nits

compiler/rustc_middle/src/mir/query.rs

 //! Values computed by queries that use MIR.
 
 use crate::mir::{Body, Promoted};
-use crate::thir::abstract_const;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::vec_map::VecMap;
@@ -432,16 +431,4 @@ pub fn mir_for_ctfe_opt_const_arg(self, def: ty::WithOptConstParam<DefId>) -> &'
             self.mir_for_ctfe(def.did)
         }
     }
-
-    #[inline]
-    pub fn thir_abstract_const_opt_const_arg(
-        self,
-        def: ty::WithOptConstParam<DefId>,
-    ) -> Result<Option<&'tcx [abstract_const::Node<'tcx>]>, ErrorReported> {
-        if let Some((did, param_did)) = def.as_const_arg() {
-            self.thir_abstract_const_of_const_arg((did, param_did))
-        } else {
-            self.thir_abstract_const(def.did)
-        }
-    }
 }

compiler/rustc_middle/src/thir/abstract_const.rs

 //! A subset of a mir body used for const evaluatability checking.
 use crate::mir;
-use crate::ty::{self, Ty};
+use crate::ty::{self, Ty, TyCtxt};
+use rustc_errors::ErrorReported;
 
 rustc_index::newtype_index! {
     /// An index into an `AbstractConst`.
@@ -22,13 +23,13 @@ pub enum Node<'tcx> {
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
 pub enum NotConstEvaluatable {
-    Error(rustc_errors::ErrorReported),
+    Error(ErrorReported),
     MentionsInfer,
     MentionsParam,
 }
 
-impl From<rustc_errors::ErrorReported> for NotConstEvaluatable {
-    fn from(e: rustc_errors::ErrorReported) -> NotConstEvaluatable {
+impl From<ErrorReported> for NotConstEvaluatable {
+    fn from(e: ErrorReported) -> NotConstEvaluatable {
         NotConstEvaluatable::Error(e)
     }
 }
@@ -36,3 +37,17 @@ fn from(e: rustc_errors::ErrorReported) -> NotConstEvaluatable {
 TrivialTypeFoldableAndLiftImpls! {
     NotConstEvaluatable,
 }
+
+impl<'tcx> TyCtxt<'tcx> {
+    #[inline]
+    pub fn thir_abstract_const_opt_const_arg(
+        self,
+        def: ty::WithOptConstParam<rustc_hir::def_id::DefId>,
+    ) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorReported> {
+        if let Some((did, param_did)) = def.as_const_arg() {
+            self.thir_abstract_const_of_const_arg((did, param_did))
+        } else {
+            self.thir_abstract_const(def.did)
+        }
+    }
+}

compiler/rustc_middle/src/thir/visit.rs

-use super::*;
+use super::{
+    Arm, Block, Expr, ExprKind, Guard, InlineAsmOperand, Pat, PatKind, Stmt, StmtKind, Thir,
+};
+use rustc_middle::ty::Const;
+
 pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn thir(&self) -> &'a Thir<'tcx>;
 

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -8,7 +8,6 @@
 //! In this case we try to build an abstract representation of this constant using
 //! `thir_abstract_const` which can then be checked for structural equality with other
 //! generic constants mentioned in the `caller_bounds` of the current environment.
-use rustc_data_structures::sync::Lrc;
 use rustc_errors::ErrorReported;
 use rustc_hir::def::DefKind;
 use rustc_index::vec::IndexVec;
@@ -227,8 +226,7 @@ pub fn root(self) -> Node<'tcx> {
 struct AbstractConstBuilder<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
     body_id: thir::ExprId,
-    /// `Lrc` is used to avoid borrowck difficulties in `recurse_build`
-    body: Lrc<&'a thir::Thir<'tcx>>,
+    body: &'a thir::Thir<'tcx>,
     /// The current WIP node tree.
     nodes: IndexVec<NodeId, Node<'tcx>>,
 }
@@ -253,8 +251,7 @@ fn new(
         tcx: TyCtxt<'tcx>,
         (body, body_id): (&'a thir::Thir<'tcx>, thir::ExprId),
     ) -> Result<Option<AbstractConstBuilder<'a, 'tcx>>, ErrorReported> {
-        let builder =
-            AbstractConstBuilder { tcx, body_id, body: Lrc::new(body), nodes: IndexVec::new() };
+        let builder = AbstractConstBuilder { tcx, body_id, body, nodes: IndexVec::new() };
 
         struct IsThirPolymorphic<'a, 'tcx> {
             is_poly: bool,
@@ -328,7 +325,7 @@ fn build(mut self) -> Result<&'tcx [Node<'tcx>], ErrorReported> {
 
     fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported> {
         use thir::ExprKind;
-        let node = &self.body.clone().exprs[node];
+        let node = &self.body.exprs[node];
         debug!("recurse_build: node={:?}", node);
         Ok(match &node.kind {
             // I dont know if handling of these 3 is correct
@@ -338,10 +335,9 @@ fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported>
 
