3 files changed, 76 insertions, 0 deletions
diff --git a/src/test/ui/array-slice-vec/suggest-array-length.fixed b/src/test/ui/array-slice-vec/suggest-array-length.fixed
new file mode 100644
index 00000000000..bae3ab74af6
--- /dev/null
+++ b/src/test/ui/array-slice-vec/suggest-array-length.fixed
@@ -0,0 +1,14 @@
+// run-rustfix
+#![allow(unused_variables, dead_code, non_upper_case_globals)]
+
+fn main() {
+    const Foo: [i32; 3] = [1, 2, 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+    let foo: [i32; 3] = [1, 2, 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+    let bar: [i32; 3] = [0; 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+}
diff --git a/src/test/ui/array-slice-vec/suggest-array-length.rs b/src/test/ui/array-slice-vec/suggest-array-length.rs
new file mode 100644
index 00000000000..b0867f4e396
--- /dev/null
+++ b/src/test/ui/array-slice-vec/suggest-array-length.rs
@@ -0,0 +1,14 @@
+// run-rustfix
+#![allow(unused_variables, dead_code, non_upper_case_globals)]
+
+fn main() {
+    const Foo: [i32; _] = [1, 2, 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+    let foo: [i32; _] = [1, 2, 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+    let bar: [i32; _] = [0; 3];
+    //~^ ERROR in expressions, `_` can only be used on the left-hand side of an assignment
+    //~| ERROR using `_` for array lengths is unstable
+}
diff --git a/src/test/ui/array-slice-vec/suggest-array-length.stderr b/src/test/ui/array-slice-vec/suggest-array-length.stderr
new file mode 100644
index 00000000000..9000f716028
--- /dev/null
+++ b/src/test/ui/array-slice-vec/suggest-array-length.stderr
@@ -0,0 +1,48 @@
+error: in expressions, `_` can only be used on the left-hand side of an assignment
+  --> $DIR/suggest-array-length.rs:8:20
+   |
+LL |     let foo: [i32; _] = [1, 2, 3];
+   |                    ^ `_` not allowed here
+
+error: in expressions, `_` can only be used on the left-hand side of an assignment
+  --> $DIR/suggest-array-length.rs:11:20
+   |
+LL |     let bar: [i32; _] = [0; 3];
+   |                    ^ `_` not allowed here
+
+error: in expressions, `_` can only be used on the left-hand side of an assignment
+  --> $DIR/suggest-array-length.rs:5:22
+   |
+LL |     const Foo: [i32; _] = [1, 2, 3];
+   |                      ^ `_` not allowed here
+
+error[E0658]: using `_` for array lengths is unstable
+  --> $DIR/suggest-array-length.rs:5:22
+   |
+LL |     const Foo: [i32; _] = [1, 2, 3];
+   |                      ^ help: consider specifying the array length: `3`
+   |
+   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
+   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
+
+error[E0658]: using `_` for array lengths is unstable
+  --> $DIR/suggest-array-length.rs:8:20
+   |
+LL |     let foo: [i32; _] = [1, 2, 3];
+   |                    ^ help: consider specifying the array length: `3`
+   |
+   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
+   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
+
+error[E0658]: using `_` for array lengths is unstable
+  --> $DIR/suggest-array-length.rs:11:20
+   |
+LL |     let bar: [i32; _] = [0; 3];
+   |                    ^ help: consider specifying the array length: `3`
+   |
+   = note: see issue #85077 <https://github.com/rust-lang/rust/issues/85077> for more information
+   = help: add `#![feature(generic_arg_infer)]` to the crate attributes to enable
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0658`.