Make the inline field on the Const ConstContext more clearly targetted at what it does

Author: oli-obk

compiler/rustc_hir/src/hir.rs

@@ -2264,10 +2264,12 @@ pub enum ConstContext {
     /// - Array length expressions
     /// - Enum discriminants
     /// - Const generics
-    ///
-    /// For the most part, other contexts are treated just like a regular `const`, so they are
-    /// lumped into the same category.
-    Const { inline: bool },
+    Const {
+        /// For backwards compatibility `const` items allow
+        /// calls to `const fn` to get promoted.
+        /// We forbid that in comptime fns and inline consts.
+        allow_const_fn_promotion: bool,
+    },
 }
 
 impl ConstContext {

compiler/rustc_middle/src/hir/map.rs

@@ -314,13 +314,15 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn hir_body_const_context(self, def_id: LocalDefId) -> Option<ConstContext> {
         let def_id = def_id.into();
         let ccx = match self.hir_body_owner_kind(def_id) {
-            BodyOwnerKind::Const { inline } => ConstContext::Const { inline },
+            BodyOwnerKind::Const { inline } => {
+                ConstContext::Const { allow_const_fn_promotion: !inline }
+            }
             BodyOwnerKind::Static(mutability) => ConstContext::Static(mutability),
 
             BodyOwnerKind::Fn if self.is_constructor(def_id) => return None,
             BodyOwnerKind::Fn | BodyOwnerKind::Closure if self.is_const_fn(def_id) => {
                 if self.constness(def_id) == rustc_hir::Constness::Comptime {
-                    ConstContext::Const { inline: true }
+                    ConstContext::Const { allow_const_fn_promotion: false }
                 } else {
                     ConstContext::ConstFn
                 }

compiler/rustc_mir_transform/src/promote_consts.rs

@@ -668,7 +668,10 @@ impl<'tcx> Validator<'_, 'tcx> {
         // backwards compatibility reason to allow more promotion inside of them.
         let promote_all_fn = matches!(
             self.const_kind,
-            Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { inline: false })
+            Some(
+                hir::ConstContext::Static(_)
+                    | hir::ConstContext::Const { allow_const_fn_promotion: false }
+            )
         );
         if !promote_all_fn {
             return Err(Unpromotable);