Rollup merge of #67781 - cjgillot:passes-const, r=oli-obk

Move `is_min_const_fn` query to librustc_mir.

The only two uses of the associated methods are in `librustc_mir` and
`librustdoc`. Please tell me if there is a better choice.

cc #65031

12 files changed, 170 insertions, 168 deletions

diff --git a/src/librustc/ty/constness.rs b/src/librustc/ty/constness.rs
deleted file mode 100644
index cc5131cb217..00000000000
--- a/src/librustc/ty/constness.rs
+++ /dev/null
@@ -1,156 +0,0 @@
-use crate::hir::map::blocks::FnLikeNode;
-use crate::ty::query::Providers;
-use crate::ty::TyCtxt;
-use rustc_hir as hir;
-use rustc_hir::def_id::DefId;
-use rustc_span::symbol::Symbol;
-use rustc_target::spec::abi::Abi;
-use syntax::attr;
-
-impl<'tcx> TyCtxt<'tcx> {
-    /// Whether the `def_id` counts as const fn in your current crate, considering all active
-    /// feature gates
-    pub fn is_const_fn(self, def_id: DefId) -> bool {
-        self.is_const_fn_raw(def_id)
-            && match self.is_unstable_const_fn(def_id) {
-                Some(feature_name) => {
-                    // has a `rustc_const_unstable` attribute, check whether the user enabled the
-                    // corresponding feature gate.
-                    self.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(self, def_id: DefId) -> Option<Symbol> {
-        if self.is_const_fn_raw(def_id) {
-            let const_stab = self.lookup_const_stability(def_id)?;
-            if const_stab.level.is_unstable() { Some(const_stab.feature) } else { None }
-        } else {
-            None
-        }
-    }
-
-    /// Returns `true` if this function must conform to `min_const_fn`
-    pub fn is_min_const_fn(self, def_id: DefId) -> bool {
-        // Bail out if the signature doesn't contain `const`
-        if !self.is_const_fn_raw(def_id) {
-            return false;
-        }
-
-        if self.features().staged_api {
-            // In order for a libstd function to be considered min_const_fn
-            // it needs to be stable and have no `rustc_const_unstable` attribute.
-            match self.lookup_const_stability(def_id) {
-                // `rustc_const_unstable` functions don't need to conform.
-                Some(&attr::ConstStability { ref level, .. }) if level.is_unstable() => false,
-                None => {
-                    if let Some(stab) = self.lookup_stability(def_id) {
-                        if stab.level.is_stable() {
-                            self.sess.span_err(
-                                self.def_span(def_id),
-                                "stable const functions must have either `rustc_const_stable` or \
-                            `rustc_const_unstable` attribute",
-                            );
-                            // While we errored above, because we don't know if we need to conform, we
-                            // err on the "safe" side and require min_const_fn.
-                            true
-                        } else {
-                            // Unstable functions need not conform to min_const_fn.
-                            false
-                        }
-                    } else {
-                        // Internal functions are forced to conform to min_const_fn.
-                        // Annotate the internal function with a const stability attribute if
-                        // you need to use unstable features.
-                        // Note: this is an arbitrary choice that does not affect stability or const
-                        // safety or anything, it just changes whether we need to annotate some
-                        // internal functions with `rustc_const_stable` or with `rustc_const_unstable`
-                        true
-                    }
-                }
-                // Everything else needs to conform, because it would be callable from
-                // other `min_const_fn` functions.
-                _ => true,
-            }
-        } else {
-            // users enabling the `const_fn` feature gate can do what they want
-            !self.features().const_fn
-        }
-    }
-}
-
-pub fn provide(providers: &mut Providers<'_>) {
-    /// Const evaluability whitelist is here to check evaluability at the
-    /// top level beforehand.
-    fn is_const_intrinsic(tcx: TyCtxt<'_>, def_id: DefId) -> Option<bool> {
-        match tcx.fn_sig(def_id).abi() {
-            Abi::RustIntrinsic | Abi::PlatformIntrinsic => {
-                Some(tcx.lookup_const_stability(def_id).is_some())
-            }
-            _ => None,
-        }
-    }
-
-    /// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether
-    /// said intrinsic is on the whitelist for being const callable.
-    fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-        let hir_id = tcx
-            .hir()
-            .as_local_hir_id(def_id)
-            .expect("Non-local call to local provider is_const_fn");
-
-        let node = tcx.hir().get(hir_id);
-
-        if let Some(whitelisted) = is_const_intrinsic(tcx, def_id) {
-            whitelisted
-        } else if let Some(fn_like) = FnLikeNode::from_node(node) {
-            fn_like.constness() == hir::Constness::Const
-        } else if let hir::Node::Ctor(_) = node {
-            true
-        } else {
-            false
-        }
-    }
-
-    fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-        tcx.is_const_fn(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,
-            }
-    }
-
-    fn const_fn_is_allowed_fn_ptr(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-        tcx.is_const_fn(def_id)
-            && tcx
-                .lookup_const_stability(def_id)
-                .map(|stab| stab.allow_const_fn_ptr)
-                .unwrap_or(false)
-    }
-
-    *providers = Providers {
-        is_const_fn_raw,
-        is_promotable_const_fn,
-        const_fn_is_allowed_fn_ptr,
-        ..*providers
-    };
-}
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 7cca12308e6..747e6e8da99 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -97,7 +97,6 @@ pub mod cast;
 #[macro_use]
 pub mod codec;
 pub mod _match;
-mod constness;
 mod erase_regions;
 pub mod error;
 pub mod fast_reject;
@@ -3318,7 +3317,6 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
     context::provide(providers);
     erase_regions::provide(providers);
     layout::provide(providers);
-    constness::provide(providers);
     *providers = ty::query::Providers {
         asyncness,
         associated_item,
diff --git a/src/librustc_mir/const_eval.rs b/src/librustc_mir/const_eval.rs
index ac04ae28588..7b2ce7f9ac7 100644
--- a/src/librustc_mir/const_eval.rs
+++ b/src/librustc_mir/const_eval.rs
@@ -9,10 +9,12 @@ use crate::interpret::{intern_const_alloc_recursive, ConstValue, InterpCx};
 
