Use match_trait_method to detect an another method of struct

Author: chansuke

clippy_lints/src/to_string_in_display.rs

@@ -1,4 +1,4 @@
-use crate::utils::{match_def_path, paths, span_lint};
+use crate::utils::{match_def_path, match_trait_method, paths, span_lint};
 use if_chain::if_chain;
 use rustc_hir::*;
 use rustc_lint::{LateContext, LateLintPass};
@@ -51,6 +51,8 @@ impl LateLintPass<'_> for ToStringInDisplay {
 
         if_chain! {
             if let ExprKind::MethodCall(ref path, _, _, _) = expr.kind;
+            if path.ident.name == sym!(to_string)
+                    && match_trait_method(cx, expr, &paths::TO_STRING);
             if path.ident.as_str() == "to_string";
             if let Some(Node::ImplItem(ImplItem {ident, kind, ..})) = parent_node;
             if ident.as_str() == "fmt";
@@ -63,6 +65,7 @@ impl LateLintPass<'_> for ToStringInDisplay {
             if let Path{res, ..} = path;
             if let def::Res::SelfTy(Some(did), _) = res;
             if match_def_path(cx, *did, &paths::DISPLAY_TRAIT);
+
             then {
                 span_lint(
                     cx,

tests/ui/to_string_in_display.stderr

@@ -6,11 +6,5 @@ LL |         write!(f, "{}", self.to_string())
    |
    = note: `-D clippy::to-string-in-display` implied by `-D warnings`
 
-error: Using to_string in fmt::Display implementation might lead to infinite recursion
-  --> $DIR/to_string_in_display.rs:43:25
-   |
-LL |         write!(f, "{}", self.to_string())
-   |                         ^^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error