Rollup merge of rust-lang#74392 - lcnr:const-generics-update, r=varkor

const generics triage

I went through all const generics issues and closed all issues which are already fixed.

Some issues already have a regression test but were not closed. Also doing this as part of this PR.

uff r? @eddyb @varkor

closes rust-lang#61936
closes rust-lang#62878
closes rust-lang#63695
closes rust-lang#67144
closes rust-lang#68596
closes rust-lang#69816
closes rust-lang#70217
closes rust-lang#70507
closes rust-lang#70586
closes rust-lang#71348
closes rust-lang#71805
closes rust-lang#73120
closes rust-lang#73508
closes rust-lang#73730
closes rust-lang#74255

src/test/ui/const-generics/issues/auxiliary/const_generic_issues_lib.rs

@@ -0,0 +1,14 @@
+#![feature(const_generics)]
+
+// All of these three items must be in `lib2` to reproduce the error
+
+pub trait TypeFn {
+    type Output;
+}
+
+pub struct GenericType<const B: i8>;
+
+// Removing the braces around `42` resolves the crash
+impl TypeFn for GenericType<{ 42 }> {
+    type Output = ();
+}

src/test/ui/const-generics/issues/issue-68596.rs

@@ -0,0 +1,18 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+pub struct S(u8);
+
+impl S {
+    pub fn get<const A: u8>(&self) -> &u8 {
+        &self.0
+    }
+}
+
+fn main() {
+    const A: u8 = 5;
+    let s = S(0);
+
+    s.get::<A>();
+}

src/test/ui/const-generics/issues/issue-73120.rs

@@ -0,0 +1,8 @@
+// check-pass
+// aux-build:const_generic_issues_lib.rs
+extern crate const_generic_issues_lib as lib2;
+fn unused_function(
+    _: <lib2::GenericType<42> as lib2::TypeFn>::Output
+) {}
+
+fn main() {}

src/test/ui/const-generics/issues/issue-73508.rs

@@ -0,0 +1,6 @@
+#![feature(const_generics)] //~ WARN the feature `const_generics` is incomplete
+
+pub const fn func_name<const X: *const u32>() {}
+//~^ ERROR using raw pointers
+
+fn main() {}

src/test/ui/const-generics/issues/issue-73508.stderr

@@ -0,0 +1,17 @@
+warning: the feature `const_generics` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-73508.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+
+error: using raw pointers as const generic parameters is forbidden
+  --> $DIR/issue-73508.rs:3:33
+   |
+LL | pub const fn func_name<const X: *const u32>() {}
+   |                                 ^^^^^^^^^^
+
+error: aborting due to previous error; 1 warning emitted
+

src/test/ui/const-generics/issues/issue-74255.rs

@@ -0,0 +1,18 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(dead_code, incomplete_features)]
+
+#[derive(PartialEq, Eq)]
+enum IceEnum {
+    Variant
+}
+
+struct IceStruct;
+
+impl IceStruct {
+    fn ice_struct_fn<const I: IceEnum>() {}
+}
+
+fn main() {
+    IceStruct::ice_struct_fn::<{IceEnum::Variant}>();
+}

src/test/ui/const-generics/type-dependent/issue-67144-1.rs

@@ -0,0 +1,28 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+struct X;
+
+impl X {
+    pub fn getn<const N: usize>(&self) -> [u8; N] {
+        getn::<N>()
+    }
+}
+
+fn getn<const N: usize>() -> [u8; N] {
+    unsafe {
+        std::mem::zeroed()
+    }
+}
+
+fn main() {
+    // works
+    let [a,b,c] = getn::<3>();
+
+    // cannot pattern-match on an array without a fixed length
+    let [a,b,c] = X.getn::<3>();
+
+    // mismatched types, expected array `[u8; 3]` found array `[u8; _]`
+    let arr: [u8; 3] = X.getn::<3>();
+}

src/test/ui/const-generics/type-dependent/issue-67144-2.rs

@@ -0,0 +1,22 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+struct A<const N: usize>;
+
+struct X;
+
+impl X {
+    fn inner<const N: usize>() -> A<N> {
+        outer::<N>()
+    }
+}
+
+fn outer<const N: usize>() -> A<N> {
+    A
+}
+
+fn main() {
+    let i: A<3usize> = outer::<3usize>();
+    let o: A<3usize> = X::inner::<3usize>();
+}