 mod error;
 mod eval_queries;
+mod fn_queries;
 mod machine;
 
 pub use error::*;
 pub use eval_queries::*;
+pub use fn_queries::*;
 pub use machine::*;
 
 /// Extracts a field of a (variant of a) const.
diff --git a/src/librustc_mir/const_eval/fn_queries.rs b/src/librustc_mir/const_eval/fn_queries.rs
new file mode 100644
index 00000000000..2443e1e91d3
--- /dev/null
+++ b/src/librustc_mir/const_eval/fn_queries.rs
@@ -0,0 +1,151 @@
+use rustc::hir::map::blocks::FnLikeNode;
+use rustc::ty::query::Providers;
+use rustc::ty::TyCtxt;
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_span::symbol::Symbol;
+use rustc_target::spec::abi::Abi;
+use syntax::attr;
+
+/// 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
+    }
+}
+
+/// Returns `true` if this function must conform to `min_const_fn`
+pub fn is_min_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+    // Bail out if the signature doesn't contain `const`
+    if !tcx.is_const_fn_raw(def_id) {
+        return false;
+    }
+
+    if tcx.features().staged_api {
+        // In order for a libstd function to be considered min_const_fn
+        // it needs to be stable and have no `rustc_const_unstable` attribute.
+        match tcx.lookup_const_stability(def_id) {
+            // `rustc_const_unstable` functions don't need to conform.
+            Some(&attr::ConstStability { ref level, .. }) if level.is_unstable() => false,
+            None => {
+                if let Some(stab) = tcx.lookup_stability(def_id) {
+                    if stab.level.is_stable() {
+                        tcx.sess.span_err(
+                            tcx.def_span(def_id),
+                            "stable const functions must have either `rustc_const_stable` or \
+                             `rustc_const_unstable` attribute",
+                        );
+                        // While we errored above, because we don't know if we need to conform, we
+                        // err on the "safe" side and require min_const_fn.
+                        true
+                    } else {
+                        // Unstable functions need not conform to min_const_fn.
+                        false
+                    }
+                } else {
+                    // Internal functions are forced to conform to min_const_fn.
+                    // Annotate the internal function with a const stability attribute if
+                    // you need to use unstable features.
+                    // Note: this is an arbitrary choice that does not affect stability or const
+                    // safety or anything, it just changes whether we need to annotate some
+                    // internal functions with `rustc_const_stable` or with `rustc_const_unstable`
+                    true
+                }
+            }
+            // Everything else needs to conform, because it would be callable from
+            // other `min_const_fn` functions.
+            _ => true,
+        }
+    } else {
+        // users enabling the `const_fn` feature gate can do what they want
+        !tcx.features().const_fn
+    }
+}
+
+pub fn provide(providers: &mut Providers<'_>) {
+    /// Const evaluability whitelist is here to check evaluability at the
+    /// top level beforehand.
+    fn is_const_intrinsic(tcx: TyCtxt<'_>, def_id: DefId) -> Option<bool> {
+        match tcx.fn_sig(def_id).abi() {
+            Abi::RustIntrinsic | Abi::PlatformIntrinsic => {
+                Some(tcx.lookup_const_stability(def_id).is_some())
+            }
+            _ => None,
+        }
+    }
+
+    /// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether
+    /// said intrinsic is on the whitelist for being const callable.
+    fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+        let hir_id = tcx
+            .hir()
+            .as_local_hir_id(def_id)
+            .expect("Non-local call to local provider is_const_fn");
+
+        let node = tcx.hir().get(hir_id);
+
+        if let Some(whitelisted) = is_const_intrinsic(tcx, def_id) {
+            whitelisted
+        } else if let Some(fn_like) = FnLikeNode::from_node(node) {
+            fn_like.constness() == hir::Constness::Const
+        } else if let hir::Node::Ctor(_) = node {
+            true
+        } else {
+            false
+        }
+    }
+
+    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,
+            }
+    }
+
+    fn const_fn_is_allowed_fn_ptr(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+        is_const_fn(tcx, def_id)
+            && tcx
+                .lookup_const_stability(def_id)
+                .map(|stab| stab.allow_const_fn_ptr)
+                .unwrap_or(false)
+    }
+
+    *providers = Providers {
+        is_const_fn_raw,
+        is_promotable_const_fn,
+        const_fn_is_allowed_fn_ptr,
+        ..*providers
+    };
+}
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index 9f70f1dd576..36c6568029d 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -52,6 +52,7 @@ use rustc::ty::query::Providers;
 
