Add regression test

src/test/ui/lint/issue-81314-unused-span-ident.fixed

@@ -0,0 +1,12 @@
+// run-rustfix
+// Regression test for #81314: Unused variable lint should
+// span only the identifier and not the rest of the pattern
+
+#![deny(unused)]
+
+fn main() {
+    let [_rest @ ..] = [1, 2, 3]; //~ ERROR unused variable
+}
+
+pub fn foo([_rest @ ..]: &[i32]) { //~ ERROR unused variable
+}

src/test/ui/lint/issue-81314-unused-span-ident.rs

@@ -0,0 +1,12 @@
+// run-rustfix
+// Regression test for #81314: Unused variable lint should
+// span only the identifier and not the rest of the pattern
+
+#![deny(unused)]
+
+fn main() {
+    let [rest @ ..] = [1, 2, 3]; //~ ERROR unused variable
+}
+
+pub fn foo([rest @ ..]: &[i32]) { //~ ERROR unused variable
+}

src/test/ui/lint/issue-81314-unused-span-ident.stderr

@@ -0,0 +1,21 @@
+error: unused variable: `rest`
+  --> $DIR/issue-81314-unused-span-ident.rs:8:10
+   |
+LL |     let [rest @ ..] = [1, 2, 3];
+   |          ^^^^ help: if this is intentional, prefix it with an underscore: `_rest`
+   |
+note: the lint level is defined here
+  --> $DIR/issue-81314-unused-span-ident.rs:5:9
+   |
+LL | #![deny(unused)]
+   |         ^^^^^^
+   = note: `#[deny(unused_variables)]` implied by `#[deny(unused)]`
+
+error: unused variable: `rest`
+  --> $DIR/issue-81314-unused-span-ident.rs:11:13
+   |
+LL | pub fn foo([rest @ ..]: &[i32]) {
+   |             ^^^^ help: if this is intentional, prefix it with an underscore: `_rest`
+
+error: aborting due to 2 previous errors
+