Auto merge of #143897 - cjgillot:derive-walk, r=<try>

Implement AST visitors using a derive macro.

AST visitors are large and error-prone beasts. This PR attempts to write them using a derive macro.

The design uses three traits: `Visitor`, `Visitable`, `Walkable`.
- `Visitor` is the trait implemented by downstream crates, it lists `visit_stuff` methods, which call `Walkable::walk_ref` by default;
- `Walkable` is derived using the macro, the generated `walk_ref` method calls `Visitable::visit` on each component;
- `Visitable` is implemented by `common_visitor_and_walkers` macro, to call the proper `Visitor::visit_stuff` method if it exists, to call `Walkable::walk_ref` if there is none.

I agree this is quite a lot of spaghetti macros. I'm open to suggestions on how to reduce the amount of boilerplate code.

If this PR is accepted, I believe the same design can be used for the HIR visitor.

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -1,5 +1,5 @@
 use rustc_data_structures::fx::FxHashMap;
-use rustc_macros::{Decodable, Encodable};
+use rustc_macros::{Decodable, Encodable, Walkable};
 use rustc_span::{Ident, Span, Symbol};
 
 use crate::Expr;
@@ -41,7 +41,7 @@ use crate::token::LitKind;
 /// Basically the "AST" for a complete `format_args!()`.
 ///
 /// E.g., `format_args!("hello {name}");`.
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct FormatArgs {
     pub span: Span,
     pub template: Vec<FormatArgsPiece>,
@@ -63,7 +63,7 @@ pub struct FormatArgs {
 /// A piece of a format template string.
 ///
 /// E.g. "hello" or "{name}".
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum FormatArgsPiece {
     Literal(Symbol),
     Placeholder(FormatPlaceholder),
@@ -73,7 +73,7 @@ pub enum FormatArgsPiece {
 ///
 /// E.g. `1, 2, name="ferris", n=3`,
 /// but also implicit captured arguments like `x` in `format_args!("{x}")`.
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct FormatArguments {
     arguments: Vec<FormatArgument>,
     num_unnamed_args: usize,
@@ -144,13 +144,13 @@ impl FormatArguments {
     }
 }
 
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct FormatArgument {
     pub kind: FormatArgumentKind,
     pub expr: P<Expr>,
 }
 
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum FormatArgumentKind {
     /// `format_args(…, arg)`
     Normal,
@@ -170,24 +170,28 @@ impl FormatArgumentKind {
     }
 }
 
-#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq, Walkable)]
 pub struct FormatPlaceholder {
     /// Index into [`FormatArgs::arguments`].
     pub argument: FormatArgPosition,
     /// The span inside the format string for the full `{…}` placeholder.
     pub span: Option<Span>,
     /// `{}`, `{:?}`, or `{:x}`, etc.
+    #[visitable(ignore)]
     pub format_trait: FormatTrait,
     /// `{}` or `{:.5}` or `{:-^20}`, etc.
+    #[visitable(ignore)]
     pub format_options: FormatOptions,
 }
 
-#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
+#[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq, Walkable)]
 pub struct FormatArgPosition {
     /// Which argument this position refers to (Ok),
     /// or would've referred to if it existed (Err).
+    #[visitable(ignore)]
     pub index: Result<usize, usize>,
     /// What kind of position this is. See [`FormatArgPositionKind`].
+    #[visitable(ignore)]
     pub kind: FormatArgPositionKind,
     /// The span of the name or number.
     pub span: Option<Span>,

compiler/rustc_ast/src/format.rs

@@ -12,14 +12,19 @@ use std::panic;
 
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
 use rustc_span::source_map::Spanned;
-use rustc_span::{Ident, Span};
+use rustc_span::{Ident, Span, Symbol};
 use smallvec::{SmallVec, smallvec};
 use thin_vec::ThinVec;
 
 use crate::ast::*;
 use crate::ptr::P;
 use crate::tokenstream::*;
-use crate::visit::{AssocCtxt, BoundKind, FnCtxt, VisitorResult, try_visit, visit_opt, walk_list};
+use crate::visit::{AssocCtxt, BoundKind, FnCtxt, LifetimeCtxt, VisitorResult, try_visit};
+use crate::{
+    define_named_walk, impl_visitable, impl_visitable_calling, impl_visitable_calling_walkable,
+    impl_visitable_direct, impl_visitable_list, impl_visitable_noop, impl_walkable,
+    visit_visitable, visit_visitable_with, walk_walkable,
+};
 
 mod sealed {
     use rustc_ast_ir::visit::VisitorResult;
@@ -36,11 +41,144 @@ mod sealed {
 
 use sealed::MutVisitorResult;
 
