Add tests for stable unsafe features in const fn

src/test/ui/unsafe/ranged_ints2_const.rs

@@ -0,0 +1,20 @@
+#![feature(rustc_attrs, const_let, const_fn)]
+
+#[rustc_layout_scalar_valid_range_start(1)]
+#[repr(transparent)]
+pub(crate) struct NonZero<T>(pub(crate) T);
+fn main() {
+}
+
+const fn foo() -> NonZero<u32> {
+    let mut x = unsafe { NonZero(1) };
+    let y = &mut x.0; //~ ERROR references in constant functions may only refer to immutable
+    //~^ ERROR mutation of layout constrained field is unsafe
+    unsafe { NonZero(1) }
+}
+
+const fn bar() -> NonZero<u32> {
+    let mut x = unsafe { NonZero(1) };
+    let y = unsafe { &mut x.0 }; //~ ERROR references in constant functions may only refer to immut
+    unsafe { NonZero(1) }
+}

src/test/ui/unsafe/ranged_ints2_const.stderr

@@ -0,0 +1,24 @@
+error[E0017]: references in constant functions may only refer to immutable values
+  --> $DIR/ranged_ints2_const.rs:11:13
+   |
+LL |     let y = &mut x.0; //~ ERROR references in constant functions may only refer to immutable
+   |             ^^^^^^^^ constant functions require immutable values
+
+error[E0017]: references in constant functions may only refer to immutable values
+  --> $DIR/ranged_ints2_const.rs:18:22
+   |
+LL |     let y = unsafe { &mut x.0 }; //~ ERROR references in constant functions may only refer to immut
+   |                      ^^^^^^^^ constant functions require immutable values
+
+error[E0133]: mutation of layout constrained field is unsafe and requires unsafe function or block
+  --> $DIR/ranged_ints2_const.rs:11:13
+   |
+LL |     let y = &mut x.0; //~ ERROR references in constant functions may only refer to immutable
+   |             ^^^^^^^^ mutation of layout constrained field
+   |
+   = note: mutating layout constrained fields cannot statically be checked for valid values
+
+error: aborting due to 3 previous errors
+
+Some errors occurred: E0017, E0133.
+For more information about an error, try `rustc --explain E0017`.

src/test/ui/unsafe/ranged_ints3_const.rs

@@ -0,0 +1,21 @@
+#![feature(rustc_attrs, const_let, const_fn)]
+
+use std::cell::Cell;
+
+#[rustc_layout_scalar_valid_range_start(1)]
+#[repr(transparent)]
+pub(crate) struct NonZero<T>(pub(crate) T);
+fn main() {}
+
+const fn foo() -> NonZero<Cell<u32>> {
+    let mut x = unsafe { NonZero(Cell::new(1)) };
+    let y = &x.0; //~ ERROR cannot borrow a constant which may contain interior mutability
+    //~^ ERROR borrow of layout constrained field with interior mutability
+    unsafe { NonZero(Cell::new(1)) }
+}
+
+const fn bar() -> NonZero<Cell<u32>> {
+    let mut x = unsafe { NonZero(Cell::new(1)) };
+    let y = unsafe { &x.0 }; //~ ERROR cannot borrow a constant which may contain interior mut
+    unsafe { NonZero(Cell::new(1)) }
+}

src/test/ui/unsafe/ranged_ints3_const.stderr

@@ -0,0 +1,24 @@
+error[E0492]: cannot borrow a constant which may contain interior mutability, create a static instead
+  --> $DIR/ranged_ints3_const.rs:12:13
+   |
+LL |     let y = &x.0; //~ ERROR cannot borrow a constant which may contain interior mutability
+   |             ^^^^
+
+error[E0492]: cannot borrow a constant which may contain interior mutability, create a static instead
+  --> $DIR/ranged_ints3_const.rs:19:22
+   |
+LL |     let y = unsafe { &x.0 }; //~ ERROR cannot borrow a constant which may contain interior mut
+   |                      ^^^^
+
+error[E0133]: borrow of layout constrained field with interior mutability is unsafe and requires unsafe function or block
+  --> $DIR/ranged_ints3_const.rs:12:13
+   |
+LL |     let y = &x.0; //~ ERROR cannot borrow a constant which may contain interior mutability
+   |             ^^^^ borrow of layout constrained field with interior mutability
+   |
+   = note: references to fields of layout constrained fields lose the constraints. Coupled with interior mutability, the field can be changed to invalid values
+
+error: aborting due to 3 previous errors
+
+Some errors occurred: E0133, E0492.
+For more information about an error, try `rustc --explain E0133`.

