Rollup merge of #78916 - lcnr:const-generics-tests, r=varkor

extend const generics test suite

should implement most of #78433, especially all parts of [the hackmd](https://hackmd.io/WnFmN4MjRCqAjGmYfYcu2A?view) which I did not explicitly mention in that issue.

r? ``@varkor``

src/test/rustdoc-ui/error-in-impl-trait/const-generics.rs

@@ -0,0 +1,24 @@
+// check-pass
+// edition:2018
+#![feature(min_const_generics)]
+trait ValidTrait {}
+
+/// This has docs
+pub fn extern_fn<const N: usize>() -> impl Iterator<Item = [u8; N]> {
+    loop {}
+}
+
+pub trait Trait<const N: usize> {}
+impl Trait<1> for u8 {}
+impl Trait<2> for u8 {}
+impl<const N: usize> Trait<N> for [u8; N] {}
+
+/// This also has docs
+pub fn test<const N: usize>() -> impl Trait<N> where u8: Trait<N> {
+    loop {}
+}
+
+/// Document all the functions
+pub async fn a_sink<const N: usize>(v: [u8; N]) -> impl Trait<N> {
+    loop {}
+}

src/test/rustdoc/const-generics/auxiliary/extern_crate.rs

@@ -0,0 +1,18 @@
+// edition:2018
+#![feature(min_const_generics)]
+
+pub fn extern_fn<const N: usize>() -> impl Iterator<Item = [u8; N]> {
+    [[0; N]; N].iter().copied()
+}
+
+pub struct ExternTy<const N: usize> {
+    pub inner: [u8; N],
+}
+
+pub type TyAlias<const N: usize> = ExternTy<N>;
+
+pub trait WTrait<const N: usize, const M: usize> {
+    fn hey<const P: usize>() -> usize {
+        N + M + P
+    }
+}

