Refactor trait signature lookup and param parsing

Author: reddevilmidzy

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1698,11 +1698,14 @@ fn compare_number_of_method_arguments<'tcx>(
     let impl_number_args = impl_m_fty.skip_binder().inputs().skip_binder().len();
 
     if trait_number_args != impl_number_args {
-        let trait_span = trait_m
-            .def_id
-            .as_local()
-            .and_then(|def_id| {
-                let (trait_m_sig, _) = &tcx.hir_expect_trait_item(def_id).expect_fn();
+        let trait_sig = trait_m.def_id.as_local().and_then(|def_id| {
+            let (trait_m_sig, _) = tcx.hir_expect_trait_item(def_id).expect_fn();
+            Some((def_id, trait_m_sig))
+        });
+
+        let trait_span = trait_sig
+            .as_ref()
+            .and_then(|(_, trait_m_sig)| {
                 let pos = trait_number_args.saturating_sub(1);
                 trait_m_sig.decl.inputs.get(pos).map(|arg| {
                     if pos == 0 {
@@ -1762,15 +1765,16 @@ fn compare_number_of_method_arguments<'tcx>(
         );
 
         let sm = tcx.sess.source_map();
-        let find_param_bounds = |snippet: &str| -> Option<(usize, usize)> {
+
+        fn find_param_bounds(snippet: &str) -> Option<(usize, usize)> {
             let start = snippet.find('(')?;
             let mut depth = 1usize;
             let bytes = snippet.as_bytes();
             let mut i = start + 1;
             while i < bytes.len() {
-                match bytes[i] as char {
-                    '(' => depth += 1,
-                    ')' => {
+                match bytes[i] {
+                    b'(' => depth += 1,
+                    b')' => {
                         depth -= 1;
                         if depth == 0 {
                             return Some((start + 1, i));
@@ -1781,7 +1785,7 @@ fn compare_number_of_method_arguments<'tcx>(
                 i += 1;
             }
             None
-        };
+        }
 
         let impl_inputs_span = (!impl_m_sig.span.is_dummy())
             .then(|| {
@@ -1795,11 +1799,8 @@ fn compare_number_of_method_arguments<'tcx>(
             })
             .flatten();
 
-        let suggestion = trait_m
-            .def_id
-            .as_local()
-            .and_then(|def_id| {
-                let (trait_sig, _) = tcx.hir_expect_trait_item(def_id).expect_fn();
+        let suggestion = trait_sig
+            .and_then(|(_, trait_sig)| {
                 sm.span_to_snippet(trait_sig.span).ok().and_then(|snippet| {
                     find_param_bounds(&snippet)
                         .map(|(lo_rel, hi_rel)| snippet[lo_rel..hi_rel].to_string())