Rollup merge of #64986 - skinny121:fn-ptr-const-generics, r=varkor

Function pointers as const generic arguments

Makes function pointers as const generic arguments usable.

Fixes #62395

r? @varkor

src/test/mir-opt/const_prop/reify_fn_ptr.rs

@@ -16,7 +16,7 @@ fn main() {
 // START rustc.main.ConstProp.after.mir
 //  bb0: {
 //      ...
-//      _3 = const Scalar(AllocId(0).0x0) : fn();
+//      _3 = const main;
 //      _2 = move _3 as usize (Misc);
 //      ...
 //      _1 = move _2 as *const fn() (Misc);

src/test/ui/const-generics/fn-const-param-call.rs

@@ -0,0 +1,20 @@
+// run-pass
+
+#![feature(const_generics, const_compare_raw_pointers)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+fn function() -> u32 {
+    17
+}
+
+struct Wrapper<const F: fn() -> u32>;
+
+impl<const F: fn() -> u32> Wrapper<{F}> {
+    fn call() -> u32 {
+        F()
+    }
+}
+
+fn main() {
+    assert_eq!(Wrapper::<{function}>::call(), 17);
+}

src/test/ui/const-generics/fn-const-param-call.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/fn-const-param-call.rs:3:12
+   |
+LL | #![feature(const_generics, const_compare_raw_pointers)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+

src/test/ui/const-generics/fn-const-param-infer.rs

@@ -0,0 +1,26 @@
+#![feature(const_generics, const_compare_raw_pointers)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct Checked<const F: fn(usize) -> bool>;
+
+fn not_one(val: usize) -> bool { val != 1 }
+fn not_two(val: usize) -> bool { val != 2 }
+
+fn generic_arg<T>(val: T) -> bool { true }
+
+fn generic<T>(val: usize) -> bool { val != 1 }
+
+fn main() {
+    let _: Option<Checked<{not_one}>> = None;
+    let _: Checked<{not_one}> = Checked::<{not_one}>;
+    let _: Checked<{not_one}> = Checked::<{not_two}>; //~ mismatched types
+
+    let _ = Checked::<{generic_arg}>;
+    let _ = Checked::<{generic_arg::<usize>}>;
+    let _ = Checked::<{generic_arg::<u32>}>;  //~ mismatched types
+
+    let _ = Checked::<{generic}>; //~ type annotations needed
+    let _ = Checked::<{generic::<u16>}>;
+    let _: Checked<{generic::<u16>}> = Checked::<{generic::<u16>}>;
+    let _: Checked<{generic::<u32>}> = Checked::<{generic::<u16>}>; //~ mismatched types
+}

src/test/ui/const-generics/fn-const-param-infer.stderr

@@ -0,0 +1,45 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/fn-const-param-infer.rs:1:12
+   |
+LL | #![feature(const_generics, const_compare_raw_pointers)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0308]: mismatched types
+  --> $DIR/fn-const-param-infer.rs:16:33
+   |
+LL |     let _: Checked<{not_one}> = Checked::<{not_two}>;
+   |                                 ^^^^^^^^^^^^^^^^^^^^ expected `not_one`, found `not_two`
+   |
+   = note: expected type `Checked<not_one>`
+              found type `Checked<not_two>`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-const-param-infer.rs:20:24
+   |
+LL |     let _ = Checked::<{generic_arg::<u32>}>;
+   |                        ^^^^^^^^^^^^^^^^^^ expected usize, found u32
+   |
+   = note: expected type `fn(usize) -> bool`
+              found type `fn(u32) -> bool {generic_arg::<u32>}`
+
+error[E0282]: type annotations needed
+  --> $DIR/fn-const-param-infer.rs:22:24
+   |
+LL |     let _ = Checked::<{generic}>;
+   |                        ^^^^^^^ cannot infer type for `T`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-const-param-infer.rs:25:40
+   |
+LL |     let _: Checked<{generic::<u32>}> = Checked::<{generic::<u16>}>;
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `generic::<u32>`, found `generic::<u16>`
+   |
+   = note: expected type `Checked<generic::<u32>>`
+              found type `Checked<generic::<u16>>`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0282, E0308.
+For more information about an error, try `rustc --explain E0282`.

src/test/ui/const-generics/raw-ptr-const-param-deref.rs

@@ -0,0 +1,19 @@
+// run-pass
+#![feature(const_generics, const_compare_raw_pointers)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+const A: u32 = 3;
+
+struct Const<const P: *const u32>;
+
+impl<const P: *const u32> Const<{P}> {
+    fn get() -> u32 {
+        unsafe {
+            *P
+        }
+    }
+}
+
+fn main() {
+    assert_eq!(Const::<{&A as *const _}>::get(), 3)
+}

src/test/ui/const-generics/raw-ptr-const-param-deref.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/raw-ptr-const-param-deref.rs:2:12
+   |
+LL | #![feature(const_generics, const_compare_raw_pointers)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+

src/test/ui/const-generics/raw-ptr-const-param.rs

@@ -0,0 +1,9 @@
+#![feature(const_generics, const_compare_raw_pointers)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct Const<const P: *const u32>;
+
+fn main() {
+    let _: Const<{15 as *const _}> = Const::<{10 as *const _}>; //~ mismatched types
+    let _: Const<{10 as *const _}> = Const::<{10 as *const _}>;
+}

src/test/ui/const-generics/raw-ptr-const-param.stderr

@@ -0,0 +1,20 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/raw-ptr-const-param.rs:1:12
+   |
+LL | #![feature(const_generics, const_compare_raw_pointers)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0308]: mismatched types
+  --> $DIR/raw-ptr-const-param.rs:7:38
+   |
+LL |     let _: Const<{15 as *const _}> = Const::<{10 as *const _}>;
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{pointer}`, found `{pointer}`
+   |
+   = note: expected type `Const<{pointer}>`
+              found type `Const<{pointer}>`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/feature-gates/feature-gate-const_generics-ptr.rs

@@ -0,0 +1,9 @@
+struct ConstFn<const F: fn()>;
+//~^ ERROR const generics are unstable
+//~^^ ERROR using function pointers as const generic parameters is unstable
+
+struct ConstPtr<const P: *const u32>;
+//~^ ERROR const generics are unstable
+//~^^ ERROR using raw pointers as const generic parameters is unstable
+
+fn main() {}

src/test/ui/feature-gates/feature-gate-const_generics-ptr.stderr

@@ -0,0 +1,39 @@
+error[E0658]: const generics are unstable
+  --> $DIR/feature-gate-const_generics-ptr.rs:1:22
+   |
+LL | struct ConstFn<const F: fn()>;
+   |                      ^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/44580
+   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+
+error[E0658]: const generics are unstable
+  --> $DIR/feature-gate-const_generics-ptr.rs:5:23
+   |
+LL | struct ConstPtr<const P: *const u32>;
+   |                       ^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/44580
+   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+
+error[E0658]: using function pointers as const generic parameters is unstable
+  --> $DIR/feature-gate-const_generics-ptr.rs:1:25
+   |
+LL | struct ConstFn<const F: fn()>;
+   |                         ^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/53020
+   = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
+
+error[E0658]: using raw pointers as const generic parameters is unstable
+  --> $DIR/feature-gate-const_generics-ptr.rs:5:26
+   |
+LL | struct ConstPtr<const P: *const u32>;
+   |                          ^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/53020
+   = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.