fix &str type check in from_str_radix_10 (rust-lang#15410)

minor fix in `from_str_radix_10` lint, `is_type_diagnostic_item` only
checks `Adt`, use `.is_str()` instead

changelog: [`from_str_radix_10`]: properly lint references to `&str` as
well

Author: samueltardieu

clippy_lints/src/from_str_radix_10.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::sugg::Sugg;
-use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item};
+use clippy_utils::ty::is_type_lang_item;
 use clippy_utils::{is_in_const_context, is_integer_literal, sym};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, LangItem, PrimTy, QPath, TyKind, def};
@@ -89,5 +89,5 @@ impl<'tcx> LateLintPass<'tcx> for FromStrRadix10 {
 
 /// Checks if a Ty is `String` or `&str`
 fn is_ty_stringish(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
-    is_type_lang_item(cx, ty, LangItem::String) || is_type_diagnostic_item(cx, ty, sym::str)
+    is_type_lang_item(cx, ty, LangItem::String) || ty.peel_refs().is_str()
 }

tests/ui/from_str_radix_10.fixed

@@ -74,3 +74,13 @@ fn issue_12731() {
         let _ = u32::from_str_radix("123", 10);
     }
 }
+
+fn fix_str_ref_check() {
+    #![allow(clippy::needless_borrow)]
+    let s = "1";
+    let _ = s.parse::<u32>().unwrap();
+    //~^ from_str_radix_10
+    let s_ref = &s;
+    let _ = s_ref.parse::<u32>().unwrap();
+    //~^ from_str_radix_10
+}

tests/ui/from_str_radix_10.rs

@@ -74,3 +74,13 @@ fn issue_12731() {
         let _ = u32::from_str_radix("123", 10);
     }
 }
+
+fn fix_str_ref_check() {
+    #![allow(clippy::needless_borrow)]
+    let s = "1";
+    let _ = u32::from_str_radix(&s, 10).unwrap();
+    //~^ from_str_radix_10
+    let s_ref = &s;
+    let _ = u32::from_str_radix(&s_ref, 10).unwrap();
+    //~^ from_str_radix_10
+}

tests/ui/from_str_radix_10.stderr

@@ -49,5 +49,17 @@ error: this call to `from_str_radix` can be replaced with a call to `str::parse`
 LL |     i32::from_str_radix(&stringier, 10)?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `stringier.parse::<i32>()`
 
-error: aborting due to 8 previous errors
+error: this call to `from_str_radix` can be replaced with a call to `str::parse`
+  --> tests/ui/from_str_radix_10.rs:81:13
+   |
+LL |     let _ = u32::from_str_radix(&s, 10).unwrap();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `s.parse::<u32>()`
+
+error: this call to `from_str_radix` can be replaced with a call to `str::parse`
+  --> tests/ui/from_str_radix_10.rs:84:13
+   |
+LL |     let _ = u32::from_str_radix(&s_ref, 10).unwrap();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `s_ref.parse::<u32>()`
+
+error: aborting due to 10 previous errors