Auto merge of #100759 - fee1-dead-contrib:const_eval_select_real_intrinsic, r=oli-obk,RalfJung

Make `const_eval_select` a real intrinsic

This fixes issues where `track_caller` functions do not have nice panic
messages anymore when there is a call to the function, and uses the
MIR system to replace the call instead of dispatching via lang items.

Fixes #100696.

7 files changed, 89 insertions, 70 deletions

diff --git a/src/test/ui/consts/const-float-bits-reject-conv.stderr b/src/test/ui/consts/const-float-bits-reject-conv.stderr
index d6e993a1010..01f2f489564 100644
--- a/src/test/ui/consts/const-float-bits-reject-conv.stderr
+++ b/src/test/ui/consts/const-float-bits-reject-conv.stderr
@@ -10,16 +10,6 @@ LL |                     panic!("const-eval error: cannot use f32::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
    |                  -------------------------------------------------------------------- inside `core::f32::<impl f32>::to_bits` at $SRC_DIR/core/src/num/f32.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32} as FnOnce<(f32,)>>::call_once - shim(fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f32,), fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32}, [closure@core::f32::<impl f32>::to_bits::{closure#0}], u32>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:27:30
    |
 LL |     const MASKED_NAN1: u32 = f32::NAN.to_bits() ^ 0x002A_AAAA;
@@ -39,16 +29,6 @@ LL |                     panic!("const-eval error: cannot use f32::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f32_to_u32, rt_f32_to_u32) }
    |                  -------------------------------------------------------------------- inside `core::f32::<impl f32>::to_bits` at $SRC_DIR/core/src/num/f32.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32} as FnOnce<(f32,)>>::call_once - shim(fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f32,), fn(f32) -> u32 {core::f32::<impl f32>::to_bits::ct_f32_to_u32}, [closure@core::f32::<impl f32>::to_bits::{closure#0}], u32>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:28:30
    |
 LL |     const MASKED_NAN2: u32 = f32::NAN.to_bits() ^ 0x0055_5555;
@@ -117,16 +97,6 @@ LL |                     panic!("const-eval error: cannot use f64::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
    |                  -------------------------------------------------------------------- inside `core::f64::<impl f64>::to_bits` at $SRC_DIR/core/src/num/f64.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64} as FnOnce<(f64,)>>::call_once - shim(fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f64,), fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64}, [closure@core::f64::<impl f64>::to_bits::{closure#0}], u64>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:54:30
    |
 LL |     const MASKED_NAN1: u64 = f64::NAN.to_bits() ^ 0x000A_AAAA_AAAA_AAAA;
@@ -146,16 +116,6 @@ LL |                     panic!("const-eval error: cannot use f64::to_bits on a
 LL |         unsafe { intrinsics::const_eval_select((self,), ct_f64_to_u64, rt_f64_to_u64) }
    |                  -------------------------------------------------------------------- inside `core::f64::<impl f64>::to_bits` at $SRC_DIR/core/src/num/f64.rs:LL:COL
    |
-  ::: $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-LL |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
-   |     ------------------------------------------------------------------ inside `<fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64} as FnOnce<(f64,)>>::call_once - shim(fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64})` at $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-  ::: $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
-LL |     called_in_const.call_once(arg)
-   |     ------------------------------ inside `const_eval_select::<(f64,), fn(f64) -> u64 {core::f64::<impl f64>::to_bits::ct_f64_to_u64}, [closure@core::f64::<impl f64>::to_bits::{closure#0}], u64>` at $SRC_DIR/core/src/intrinsics.rs:LL:COL
-   |
   ::: $DIR/const-float-bits-reject-conv.rs:55:30
    |
 LL |     const MASKED_NAN2: u64 = f64::NAN.to_bits() ^ 0x0005_5555_5555_5555;
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs b/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs
new file mode 100644
index 00000000000..29aefe07162
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace-std.rs
@@ -0,0 +1,6 @@
+// See issue #100696.
+// run-fail
+// check-run-results
+fn main() {
+    &""[1..];
+}
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr b/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr
new file mode 100644
index 00000000000..e53e6034620
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace-std.run.stderr
@@ -0,0 +1,2 @@
+thread 'main' panicked at 'byte index 1 is out of bounds of ``', $DIR/const-eval-select-backtrace-std.rs:5:6
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace.rs b/src/test/ui/intrinsics/const-eval-select-backtrace.rs
new file mode 100644
index 00000000000..99f0725200c
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace.rs
@@ -0,0 +1,18 @@
+#![feature(core_intrinsics)]
+// See issue #100696.
+// run-fail
+// check-run-results
+
+#[track_caller]
+fn uhoh() {
+    panic!("Aaah!")
+}
+
+const fn c() {}
+
+fn main() {
+    // safety: this is unsound and just used to test
+    unsafe {
+        std::intrinsics::const_eval_select((), c, uhoh);
+    }
+}
diff --git a/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr b/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr
new file mode 100644
index 00000000000..2fd730ac7a6
--- /dev/null
+++ b/src/test/ui/intrinsics/const-eval-select-backtrace.run.stderr
@@ -0,0 +1,2 @@
+thread 'main' panicked at 'Aaah!', $DIR/const-eval-select-backtrace.rs:16:9
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
diff --git a/src/test/ui/intrinsics/const-eval-select-bad.rs b/src/test/ui/intrinsics/const-eval-select-bad.rs
index e5640f5ab53..fa14efad7b4 100644
--- a/src/test/ui/intrinsics/const-eval-select-bad.rs
+++ b/src/test/ui/intrinsics/const-eval-select-bad.rs
@@ -5,10 +5,13 @@ use std::intrinsics::const_eval_select;
 
