Add UI tests for generic const items

Author: fmease

src/tools/tidy/src/ui_tests.rs

@@ -11,7 +11,7 @@ use std::path::{Path, PathBuf};
 const ENTRY_LIMIT: usize = 900;
 // FIXME: The following limits should be reduced eventually.
 const ISSUES_ENTRY_LIMIT: usize = 1893;
-const ROOT_ENTRY_LIMIT: usize = 871;
+const ROOT_ENTRY_LIMIT: usize = 872;
 
 const EXPECTED_TEST_FILE_EXTENSIONS: &[&str] = &[
     "rs",     // test source files

tests/ui/generic-const-items/associated-const-equality.rs

@@ -0,0 +1,22 @@
+// check-pass
+
+#![feature(generic_const_items, associated_const_equality)]
+#![allow(incomplete_features)]
+
+trait Owner {
+    const C<const N: u32>: u32;
+    const K<const N: u32>: u32;
+}
+
+impl Owner for () {
+    const C<const N: u32>: u32 = N;
+    const K<const N: u32>: u32 = N + 1;
+}
+
+fn take0<const N: u32>(_: impl Owner<C<N> = { N }>) {}
+fn take1(_: impl Owner<K<99> = 100>) {}
+
+fn main() {
+    take0::<128>(());
+    take1(());
+}

tests/ui/generic-const-items/basic.rs

@@ -0,0 +1,61 @@
+// check-pass
+
+// Basic usage patterns of free & associated generic const items.
+
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+fn main() {
+    const NULL<T>: Option<T> = None::<T>;
+    const NOTHING<T>: Option<T> = None; // arg inferred
+
+    let _ = NOTHING::<String>;
+    let _: Option<u8> = NULL; // arg inferred
+
+    const IDENTITY<const X: u64>: u64 = X;
+
+    const COUNT: u64 = IDENTITY::<48>;
+    const AMOUNT: u64 = IDENTITY::<COUNT>;
+    const NUMBER: u64 = IDENTITY::<{ AMOUNT * 2 }>;
+    let _ = NUMBER;
+    let _ = IDENTITY::<0>;
+
+    let _ = match 0 {
+        IDENTITY::<1> => 2,
+        IDENTITY::<{ 1 + 1 }> => 4,
+        _ => 0,
+    };
+
+    const CREATE<I: Inhabited>: I = I::PROOF;
+    let _ = CREATE::<u64>;
+    let _: u64 = CREATE; // arg inferred
+
+    let _ = <() as Main<u64>>::MAKE::<u64>;
+    let _: (u64, u64) = <()>::MAKE; // args inferred
+}
+
+pub fn usage<'any>() {
+    const REGION_POLY<'a>: &'a () = &();
+
+    let _: &'any () = REGION_POLY::<'any>;
+    let _: &'any () = REGION_POLY::<'_>;
+    let _: &'static () = REGION_POLY;
+}
+
+trait Main<O> {
+    type Output<I>;
+    const MAKE<I: Inhabited>: Self::Output<I>;
+}
+
+impl<O: Inhabited> Main<O> for () {
+    type Output<I> = (O, I);
+    const MAKE<I: Inhabited>: Self::Output<I> = (O::PROOF, I::PROOF);
+}
+
+trait Inhabited {
+    const PROOF: Self;
+}
+
+impl Inhabited for u64 {
+    const PROOF: Self = 512;
+}

tests/ui/generic-const-items/compare-impl-item.rs

@@ -0,0 +1,30 @@
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+trait Trait<P> {
+    const A: ();
+    const B<const K: u64, const Q: u64>: u64;
+    const C<T>: T;
+    const D<const N: usize>: usize;
+
+    const E: usize;
+    const F<T: PartialEq>: ();
+}
+
+impl<P> Trait<P> for () {
+    const A<T>: () = ();
+    //~^ ERROR const `A` has 1 type parameter but its trait declaration has 0 type parameters
+    const B<const K: u64>: u64 = 0;
+    //~^ ERROR const `B` has 1 const parameter but its trait declaration has 2 const parameters
+    const C<'a>: &'a str = "";
+    //~^ ERROR const `C` has 0 type parameters but its trait declaration has 1 type parameter
+    const D<const N: u16>: u16 = N;
+    //~^ ERROR const `D` has an incompatible generic parameter for trait `Trait`
+
+    const E: usize = 1024
+    where
+        P: Copy; //~ ERROR impl has stricter requirements than trait
+    const F<T: Eq>: () = (); //~ ERROR impl has stricter requirements than trait
+}
+
+fn main() {}

