[`inherent_to_string`]: Don't lint `unsafe` or `extern` fns

3 files changed, 44 insertions, 27 deletions

diff --git a/clippy_lints/src/inherent_to_string.rs b/clippy_lints/src/inherent_to_string.rs
index d43e5cc9b2c..bc4ec33b733 100644
--- a/clippy_lints/src/inherent_to_string.rs
+++ b/clippy_lints/src/inherent_to_string.rs
@@ -1,11 +1,11 @@
 use clippy_utils::diagnostics::span_lint_and_help;
 use clippy_utils::ty::{implements_trait, is_type_lang_item};
 use clippy_utils::{return_ty, trait_ref_of_method};
-use if_chain::if_chain;
-use rustc_hir::{GenericParamKind, ImplItem, ImplItemKind, LangItem};
+use rustc_hir::{GenericParamKind, ImplItem, ImplItemKind, LangItem, Unsafety};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
+use rustc_target::spec::abi::Abi;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -95,24 +95,23 @@ impl<'tcx> LateLintPass<'tcx> for InherentToString {
             return;
         }
 
-        if_chain! {
-            // Check if item is a method, called to_string and has a parameter 'self'
-            if let ImplItemKind::Fn(ref signature, _) = impl_item.kind;
-            if impl_item.ident.name == sym::to_string;
-            let decl = &signature.decl;
-            if decl.implicit_self.has_implicit_self();
-            if decl.inputs.len() == 1;
-            if impl_item.generics.params.iter().all(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }));
-
+        // Check if item is a method called `to_string` and has a parameter 'self'
+        if let ImplItemKind::Fn(ref signature, _) = impl_item.kind
+            // #11201
+            && let header = signature.header
+            && header.unsafety == Unsafety::Normal
+            && header.abi == Abi::Rust
+            && impl_item.ident.name == sym::to_string
+            && let decl = signature.decl
+            && decl.implicit_self.has_implicit_self()
+            && decl.inputs.len() == 1
+            && impl_item.generics.params.iter().all(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
             // Check if return type is String
-            if is_type_lang_item(cx, return_ty(cx, impl_item.owner_id), LangItem::String);
-
+            && is_type_lang_item(cx, return_ty(cx, impl_item.owner_id), LangItem::String)
             // Filters instances of to_string which are required by a trait
-            if trait_ref_of_method(cx, impl_item.owner_id.def_id).is_none();
-
-            then {
-                show_lint(cx, impl_item);
-            }
+            && trait_ref_of_method(cx, impl_item.owner_id.def_id).is_none()
+        {
+            show_lint(cx, impl_item);
         }
     }
 }
diff --git a/tests/ui/inherent_to_string.rs b/tests/ui/inherent_to_string.rs
index aeb0a0c1e2e..adb0389a043 100644
--- a/tests/ui/inherent_to_string.rs
+++ b/tests/ui/inherent_to_string.rs
@@ -1,5 +1,4 @@
-#![warn(clippy::inherent_to_string)]
-#![deny(clippy::inherent_to_string_shadow_display)]
+#![allow(improper_ctypes_definitions)]
 
 use std::fmt;
 
@@ -14,6 +13,9 @@ struct D;
 struct E;
 struct F;
 struct G;
+struct H;
+struct I;
+struct J;
 
 impl A {
     // Should be detected; emit warning
@@ -80,6 +82,26 @@ impl G {
     }
 }
 
+// Issue #11201
+
+impl H {
+    unsafe fn to_string(&self) -> String {
+        "G.to_string()".to_string()
+    }
+}
+
+impl I {
+    extern "C" fn to_string(&self) -> String {
+        "G.to_string()".to_string()
+    }
+}
+
+impl J {
+    unsafe extern "C" fn to_string(&self) -> String {
+        "G.to_string()".to_string()
+    }
+}
+
 fn main() {
     let a = A;
     a.to_string();
diff --git a/tests/ui/inherent_to_string.stderr b/tests/ui/inherent_to_string.stderr
index 443fecae1aa..579b3c8c56f 100644
--- a/tests/ui/inherent_to_string.stderr
+++ b/tests/ui/inherent_to_string.stderr
@@ -1,5 +1,5 @@
 error: implementation of inherent method `to_string(&self) -> String` for type `A`
-  --> $DIR/inherent_to_string.rs:20:5
+  --> $DIR/inherent_to_string.rs:22:5
    |
 LL | /     fn to_string(&self) -> String {
 LL | |         "A.to_string()".to_string()
@@ -10,7 +10,7 @@ LL | |     }
    = note: `-D clippy::inherent-to-string` implied by `-D warnings`
 
 error: type `C` implements inherent method `to_string(&self) -> String` which shadows the implementation of `Display`
-  --> $DIR/inherent_to_string.rs:44:5
+  --> $DIR/inherent_to_string.rs:46:5
    |
 LL | /     fn to_string(&self) -> String {
 LL | |         "C.to_string()".to_string()
@@ -18,11 +18,7 @@ LL | |     }
    | |_____^
    |
    = help: remove the inherent method from type `C`
-note: the lint level is defined here
-  --> $DIR/inherent_to_string.rs:2:9
-   |
-LL | #![deny(clippy::inherent_to_string_shadow_display)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `#[deny(clippy::inherent_to_string_shadow_display)]` on by default
 
 error: aborting due to 2 previous errors