add utils is_inside_always_const_context

Author: tesuji

clippy_lints/src/default_numeric_fallback.rs

@@ -51,6 +51,8 @@ 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();
+        // NOTE: this is different from `clippy_utils::is_inside_always_const_context`.
+        // Inline const supports type inference.
         let is_parent_const = matches!(
             hir.body_const_context(hir.body_owner_def_id(body.id())),
             Some(ConstContext::Const { inline: false } | ConstContext::Static(_))

clippy_utils/src/lib.rs

@@ -208,7 +208,10 @@ pub fn local_is_initialized(cx: &LateContext<'_>, local: HirId) -> bool {
     false
 }
 
-/// Returns `true` if the given `NodeId` is inside a constant context
+/// Returns `true` if the given `HirId` is inside a constant context.
+///
+/// This is the same as `is_inside_always_const_context`, but also includes
+/// `const fn`.
 ///
 /// # Example
 ///
@@ -221,6 +224,24 @@ pub fn in_constant(cx: &LateContext<'_>, id: HirId) -> bool {
     cx.tcx.hir().is_inside_const_context(id)
 }
 
+/// Returns `true` if the given `HirId` is inside an always constant context.
+///
+/// This context includes:
+///  * const/static items
+///  * const blocks (or inline consts)
+///  * associated constants
+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,
+    }
+}
+
 /// Checks if a `Res` refers to a constructor of a `LangItem`
 /// For example, use this to check whether a function call or a pattern is `Some(..)`.
 pub fn is_res_lang_ctor(cx: &LateContext<'_>, res: Res, lang_item: LangItem) -> bool {