Rollup merge of #127818 - oli-obk:ast_validation_simplifications, r=petrochenkov

Various ast validation simplifications

Changes pulled out of #127524

These are needed to make ast validation a mutable visitor, as we can't keep immutable references to the AST around in that case. But I think they are simplifying things in general and can stand on their own

Author: matthiaskrgr

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -38,35 +38,20 @@ use std::mem;
 use std::ops::{Deref, DerefMut};
 use thin_vec::thin_vec;
 
-use crate::errors;
+use crate::errors::{self, TildeConstReason};
 
 /// Is `self` allowed semantically as the first parameter in an `FnDecl`?
 enum SelfSemantic {
     Yes,
     No,
 }
 
-/// What is the context that prevents using `~const`?
-// FIXME(effects): Consider getting rid of this in favor of `errors::TildeConstReason`, they're
-// almost identical. This gets rid of an abstraction layer which might be considered bad.
-enum DisallowTildeConstContext<'a> {
-    TraitObject,
-    Fn(FnKind<'a>),
-    Trait(Span),
-    TraitImpl(Span),
-    Impl(Span),
-    TraitAssocTy(Span),
-    TraitImplAssocTy(Span),
-    InherentAssocTy(Span),
-    Item,
-}
-
-enum TraitOrTraitImpl<'a> {
+enum TraitOrTraitImpl {
     Trait { span: Span, constness: Option<Span> },
-    TraitImpl { constness: Const, polarity: ImplPolarity, trait_ref: &'a TraitRef },
+    TraitImpl { constness: Const, polarity: ImplPolarity, trait_ref: Span },
 }
 
-impl<'a> TraitOrTraitImpl<'a> {
+impl TraitOrTraitImpl {
     fn constness(&self) -> Option<Span> {
         match self {
             Self::Trait { constness: Some(span), .. }
@@ -81,9 +66,9 @@ struct AstValidator<'a> {
     features: &'a Features,
 
     /// The span of the `extern` in an `extern { ... }` block, if any.
-    extern_mod: Option<&'a Item>,
+    extern_mod: Option<Span>,
 
-    outer_trait_or_trait_impl: Option<TraitOrTraitImpl<'a>>,
+    outer_trait_or_trait_impl: Option<TraitOrTraitImpl>,
 
     has_proc_macro_decls: bool,
 
@@ -92,7 +77,7 @@ struct AstValidator<'a> {
     /// e.g., `impl Iterator<Item = impl Debug>`.
     outer_impl_trait: Option<Span>,
 
-    disallow_tilde_const: Option<DisallowTildeConstContext<'a>>,
+    disallow_tilde_const: Option<TildeConstReason>,
 
     /// Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
     /// or `Foo::Bar<impl Trait>`
@@ -115,7 +100,7 @@ impl<'a> AstValidator<'a> {
             trait_.map(|(constness, polarity, trait_ref)| TraitOrTraitImpl::TraitImpl {
                 constness,
                 polarity,
-                trait_ref,
+                trait_ref: trait_ref.path.span,
             }),
         );
         f(self);
@@ -145,7 +130,7 @@ impl<'a> AstValidator<'a> {
 
     fn with_tilde_const(
         &mut self,
-        disallowed: Option<DisallowTildeConstContext<'a>>,
+        disallowed: Option<TildeConstReason>,
         f: impl FnOnce(&mut Self),
     ) {
         let old = mem::replace(&mut self.disallow_tilde_const, disallowed);
@@ -224,7 +209,7 @@ impl<'a> AstValidator<'a> {
                 }
             }
             TyKind::TraitObject(..) => self
-                .with_tilde_const(Some(DisallowTildeConstContext::TraitObject), |this| {
+                .with_tilde_const(Some(TildeConstReason::TraitObject), |this| {
                     visit::walk_ty(this, t)
                 }),
             TyKind::Path(qself, path) => {
@@ -354,7 +339,7 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn check_trait_fn_not_const(&self, constness: Const, parent: &TraitOrTraitImpl<'a>) {
+    fn check_trait_fn_not_const(&self, constness: Const, parent: &TraitOrTraitImpl) {
         let Const::Yes(span) = constness else {
             return;
         };
@@ -367,7 +352,7 @@ impl<'a> AstValidator<'a> {
                 ..
             } = parent
         {
-            Some(trait_ref.path.span.shrink_to_lo())
+            Some(trait_ref.shrink_to_lo())
         } else {
             None
         };
@@ -579,7 +564,7 @@ impl<'a> AstValidator<'a> {
     }
 
     fn current_extern_span(&self) -> Span {
-        self.session.source_map().guess_head_span(self.extern_mod.unwrap().span)
+        self.session.source_map().guess_head_span(self.extern_mod.unwrap())
     }
 