src/test/ui/const-generics/type-dependent/issue-70217.rs

@@ -0,0 +1,16 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+struct Struct<const N: usize>;
+
+impl<const N: usize> Struct<N> {
+    fn method<const M: usize>(&self) {}
+}
+
+fn test<const N: usize, const M: usize>(x: Struct<N>) {
+    Struct::<N>::method::<M>(&x);
+    x.method::<N>();
+}
+
+fn main() {}

src/test/ui/const-generics/type-dependent/issue-70586.rs

@@ -0,0 +1,33 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+use std::marker::PhantomData;
+
+// This namespace is necessary for the ICE to trigger
+struct Namespace;
+
+impl Namespace {
+    pub fn const_chunks_exact<T, const N: usize>() -> ConstChunksExact<'static, T, N> {
+        ConstChunksExact { inner: PhantomData }
+    }
+}
+
+
+#[derive(Debug)]
+pub struct ConstChunksExact<'a, T, const N: usize> {
+    inner:  PhantomData<&'a T>
+}
+
+impl <'a, T, const N: usize> Iterator for ConstChunksExact<'a, T, { N }> {
+    type Item = &'a [T; N];
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unreachable!()
+    }
+}
+
+fn main() {
+    let mut chunks = Namespace::const_chunks_exact::<i32, 3usize>();
+    let _next: &[i32; 3] = chunks.next().unwrap();
+}

src/test/ui/const-generics/type-dependent/issue-71348.rs

@@ -0,0 +1,35 @@
+// run-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+struct Foo {
+    i: i32,
+}
+
+trait Get<'a, const N: &'static str> {
+    type Target: 'a;
+
+    fn get(&'a self) -> &'a Self::Target;
+}
+
+impl Foo {
+    fn ask<'a, const N: &'static str>(&'a self) -> &'a <Self as Get<N>>::Target
+    where
+        Self: Get<'a, N>,
+    {
+        self.get()
+    }
+}
+
+impl<'a> Get<'a, "int"> for Foo {
+    type Target = i32;
+
+    fn get(&'a self) -> &'a Self::Target {
+        &self.i
+    }
+}
+
+fn main() {
+    let foo = Foo { i: 123 };
+    assert_eq!(foo.ask::<"int">(), &123);
+}

src/test/ui/const-generics/type-dependent/issue-71805.rs

@@ -0,0 +1,41 @@
+// run-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+use std::mem::MaybeUninit;
+
+trait CollectSlice<'a>: Iterator {
+    fn inner_array<const N: usize>(&mut self) -> [Self::Item; N];
+
+    fn collect_array<const N: usize>(&mut self) -> [Self::Item; N] {
+        let result = self.inner_array();
+        assert!(self.next().is_none());
+        result
+    }
+}
+
+impl<'a, I: ?Sized> CollectSlice<'a> for I
+where
+    I: Iterator,
+{
+    fn inner_array<const N: usize>(&mut self) -> [Self::Item; N] {
+        let mut result: [MaybeUninit<Self::Item>; N] =
+            unsafe { MaybeUninit::uninit().assume_init() };
+
+        let mut count = 0;
+        for (dest, item) in result.iter_mut().zip(self) {
+            *dest = MaybeUninit::new(item);
+            count += 1;
+        }
+
+        assert_eq!(N, count);
+
+        let temp_ptr: *const [MaybeUninit<Self::Item>; N] = &result;
+        unsafe { std::ptr::read(temp_ptr as *const [Self::Item; N]) }
+    }
+}
+
+fn main() {
+    let mut foos = [0u64; 9].iter().cloned();
+    let _bar: [u64; 9] = foos.collect_array::<9_usize>();
+}

src/test/ui/const-generics/type-dependent/issue-73730.rs

@@ -0,0 +1,17 @@
+// check-pass
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+trait Foo<'a, A>: Iterator<Item=A> {
+    fn bar<const N: usize>(&mut self) -> *const [A; N];
+}
+
+impl<'a, A, I: ?Sized> Foo<'a, A> for I where I: Iterator<Item=A>  {
+    fn bar<const N: usize>(&mut self) -> *const [A; N] {
+        std::ptr::null()
+    }
+}
+
+fn main() {
+    (0_u8 .. 10).bar::<10_usize>();
+}