Rename rustc_mir to rustc_const_eval.

compiler/rustc_const_eval/src/const_eval/fn_queries.rs

@@ -0,0 +1,112 @@
+use rustc_hir as hir;
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_middle::hir::map::blocks::FnLikeNode;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::symbol::Symbol;
+use rustc_target::spec::abi::Abi;
+
+/// Whether the `def_id` counts as const fn in your current crate, considering all active
+/// feature gates
+pub fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    tcx.is_const_fn_raw(def_id)
+        && match is_unstable_const_fn(tcx, def_id) {
+            Some(feature_name) => {
+                // has a `rustc_const_unstable` attribute, check whether the user enabled the
+                // corresponding feature gate.
+                tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == feature_name)
+            }
+            // functions without const stability are either stable user written
+            // const fn or the user is using feature gates and we thus don't
+            // care what they do
+            None => true,
+        }
+}
+
+/// Whether the `def_id` is an unstable const fn and what feature gate is necessary to enable it
+pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
+    if tcx.is_const_fn_raw(def_id) {
+        let const_stab = tcx.lookup_const_stability(def_id)?;
+        if const_stab.level.is_unstable() { Some(const_stab.feature) } else { None }
+    } else {
+        None
+    }
+}
+
+pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
+    let parent_id = tcx.hir().get_parent_did(hir_id);
+    if !parent_id.is_top_level_module() { is_const_impl_raw(tcx, parent_id) } else { false }
+}
+
+/// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether
+/// said intrinsic has a `rustc_const_{un,}stable` attribute.
+fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
+
+    let node = tcx.hir().get(hir_id);
+
+    if let hir::Node::ForeignItem(hir::ForeignItem { kind: hir::ForeignItemKind::Fn(..), .. }) =
+        node
+    {
+        // Intrinsics use `rustc_const_{un,}stable` attributes to indicate constness. All other
+        // foreign items cannot be evaluated at compile-time.
+        if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = tcx.hir().get_foreign_abi(hir_id) {
+            tcx.lookup_const_stability(def_id).is_some()
+        } else {
+            false
+        }
+    } else if let Some(fn_like) = FnLikeNode::from_node(node) {
+        if fn_like.constness() == hir::Constness::Const {
+            return true;
+        }
+
+        // If the function itself is not annotated with `const`, it may still be a `const fn`
+        // if it resides in a const trait impl.
+        is_parent_const_impl_raw(tcx, hir_id)
+    } else if let hir::Node::Ctor(_) = node {
+        true
+    } else {
+        false
+    }
+}
+
+/// Checks whether the given item is an `impl` that has a `const` modifier.
+fn is_const_impl_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+    let node = tcx.hir().get(hir_id);
+    matches!(
+        node,
+        hir::Node::Item(hir::Item {
+            kind: hir::ItemKind::Impl(hir::Impl { constness: hir::Constness::Const, .. }),
+            ..
+        })
+    )
+}
+
+fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    is_const_fn(tcx, def_id)
+        && match tcx.lookup_const_stability(def_id) {
+            Some(stab) => {
+                if cfg!(debug_assertions) && stab.promotable {
+                    let sig = tcx.fn_sig(def_id);
+                    assert_eq!(
+                        sig.unsafety(),
+                        hir::Unsafety::Normal,
+                        "don't mark const unsafe fns as promotable",
+                        // https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682
+                    );
+                }
+                stab.promotable
+            }
+            None => false,
+        }
+}
+
+pub fn provide(providers: &mut Providers) {
+    *providers = Providers {
+        is_const_fn_raw,
+        is_const_impl_raw: |tcx, def_id| is_const_impl_raw(tcx, def_id.expect_local()),
+        is_promotable_const_fn,
+        ..*providers
+    };
+}