src/test/ui/unsafe/ranged_ints4_const.rs

@@ -0,0 +1,19 @@
+#![feature(rustc_attrs, const_let, const_fn)]
+
+#[rustc_layout_scalar_valid_range_start(1)]
+#[repr(transparent)]
+pub(crate) struct NonZero<T>(pub(crate) T);
+fn main() {}
+
+const fn foo() -> NonZero<u32> {
+    let mut x = unsafe { NonZero(1) };
+    x.0 = 0; //~ ERROR statements in constant functions are unstable
+    //~^ ERROR mutation of layout constrained field is unsafe
+    x
+}
+
+const fn bar() -> NonZero<u32> {
+    let mut x = unsafe { NonZero(1) };
+    unsafe { x.0 = 0 }; //~ ERROR statements in constant functions are unstable
+    x
+}

src/test/ui/unsafe/ranged_ints4_const.stderr

@@ -0,0 +1,28 @@
+error[E0658]: statements in constant functions are unstable (see issue #48821)
+  --> $DIR/ranged_ints4_const.rs:10:5
+   |
+LL |     x.0 = 0; //~ ERROR statements in constant functions are unstable
+   |     ^^^^^^^
+   |
+   = help: add #![feature(const_let)] to the crate attributes to enable
+
+error[E0658]: statements in constant functions are unstable (see issue #48821)
+  --> $DIR/ranged_ints4_const.rs:17:14
+   |
+LL |     unsafe { x.0 = 0 }; //~ ERROR statements in constant functions are unstable
+   |              ^^^^^^^
+   |
+   = help: add #![feature(const_let)] to the crate attributes to enable
+
+error[E0133]: mutation of layout constrained field is unsafe and requires unsafe function or block
+  --> $DIR/ranged_ints4_const.rs:10:5
+   |
+LL |     x.0 = 0; //~ ERROR statements in constant functions are unstable
+   |     ^^^^^^^ mutation of layout constrained field
+   |
+   = note: mutating layout constrained fields cannot statically be checked for valid values
+
+error: aborting due to 3 previous errors
+
+Some errors occurred: E0133, E0658.
+For more information about an error, try `rustc --explain E0133`.

src/test/ui/unsafe/ranged_ints_const.rs

@@ -0,0 +1,11 @@
+#![feature(rustc_attrs)]
+
+#[rustc_layout_scalar_valid_range_start(1)]
+#[repr(transparent)]
+pub(crate) struct NonZero<T>(pub(crate) T);
+fn main() {}
+
+const fn foo() -> NonZero<u32> { NonZero(0) }
+//~^ ERROR initializing type with `rustc_layout_scalar_valid_range` attr is unsafe
+
+const fn bar() -> NonZero<u32> { unsafe { NonZero(0) } }

src/test/ui/unsafe/ranged_ints_const.stderr

@@ -0,0 +1,11 @@
+error[E0133]: initializing type with `rustc_layout_scalar_valid_range` attr is unsafe and requires unsafe function or block
+  --> $DIR/ranged_ints_const.rs:8:34
+   |
+LL | const fn foo() -> NonZero<u32> { NonZero(0) }
+   |                                  ^^^^^^^^^^ initializing type with `rustc_layout_scalar_valid_range` attr
+   |
+   = note: initializing a layout restricted type's field with a value outside the valid range is undefined behavior
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0133`.