add utils is_inside_always_const_context

Author: tesuji

clippy_lints/src/default_numeric_fallback.rs

@@ -51,6 +51,7 @@ declare_lint_pass!(DefaultNumericFallback => [DEFAULT_NUMERIC_FALLBACK]);
 impl<'tcx> LateLintPass<'tcx> for DefaultNumericFallback {
     fn check_body(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
         let hir = cx.tcx.hir();
+        // FIXME: maybe use `clippy_utils::is_inside_always_const_context` instead.
         let is_parent_const = matches!(
             hir.body_const_context(hir.body_owner_def_id(body.id())),
             Some(ConstContext::Const { inline: false } | ConstContext::Static(_))

clippy_lints/src/no_effect.rs

@@ -1,4 +1,5 @@
 use clippy_utils::diagnostics::{span_lint_hir, span_lint_hir_and_then};
+use clippy_utils::qualify_min_const_fn::is_inside_always_const_context;
 use clippy_utils::source::snippet_opt;
 use clippy_utils::ty::has_drop;
 use clippy_utils::{any_parent_is_automatically_derived, is_lint_allowed, path_to_local, peel_blocks};

clippy_utils/src/qualify_min_const_fn.rs

@@ -9,6 +9,7 @@ use rustc_attr::StableSince;
 use rustc_const_eval::transform::check_consts::ConstCx;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_hir::{ConstContext, HirId};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::Obligation;
 use rustc_middle::mir::{
@@ -398,6 +399,18 @@ fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId, msrv: &Msrv) -> bool {
         })
 }
 
+pub fn is_inside_always_const_context(tcx: TyCtxt<'_>, hir_id: HirId) -> bool {
+    use ConstContext::{Const, ConstFn, Static};
+    let hir = tcx.hir();
+    let Some(ctx) = hir.body_const_context(hir.enclosing_body_owner(hir_id)) else {
+        return false;
+    };
+    match ctx {
+        ConstFn => false,
+        Static(_) | Const { inline: _ } => true,
+    }
+}
+
 fn is_ty_const_destruct<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, body: &Body<'tcx>) -> bool {
     // FIXME(effects, fee1-dead) revert to const destruct once it works again
     #[expect(unused)]