const_panic: Allow panicking in const fn

compiler/rustc_mir/src/transform/qualify_min_const_fn.rs

@@ -407,6 +407,10 @@ fn check_terminator(
         } => {
             let fn_ty = func.ty(body, tcx);
             if let ty::FnDef(fn_def_id, _) = *fn_ty.kind() {
+                // Panic functions (with one argument) might be const fn.
+                if super::check_consts::is_lang_panic_fn(tcx, fn_def_id) {
+                    return Ok(());
+                }
                 // Allow unstable const if we opt in by using #[allow_internal_unstable]
                 // on function or macro declaration.
                 if !crate::const_eval::is_min_const_fn(tcx, fn_def_id)

src/test/ui/consts/const-eval/const_fn_panic.rs

@@ -0,0 +1,30 @@
+// check-pass
+
+#![crate_type = "lib"]
+#![feature(const_panic)]
+
+// Can't use assert_{eq, ne}!() yet as panic!() only supports a single argument.
+
+pub const fn always_panic_std() {
+    std::panic!("always");
+}
+
+pub const fn assert_truth_std() {
+    std::assert!(2 + 2 == 4);
+}
+
+pub const fn assert_false_std() {
+    std::assert!(2 + 2 != 4);
+}
+
+pub const fn always_panic_core() {
+    core::panic!("always");
+}
+
+pub const fn assert_truth_core() {
+    core::assert!(2 + 2 == 4);
+}
+
+pub const fn assert_false_core() {
+    core::assert!(2 + 2 != 4);
+}

src/test/ui/consts/const-eval/const_panic.rs

@@ -1,11 +1,20 @@
 #![feature(const_panic)]
 #![crate_type = "lib"]
 
-pub const Z: () = panic!("cheese");
+pub const Z: () = std::panic!("cheese");
 //~^ ERROR any use of this value will cause an error
 
-pub const Y: () = unreachable!();
+pub const Y: () = std::assert!(1 == 2);
 //~^ ERROR any use of this value will cause an error
 
-pub const X: () = unimplemented!();
+pub const X: () = std::unimplemented!();
+//~^ ERROR any use of this value will cause an error
+
+pub const W: () = core::panic!("cheese");
+//~^ ERROR any use of this value will cause an error
+
+pub const V: () = core::assert!(1.2 < 1.0);
+//~^ ERROR any use of this value will cause an error
+
+pub const U: () = core::unimplemented!();
 //~^ ERROR any use of this value will cause an error

src/test/ui/consts/const-eval/const_panic.stderr

@@ -1,8 +1,8 @@
 error: any use of this value will cause an error
   --> $DIR/const_panic.rs:4:19
    |
-LL | pub const Z: () = panic!("cheese");
-   | ------------------^^^^^^^^^^^^^^^^-
+LL | pub const Z: () = std::panic!("cheese");
+   | ------------------^^^^^^^^^^^^^^^^^^^^^-
    |                   |
    |                   the evaluated program panicked at 'cheese', $DIR/const_panic.rs:4:19
    |
@@ -12,22 +12,52 @@ LL | pub const Z: () = panic!("cheese");
 error: any use of this value will cause an error
   --> $DIR/const_panic.rs:7:19
    |
-LL | pub const Y: () = unreachable!();
-   | ------------------^^^^^^^^^^^^^^-
+LL | pub const Y: () = std::assert!(1 == 2);
+   | ------------------^^^^^^^^^^^^^^^^^^^^-
    |                   |
-   |                   the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic.rs:7:19
+   |                   the evaluated program panicked at 'assertion failed: 1 == 2', $DIR/const_panic.rs:7:19
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
   --> $DIR/const_panic.rs:10:19
    |
-LL | pub const X: () = unimplemented!();
-   | ------------------^^^^^^^^^^^^^^^^-
+LL | pub const X: () = std::unimplemented!();
+   | ------------------^^^^^^^^^^^^^^^^^^^^^-
    |                   |
    |                   the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:10:19
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 3 previous errors
+error: any use of this value will cause an error
+  --> $DIR/const_panic.rs:13:19
+   |
+LL | pub const W: () = core::panic!("cheese");
+   | ------------------^^^^^^^^^^^^^^^^^^^^^^-
+   |                   |
+   |                   the evaluated program panicked at 'cheese', $DIR/const_panic.rs:13:19
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: any use of this value will cause an error
+  --> $DIR/const_panic.rs:16:19
+   |
+LL | pub const V: () = core::assert!(1.2 < 1.0);
+   | ------------------^^^^^^^^^^^^^^^^^^^^^^^^-
+   |                   |
+   |                   the evaluated program panicked at 'assertion failed: 1.2 < 1.0', $DIR/const_panic.rs:16:19
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: any use of this value will cause an error
+  --> $DIR/const_panic.rs:19:19
+   |
+LL | pub const U: () = core::unimplemented!();
+   | ------------------^^^^^^^^^^^^^^^^^^^^^^-
+   |                   |
+   |                   the evaluated program panicked at 'not implemented', $DIR/const_panic.rs:19:19
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 6 previous errors
 

src/test/ui/consts/const-eval/feature-gate-const_panic.rs

@@ -8,3 +8,18 @@ const Y: () = unreachable!();
 
 const X: () = unimplemented!();
 //~^ ERROR panicking in constants is unstable
+
+const fn a() {
+    assert!(2 + 2 == 4);
+    //~^ ERROR panicking in constant functions is unstable
+}
+
+const fn b() {
+    panic!("oh no");
+    //~^ ERROR panicking in constant functions is unstable
+}
+
+const fn c() {
+    unimplemented!();
+    //~^ ERROR panicking in constant functions is unstable
+}

src/test/ui/consts/const-eval/feature-gate-const_panic.stderr

@@ -1,3 +1,33 @@
+error[E0658]: panicking in constant functions is unstable
+  --> $DIR/feature-gate-const_panic.rs:13:5
+   |
+LL |     assert!(2 + 2 == 4);
+   |     ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51999 <https://github.com/rust-lang/rust/issues/51999> for more information
+   = help: add `#![feature(const_panic)]` to the crate attributes to enable
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: panicking in constant functions is unstable
+  --> $DIR/feature-gate-const_panic.rs:18:5
+   |
+LL |     panic!("oh no");
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51999 <https://github.com/rust-lang/rust/issues/51999> for more information
+   = help: add `#![feature(const_panic)]` to the crate attributes to enable
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0658]: panicking in constant functions is unstable
+  --> $DIR/feature-gate-const_panic.rs:23:5
+   |
+LL |     unimplemented!();
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #51999 <https://github.com/rust-lang/rust/issues/51999> for more information
+   = help: add `#![feature(const_panic)]` to the crate attributes to enable
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0658]: panicking in constants is unstable
   --> $DIR/feature-gate-const_panic.rs:3:15
    |
@@ -28,6 +58,6 @@ LL | const Y: () = unreachable!();
    = help: add `#![feature(const_panic)]` to the crate attributes to enable
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 3 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0658`.