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Rollup merge of rust-lang#64635 - gnzlbg:const_fn_ptr, r=oli-obk
Allow using fn pointers in const fn with unleash miri This allows using function pointers in const fns when `-Zunleash-the-miri-within-you` is enabled. If the call to the `const fn` happens in a `const`-context, the function pointer is required to point to a `const fn`: ```rust fn non_const_fn() -> i32 { 42 } const fn const_fn() -> i32 { 42 } const fn foo(x: fn() -> i32) -> i32 { x() } let x: i32 = foo(non_const_fn_ptr); // OK let y: i32 = foo(const_fn_ptr); // OK const X: i32 = foo(non_const_fn_ptr); // ERROR: `non_const_fn` is not `const fn` const Y: i32 = foo(const_fn_ptr); // OK ``` r? @oli-obk
2 parents 05d7ae2 + 9d4053f commit 25bdd76

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Diff for: ‎src/librustc_mir/transform/qualify_consts.rs

+9-2
Original file line numberDiff line numberDiff line change
@@ -1407,10 +1407,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
14071407
}
14081408
}
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ty::FnPtr(_) => {
1410-
if self.mode.requires_const_checking() {
1410+
let unleash_miri = self
1411+
.tcx
1412+
.sess
1413+
.opts
1414+
.debugging_opts
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.unleash_the_miri_inside_of_you;
1416+
if self.mode.requires_const_checking() && !unleash_miri {
14111417
let mut err = self.tcx.sess.struct_span_err(
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self.span,
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&format!("function pointers are not allowed in const fn"));
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"function pointers are not allowed in const fn"
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);
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err.emit();
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}
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}

Diff for: ‎src/test/ui/consts/const-eval/const_fn_ptr.rs

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@@ -0,0 +1,37 @@
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// run-pass
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// compile-flags: -Zunleash-the-miri-inside-of-you
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#![feature(const_fn)]
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fn double(x: usize) -> usize { x * 2 }
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const fn double_const(x: usize) -> usize { x * 2 }
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const X: fn(usize) -> usize = double;
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const X_const: fn(usize) -> usize = double_const;
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const fn bar(x: usize) -> usize {
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X(x)
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}
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const fn bar_const(x: usize) -> usize {
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X_const(x)
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}
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const fn foo(x: fn(usize) -> usize, y: usize) -> usize {
20+
x(y)
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}
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fn main() {
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const Y: usize = bar_const(2);
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assert_eq!(Y, 4);
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let y = bar_const(2);
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assert_eq!(y, 4);
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let y = bar(2);
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assert_eq!(y, 4);
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const Z: usize = foo(double_const, 2);
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assert_eq!(Z, 4);
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let z = foo(double_const, 2);
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assert_eq!(z, 4);
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let z = foo(double, 2);
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assert_eq!(z, 4);
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}

Diff for: ‎src/test/ui/consts/const-eval/const_fn_ptr.stderr

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@@ -0,0 +1,152 @@
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:25:5
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|
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LL | assert_eq!(Y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:25:5
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|
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LL | assert_eq!(Y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:25:5
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|
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LL | assert_eq!(Y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:27:5
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|
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LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:27:5
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|
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LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:27:5
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|
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LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:29:5
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|
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LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:29:5
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|
60+
LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:29:5
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|
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LL | assert_eq!(y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:32:5
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|
76+
LL | assert_eq!(Z, 4);
77+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:32:5
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|
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LL | assert_eq!(Z, 4);
85+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:32:5
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|
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LL | assert_eq!(Z, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
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--> $DIR/const_fn_ptr.rs:34:5
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|
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LL | assert_eq!(z, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
106+
--> $DIR/const_fn_ptr.rs:34:5
107+
|
108+
LL | assert_eq!(z, 4);
109+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
112+
113+
warning: skipping const checks
114+
--> $DIR/const_fn_ptr.rs:34:5
115+
|
116+
LL | assert_eq!(z, 4);
117+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
120+
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warning: skipping const checks
122+
--> $DIR/const_fn_ptr.rs:36:5
123+
|
124+
LL | assert_eq!(z, 4);
125+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
128+
129+
warning: skipping const checks
130+
--> $DIR/const_fn_ptr.rs:36:5
131+
|
132+
LL | assert_eq!(z, 4);
133+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
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warning: skipping const checks
138+
--> $DIR/const_fn_ptr.rs:36:5
139+
|
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LL | assert_eq!(z, 4);
141+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
144+
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warning: constant `X_const` should have an upper case name
146+
--> $DIR/const_fn_ptr.rs:9:7
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|
148+
LL | const X_const: fn(usize) -> usize = double_const;
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| ^^^^^^^ help: convert the identifier to upper case: `X_CONST`
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|
151+
= note: `#[warn(non_upper_case_globals)]` on by default
152+