     /// An `fn` in `extern { ... }` cannot have qualifiers, e.g. `async fn`.
@@ -980,7 +965,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     this.visit_vis(&item.vis);
                     this.visit_ident(item.ident);
                     let disallowed = matches!(constness, Const::No)
-                        .then(|| DisallowTildeConstContext::TraitImpl(item.span));
+                        .then(|| TildeConstReason::TraitImpl { span: item.span });
                     this.with_tilde_const(disallowed, |this| this.visit_generics(generics));
                     this.visit_trait_ref(t);
                     this.visit_ty(self_ty);
@@ -1035,7 +1020,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     this.visit_vis(&item.vis);
                     this.visit_ident(item.ident);
                     this.with_tilde_const(
-                        Some(DisallowTildeConstContext::Impl(item.span)),
+                        Some(TildeConstReason::Impl { span: item.span }),
                         |this| this.visit_generics(generics),
                     );
                     this.visit_ty(self_ty);
@@ -1080,7 +1065,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             }
             ItemKind::ForeignMod(ForeignMod { abi, safety, .. }) => {
                 self.with_in_extern_mod(*safety, |this| {
-                    let old_item = mem::replace(&mut this.extern_mod, Some(item));
+                    let old_item = mem::replace(&mut this.extern_mod, Some(item.span));
                     this.visibility_not_permitted(
                         &item.vis,
                         errors::VisibilityNotPermittedNote::IndividualForeignItems,
@@ -1154,7 +1139,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     this.visit_ident(item.ident);
                     let disallowed = is_const_trait
                         .is_none()
-                        .then(|| DisallowTildeConstContext::Trait(item.span));
+                        .then(|| TildeConstReason::Trait { span: item.span });
                     this.with_tilde_const(disallowed, |this| {
                         this.visit_generics(generics);
                         walk_list!(this, visit_param_bound, bounds, BoundKind::SuperTraits)
@@ -1399,40 +1384,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                         self.dcx().emit_err(errors::ConstBoundTraitObject { span: trait_ref.span });
                     }
                     (_, BoundConstness::Maybe(span), BoundPolarity::Positive)
-                        if let Some(reason) = &self.disallow_tilde_const =>
+                        if let Some(reason) = self.disallow_tilde_const =>
                     {
-                        let reason = match reason {
-                            DisallowTildeConstContext::Fn(FnKind::Closure(..)) => {
-                                errors::TildeConstReason::Closure
-                            }
-                            DisallowTildeConstContext::Fn(FnKind::Fn(_, ident, ..)) => {
-                                errors::TildeConstReason::Function { ident: ident.span }
-                            }
-                            &DisallowTildeConstContext::Trait(span) => {
-                                errors::TildeConstReason::Trait { span }
-                            }
-                            &DisallowTildeConstContext::TraitImpl(span) => {
-                                errors::TildeConstReason::TraitImpl { span }
-                            }
-                            &DisallowTildeConstContext::Impl(span) => {
-                                // FIXME(effects): Consider providing a help message or even a structured
-                                // suggestion for moving such bounds to the assoc const fns if available.
-                                errors::TildeConstReason::Impl { span }
-                            }
-                            &DisallowTildeConstContext::TraitAssocTy(span) => {
-                                errors::TildeConstReason::TraitAssocTy { span }
-                            }
-                            &DisallowTildeConstContext::TraitImplAssocTy(span) => {
-                                errors::TildeConstReason::TraitImplAssocTy { span }
-                            }
-                            &DisallowTildeConstContext::InherentAssocTy(span) => {
-                                errors::TildeConstReason::InherentAssocTy { span }
-                            }
-                            DisallowTildeConstContext::TraitObject => {
-                                errors::TildeConstReason::TraitObject
-                            }
-                            DisallowTildeConstContext::Item => errors::TildeConstReason::Item,
-                        };
                         self.dcx().emit_err(errors::TildeConstDisallowed { span, reason });
                     }
                     (
@@ -1569,7 +1522,10 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                         .and_then(TraitOrTraitImpl::constness)
                         .is_some();
 
-        let disallowed = (!tilde_const_allowed).then(|| DisallowTildeConstContext::Fn(fk));
+        let disallowed = (!tilde_const_allowed).then(|| match fk {
+            FnKind::Fn(_, ident, _, _, _, _) => TildeConstReason::Function { ident: ident.span },
+            FnKind::Closure(_, _, _) => TildeConstReason::Closure,
+        });
         self.with_tilde_const(disallowed, |this| visit::walk_fn(this, fk));
     }
 
@@ -1664,12 +1620,12 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             AssocItemKind::Type(_) => {
                 let disallowed = (!parent_is_const).then(|| match self.outer_trait_or_trait_impl {
                     Some(TraitOrTraitImpl::Trait { .. }) => {
-                        DisallowTildeConstContext::TraitAssocTy(item.span)
+                        TildeConstReason::TraitAssocTy { span: item.span }
                     }
                     Some(TraitOrTraitImpl::TraitImpl { .. }) => {
-                        DisallowTildeConstContext::TraitImplAssocTy(item.span)
+                        TildeConstReason::TraitImplAssocTy { span: item.span }
                     }
-                    None => DisallowTildeConstContext::InherentAssocTy(item.span),
+                    None => TildeConstReason::InherentAssocTy { span: item.span },
                 });
                 self.with_tilde_const(disallowed, |this| {
                     this.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt))
@@ -1852,7 +1808,7 @@ pub fn check_crate(
         outer_trait_or_trait_impl: None,
         has_proc_macro_decls: false,
         outer_impl_trait: None,
-        disallow_tilde_const: Some(DisallowTildeConstContext::Item),
+        disallow_tilde_const: Some(TildeConstReason::Item),
         is_impl_trait_banned: false,
         extern_mod_safety: None,
         lint_buffer: lints,

compiler/rustc_ast_passes/src/errors.rs

@@ -612,7 +612,7 @@ pub struct TildeConstDisallowed {
     pub reason: TildeConstReason,
 }
 
-#[derive(Subdiagnostic)]
+#[derive(Subdiagnostic, Copy, Clone)]
 pub enum TildeConstReason {
     #[note(ast_passes_closure)]
     Closure,