tests/ui/generic-const-items/compare-impl-item.stderr

@@ -0,0 +1,66 @@
+error[E0049]: const `A` has 1 type parameter but its trait declaration has 0 type parameters
+  --> $DIR/compare-impl-item.rs:15:13
+   |
+LL |     const A: ();
+   |            - expected 0 type parameters
+...
+LL |     const A<T>: () = ();
+   |             ^ found 1 type parameter
+
+error[E0049]: const `B` has 1 const parameter but its trait declaration has 2 const parameters
+  --> $DIR/compare-impl-item.rs:17:13
+   |
+LL |     const B<const K: u64, const Q: u64>: u64;
+   |             ------------  ------------
+   |             |
+   |             expected 2 const parameters
+...
+LL |     const B<const K: u64>: u64 = 0;
+   |             ^^^^^^^^^^^^ found 1 const parameter
+
+error[E0049]: const `C` has 0 type parameters but its trait declaration has 1 type parameter
+  --> $DIR/compare-impl-item.rs:19:13
+   |
+LL |     const C<T>: T;
+   |             - expected 1 type parameter
+...
+LL |     const C<'a>: &'a str = "";
+   |             ^^ found 0 type parameters
+
+error[E0053]: const `D` has an incompatible generic parameter for trait `Trait`
+  --> $DIR/compare-impl-item.rs:21:13
+   |
+LL | trait Trait<P> {
+   |       -----
+...
+LL |     const D<const N: usize>: usize;
+   |             -------------- expected const parameter of type `usize`
+...
+LL | impl<P> Trait<P> for () {
+   | -----------------------
+...
+LL |     const D<const N: u16>: u16 = N;
+   |             ^^^^^^^^^^^^ found const parameter of type `u16`
+
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/compare-impl-item.rs:26:12
+   |
+LL |     const E: usize;
+   |     -------------- definition of `E` from trait
+...
+LL |         P: Copy;
+   |            ^^^^ impl has extra requirement `P: Copy`
+
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/compare-impl-item.rs:27:16
+   |
+LL |     const F<T: PartialEq>: ();
+   |     ------------------------- definition of `F` from trait
+...
+LL |     const F<T: Eq>: () = ();
+   |                ^^ impl has extra requirement `T: Eq`
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0049, E0053, E0276.
+For more information about an error, try `rustc --explain E0049`.

tests/ui/generic-const-items/const-trait-impl.rs

@@ -0,0 +1,24 @@
+// check-pass
+
+// Test that we can call methods from const trait impls inside of generic const items.
+
+#![feature(generic_const_items, const_trait_impl)]
+#![allow(incomplete_features)]
+#![crate_type = "lib"]
+
+// FIXME(generic_const_items): Interpret `~const` as always-const.
+const CREATE<T: ~const Create>: T = T::create();
+
+pub const K0: i32 = CREATE::<i32>;
+pub const K1: i32 = CREATE; // arg inferred
+
+#[const_trait]
+trait Create {
+    fn create() -> Self;
+}
+
+impl const Create for i32 {
+    fn create() -> i32 {
+        4096
+    }
+}

tests/ui/generic-const-items/duplicate-where-clause.rs

@@ -0,0 +1,27 @@
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+trait Tr<P> {
+    const K: ()
+    where
+        P: Copy
+    where
+        P: Eq;
+    //~^ ERROR cannot define duplicate `where` clauses on an item
+}
+
+// Test that we error on the first where-clause but also that we don't suggest to swap it with the
+// body as it would conflict with the second where-clause.
+// FIXME(generic_const_items): We should provide a structured sugg to merge the 1st into the 2nd WC.
+
+impl<P> Tr<P> for () {
+    const K: ()
+    where
+        P: Eq
+    = ()
+    where
+        P: Copy;
+    //~^^^^^ ERROR where clauses are not allowed before const item bodies
+}
+
+fn main() {}