+pub(crate) trait MutVisitable<V: MutVisitor> {
+    type Extra: Copy;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra);
+}
+
+impl<V: MutVisitor, T: ?Sized> MutVisitable<V> for P<T>
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        (**self).visit_mut(visitor, extra)
+    }
+}
+
+impl<V: MutVisitor, T> MutVisitable<V> for Option<T>
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        if let Some(this) = self {
+            this.visit_mut(visitor, extra)
+        }
+    }
+}
+
+impl<V: MutVisitor, T> MutVisitable<V> for Spanned<T>
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        let Spanned { span, node } = self;
+        span.visit_mut(visitor, ());
+        node.visit_mut(visitor, extra);
+    }
+}
+
+impl<V: MutVisitor, T> MutVisitable<V> for [T]
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        for item in self {
+            item.visit_mut(visitor, extra);
+        }
+    }
+}
+
+impl<V: MutVisitor, T> MutVisitable<V> for Vec<T>
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        for item in self {
+            item.visit_mut(visitor, extra);
+        }
+    }
+}
+
+impl<V: MutVisitor, T> MutVisitable<V> for (T,)
+where
+    T: MutVisitable<V>,
+{
+    type Extra = T::Extra;
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        self.0.visit_mut(visitor, extra);
+    }
+}
+
+impl<V: MutVisitor, T1, T2> MutVisitable<V> for (T1, T2)
+where
+    T1: MutVisitable<V, Extra = ()>,
+    T2: MutVisitable<V, Extra = ()>,
+{
+    type Extra = ();
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        self.0.visit_mut(visitor, extra);
+        self.1.visit_mut(visitor, extra);
+    }
+}
+
+impl<V: MutVisitor, T1, T2, T3> MutVisitable<V> for (T1, T2, T3)
+where
+    T1: MutVisitable<V, Extra = ()>,
+    T2: MutVisitable<V, Extra = ()>,
+    T3: MutVisitable<V, Extra = ()>,
+{
+    type Extra = ();
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        self.0.visit_mut(visitor, extra);
+        self.1.visit_mut(visitor, extra);
+        self.2.visit_mut(visitor, extra);
+    }
+}
+
+impl<V: MutVisitor, T1, T2, T3, T4> MutVisitable<V> for (T1, T2, T3, T4)
+where
+    T1: MutVisitable<V, Extra = ()>,
+    T2: MutVisitable<V, Extra = ()>,
+    T3: MutVisitable<V, Extra = ()>,
+    T4: MutVisitable<V, Extra = ()>,
+{
+    type Extra = ();
+    fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra) {
+        self.0.visit_mut(visitor, extra);
+        self.1.visit_mut(visitor, extra);
+        self.2.visit_mut(visitor, extra);
+        self.3.visit_mut(visitor, extra);
+    }
+}
+
+pub trait MutWalkable<V: MutVisitor> {
+    fn walk_mut(&mut self, visitor: &mut V);
+}
+
 super::common_visitor_and_walkers!((mut) MutVisitor);
 
 macro_rules! generate_flat_map_visitor_fns {
     ($($name:ident, $Ty:ty, $flat_map_fn:ident$(, $param:ident: $ParamTy:ty)*;)+) => {
         $(
+            #[allow(unused_parens)]
+            impl<V: MutVisitor> MutVisitable<V> for ThinVec<$Ty> {
+                type Extra = ($($ParamTy),*);
+
+                #[inline]
+                fn visit_mut(
+                    &mut self,
+                    visitor: &mut V,
+                    ($($param),*): Self::Extra,
+                ) -> V::Result {
+                    $name(visitor, self $(, $param)*)
+                }
+            }
+
             fn $name<V: MutVisitor>(
                 vis: &mut V,
                 values: &mut ThinVec<$Ty>,
@@ -78,15 +216,6 @@ pub fn walk_flat_map_pat_field<T: MutVisitor>(
     smallvec![fp]
 }
 
-fn visit_nested_use_tree<V: MutVisitor>(
-    vis: &mut V,
-    nested_tree: &mut UseTree,
-    nested_id: &mut NodeId,
-) {
-    vis.visit_id(nested_id);
-    vis.visit_use_tree(nested_tree);
-}
-
 macro_rules! generate_walk_flat_map_fns {
     ($($fn_name:ident($Ty:ty$(,$extra_name:ident: $ExtraTy:ty)*) => $visit_fn_name:ident;)+) => {$(
         pub fn $fn_name<V: MutVisitor>(vis: &mut V, mut value: $Ty$(,$extra_name: $ExtraTy)*) -> SmallVec<[$Ty; 1]> {
@@ -109,14 +238,6 @@ generate_walk_flat_map_fns! {
     walk_flat_map_assoc_item(P<AssocItem>, ctxt: AssocCtxt) => visit_assoc_item;
 }
 
-fn walk_ty_alias_where_clauses<T: MutVisitor>(vis: &mut T, tawcs: &mut TyAliasWhereClauses) {
-    let TyAliasWhereClauses { before, after, split: _ } = tawcs;
-    let TyAliasWhereClause { has_where_token: _, span: span_before } = before;
-    let TyAliasWhereClause { has_where_token: _, span: span_after } = after;
-    vis.visit_span(span_before);
-    vis.visit_span(span_after);
-}
-
 pub fn walk_filter_map_expr<T: MutVisitor>(vis: &mut T, mut e: P<Expr>) -> Option<P<Expr>> {
     vis.visit_expr(&mut e);
     Some(e)

compiler/rustc_ast/src/mut_visit.rs

@@ -20,7 +20,7 @@ use std::{cmp, fmt, iter, mem};
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync;
-use rustc_macros::{Decodable, Encodable, HashStable_Generic};
+use rustc_macros::{Decodable, Encodable, HashStable_Generic, Walkable};
 use rustc_serialize::{Decodable, Encodable};
 use rustc_span::{DUMMY_SP, Span, SpanDecoder, SpanEncoder, Symbol, sym};
 use thin_vec::ThinVec;
@@ -977,7 +977,7 @@ impl TokenCursor {
     }
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Encodable, Decodable, HashStable_Generic)]
+#[derive(Debug, Copy, Clone, PartialEq, Encodable, Decodable, HashStable_Generic, Walkable)]
 pub struct DelimSpan {
     pub open: Span,
     pub close: Span,