Allow constants to refer statics

Author: spastorino

src/librustc_mir/error_codes.rs

@@ -228,27 +228,6 @@ const CON : Box<i32> = box 0;
 ```
 "##,
 
-E0013: r##"
-Static and const variables can refer to other const variables. But a const
-variable cannot refer to a static variable.
-
-Erroneous code example:
-
-```compile_fail,E0013
-static X: i32 = 42;
-const Y: i32 = X;
-```
-
-In this example, `Y` cannot refer to `X` here. To fix this, the value can be
-extracted as a const and then used:
-
-```
-const A: i32 = 42;
-static X: i32 = A;
-const Y: i32 = A;
-```
-"##,
-
 // FIXME(#57563) Change the language here when const fn stabilizes
 E0015: r##"
 The only functions that can be called in static or constant expressions are

src/librustc_mir/transform/check_consts/ops.rs

@@ -262,31 +262,6 @@ impl NonConstOp for RawPtrToIntCast {
     }
 }
 
-/// An access to a (non-thread-local) `static`.
-#[derive(Debug)]
-pub struct StaticAccess;
-impl NonConstOp for StaticAccess {
-    fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
-        item.const_kind().is_static()
-    }
-
-    fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
-        let mut err = struct_span_err!(item.tcx.sess, span, E0013,
-                                        "{}s cannot refer to statics, use \
-                                        a constant instead", item.const_kind());
-        if item.tcx.sess.teach(&err.get_code().unwrap()) {
-            err.note(
-                "Static and const variables can refer to other const variables. \
-                    But a const variable cannot refer to a static variable."
-            );
-            err.help(
-                "To fix this, the value can be extracted as a const and then used."
-            );
-        }
-        err.emit();
-    }
-}
-
 /// An access to a thread-local `static`.
 #[derive(Debug)]
 pub struct ThreadLocalAccess;

src/librustc_mir/transform/check_consts/validation.rs

@@ -336,8 +336,6 @@ impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
                         self.span,
                         "cannot mutate statics in the initializer of another static",
                     );
-                } else {
-                    self.check_op(ops::StaticAccess);
                 }
             }
         }

src/librustc_mir/transform/qualify_consts.rs

@@ -798,23 +798,6 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
                     return;
                 }
                 unleash_miri!(self);
-
-                if self.mode.requires_const_checking() && !self.suppress_errors {
-                    self.record_error(ops::StaticAccess);
-                    let mut err = struct_span_err!(self.tcx.sess, self.span, E0013,
-                                                    "{}s cannot refer to statics, use \
-                                                    a constant instead", self.mode);
-                    if self.tcx.sess.teach(&err.get_code().unwrap()) {
-                        err.note(
-                            "Static and const variables can refer to other const variables. \
-                                But a const variable cannot refer to a static variable."
-                        );
-                        err.help(
-                            "To fix this, the value can be extracted as a const and then used."
-                        );
-                    }
-                    err.emit()
-                }
             }
         }
     }

src/test/ui/consts/const-fn-not-safe-for-const.rs

@@ -18,12 +18,10 @@ static Y: u32 = 0;
 
 const fn get_Y() -> u32 {
     Y
-        //~^ ERROR E0013
 }
 
 const fn get_Y_addr() -> &'static u32 {
     &Y
-        //~^ ERROR E0013
 }
 
 const fn get() -> u32 {

src/test/ui/consts/const-fn-not-safe-for-const.stderr

@@ -4,19 +4,6 @@ error[E0015]: calls in constant functions are limited to constant functions, tup
 LL |     random()
    |     ^^^^^^^^
 
-error[E0013]: constant functions cannot refer to statics, use a constant instead
-  --> $DIR/const-fn-not-safe-for-const.rs:20:5
-   |
-LL |     Y
-   |     ^
-
-error[E0013]: constant functions cannot refer to statics, use a constant instead
-  --> $DIR/const-fn-not-safe-for-const.rs:25:5
-   |
-LL |     &Y
-   |     ^^
-
-error: aborting due to 3 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0013, E0015.
-For more information about an error, try `rustc --explain E0013`.
+For more information about this error, try `rustc --explain E0015`.

src/test/ui/consts/const-prop-read-static-in-const.rs

@@ -3,7 +3,6 @@ const C1: &'static mut [usize] = &mut [];
 
 static mut S: usize = 3;
 const C2: &'static mut usize = unsafe { &mut S };
-//~^ ERROR: constants cannot refer to statics
-//~| ERROR: references in constants may only refer to immutable values
+//~^ ERROR: references in constants may only refer to immutable values
 
 fn main() {}

src/test/ui/consts/const-prop-read-static-in-const.stderr

@@ -10,13 +10,6 @@ error[E0017]: references in constants may only refer to immutable values
 LL | const C2: &'static mut usize = unsafe { &mut S };
    |                                         ^^^^^^ constants require immutable values
 
-error[E0013]: constants cannot refer to statics, use a constant instead
-  --> $DIR/issue-17718-const-bad-values.rs:5:41
-   |
-LL | const C2: &'static mut usize = unsafe { &mut S };
-   |                                         ^^^^^^
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0013, E0017.
-For more information about an error, try `rustc --explain E0013`.
+For more information about this error, try `rustc --explain E0017`.