Don't allow repeat expr count inference side effects to propagate

4 files changed, 77 insertions, 2 deletions

diff --git a/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs
index 4654d7483a6..bf519febb30 100644
--- a/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs
+++ b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs
@@ -1,5 +1,3 @@
-//@ check-pass
-
 #![feature(generic_arg_infer)]
 
 // Test that if we defer repeat expr copy checks to end of typechecking they're
@@ -37,6 +35,7 @@ fn main() {
     let b: [Foo<_>; 2] = [Foo(PhantomData); _];
     tie(&a, b);
     let c = [NotCopy; _];
+    //~^ ERROR: type annotations needed for `[NotCopy; _]`
 
     // a is of type `?y`
     // b is of type `[Foo<?y>; 2]`
diff --git a/tests/ui/repeat-expr/copy-check-deferred-before-fallback.stderr b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.stderr
new file mode 100644
index 00000000000..d6189329c92
--- /dev/null
+++ b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.stderr
@@ -0,0 +1,14 @@
+error[E0282]: type annotations needed for `[NotCopy; _]`
+  --> $DIR/copy-check-deferred-before-fallback.rs:37:9
+   |
+LL |     let c = [NotCopy; _];
+   |         ^    ------- type must be known at this point
+   |
+help: consider giving `c` an explicit type, where the value of const parameter `N` is specified
+   |
+LL |     let c: [_; N] = [NotCopy; _];
+   |          ++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/repeat-expr/copy-check-inference-side-effects.rs b/tests/ui/repeat-expr/copy-check-inference-side-effects.rs
new file mode 100644
index 00000000000..416a20169fb
--- /dev/null
+++ b/tests/ui/repeat-expr/copy-check-inference-side-effects.rs
@@ -0,0 +1,34 @@
+#![feature(generic_arg_infer)]
+
+struct Foo<const N: usize>;
+
+impl Clone for Foo<1> {
+    fn clone(&self) -> Self {
+        Self
+    }
+}
+impl Copy for Foo<1> {}
+
+fn unify<const N: usize>(_: &[Foo<N>; 2], _: &[String; N]) {}
+
+fn works_if_inference_side_effects() {
+    // This will only pass if inference side effectrs from proving `Foo<?x>: Copy` are
+    // able to be relied upon by other repeat expressions.
+    let a /* : [Foo<?x>; 2] */ = [Foo::<_>; 2];
+    //~^ ERROR: type annotations needed for `[Foo<_>; 2]`
+    let b /* : [String; ?x] */ = ["string".to_string(); _];
+
+    unify(&a, &b);
+}
+
+fn works_if_fixed_point() {
+    // This will only pass if the *second* array repeat expr is checked first
+    // allowing `Foo<?x>: Copy` to infer the array length of the first repeat expr.
+    let b /* : [String; ?x] */ = ["string".to_string(); _];
+    //~^ ERROR: type annotations needed for `[String; _]`
+    let a /* : [Foo<?x>; 2] */ = [Foo::<_>; 2];
+
+    unify(&a, &b);
+}
+
+fn main() {}
diff --git a/tests/ui/repeat-expr/copy-check-inference-side-effects.stderr b/tests/ui/repeat-expr/copy-check-inference-side-effects.stderr
new file mode 100644
index 00000000000..505beff0f6b
--- /dev/null
+++ b/tests/ui/repeat-expr/copy-check-inference-side-effects.stderr
@@ -0,0 +1,28 @@
+error[E0282]: type annotations needed for `[Foo<_>; 2]`
+  --> $DIR/copy-check-inference-side-effects.rs:17:9
+   |
+LL |     let a /* : [Foo<?x>; 2] */ = [Foo::<_>; 2];
+   |         ^
+LL |
+LL |     let b /* : [String; ?x] */ = ["string".to_string(); _];
+   |                                   -------------------- type must be known at this point
+   |
+help: consider giving `a` an explicit type, where the value of const parameter `N` is specified
+   |
+LL |     let a: [Foo<N>; 2] /* : [Foo<?x>; 2] */ = [Foo::<_>; 2];
+   |          +++++++++++++
+
+error[E0282]: type annotations needed for `[String; _]`
+  --> $DIR/copy-check-inference-side-effects.rs:27:9
+   |
+LL |     let b /* : [String; ?x] */ = ["string".to_string(); _];
+   |         ^                         -------------------- type must be known at this point
+   |
+help: consider giving `b` an explicit type, where the value of const parameter `N` is specified
+   |
+LL |     let b: [_; N] /* : [String; ?x] */ = ["string".to_string(); _];
+   |          ++++++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0282`.