Fix 'self' in method signature suggestions

Author: reddevilmidzy

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1814,7 +1814,13 @@ fn compare_number_of_method_arguments<'tcx>(
             })
             .or_else(|| {
                 let signature = trait_m.signature(tcx);
-                find_param_bounds(&signature).map(|(lo, hi)| signature[lo..hi].trim().to_string())
+                find_param_bounds(&signature).map(|(lo, hi)| {
+                    let mut params = signature[lo..hi].trim().to_string();
+                    if trait_m.is_method() {
+                        params = params.replacen("Self", "self", 1);
+                    }
+                    params
+                })
             });
 
         if let (Some(span), Some(missing)) = (impl_inputs_span, missing_params) {

tests/ui/fn/issue-39259.stderr

@@ -19,9 +19,8 @@ LL |     fn call(&self) -> u32 {
    = note: `call` from trait: `extern "rust-call" fn(&Self, Args) -> <Self as FnOnce<Args>>::Output`
 help: modify the signature to match the trait definition
    |
-LL -     fn call(&self) -> u32 {
-LL +     fn call(&Self, Args) -> u32 {
-   |
+LL |     fn call(&self, Args) -> u32 {
+   |                  ++++++
 
 error[E0277]: expected a `FnMut(u32)` closure, found `S`
   --> $DIR/issue-39259.rs:6:25

tests/ui/impl-trait/trait_type.stderr

@@ -21,9 +21,8 @@ LL |    fn fmt(&self) -> () { }
    = note: `fmt` from trait: `fn(&Self, &mut Formatter<'_>) -> Result<(), std::fmt::Error>`
 help: modify the signature to match the trait definition
    |
-LL -    fn fmt(&self) -> () { }
-LL +    fn fmt(&Self, &mut Formatter<'_>) -> () { }
-   |
+LL |    fn fmt(&self, &mut Formatter<'_>) -> () { }
+   |                ++++++++++++++++++++
 
 error[E0186]: method `fmt` has a `&self` declaration in the trait, but not in the impl
   --> $DIR/trait_type.rs:17:4