 pub fn provide(providers: &mut Providers<'_>) {
     borrow_check::provide(providers);
+    const_eval::provide(providers);
     shim::provide(providers);
     transform::provide(providers);
     monomorphize::partitioning::provide(providers);
diff --git a/src/librustc_mir/transform/check_consts/validation.rs b/src/librustc_mir/transform/check_consts/validation.rs
index 0aa42de538d..b8183972476 100644
--- a/src/librustc_mir/transform/check_consts/validation.rs
+++ b/src/librustc_mir/transform/check_consts/validation.rs
@@ -21,6 +21,7 @@ use super::ops::{self, NonConstOp};
 use super::qualifs::{self, HasMutInterior, NeedsDrop};
 use super::resolver::FlowSensitiveAnalysis;
 use super::{is_lang_panic_fn, ConstKind, Item, Qualif};
+use crate::const_eval::{is_const_fn, is_unstable_const_fn};
 use crate::dataflow::{self as old_dataflow, generic as dataflow};
 
 pub type IndirectlyMutableResults<'mir, 'tcx> =
@@ -173,7 +174,7 @@ impl Validator<'a, 'mir, 'tcx> {
         let Item { tcx, body, def_id, const_kind, .. } = *self.item;
 
         let use_min_const_fn_checks = (const_kind == Some(ConstKind::ConstFn)
-            && tcx.is_min_const_fn(def_id))
+            && crate::const_eval::is_min_const_fn(tcx, def_id))
             && !tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you;
 
         if use_min_const_fn_checks {
@@ -560,13 +561,13 @@ impl Visitor<'tcx> for Validator<'_, 'mir, 'tcx> {
                 };
 
                 // At this point, we are calling a function whose `DefId` is known...
-                if self.tcx.is_const_fn(def_id) {
+                if is_const_fn(self.tcx, def_id) {
                     return;
                 }
 
                 if is_lang_panic_fn(self.tcx, def_id) {
                     self.check_op(ops::Panic);
-                } else if let Some(feature) = self.tcx.is_unstable_const_fn(def_id) {
+                } else if let Some(feature) = is_unstable_const_fn(self.tcx, def_id) {
                     // Exempt unstable const fns inside of macros with
                     // `#[allow_internal_unstable]`.
                     if !self.span.allows_unstable(feature) {
diff --git a/src/librustc_mir/transform/check_unsafety.rs b/src/librustc_mir/transform/check_unsafety.rs
index 5cf5c54dd48..d07e58b7447 100644
--- a/src/librustc_mir/transform/check_unsafety.rs
+++ b/src/librustc_mir/transform/check_unsafety.rs
@@ -14,6 +14,7 @@ use rustc_span::symbol::{sym, Symbol};
 
 use std::ops::Bound;
 