Diff for: ‎src/test/ui/consts/const-eval/const_fn_ptr_fail.rs

+13
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,13 @@
1+
// run-pass
2+
// compile-flags: -Zunleash-the-miri-inside-of-you
3+
#![feature(const_fn)]
4+
#![allow(unused)]
5+
6+
fn double(x: usize) -> usize { x * 2 }
7+
const X: fn(usize) -> usize = double;
8+
9+
const fn bar(x: usize) -> usize {
10+
X(x) // FIXME: this should error someday
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}
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fn main() {}

Diff for: ‎src/test/ui/consts/const-eval/const_fn_ptr_fail2.rs

+26
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@@ -0,0 +1,26 @@
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// compile-flags: -Zunleash-the-miri-inside-of-you
2+
#![feature(const_fn)]
3+
#![allow(const_err)]
4+
5+
fn double(x: usize) -> usize { x * 2 }
6+
const X: fn(usize) -> usize = double;
7+
8+
const fn bar(x: fn(usize) -> usize, y: usize) -> usize {
9+
x(y)
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}
11+
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const Y: usize = bar(X, 2); // FIXME: should fail to typeck someday
13+
const Z: usize = bar(double, 2); // FIXME: should fail to typeck someday
14+
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fn main() {
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assert_eq!(Y, 4);
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//~^ ERROR evaluation of constant expression failed
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//~^^ WARN skipping const checks
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//~^^^ WARN skipping const checks
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//~^^^^ WARN skipping const checks
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assert_eq!(Z, 4);
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//~^ ERROR evaluation of constant expression failed
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//~^^ WARN skipping const checks
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//~^^^ WARN skipping const checks
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//~^^^^ WARN skipping const checks
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}

Diff for: ‎src/test/ui/consts/const-eval/const_fn_ptr_fail2.stderr

+71
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,71 @@
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warning: skipping const checks
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--> $DIR/const_fn_ptr_fail2.rs:16:5
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|
4+
LL | assert_eq!(Y, 4);
5+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
8+
9+
warning: skipping const checks
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--> $DIR/const_fn_ptr_fail2.rs:16:5
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|
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LL | assert_eq!(Y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
16+
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warning: skipping const checks
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--> $DIR/const_fn_ptr_fail2.rs:16:5
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|
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LL | assert_eq!(Y, 4);
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| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
24+
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warning: skipping const checks
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--> $DIR/const_fn_ptr_fail2.rs:21:5
27+
|
28+
LL | assert_eq!(Z, 4);
29+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
32+
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warning: skipping const checks
34+
--> $DIR/const_fn_ptr_fail2.rs:21:5
35+
|
36+
LL | assert_eq!(Z, 4);
37+
| ^^^^^^^^^^^^^^^^^
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|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
40+
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warning: skipping const checks
42+
--> $DIR/const_fn_ptr_fail2.rs:21:5
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|
44+
LL | assert_eq!(Z, 4);
45+
| ^^^^^^^^^^^^^^^^^
46+
|
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= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
48+
49+
error[E0080]: evaluation of constant expression failed
50+
--> $DIR/const_fn_ptr_fail2.rs:16:5
51+
|
52+
LL | assert_eq!(Y, 4);
53+
| ^^^^^^^^^^^-^^^^^
54+
| |
55+
| referenced constant has errors
56+
|
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= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
58+
59+
error[E0080]: evaluation of constant expression failed
60+
--> $DIR/const_fn_ptr_fail2.rs:21:5
61+
|
62+
LL | assert_eq!(Z, 4);
63+
| ^^^^^^^^^^^-^^^^^
64+
| |
65+
| referenced constant has errors
66+
|
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= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
68+
69+
error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0080`.

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