
-            (Safety::BuiltinUnsafe, true) |
-            // mir building encodes const fn bodies as safe, even for `const unsafe fn`
-            (Safety::FnUnsafe, true) => bug!("const unsafe fn body treated as inherently unsafe"),
+        let within_unsafe = match safety {
             // `unsafe` blocks are required in safe code
-            (Safety::Safe, _) => {
+            Safety::Safe => {
                 for violation in violations {
                     let mut violation = violation.clone();
                     match violation.kind {
@@ -342,9 +338,9 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
                 }
                 false
             }
-            // regular `unsafe` function bodies allow unsafe without additional unsafe blocks
-            (Safety::BuiltinUnsafe, false) | (Safety::FnUnsafe, false) => true,
-            (Safety::ExplicitUnsafe(node_id), _) => {
+            // `unsafe` function bodies allow unsafe without additional unsafe blocks
+            Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
+            Safety::ExplicitUnsafe(node_id) => {
                 // mark unsafe block as used if there are any unsafe operations inside
                 if !violations.is_empty() {
                     self.used_unsafe.insert(node_id);
@@ -616,21 +612,6 @@ pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
     } in violations.iter() {
         // Report an error.
         match kind {
-            UnsafetyViolationKind::General if tcx.is_min_const_fn(def_id) => {
-                let mut err = tcx.sess.struct_span_err(
-                    source_info.span,
-                    &format!("{} is unsafe and unsafe operations \
-                            are not allowed in const fn", description));
-                err.span_label(source_info.span, &description.as_str()[..])
-                    .note(&details.as_str()[..]);
-                if tcx.fn_sig(def_id).unsafety() == hir::Unsafety::Unsafe {
-                    err.note(
-                        "unsafe action within a `const unsafe fn` still require an `unsafe` \
-                        block in contrast to regular `unsafe fn`."
-                    );
-                }
-                err.emit();
-            }
             UnsafetyViolationKind::GeneralAndConstFn |
             UnsafetyViolationKind::General => {
                 struct_span_err!(
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.rs b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.rs
index f11b43dcd86..92e99c6228a 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.rs
+++ b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.rs
@@ -28,13 +28,13 @@ const fn call_unsafe_generic_cell_const_fn() -> *const Vec<std::cell::Cell<u32>>
     unsafe { ret_null_mut_ptr_no_unsafe::<Vec<std::cell::Cell<u32>>>() }
     //~^ ERROR calls to `const unsafe fn` in const fns
 }
-const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
+const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x }
 //~^ dereferencing raw pointers in constant functions
 
 fn main() {}
 
 const unsafe fn no_union() {
     union Foo { x: (), y: () }
-    Foo { x: () }.y //~ ERROR not allowed in const fn
+    Foo { x: () }.y
     //~^ unions in const fn
 }
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.stderr b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.stderr
index 922a7883b9f..fafc89d1493 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.stderr
+++ b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe.stderr
@@ -1,7 +1,7 @@
 error[E0658]: dereferencing raw pointers in constant functions is unstable (see issue #51911)
   --> $DIR/min_const_fn_unsafe.rs:31:59
    |
-LL | const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
+LL | const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x }
    |                                                           ^^
    |
    = help: add #![feature(const_raw_ptr_deref)] to the crate attributes to enable
@@ -9,7 +9,7 @@ LL | const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x } //~ ERROR no
 error[E0658]: unions in const fn are unstable (see issue #51909)
   --> $DIR/min_const_fn_unsafe.rs:38:5
    |
-LL |     Foo { x: () }.y //~ ERROR not allowed in const fn
+LL |     Foo { x: () }.y
    |     ^^^^^^^^^^^^^^^
    |
    = help: add #![feature(const_fn_union)] to the crate attributes to enable
@@ -38,24 +38,6 @@ LL |     unsafe { ret_null_mut_ptr_no_unsafe::<Vec<std::cell::Cell<u32>>>() }
    |
    = help: add #![feature(min_const_unsafe_fn)] to the crate attributes to enable
 
-error: dereference of raw pointer is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe.rs:31:59
-   |
-LL | const unsafe fn deref_forbidden(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
-   |                                                           ^^ dereference of raw pointer
-   |
-   = note: raw pointers may be NULL, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: access to union field is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe.rs:38:5
-   |
-LL |     Foo { x: () }.y //~ ERROR not allowed in const fn
-   |     ^^^^^^^^^^^^^^^ access to union field
-   |
-   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: aborting due to 7 previous errors
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.rs b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.rs
index 8a6884bc6b9..67a48206126 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.rs
+++ b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.rs
@@ -34,29 +34,28 @@ const unsafe fn foo9_3() -> *const String {
 const unsafe fn foo10_3() -> *const Vec<std::cell::Cell<u32>> {
     unsafe { foo6::<Vec<std::cell::Cell<u32>>>() }
 }
-// not ok
 const unsafe fn foo8_2() -> i32 {
-    foo4() //~ ERROR not allowed in const fn
+    foo4()
 }
 const unsafe fn foo9_2() -> *const String {
-    foo5::<String>() //~ ERROR not allowed in const fn
+    foo5::<String>()
 }
 const unsafe fn foo10_2() -> *const Vec<std::cell::Cell<u32>> {
-    foo6::<Vec<std::cell::Cell<u32>>>() //~ ERROR not allowed in const fn
+    foo6::<Vec<std::cell::Cell<u32>>>()
 }
-const unsafe fn foo30_3(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
+const unsafe fn foo30_3(x: *mut usize) -> usize { *x }
 //~^ dereferencing raw pointers in constant functions
 
