Auto merge of rust-lang#139768 - compiler-errors:split-fold, r=lcnr

Split `TypeFolder` and `FallibleTypeFolder` atwain

Right now there is a coherence problem with `TypeFolder` and `FallibleTypeFolder`. Namely, it's impossible to implement a `FallibleTypeFolder` that is generic over interner, b/c it has a *downstream* conflict with the blanket impl:

```
impl<I, F> FallibleTypeFolder<I> for F where F: TypeFolder<I> {}
```

Because downstream crates may implement `TypeFolder<SomeLocalInterner>` for the fallible type folder.

This PR removes the relationship between `FallibleTypeFolder` and `TypeFolder`; it leads to *modest* code duplication, but otherwise does not affect perf and really doesn't matter in general.

Author: bors

Diff for: compiler/rustc_infer/src/traits/mod.rs

@@ -12,6 +12,7 @@ use std::hash::{Hash, Hasher};
 
 use hir::def_id::LocalDefId;
 use rustc_hir as hir;
+use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::Certainty;
 pub use rustc_middle::traits::*;
@@ -35,9 +36,11 @@ use crate::infer::InferCtxt;
 /// either identifying an `impl` (e.g., `impl Eq for i32`) that
 /// satisfies the obligation, or else finding a bound that is in
 /// scope. The eventual result is usually a `Selection` (defined below).
-#[derive(Clone)]
+#[derive(Clone, TypeFoldable, TypeVisitable)]
 pub struct Obligation<'tcx, T> {
     /// The reason we have to prove this thing.
+    #[type_foldable(identity)]
+    #[type_visitable(ignore)]
     pub cause: ObligationCause<'tcx>,
 
     /// The environment in which we should prove this thing.
@@ -51,6 +54,8 @@ pub struct Obligation<'tcx, T> {
     /// If this goes over a certain threshold, we abort compilation --
     /// in such cases, we can not say whether or not the predicate
     /// holds for certain. Stupid halting problem; such a drag.
+    #[type_foldable(identity)]
+    #[type_visitable(ignore)]
     pub recursion_depth: usize,
 }
 

Diff for: compiler/rustc_infer/src/traits/structural_impls.rs

@@ -1,8 +1,6 @@
 use std::fmt;
 
-use rustc_middle::ty::{
-    self, FallibleTypeFolder, TyCtxt, TypeFoldable, TypeVisitable, TypeVisitor, try_visit,
-};
+use rustc_middle::ty;
 
 use crate::traits;
 use crate::traits::project::Normalized;
@@ -34,31 +32,3 @@ impl<'tcx> fmt::Debug for traits::MismatchedProjectionTypes<'tcx> {
         write!(f, "MismatchedProjectionTypes({:?})", self.err)
     }
 }
-
-///////////////////////////////////////////////////////////////////////////
-// TypeFoldable implementations.
-
-impl<'tcx, O: TypeFoldable<TyCtxt<'tcx>>> TypeFoldable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        Ok(traits::Obligation {
-            cause: self.cause,
-            recursion_depth: self.recursion_depth,
-            predicate: self.predicate.try_fold_with(folder)?,
-            param_env: self.param_env.try_fold_with(folder)?,
-        })
-    }
-}
-
-impl<'tcx, O: TypeVisitable<TyCtxt<'tcx>>> TypeVisitable<TyCtxt<'tcx>>
-    for traits::Obligation<'tcx, O>
-{
-    fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(&self, visitor: &mut V) -> V::Result {
-        try_visit!(self.predicate.visit_with(visitor));
-        self.param_env.visit_with(visitor)
-    }
-}

Diff for: compiler/rustc_macros/src/type_foldable.rs

@@ -14,27 +14,13 @@ pub(super) fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_m
 
     s.add_bounds(synstructure::AddBounds::Generics);
     s.bind_with(|_| synstructure::BindStyle::Move);
-    let body_fold = s.each_variant(|vi| {
+    let try_body_fold = s.each_variant(|vi| {
         let bindings = vi.bindings();
         vi.construct(|_, index| {
             let bind = &bindings[index];
 
-            let mut fixed = false;
-
             // retain value of fields with #[type_foldable(identity)]
-            bind.ast().attrs.iter().for_each(|x| {
-                if !x.path().is_ident("type_foldable") {
-                    return;
-                }
-                let _ = x.parse_nested_meta(|nested| {
-                    if nested.path.is_ident("identity") {
-                        fixed = true;
-                    }
-                    Ok(())
-                });
-            });
-
-            if fixed {
+            if has_ignore_attr(&bind.ast().attrs, "type_foldable", "identity") {
                 bind.to_token_stream()
             } else {
                 quote! {
@@ -44,15 +30,55 @@ pub(super) fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_m
         })
     });
 
+    let body_fold = s.each_variant(|vi| {
+        let bindings = vi.bindings();
+        vi.construct(|_, index| {
+            let bind = &bindings[index];
+
+            // retain value of fields with #[type_foldable(identity)]
+            if has_ignore_attr(&bind.ast().attrs, "type_foldable", "identity") {
+                bind.to_token_stream()
+            } else {
+                quote! {
+                    ::rustc_middle::ty::TypeFoldable::fold_with(#bind, __folder)
+                }
+            }
+        })
+    });
+
     s.bound_impl(
         quote!(::rustc_middle::ty::TypeFoldable<::rustc_middle::ty::TyCtxt<'tcx>>),
         quote! {
             fn try_fold_with<__F: ::rustc_middle::ty::FallibleTypeFolder<::rustc_middle::ty::TyCtxt<'tcx>>>(
                 self,
                 __folder: &mut __F
             ) -> Result<Self, __F::Error> {
-                Ok(match self { #body_fold })
+                Ok(match self { #try_body_fold })
+            }
+
+            fn fold_with<__F: ::rustc_middle::ty::TypeFolder<::rustc_middle::ty::TyCtxt<'tcx>>>(
+                self,
+                __folder: &mut __F
+            ) -> Self {
+                match self { #body_fold }
             }
         },
     )
 }
+
+fn has_ignore_attr(attrs: &[syn::Attribute], name: &'static str, meta: &'static str) -> bool {
+    let mut ignored = false;
+    attrs.iter().for_each(|attr| {
+        if !attr.path().is_ident(name) {
+            return;
+        }
+        let _ = attr.parse_nested_meta(|nested| {
+            if nested.path.is_ident(meta) {
+                ignored = true;
+            }
+            Ok(())
+        });
+    });
+
+    ignored
+}

