[Clippy] Swap single_char_add_str/format_push_string to use diagnostic items instead of paths

compiler/rustc_span/src/symbol.rs

@@ -1882,6 +1882,8 @@ symbols! {
         string_as_mut_str,
         string_as_str,
         string_deref_patterns,
+        string_insert_str,
+        string_push_str,
         stringify,
         struct_field_attributes,
         struct_inherit,

library/alloc/src/string.rs

@@ -1113,6 +1113,7 @@ impl String {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_confusables("append", "push")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_push_str")]
     pub fn push_str(&mut self, string: &str) {
         self.vec.extend_from_slice(string.as_bytes())
     }
@@ -1747,6 +1748,7 @@ impl String {
     #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[stable(feature = "insert_str", since = "1.16.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "string_insert_str")]
     pub fn insert_str(&mut self, idx: usize, string: &str) {
         assert!(self.is_char_boundary(idx));
 

src/tools/clippy/clippy_lints/src/format_push_string.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::ty::is_type_lang_item;
-use clippy_utils::{higher, match_def_path, paths};
+use clippy_utils::higher;
 use rustc_hir::{BinOpKind, Expr, ExprKind, LangItem, MatchSource};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
@@ -70,7 +70,7 @@ impl<'tcx> LateLintPass<'tcx> for FormatPushString {
         let arg = match expr.kind {
             ExprKind::MethodCall(_, _, [arg], _) => {
                 if let Some(fn_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
-                    && match_def_path(cx, fn_def_id, &paths::PUSH_STR)
+                    && cx.tcx.is_diagnostic_item(sym::string_push_str, fn_def_id)
                 {
                     arg
                 } else {

src/tools/clippy/clippy_lints/src/methods/single_char_add_str.rs

@@ -1,13 +1,13 @@
 use crate::methods::{single_char_insert_string, single_char_push_string};
-use clippy_utils::{match_def_path, paths};
 use rustc_hir as hir;
 use rustc_lint::LateContext;
+use rustc_span::sym;
 
 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, receiver: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
     if let Some(fn_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
-        if match_def_path(cx, fn_def_id, &paths::PUSH_STR) {
+        if cx.tcx.is_diagnostic_item(sym::string_push_str, fn_def_id) {
             single_char_push_string::check(cx, expr, receiver, args);
-        } else if match_def_path(cx, fn_def_id, &paths::INSERT_STR) {
+        } else if cx.tcx.is_diagnostic_item(sym::string_insert_str, fn_def_id) {
             single_char_insert_string::check(cx, expr, receiver, args);
         }
     }

src/tools/clippy/clippy_utils/src/paths.rs

@@ -29,7 +29,6 @@ pub const HASHSET_ITER_TY: [&str; 5] = ["std", "collections", "hash", "set", "It
 pub const HASHSET_DRAIN: [&str; 5] = ["std", "collections", "hash", "set", "Drain"];
 pub const IDENT: [&str; 3] = ["rustc_span", "symbol", "Ident"];
 pub const IDENT_AS_STR: [&str; 4] = ["rustc_span", "symbol", "Ident", "as_str"];
-pub const INSERT_STR: [&str; 4] = ["alloc", "string", "String", "insert_str"];
 pub const ITERTOOLS_NEXT_TUPLE: [&str; 3] = ["itertools", "Itertools", "next_tuple"];
 pub const KW_MODULE: [&str; 3] = ["rustc_span", "symbol", "kw"];
 pub const LATE_CONTEXT: [&str; 2] = ["rustc_lint", "LateContext"];
@@ -42,7 +41,6 @@ pub const PARKING_LOT_RWLOCK_READ_GUARD: [&str; 3] = ["lock_api", "rwlock", "RwL
 pub const PARKING_LOT_RWLOCK_WRITE_GUARD: [&str; 3] = ["lock_api", "rwlock", "RwLockWriteGuard"];
 #[cfg_attr(not(unix), allow(clippy::invalid_paths))]
 pub const PERMISSIONS_FROM_MODE: [&str; 6] = ["std", "os", "unix", "fs", "PermissionsExt", "from_mode"];
-pub const PUSH_STR: [&str; 4] = ["alloc", "string", "String", "push_str"];
 pub const REGEX_BUILDER_NEW: [&str; 3] = ["regex", "RegexBuilder", "new"];
 pub const REGEX_BYTES_BUILDER_NEW: [&str; 4] = ["regex", "bytes", "RegexBuilder", "new"];
 pub const REGEX_BYTES_NEW: [&str; 4] = ["regex", "bytes", "Regex", "new"];