tests/ui/generic-const-items/duplicate-where-clause.stderr

@@ -0,0 +1,27 @@
+error: cannot define duplicate `where` clauses on an item
+  --> $DIR/duplicate-where-clause.rs:9:9
+   |
+LL |         P: Copy
+   |         - previous `where` clause starts here
+LL |     where
+LL |         P: Eq;
+   |         ^
+   |
+help: consider joining the two `where` clauses into one
+   |
+LL |         P: Copy,
+   |                ~
+
+error: where clauses are not allowed before const item bodies
+  --> $DIR/duplicate-where-clause.rs:19:5
+   |
+LL |       const K: ()
+   |             - while parsing this const item
+LL | /     where
+LL | |         P: Eq
+   | |_____________^ unexpected where clause
+LL |       = ()
+   |         -- the item body
+
+error: aborting due to 2 previous errors
+

tests/ui/generic-const-items/elided-lifetimes.rs

@@ -0,0 +1,18 @@
+#![feature(generic_const_items)]
+#![allow(incomplete_features)]
+
+// Check that we forbid elided lifetimes inside the generics of const items.
+
+const K<T>: () = ()
+where
+    &T: Copy; //~ ERROR `&` without an explicit lifetime name cannot be used here
+
+const I<const S: &str>: &str = "";
+//~^ ERROR `&` without an explicit lifetime name cannot be used here
+//~| ERROR `&str` is forbidden as the type of a const generic parameter
+
+const B<T: Trait<'_>>: () = (); //~ ERROR `'_` cannot be used here
+
+trait Trait<'a> {}
+
+fn main() {}

tests/ui/generic-const-items/elided-lifetimes.stderr

@@ -0,0 +1,35 @@
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/elided-lifetimes.rs:8:5
+   |
+LL |     &T: Copy;
+   |     ^ explicit lifetime name needed here
+   |
+help: consider introducing a higher-ranked lifetime here
+   |
+LL |     for<'a> &'a T: Copy;
+   |     +++++++  ++
+
+error[E0637]: `&` without an explicit lifetime name cannot be used here
+  --> $DIR/elided-lifetimes.rs:10:18
+   |
+LL | const I<const S: &str>: &str = "";
+   |                  ^ explicit lifetime name needed here
+
+error[E0637]: `'_` cannot be used here
+  --> $DIR/elided-lifetimes.rs:14:18
+   |
+LL | const B<T: Trait<'_>>: () = ();
+   |                  ^^ `'_` is a reserved lifetime name
+
+error: `&str` is forbidden as the type of a const generic parameter
+  --> $DIR/elided-lifetimes.rs:10:18
+   |
+LL | const I<const S: &str>: &str = "";
+   |                  ^^^^
+   |
+   = note: the only supported types are integers, `bool` and `char`
+   = help: more complex types are supported with `#![feature(adt_const_params)]`
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0637`.

tests/ui/generic-const-items/evaluatable-bounds.rs

@@ -0,0 +1,31 @@
+// This is a regression test for issue #104400.
+
+// revisions: unconstrained constrained
+//[constrained] check-pass
+
+// Test that we can constrain generic const items that appear inside associated consts by
+// adding a (makeshift) "evaluatable"-bound to the item.
+
+#![feature(generic_const_items, generic_const_exprs)]
+#![allow(incomplete_features)]
+
+trait Trait {
+    const LEN: usize;
+
+    #[cfg(unconstrained)]
+    const ARRAY: [i32; Self::LEN]; //[unconstrained]~ ERROR unconstrained generic constant
+
+    #[cfg(constrained)]
+    const ARRAY: [i32; Self::LEN]
+    where
+        [(); Self::LEN]:;
+}
+
+impl Trait for () {
+    const LEN: usize = 2;
+    const ARRAY: [i32; Self::LEN] = [360, 720];
+}
+
+fn main() {
+    let [_, _] = <() as Trait>::ARRAY;
+}

tests/ui/generic-const-items/evaluatable-bounds.unconstrained.stderr

@@ -0,0 +1,10 @@
+error: unconstrained generic constant
+  --> $DIR/evaluatable-bounds.rs:16:5
+   |
+LL |     const ARRAY: [i32; Self::LEN];
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: try adding a `where` bound using this expression: `where [(); Self::LEN]:`
+
+error: aborting due to previous error
+