Fix min_ident_chars: lint on single chars if method only declared not defined

Author: t-webber

clippy_lints/src/min_ident_chars.rs

@@ -82,6 +82,15 @@ impl LateLintPass<'_> for MinIdentChars {
             return;
         }
 
+        // If the function is declared but not defined in a trait, check_pat isn't called so we need to
+        // check this explicitly
+        if matches!(&item.kind, rustc_hir::TraitItemKind::Fn(_, _)) {
+            let param_names = cx.tcx.fn_arg_idents(item.owner_id.to_def_id());
+            for ident in param_names.iter().flatten() {
+                emit_min_ident_chars(self, cx, ident.as_str(), ident.span);
+            }
+        }
+
         walk_trait_item(&mut IdentVisitor { conf: self, cx }, item);
     }
 

tests/ui/min_ident_chars.rs

@@ -142,7 +142,7 @@ impl core::fmt::Debug for Issue13396 {
 
 trait D {
     //~^ min_ident_chars
-    fn f(g: i32) {}
+    fn f(g: i32);
     //~^ min_ident_chars
     //~| min_ident_chars
 }

tests/ui/min_ident_chars.stderr

@@ -206,16 +206,16 @@ LL | trait D {
    |       ^
 
 error: this ident consists of a single char
-  --> tests/ui/min_ident_chars.rs:145:8
+  --> tests/ui/min_ident_chars.rs:145:10
    |
-LL |     fn f(g: i32) {}
-   |        ^
+LL |     fn f(g: i32);
+   |          ^
 
 error: this ident consists of a single char
-  --> tests/ui/min_ident_chars.rs:145:10
+  --> tests/ui/min_ident_chars.rs:145:8
    |
-LL |     fn f(g: i32) {}
-   |          ^
+LL |     fn f(g: i32);
+   |        ^
 
 error: aborting due to 36 previous errors