Move concat macro path into clippy_utils::paths

clippy_lints/src/useless_concat.rs

@@ -1,5 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::macros::macro_backtrace;
+use clippy_utils::paths::CONCAT;
 use clippy_utils::source::snippet_opt;
 use clippy_utils::{match_def_path, tokenize_with_text};
 use rustc_ast::LitKind;
@@ -42,7 +43,7 @@ impl LateLintPass<'_> for UselessConcat {
             // Get the direct parent of the expression.
             && let Some(macro_call) = macro_backtrace(expr.span).next()
             // Check if the `concat` macro from the `core` library.
-            && match_def_path(cx, macro_call.def_id, &["core", "macros", "builtin", "concat"])
+            && match_def_path(cx, macro_call.def_id, &CONCAT)
             // We get the original code to parse it.
             && let Some(original_code) = snippet_opt(cx, macro_call.span)
             // This check allows us to ensure that the code snippet:

clippy_lints/src/utils/internal_lints/invalid_paths.rs

@@ -61,6 +61,10 @@ pub fn check_path(cx: &LateContext<'_>, path: &[&str]) -> bool {
     if !def_path_res(cx.tcx, path).is_empty() {
         return true;
     }
+    // `builtin` macros don't seem to be found in `def_path_res`...
+    if path == ["core", "macros", "builtin", "concat"] {
+        return true;
+    }
 
     // Some implementations can't be found by `path_to_res`, particularly inherent
     // implementations of native types. Check lang items.
@@ -77,6 +81,7 @@ pub fn check_path(cx: &LateContext<'_>, path: &[&str]) -> bool {
     .iter()
     .flat_map(|&ty| cx.tcx.incoherent_impls(ty).iter())
     .copied();
+
     for item_def_id in lang_items.iter().map(|(_, def_id)| def_id).chain(incoherent_impls) {
         let lang_item_path = cx.get_def_path(item_def_id);
         if path_syms.starts_with(&lang_item_path) {

clippy_utils/src/paths.rs

@@ -33,6 +33,7 @@ pub const CHILD: [&str; 3] = ["std", "process", "Child"];
 pub const CHILD_ID: [&str; 4] = ["std", "process", "Child", "id"];
 pub const CHILD_KILL: [&str; 4] = ["std", "process", "Child", "kill"];
 pub const PANIC_ANY: [&str; 3] = ["std", "panic", "panic_any"];
+pub const CONCAT: [&str; 4] = ["core", "macros", "builtin", "concat"];
 
 // Paths in clippy itself
 pub const MSRV: [&str; 3] = ["clippy_utils", "msrvs", "Msrv"];