Diff for: compiler/rustc_middle/src/infer/canonical.rs

@@ -39,15 +39,6 @@ pub type CanonicalVarInfo<'tcx> = ir::CanonicalVarInfo<TyCtxt<'tcx>>;
 pub type CanonicalVarValues<'tcx> = ir::CanonicalVarValues<TyCtxt<'tcx>>;
 pub type CanonicalVarInfos<'tcx> = &'tcx List<CanonicalVarInfo<'tcx>>;
 
-impl<'tcx> ty::TypeFoldable<TyCtxt<'tcx>> for CanonicalVarInfos<'tcx> {
-    fn try_fold_with<F: ty::FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_canonical_var_infos(v))
-    }
-}
-
 /// When we canonicalize a value to form a query, we wind up replacing
 /// various parts of it with canonical variables. This struct stores
 /// those replaced bits to remember for when we process the query

Diff for: compiler/rustc_middle/src/mir/syntax.rs

@@ -931,6 +931,8 @@ pub enum TerminatorKind<'tcx> {
         asm_macro: InlineAsmMacro,
 
         /// The template for the inline assembly, with placeholders.
+        #[type_foldable(identity)]
+        #[type_visitable(ignore)]
         template: &'tcx [InlineAsmTemplatePiece],
 
         /// The operands for the inline assembly, as `Operand`s or `Place`s.
@@ -941,6 +943,8 @@ pub enum TerminatorKind<'tcx> {
 
         /// Source spans for each line of the inline assembly code. These are
         /// used to map assembler errors back to the line in the source code.
+        #[type_foldable(identity)]
+        #[type_visitable(ignore)]
         line_spans: &'tcx [Span],
 
         /// Valid targets for the inline assembly.

Diff for: compiler/rustc_middle/src/ty/generic_args.rs

@@ -17,7 +17,7 @@ use smallvec::SmallVec;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::{
     self, ClosureArgs, CoroutineArgs, CoroutineClosureArgs, FallibleTypeFolder, InlineConstArgs,
-    Lift, List, Ty, TyCtxt, TypeFoldable, TypeVisitable, TypeVisitor, VisitorResult,
+    Lift, List, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor, VisitorResult,
     walk_visitable_list,
 };
 
@@ -337,6 +337,14 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for GenericArg<'tcx> {
             GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
         }
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        match self.unpack() {
+            GenericArgKind::Lifetime(lt) => lt.fold_with(folder).into(),
+            GenericArgKind::Type(ty) => ty.fold_with(folder).into(),
+            GenericArgKind::Const(ct) => ct.fold_with(folder).into(),
+        }
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for GenericArg<'tcx> {
@@ -606,6 +614,27 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for GenericArgsRef<'tcx> {
                 }
             }
             0 => Ok(self),
+            _ => ty::util::try_fold_list(self, folder, |tcx, v| tcx.mk_args(v)),
+        }
+    }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        // See justification for this behavior in `try_fold_with`.
+        match self.len() {
+            1 => {
+                let param0 = self[0].fold_with(folder);
+                if param0 == self[0] { self } else { folder.cx().mk_args(&[param0]) }
+            }
+            2 => {
+                let param0 = self[0].fold_with(folder);
+                let param1 = self[1].fold_with(folder);
+                if param0 == self[0] && param1 == self[1] {
+                    self
+                } else {
+                    folder.cx().mk_args(&[param0, param1])
+                }
+            }
+            0 => self,
             _ => ty::util::fold_list(self, folder, |tcx, v| tcx.mk_args(v)),
         }
     }
@@ -641,6 +670,22 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<Ty<'tcx>> {
                     Ok(folder.cx().mk_type_list(&[param0, param1]))
                 }
             }
+            _ => ty::util::try_fold_list(self, folder, |tcx, v| tcx.mk_type_list(v)),
+        }
+    }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        // See comment justifying behavior in `try_fold_with`.
+        match self.len() {
+            2 => {
+                let param0 = self[0].fold_with(folder);
+                let param1 = self[1].fold_with(folder);
+                if param0 == self[0] && param1 == self[1] {
+                    self
+                } else {
+                    folder.cx().mk_type_list(&[param0, param1])
+                }
+            }
             _ => ty::util::fold_list(self, folder, |tcx, v| tcx.mk_type_list(v)),
         }
     }

Diff for: compiler/rustc_middle/src/ty/mod.rs

@@ -537,6 +537,13 @@ impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for Term<'tcx> {
             ty::TermKind::Const(ct) => ct.try_fold_with(folder).map(Into::into),
         }
     }
+
+    fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
+        match self.unpack() {
+            ty::TermKind::Ty(ty) => ty.fold_with(folder).into(),
+            ty::TermKind::Const(ct) => ct.fold_with(folder).into(),
+        }
+    }
 }
 
 impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for Term<'tcx> {