src/test/rustdoc/const-generics/const-generics-docs.rs

@@ -0,0 +1,130 @@
+// edition:2018
+// aux-build: extern_crate.rs
+#![feature(min_const_generics)]
+#![crate_name = "foo"]
+
+extern crate extern_crate;
+// @has foo/fn.extern_fn.html '//pre[@class="rust fn"]' \
+//      'pub fn extern_fn<const N: usize>() -> impl Iterator<Item = [u8; N]>'
+pub use extern_crate::extern_fn;
+// @has foo/struct.ExternTy.html '//pre[@class="rust struct"]' \
+//      'pub struct ExternTy<const N: usize> {'
+pub use extern_crate::ExternTy;
+// @has foo/type.TyAlias.html '//pre[@class="rust typedef"]' \
+//      'type TyAlias<const N: usize> = ExternTy<N>;'
+pub use extern_crate::TyAlias;
+// @has foo/trait.WTrait.html '//pre[@class="rust trait"]' \
+//      'pub trait WTrait<const N: usize, const M: usize>'
+// @has - '//*[@class="rust trait"]' 'fn hey<const P: usize>() -> usize'
+pub use extern_crate::WTrait;
+
+// @has foo/trait.Trait.html '//pre[@class="rust trait"]' \
+//      'pub trait Trait<const N: usize>'
+// @has - '//*[@id="impl-Trait%3C1_usize%3E-for-u8"]//code' 'impl Trait<1_usize> for u8'
+// @has - '//*[@id="impl-Trait%3C2_usize%3E-for-u8"]//code' 'impl Trait<2_usize> for u8'
+// @has - '//*[@id="impl-Trait%3C{1%20+%202}%3E-for-u8"]//code' 'impl Trait<{1 + 2}> for u8'
+// @has - '//*[@id="impl-Trait%3CN%3E-for-%5Bu8%3B%20N%5D"]//code' \
+//      'impl<const N: usize> Trait<N> for [u8; N]'
+pub trait Trait<const N: usize> {}
+impl Trait<1> for u8 {}
+impl Trait<2> for u8 {}
+impl Trait<{1 + 2}> for u8 {}
+impl<const N: usize> Trait<N> for [u8; N] {}
+
+// @has foo/struct.Foo.html '//pre[@class="rust struct"]' \
+//      'pub struct Foo<const N: usize> where u8: Trait<N>'
+pub struct Foo<const N: usize> where u8: Trait<N>;
+// @has foo/struct.Bar.html '//pre[@class="rust struct"]' 'pub struct Bar<T, const N: usize>(_)'
+pub struct Bar<T, const N: usize>([T; N]);
+
+// @has foo/struct.Foo.html '//h3[@id="impl"]/code' 'impl<const M: usize> Foo<M> where u8: Trait<M>'
+impl<const M: usize> Foo<M> where u8: Trait<M> {
+    // @has - '//*[@id="associatedconstant.FOO_ASSOC"]' 'pub const FOO_ASSOC: usize'
+    pub const FOO_ASSOC: usize = M + 13;
+
+    // @has - '//*[@id="method.hey"]' 'pub fn hey<const N: usize>(&self) -> Bar<u8, N>'
+    pub fn hey<const N: usize>(&self) -> Bar<u8, N> {
+        Bar([0; N])
+    }
+}
+
+// @has foo/struct.Bar.html '//h3[@id="impl"]/code' 'impl<const M: usize> Bar<u8, M>'
+impl<const M: usize> Bar<u8, M> {
+    // @has - '//*[@id="method.hey"]' \
+    //      'pub fn hey<const N: usize>(&self) -> Foo<N> where u8: Trait<N>'
+    pub fn hey<const N: usize>(&self) -> Foo<N> where u8: Trait<N> {
+        Foo
+    }
+}
+
+// @has foo/fn.test.html '//pre[@class="rust fn"]' \
+//      'pub fn test<const N: usize>() -> impl Trait<N> where u8: Trait<N>'
+pub fn test<const N: usize>() -> impl Trait<N> where u8: Trait<N> {
+    2u8
+}
+
+// @has foo/fn.a_sink.html '//pre[@class="rust fn"]' \
+//      'pub async fn a_sink<const N: usize>(v: [u8; N]) -> impl Trait<N>'
+pub async fn a_sink<const N: usize>(v: [u8; N]) -> impl Trait<N> {
+    v
+}
+
+// @has foo/fn.b_sink.html '//pre[@class="rust fn"]' \
+//      'pub async fn b_sink<const N: usize>(__arg0: impl Trait<N>)'
+// FIXME(const_generics): This should be `_` not `__arg0`.
+pub async fn b_sink<const N: usize>(_: impl Trait<N>) {}
+
+// @has foo/fn.concrete.html '//pre[@class="rust fn"]' \
+//      'pub fn concrete() -> [u8; 22]'
+pub fn concrete() -> [u8; 3 + std::mem::size_of::<u64>() << 1] {
+    Default::default()
+}
+
+// @has foo/type.Faz.html '//pre[@class="rust typedef"]' \
+//      'type Faz<const N: usize> = [u8; N];'
+pub type Faz<const N: usize> = [u8; N];
+// @has foo/type.Fiz.html '//pre[@class="rust typedef"]' \
+//      'type Fiz<const N: usize> = [[u8; N]; 48];'
+pub type Fiz<const N: usize> = [[u8; N]; 3 << 4];
+
+macro_rules! define_me {
+    ($t:tt<$q:tt>) => {
+        pub struct $t<const $q: usize>([u8; $q]);
+    }
+}
+
+// @has foo/struct.Foz.html '//pre[@class="rust struct"]' \
+//      'pub struct Foz<const N: usize>(_);'
+define_me!(Foz<N>);
+
+trait Q {
+    const ASSOC: usize;
+}
+
+impl<const N: usize> Q for [u8; N] {
+    const ASSOC: usize = N;
+}
+
+// @has foo/fn.q_user.html '//pre[@class="rust fn"]' \
+//      'pub fn q_user() -> [u8; 13]'
+pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {
+    [0; <[u8; 13] as Q>::ASSOC]
+}
+
+// @has foo/union.Union.html '//pre[@class="rust union"]' \
+//      'pub union Union<const N: usize>'
+pub union Union<const N: usize> {
+    // @has - //pre "pub arr: [u8; N]"
+    pub arr: [u8; N],
+    // @has - //pre "pub another_arr: [(); N]"
+    pub another_arr: [(); N],
+}
+
+// @has foo/enum.Enum.html '//pre[@class="rust enum"]' \
+//      'pub enum Enum<const N: usize>'
+pub enum Enum<const N: usize> {
+    // @has - //pre "Variant([u8; N])"
+    Variant([u8; N]),
+    // @has - //pre "EmptyVariant"
+    EmptyVariant,
+}

