Fix suggestion for nested struct patterns

src/test/ui/suggestions/ignore-nested-field-binding.fixed

@@ -0,0 +1,20 @@
+// Regression test for #88403, where prefixing with an underscore was
+// erroneously suggested for a nested shorthand struct field binding.
+
+// run-rustfix
+#![allow(unused)]
+#![forbid(unused_variables)]
+
+struct Inner { i: i32 }
+struct Outer { o: Inner }
+
+fn foo(Outer { o: Inner { i: _ } }: Outer) {}
+//~^ ERROR: unused variable: `i`
+//~| HELP: try ignoring the field
+
+fn main() {
+    let s = Outer { o: Inner { i: 42 } };
+    let Outer { o: Inner { i: _ } } = s;
+    //~^ ERROR: unused variable: `i`
+    //~| HELP: try ignoring the field
+}

src/test/ui/suggestions/ignore-nested-field-binding.rs

@@ -0,0 +1,20 @@
+// Regression test for #88403, where prefixing with an underscore was
+// erroneously suggested for a nested shorthand struct field binding.
+
+// run-rustfix
+#![allow(unused)]
+#![forbid(unused_variables)]
+
+struct Inner { i: i32 }
+struct Outer { o: Inner }
+
+fn foo(Outer { o: Inner { i } }: Outer) {}
+//~^ ERROR: unused variable: `i`
+//~| HELP: try ignoring the field
+
+fn main() {
+    let s = Outer { o: Inner { i: 42 } };
+    let Outer { o: Inner { i } } = s;
+    //~^ ERROR: unused variable: `i`
+    //~| HELP: try ignoring the field
+}

src/test/ui/suggestions/ignore-nested-field-binding.stderr

@@ -0,0 +1,20 @@
+error: unused variable: `i`
+  --> $DIR/ignore-nested-field-binding.rs:11:27
+   |
+LL | fn foo(Outer { o: Inner { i } }: Outer) {}
+   |                           ^ help: try ignoring the field: `i: _`
+   |
+note: the lint level is defined here
+  --> $DIR/ignore-nested-field-binding.rs:6:11
+   |
+LL | #![forbid(unused_variables)]
+   |           ^^^^^^^^^^^^^^^^
+
+error: unused variable: `i`
+  --> $DIR/ignore-nested-field-binding.rs:17:28
+   |
+LL |     let Outer { o: Inner { i } } = s;
+   |                            ^ help: try ignoring the field: `i: _`
+
+error: aborting due to 2 previous errors
+