Clean up

Simplify match statement

Add multiple tests
- 1 test for checking `N + 1 + 1` does not unify with `N+1`
- 2 tests for checking that a function that uses two parameters only returns the parameter that
  is actually used.
- Check exact repeat predicates

src/test/ui/const-generics/fn_with_two_const_inputs.rs

@@ -0,0 +1,23 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+const fn both(_: usize, b: usize) -> usize {
+    b
+}
+
+fn foo<const N: usize, const M: usize>() -> [(); N + 2]
+where
+    [(); both(N + 1, M + 1)]:,
+{
+    bar()
+    //~^ ERROR: unconstrained generic constant
+}
+
+fn bar<const N: usize>() -> [(); N]
+where
+    [(); N + 1]:,
+{
+    [(); N]
+}
+
+fn main() {}

src/test/ui/const-generics/fn_with_two_const_inputs.stderr

@@ -0,0 +1,18 @@
+error: unconstrained generic constant
+  --> $DIR/fn_with_two_const_inputs.rs:12:5
+   |
+LL |     bar()
+   |     ^^^
+   |
+   = help: try adding a `where` bound using this expression: `where [(); N + 1]:`
+note: required by a bound in `bar`
+  --> $DIR/fn_with_two_const_inputs.rs:18:10
+   |
+LL | fn bar<const N: usize>() -> [(); N]
+   |    --- required by a bound in this
+LL | where
+LL |     [(); N + 1]:,
+   |          ^^^^^ required by this bound in `bar`
+
+error: aborting due to previous error
+

src/test/ui/const-generics/fn_with_two_same_const_inputs.rs

@@ -0,0 +1,22 @@
+// check-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+const fn both(_: usize, b: usize) -> usize {
+    b
+}
+
+fn foo<const N: usize>()
+where
+    [(); both(N + 1, N + 1)]:,
+{
+    bar::<N>();
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}

src/test/ui/const-generics/generic_const_exprs/const_kind_expr/wf_obligation.rs

@@ -15,8 +15,8 @@ where
     [(); (L - 1) + 1 + L]:,
 {
     foo::<_, L>([(); L + 1 + L]);
-    //~^ ERROR: unconstrained generic constant
-    //~| ERROR: mismatched types
+    //~^ ERROR: mismatched types
+    //~^^ ERROR: unconstrained generic constant
 }
 
 fn main() {}

src/test/ui/const-generics/two_matching_preds.rs

@@ -0,0 +1,19 @@
+// check-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn foo<const N: usize>()
+where
+    [(); N + 1]:,
+    [(); N + 1]:,
+{
+    bar::<N>();
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}

src/test/ui/const-generics/unify_with_nested_expr.rs

@@ -0,0 +1,18 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn foo<const N: usize>()
+where
+    [(); N + 1 + 1]:,
+{
+    bar();
+    //~^ ERROR: type annotations
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}

src/test/ui/const-generics/unify_with_nested_expr.stderr

@@ -0,0 +1,22 @@
+error[E0284]: type annotations needed
+  --> $DIR/unify_with_nested_expr.rs:8:5
+   |
+LL |     bar();
+   |     ^^^ cannot infer the value of the const parameter `N` declared on the function `bar`
+   |
+note: required by a bound in `bar`
+  --> $DIR/unify_with_nested_expr.rs:14:10
+   |
+LL | fn bar<const N: usize>()
+   |    --- required by a bound in this
+LL | where
+LL |     [(); N + 1]:,
+   |          ^^^^^ required by this bound in `bar`
+help: consider specifying the generic argument
+   |
+LL |     bar::<N>();
+   |        +++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0284`.