+use crate::const_eval::{is_const_fn, is_min_const_fn};
 use crate::util;
 
 use rustc_error_codes::*;
@@ -523,7 +524,7 @@ fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult
     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
         hir::BodyOwnerKind::Closure => (false, false),
-        hir::BodyOwnerKind::Fn => (tcx.is_const_fn(def_id), tcx.is_min_const_fn(def_id)),
+        hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
     };
     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
diff --git a/src/librustc_mir/transform/promote_consts.rs b/src/librustc_mir/transform/promote_consts.rs
index b6656e720c5..00a39905c02 100644
--- a/src/librustc_mir/transform/promote_consts.rs
+++ b/src/librustc_mir/transform/promote_consts.rs
@@ -29,6 +29,7 @@ use rustc_target::spec::abi::Abi;
 use std::cell::Cell;
 use std::{iter, mem, usize};
 
+use crate::const_eval::{is_const_fn, is_unstable_const_fn};
 use crate::transform::check_consts::{is_lang_panic_fn, qualifs, ConstKind, Item};
 use crate::transform::{MirPass, MirSource};
 
@@ -702,8 +703,8 @@ impl<'tcx> Validator<'_, 'tcx> {
 
         let is_const_fn = match fn_ty.kind {
             ty::FnDef(def_id, _) => {
-                self.tcx.is_const_fn(def_id)
-                    || self.tcx.is_unstable_const_fn(def_id).is_some()
+                is_const_fn(self.tcx, def_id)
+                    || is_unstable_const_fn(self.tcx, def_id).is_some()
                     || is_lang_panic_fn(self.tcx, self.def_id)
             }
             _ => false,
diff --git a/src/librustc_mir/transform/qualify_min_const_fn.rs b/src/librustc_mir/transform/qualify_min_const_fn.rs
index 9dea44e0200..fcdabb29cd0 100644
--- a/src/librustc_mir/transform/qualify_min_const_fn.rs
+++ b/src/librustc_mir/transform/qualify_min_const_fn.rs
@@ -327,7 +327,7 @@ fn check_terminator(
         TerminatorKind::Call { func, args, from_hir_call: _, destination: _, cleanup: _ } => {
             let fn_ty = func.ty(body, tcx);
             if let ty::FnDef(def_id, _) = fn_ty.kind {
-                if !tcx.is_min_const_fn(def_id) {
+                if !crate::const_eval::is_min_const_fn(tcx, def_id) {
                     return Err((
                         span,
                         format!(
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 2400dded666..c7e0f1e9e70 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -9,6 +9,7 @@ use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::Mutability;
 use rustc_metadata::creader::LoadedMacro;
+use rustc_mir::const_eval::is_min_const_fn;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
@@ -212,7 +213,7 @@ fn build_external_function(cx: &DocContext<'_>, did: DefId) -> clean::Function {
     let sig = cx.tcx.fn_sig(did);
 
     let constness =
-        if cx.tcx.is_min_const_fn(did) { hir::Constness::Const } else { hir::Constness::NotConst };
+        if is_min_const_fn(cx.tcx, did) { hir::Constness::Const } else { hir::Constness::NotConst };
     let asyncness = cx.tcx.asyncness(did);
     let predicates = cx.tcx.predicates_of(did);
     let (generics, decl) = clean::enter_impl_trait(cx, || {
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index bb46a15258e..be9654612f5 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -21,6 +21,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX};
 use rustc_index::vec::{Idx, IndexVec};
+use rustc_mir::const_eval::is_min_const_fn;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::{self, Pos};
@@ -895,7 +896,7 @@ impl Clean<Item> for doctree::Function<'_> {
             enter_impl_trait(cx, || (self.generics.clean(cx), (self.decl, self.body).clean(cx)));
 
         let did = cx.tcx.hir().local_def_id(self.id);
-        let constness = if cx.tcx.is_min_const_fn(did) {
+        let constness = if is_min_const_fn(cx.tcx, did) {
             hir::Constness::Const
         } else {
             hir::Constness::NotConst
@@ -1187,7 +1188,7 @@ impl Clean<Item> for ty::AssocItem {
                 };
                 let (all_types, ret_types) = get_all_types(&generics, &decl, cx);
                 if provided {
-                    let constness = if cx.tcx.is_min_const_fn(self.def_id) {
+                    let constness = if is_min_const_fn(cx.tcx, self.def_id) {
                         hir::Constness::Const
                     } else {
                         hir::Constness::NotConst
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index eeaac1d8c74..32c93ee3b16 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -32,6 +32,7 @@ extern crate rustc_interface;
 extern crate rustc_lexer;
 extern crate rustc_lint;
 extern crate rustc_metadata;
+extern crate rustc_mir;
 extern crate rustc_parse;
 extern crate rustc_resolve;
 extern crate rustc_span as rustc_span;