[Clippy] Swap filter_map_bool_then to use diagnostic item instead of path

compiler/rustc_span/src/symbol.rs

@@ -501,6 +501,7 @@
         black_box,
         block,
         bool,
+        bool_then,
         borrowck_graphviz_format,
         borrowck_graphviz_postflow,
         box_new,

library/core/src/bool.rs

@@ -55,6 +55,7 @@ pub fn then_some<T>(self, t: T) -> Option<T> {
     /// assert_eq!(a, 1);
     /// ```
     #[stable(feature = "lazy_bool_to_option", since = "1.50.0")]
+    #[cfg_attr(not(test), rustc_diagnostic_item = "bool_then")]
     #[inline]
     pub fn then<T, F: FnOnce() -> T>(self, f: F) -> Option<T> {
         if self { Some(f()) } else { None }

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

@@ -1,9 +1,8 @@
 use super::FILTER_MAP_BOOL_THEN;
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::paths::BOOL_THEN;
 use clippy_utils::source::SpanRangeExt;
 use clippy_utils::ty::is_copy;
-use clippy_utils::{is_from_proc_macro, is_trait_method, match_def_path, peel_blocks};
+use clippy_utils::{is_from_proc_macro, is_trait_method, peel_blocks};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::{LateContext, LintContext};
@@ -35,7 +34,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, arg: &
         && let ExprKind::Closure(then_closure) = then_arg.kind
         && let then_body = peel_blocks(cx.tcx.hir().body(then_closure.body).value)
         && let Some(def_id) = cx.typeck_results().type_dependent_def_id(value.hir_id)
-        && match_def_path(cx, def_id, &BOOL_THEN)
+        && cx.tcx.is_diagnostic_item(sym::bool_then, def_id)
         && !is_from_proc_macro(cx, expr)
         // Count the number of derefs needed to get to the bool because we need those in the suggestion
         && let needed_derefs = cx.typeck_results().expr_adjustments(recv)

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

@@ -74,4 +74,3 @@
 pub const TOKIO_IO_OPEN_OPTIONS_NEW: [&str; 5] = ["tokio", "fs", "open_options", "OpenOptions", "new"];
 pub const INSTANT_NOW: [&str; 4] = ["std", "time", "Instant", "now"];
 pub const WAKER: [&str; 4] = ["core", "task", "wake", "Waker"];
-pub const BOOL_THEN: [&str; 4] = ["core", "bool", "<impl bool>", "then"];