             // subtle: associated consts are literals this arm handles
             // `<T as Trait>::ASSOC` as well as `12`
-            &ExprKind::Literal { literal, .. }
-            | &ExprKind::StaticRef { literal, .. } => self.nodes.push(Node::Leaf(literal)),
+            &ExprKind::Literal { literal, .. } => self.nodes.push(Node::Leaf(literal)),
 
-            // FIXME(generic_const_exprs) handle `from_hir_call` field
+            // FIXME(generic_const_exprs): Handle `from_hir_call` field
             ExprKind::Call { fun, args,  .. } => {
                 let fun = self.recurse_build(*fun)?;
 
@@ -361,7 +357,7 @@ fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported>
                 let arg = self.recurse_build(arg)?;
                 self.nodes.push(Node::UnaryOp(op, arg))
             },
-            // this is necessary so that the following compiles:
+            // This is necessary so that the following compiles:
             //
             // ```
             // fn foo<const N: usize>(a: [(); N + 1]) {
@@ -369,16 +365,16 @@ fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported>
             // }
             // ```
             ExprKind::Block { body: thir::Block { stmts: box [], expr: Some(e), .. }} => self.recurse_build(*e)?,
-            // ExprKind::Use happens when a `hir::ExprKind::Cast` is a
+            // `ExprKind::Use` happens when a `hir::ExprKind::Cast` is a
             // "coercion cast" i.e. using a coercion or is a no-op.
-            // this is important so that `N as usize as usize` doesnt unify with `N as usize`
+            // This is important so that `N as usize as usize` doesnt unify with `N as usize`. (untested)
             &ExprKind::Use { source}
             | &ExprKind::Cast { source } => {
                 let arg = self.recurse_build(source)?;
                 self.nodes.push(Node::Cast(arg, node.ty))
             },
 
-            // FIXME(generic_const_exprs) we want to support these
+            // FIXME(generic_const_exprs): We may want to support these.
             ExprKind::AddressOf { .. }
             | ExprKind::Borrow { .. }
             | ExprKind::Deref { .. }
@@ -390,21 +386,24 @@ fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported>
             | ExprKind::Index { .. }
             | ExprKind::Field { .. }
             | ExprKind::ConstBlock { .. }
-            | ExprKind::Adt(_) => return self.error(
+            | ExprKind::Adt(_) => self.error(
                     Some(node.span),
                     "unsupported operation in generic constant, this may be supported in the future",
-                ).map(|never| never),
+                )?,
 
             ExprKind::Match { .. }
-            | ExprKind::VarRef { .. } //
-            | ExprKind::UpvarRef { .. } // we dont permit let stmts so...
+            // we dont permit let stmts so `VarRef` and `UpvarRef` cant happen
+            | ExprKind::VarRef { .. }
+            | ExprKind::UpvarRef { .. }
             | ExprKind::Closure { .. }
             | ExprKind::Let { .. } // let expressions imply control flow
             | ExprKind::Loop { .. }
             | ExprKind::Assign { .. }
+            | ExprKind::StaticRef { .. }
             | ExprKind::LogicalOp { .. }
-            | ExprKind::Unary { .. } //
-            | ExprKind::Binary { .. } // we handle valid unary/binary ops above
+            // we handle valid unary/binary ops above
+            | ExprKind::Unary { .. }
+            | ExprKind::Binary { .. }
             | ExprKind::Break { .. }
             | ExprKind::Continue { .. }
             | ExprKind::If { .. }
@@ -415,7 +414,7 @@ fn recurse_build(&mut self, node: thir::ExprId) -> Result<NodeId, ErrorReported>
             | ExprKind::Box { .. } // allocations not allowed in constants
             | ExprKind::AssignOp { .. }
             | ExprKind::InlineAsm { .. }
-            | ExprKind::Yield { .. } => return self.error(Some(node.span), "unsupported operation in generic constant").map(|never| never),
+            | ExprKind::Yield { .. } => self.error(Some(node.span), "unsupported operation in generic constant")?,
         })
     }
 }