 const fn not_fn_items() {
     const_eval_select((), || {}, || {});
-    //~^ ERROR the trait bound
+    //~^ ERROR this argument must be a function item
+    //~| ERROR this argument must be a function item
     const_eval_select((), 42, 0xDEADBEEF);
-    //~^ ERROR the trait bound
+    //~^ ERROR expected a `FnOnce<()>` closure
     //~| ERROR expected a `FnOnce<()>` closure
+    //~| ERROR this argument must be a function item
+    //~| ERROR this argument must be a function item
 }
 
 const fn foo(n: i32) -> i32 {
@@ -35,4 +38,9 @@ const fn args_ty_mismatch() {
     //~^ ERROR type mismatch
 }
 
+const fn non_const_fn() {
+    const_eval_select((1,), bar, bar);
+    //~^ ERROR this argument must be a `const fn`
+}
+
 fn main() {}
diff --git a/src/test/ui/intrinsics/const-eval-select-bad.stderr b/src/test/ui/intrinsics/const-eval-select-bad.stderr
index 904e83624b3..3720528ad4e 100644
--- a/src/test/ui/intrinsics/const-eval-select-bad.stderr
+++ b/src/test/ui/intrinsics/const-eval-select-bad.stderr
@@ -1,42 +1,57 @@
-error[E0277]: the trait bound `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]: FnOnce<()>` is not satisfied
+error: this argument must be a function item
   --> $DIR/const-eval-select-bad.rs:7:27
    |
 LL |     const_eval_select((), || {}, || {});
-   |     -----------------     ^^^^^ expected an `FnOnce<()>` closure, found `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`
-   |     |
-   |     required by a bound introduced by this call
+   |                           ^^^^^
    |
-   = help: the trait `~const FnOnce<()>` is not implemented for closure `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`
-note: the trait `FnOnce<()>` is implemented for `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]`, but that implementation is not `const`
-  --> $DIR/const-eval-select-bad.rs:7:27
+   = note: expected a function item, found [closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]
+   = help: consult the documentation on `const_eval_select` for more information
+
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:7:34
    |
 LL |     const_eval_select((), || {}, || {});
-   |                           ^^^^^
-   = note: wrap the `[closure@$DIR/const-eval-select-bad.rs:7:27: 7:29]` in a closure with no arguments: `|| { /* code */ }`
-note: required by a bound in `const_eval_select`
-  --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
+   |                                  ^^^^^
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+   = note: expected a function item, found [closure@$DIR/const-eval-select-bad.rs:7:34: 7:36]
+   = help: consult the documentation on `const_eval_select` for more information
 