-const unsafe fn foo30_4(x: *mut usize) -> &'static usize { &*x } //~ ERROR not allowed in const fn
+const unsafe fn foo30_4(x: *mut usize) -> &'static usize { &*x }
 //~^ dereferencing raw pointers in constant functions
 
-const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ ERROR not allowed
+const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ is unsafe
 //~^ dereferencing raw pointers in constant functions
 
 fn main() {}
 
 const unsafe fn no_union() {
     union Foo { x: (), y: () }
-    Foo { x: () }.y //~ ERROR not allowed in const fn
+    Foo { x: () }.y
     //~^ unions in const fn
 }
diff --git a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.stderr b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.stderr
index 20c75afbe63..63bf9a53e50 100644
--- a/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.stderr
+++ b/src/test/ui/consts/min_const_fn/min_const_fn_unsafe_feature_gate.stderr
@@ -1,97 +1,44 @@
 error[E0658]: dereferencing raw pointers in constant functions is unstable (see issue #51911)
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:47:51
+  --> $DIR/min_const_fn_unsafe_feature_gate.rs:46:51
    |
-LL | const unsafe fn foo30_3(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
+LL | const unsafe fn foo30_3(x: *mut usize) -> usize { *x }
    |                                                   ^^
    |
    = help: add #![feature(const_raw_ptr_deref)] to the crate attributes to enable
 
 error[E0658]: dereferencing raw pointers in constant functions is unstable (see issue #51911)
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:50:60
+  --> $DIR/min_const_fn_unsafe_feature_gate.rs:49:60
    |
-LL | const unsafe fn foo30_4(x: *mut usize) -> &'static usize { &*x } //~ ERROR not allowed in const fn
+LL | const unsafe fn foo30_4(x: *mut usize) -> &'static usize { &*x }
    |                                                            ^^^
    |
    = help: add #![feature(const_raw_ptr_deref)] to the crate attributes to enable
 
 error[E0658]: dereferencing raw pointers in constant functions is unstable (see issue #51911)
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:53:62
+  --> $DIR/min_const_fn_unsafe_feature_gate.rs:52:62
    |
-LL | const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ ERROR not allowed
+LL | const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ is unsafe
    |                                                              ^^^
    |
    = help: add #![feature(const_raw_ptr_deref)] to the crate attributes to enable
 
 error[E0658]: unions in const fn are unstable (see issue #51909)
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:60:5
+  --> $DIR/min_const_fn_unsafe_feature_gate.rs:59:5
    |
-LL |     Foo { x: () }.y //~ ERROR not allowed in const fn
+LL |     Foo { x: () }.y
    |     ^^^^^^^^^^^^^^^
    |
    = help: add #![feature(const_fn_union)] to the crate attributes to enable
 
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:39:5
+error[E0133]: dereference of raw pointer is unsafe and requires unsafe function or block
+  --> $DIR/min_const_fn_unsafe_feature_gate.rs:52:62
    |
-LL |     foo4() //~ ERROR not allowed in const fn
-   |     ^^^^^^ call to unsafe function
-   |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:42:5
-   |
-LL |     foo5::<String>() //~ ERROR not allowed in const fn
-   |     ^^^^^^^^^^^^^^^^ call to unsafe function
-   |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: call to unsafe function is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:45:5
-   |
-LL |     foo6::<Vec<std::cell::Cell<u32>>>() //~ ERROR not allowed in const fn
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
-   |
-   = note: consult the function's documentation for information on how to avoid undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: dereference of raw pointer is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:47:51
-   |
-LL | const unsafe fn foo30_3(x: *mut usize) -> usize { *x } //~ ERROR not allowed in const fn
-   |                                                   ^^ dereference of raw pointer
-   |
-   = note: raw pointers may be NULL, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: dereference of raw pointer is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:50:60
-   |
-LL | const unsafe fn foo30_4(x: *mut usize) -> &'static usize { &*x } //~ ERROR not allowed in const fn
-   |                                                            ^^^ dereference of raw pointer
-   |
-   = note: raw pointers may be NULL, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: dereference of raw pointer is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:53:62
-   |
-LL | const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ ERROR not allowed
+LL | const fn foo30_5(x: *mut usize) -> &'static usize { unsafe { &*x } } //~ is unsafe
    |                                                              ^^^ dereference of raw pointer
    |
    = 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: access to union field is unsafe and unsafe operations are not allowed in const fn
-  --> $DIR/min_const_fn_unsafe_feature_gate.rs:60:5
-   |
-LL |     Foo { x: () }.y //~ ERROR not allowed in const fn
-   |     ^^^^^^^^^^^^^^^ access to union field
-   |
-   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
-   = note: unsafe action within a `const unsafe fn` still require an `unsafe` block in contrast to regular `unsafe fn`.
-
-error: aborting due to 11 previous errors
+error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0658`.
+Some errors occurred: E0133, E0658.
+For more information about an error, try `rustc --explain E0133`.