Add test for extra_unused_lifetimes FP on derive

This commit adds test for a `extra_unused_lifetimes` false positive from derive (#9014).

The fix for the FP is introduced in #9037.

Author: dswij

tests/ui/auxiliary/proc_macro_derive.rs

@@ -72,3 +72,17 @@ pub fn mini_macro(_: TokenStream) -> TokenStream {
         }
     )
 }
+
+#[proc_macro_derive(ExtraLifetimeDerive)]
+#[allow(unused)]
+pub fn extra_lifetime(_input: TokenStream) -> TokenStream {
+    quote!(
+        pub struct ExtraLifetime;
+
+        impl<'b> ExtraLifetime {
+            pub fn something<'c>() -> Self {
+                Self
+            }
+        }
+    )
+}

tests/ui/extra_unused_lifetimes.rs

@@ -1,3 +1,5 @@
+// aux-build:proc_macro_derive.rs
+
 #![allow(
     unused,
     dead_code,
@@ -7,6 +9,9 @@
 )]
 #![warn(clippy::extra_unused_lifetimes)]
 
+#[macro_use]
+extern crate proc_macro_derive;
+
 fn empty() {}
 
 fn used_lt<'a>(x: &'a u8) {}
@@ -114,4 +119,11 @@ mod second_case {
     }
 }
 
+// Should not lint
+#[derive(ExtraLifetimeDerive)]
+struct Human<'a> {
+    pub bones: i32,
+    pub name: &'a str,
+}
+
 fn main() {}

tests/ui/extra_unused_lifetimes.stderr

@@ -1,37 +1,37 @@
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:14:14
+  --> $DIR/extra_unused_lifetimes.rs:19:14
    |
 LL | fn unused_lt<'a>(x: u8) {}
    |              ^^
    |
    = note: `-D clippy::extra-unused-lifetimes` implied by `-D warnings`
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:41:10
+  --> $DIR/extra_unused_lifetimes.rs:46:10
    |
 LL |     fn x<'a>(&self) {}
    |          ^^
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:67:22
+  --> $DIR/extra_unused_lifetimes.rs:72:22
    |
 LL |         fn unused_lt<'a>(x: u8) {}
    |                      ^^
 
 error: this lifetime isn't used in the impl
-  --> $DIR/extra_unused_lifetimes.rs:78:10
+  --> $DIR/extra_unused_lifetimes.rs:83:10
    |
 LL |     impl<'a> std::ops::AddAssign<&Scalar> for &mut Scalar {
    |          ^^
 
 error: this lifetime isn't used in the impl
-  --> $DIR/extra_unused_lifetimes.rs:84:10
+  --> $DIR/extra_unused_lifetimes.rs:89:10
    |
 LL |     impl<'b> Scalar {
    |          ^^
 
 error: this lifetime isn't used in the function definition
-  --> $DIR/extra_unused_lifetimes.rs:85:26
+  --> $DIR/extra_unused_lifetimes.rs:90:26
    |
 LL |         pub fn something<'c>() -> Self {
    |                          ^^