src/test/ui/const-generics/associated-type-bound-fail.full.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `u16: Bar<N>` is not satisfied
+  --> $DIR/associated-type-bound-fail.rs:14:5
+   |
+LL |     type Assoc: Bar<N>;
+   |                 ------ required by this bound in `Foo::Assoc`
+...
+LL |     type Assoc = u16;
+   |     ^^^^^^^^^^^^^^^^^ the trait `Bar<N>` is not implemented for `u16`
+   |
+   = help: the following implementations were found:
+             <u16 as Bar<3_usize>>
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/const-generics/associated-type-bound-fail.min.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `u16: Bar<N>` is not satisfied
+  --> $DIR/associated-type-bound-fail.rs:14:5
+   |
+LL |     type Assoc: Bar<N>;
+   |                 ------ required by this bound in `Foo::Assoc`
+...
+LL |     type Assoc = u16;
+   |     ^^^^^^^^^^^^^^^^^ the trait `Bar<N>` is not implemented for `u16`
+   |
+   = help: the following implementations were found:
+             <u16 as Bar<3_usize>>
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/const-generics/associated-type-bound-fail.rs

@@ -0,0 +1,17 @@
+// revisions: full min
+#![cfg_attr(full, allow(incomplete_features))]
+#![cfg_attr(full, feature(const_generics))]
+#![cfg_attr(min, feature(min_const_generics))]
+
+trait Bar<const N: usize> {}
+
+trait Foo<const N: usize> {
+    type Assoc: Bar<N>;
+}
+
+impl Bar<3> for u16 {}
+impl<const N: usize> Foo<N> for i16 {
+    type Assoc = u16; //~ ERROR the trait bound `u16: Bar<N>`
+}
+
+fn main() {}

src/test/ui/const-generics/associated-type-bound.rs

@@ -0,0 +1,24 @@
+// run-pass
+// revisions: full min
+#![cfg_attr(full, allow(incomplete_features))]
+#![cfg_attr(full, feature(const_generics))]
+#![cfg_attr(min, feature(min_const_generics))]
+
+trait Bar<const N: usize> {}
+
+trait Foo<const N: usize> {
+    type Assoc: Bar<N>;
+}
+
+impl<const N: usize> Bar<N> for u8 {}
+impl Bar<3> for u16 {}
+
+impl<const N: usize> Foo<N> for i8 {
+    type Assoc = u8;
+}
+
+impl Foo<3> for i16 {
+    type Assoc = u16;
+}
+
+fn main() {}

src/test/ui/const-generics/auxiliary/crayte.rs

@@ -0,0 +1,19 @@
+// edition:2018
+#![cfg_attr(full, feature(const_generics))]
+#![cfg_attr(full, allow(incomplete_features))]
+#![cfg_attr(min, feature(min_const_generics))]
+
+pub trait Foo<const N: usize> {}
+struct Local;
+impl<const N: usize> Foo<N> for Local {}
+
+pub fn out_foo<const N: usize>() -> impl Foo<N> { Local }
+pub fn in_foo<const N: usize>(_: impl Foo<N>) {}
+
+pub async fn async_simple<const N: usize>(_: [u8; N]) {}
+pub async fn async_out_foo<const N: usize>() -> impl Foo<N> { Local }
+pub async fn async_in_foo<const N: usize>(_: impl Foo<N>) {}
+
+pub trait Bar<const N: usize> {
+    type Assoc: Foo<N>;
+}