-error[E0277]: the trait bound `{integer}: FnOnce<()>` is not satisfied
-  --> $DIR/const-eval-select-bad.rs:9:27
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:10:27
+   |
+LL |     const_eval_select((), 42, 0xDEADBEEF);
+   |                           ^^
+   |
+   = note: expected a function item, found {integer}
+   = help: consult the documentation on `const_eval_select` for more information
+
+error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
+  --> $DIR/const-eval-select-bad.rs:10:27
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
    |     -----------------     ^^ expected an `FnOnce<()>` closure, found `{integer}`
    |     |
    |     required by a bound introduced by this call
    |
-   = help: the trait `~const FnOnce<()>` is not implemented for `{integer}`
+   = help: the trait `FnOnce<()>` is not implemented for `{integer}`
    = note: wrap the `{integer}` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         F: FnOnce<ARG, Output = RET>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+
+error: this argument must be a function item
+  --> $DIR/const-eval-select-bad.rs:10:31
+   |
+LL |     const_eval_select((), 42, 0xDEADBEEF);
+   |                               ^^^^^^^^^^
+   |
+   = note: expected a function item, found {integer}
+   = help: consult the documentation on `const_eval_select` for more information
 
 error[E0277]: expected a `FnOnce<()>` closure, found `{integer}`
-  --> $DIR/const-eval-select-bad.rs:9:31
+  --> $DIR/const-eval-select-bad.rs:10:31
    |
 LL |     const_eval_select((), 42, 0xDEADBEEF);
    |     -----------------         ^^^^^^^^^^ expected an `FnOnce<()>` closure, found `{integer}`
@@ -48,11 +63,11 @@ LL |     const_eval_select((), 42, 0xDEADBEEF);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     G: FnOnce<ARG, Output = RET> + ~const Destruct,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         G: FnOnce<ARG, Output = RET>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
 
 error[E0271]: expected `fn(i32) -> bool {bar}` to be a fn item that returns `i32`, but it returns `bool`
-  --> $DIR/const-eval-select-bad.rs:29:34
+  --> $DIR/const-eval-select-bad.rs:32:34
    |
 LL |     const_eval_select((1,), foo, bar);
    |     -----------------            ^^^ expected `i32`, found `bool`
@@ -62,11 +77,11 @@ LL |     const_eval_select((1,), foo, bar);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     G: FnOnce<ARG, Output = RET> + ~const Destruct,
-   |                    ^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         G: FnOnce<ARG, Output = RET>,
+   |                        ^^^^^^^^^^^^ required by this bound in `const_eval_select`
 
 error[E0631]: type mismatch in function arguments
-  --> $DIR/const-eval-select-bad.rs:34:32
+  --> $DIR/const-eval-select-bad.rs:37:32
    |
 LL | const fn foo(n: i32) -> i32 {
    | --------------------------- found signature defined here
@@ -81,10 +96,18 @@ LL |     const_eval_select((true,), foo, baz);
 note: required by a bound in `const_eval_select`
   --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
    |
-LL |     F: ~const FnOnce<ARG, Output = RET>,
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+LL |         F: FnOnce<ARG, Output = RET>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `const_eval_select`
+
+error: this argument must be a `const fn`
+  --> $DIR/const-eval-select-bad.rs:42:29
+   |
+LL |     const_eval_select((1,), bar, bar);
+   |                             ^^^
+   |
+   = help: consult the documentation on `const_eval_select` for more information
 
-error: aborting due to 5 previous errors
+error: aborting due to 9 previous errors
 
 Some errors have detailed explanations: E0271, E0277, E0631.
 For more information about an error, try `rustc --explain E0271`.