Auto merge of #95779 - cjgillot:ast-lifetimes-undeclared, r=petrochenkov

Report undeclared lifetimes during late resolution.

First step in #91557

We reuse the rib design of the current resolution framework. Specific `LifetimeRib` and `LifetimeRibKind` types are introduced. The most important variant is `LifetimeRibKind::Generics`, which happens each time we encounter something which may introduce generic lifetime parameters. It can be an item or a `for<...>` binder. The `LifetimeBinderKind` specifies how this rib behaves with respect to in-band lifetimes.

r? `@petrochenkov`

Author: bors

compiler/rustc_ast/src/visit.rs

@@ -35,7 +35,7 @@ pub enum FnCtxt {
 #[derive(Copy, Clone, Debug)]
 pub enum FnKind<'a> {
     /// E.g., `fn foo()`, `fn foo(&self)`, or `extern "Abi" fn foo()`.
-    Fn(FnCtxt, Ident, &'a FnSig, &'a Visibility, Option<&'a Block>),
+    Fn(FnCtxt, Ident, &'a FnSig, &'a Visibility, &'a Generics, Option<&'a Block>),
 
     /// E.g., `|x, y| body`.
     Closure(&'a FnDecl, &'a Expr),
@@ -44,7 +44,7 @@ pub enum FnKind<'a> {
 impl<'a> FnKind<'a> {
     pub fn header(&self) -> Option<&'a FnHeader> {
         match *self {
-            FnKind::Fn(_, _, sig, _, _) => Some(&sig.header),
+            FnKind::Fn(_, _, sig, _, _, _) => Some(&sig.header),
             FnKind::Closure(_, _) => None,
         }
     }
@@ -58,7 +58,7 @@ impl<'a> FnKind<'a> {
 
     pub fn decl(&self) -> &'a FnDecl {
         match self {
-            FnKind::Fn(_, _, sig, _, _) => &sig.decl,
+            FnKind::Fn(_, _, sig, _, _, _) => &sig.decl,
             FnKind::Closure(decl, _) => decl,
         }
     }
@@ -295,8 +295,8 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
             walk_list!(visitor, visit_expr, expr);
         }
         ItemKind::Fn(box Fn { defaultness: _, ref generics, ref sig, ref body }) => {
-            visitor.visit_generics(generics);
-            let kind = FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, body.as_deref());
+            let kind =
+                FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, generics, body.as_deref());
             visitor.visit_fn(kind, item.span, item.id)
         }
         ItemKind::Mod(_unsafety, ref mod_kind) => match mod_kind {
@@ -561,8 +561,7 @@ pub fn walk_foreign_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a ForeignI
             walk_list!(visitor, visit_expr, expr);
         }
         ForeignItemKind::Fn(box Fn { defaultness: _, ref generics, ref sig, ref body }) => {
-            visitor.visit_generics(generics);
-            let kind = FnKind::Fn(FnCtxt::Foreign, ident, sig, vis, body.as_deref());
+            let kind = FnKind::Fn(FnCtxt::Foreign, ident, sig, vis, generics, body.as_deref());
             visitor.visit_fn(kind, span, id);
         }
         ForeignItemKind::TyAlias(box TyAlias { generics, bounds, ty, .. }) => {
@@ -644,7 +643,8 @@ pub fn walk_fn_decl<'a, V: Visitor<'a>>(visitor: &mut V, function_declaration: &
 
 pub fn walk_fn<'a, V: Visitor<'a>>(visitor: &mut V, kind: FnKind<'a>, _span: Span) {
     match kind {
-        FnKind::Fn(_, _, sig, _, body) => {
+        FnKind::Fn(_, _, sig, _, generics, body) => {
+            visitor.visit_generics(generics);
             visitor.visit_fn_header(&sig.header);
             walk_fn_decl(visitor, &sig.decl);
             walk_list!(visitor, visit_block, body);
@@ -667,8 +667,7 @@ pub fn walk_assoc_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a AssocItem,
             walk_list!(visitor, visit_expr, expr);
         }
         AssocItemKind::Fn(box Fn { defaultness: _, ref generics, ref sig, ref body }) => {
-            visitor.visit_generics(generics);
-            let kind = FnKind::Fn(FnCtxt::Assoc(ctxt), ident, sig, vis, body.as_deref());
+            let kind = FnKind::Fn(FnCtxt::Assoc(ctxt), ident, sig, vis, generics, body.as_deref());
             visitor.visit_fn(kind, span, id);
         }
         AssocItemKind::TyAlias(box TyAlias { generics, bounds, ty, .. }) => {

compiler/rustc_ast_lowering/src/lib.rs

@@ -484,7 +484,7 @@ enum ParenthesizedGenericArgs {
 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
 /// everything into HIR lowering.
 #[derive(Copy, Clone, Debug)]
-enum AnonymousLifetimeMode {
+pub enum AnonymousLifetimeMode {
     /// For **Modern** cases, create a new anonymous region parameter
     /// and reference that.
     ///
@@ -1835,7 +1835,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // Output lifetime like `'_`:
             for (span, node_id) in lifetimes_to_define {
                 let param = this.fresh_lifetime_to_generic_param(span, node_id);
-                lifetime_params.push((span, hir::LifetimeName::Implicit(false)));
+                lifetime_params.push((span, hir::LifetimeName::Implicit));
                 generic_params.push(param);
             }
             let generic_params = this.arena.alloc_from_iter(generic_params);
@@ -2017,16 +2017,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     });
                 let param_name = match lt.name {
                     hir::LifetimeName::Param(param_name) => param_name,
-                    hir::LifetimeName::Implicit(_)
-                    | hir::LifetimeName::Underscore
-                    | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
+                    hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
+                        hir::ParamName::Plain(lt.name.ident())
+                    }
                     hir::LifetimeName::ImplicitObjectLifetimeDefault => {
                         self.sess.diagnostic().span_bug(
                             param.ident.span,
                             "object-lifetime-default should not occur here",
                         );
                     }
-                    hir::LifetimeName::Error => ParamName::Error,
+                    hir::LifetimeName::Static | hir::LifetimeName::Error => ParamName::Error,
                 };
 
                 let kind =
@@ -2397,27 +2397,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
             AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
 
-            AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span, false),
+            AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
         }
     }
 
     /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
     /// return an "error lifetime".
     fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
-        let (id, msg, label) = match id {
-            Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
-
-            None => (
-                self.resolver.next_node_id(),
-                "`&` without an explicit lifetime name cannot be used here",
-                "explicit lifetime name needed here",
-            ),
-        };
-
-        let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
-        err.span_label(span, label);
-        err.emit();
-
+        let id = id.unwrap_or_else(|| self.resolver.next_node_id());
         self.new_named_lifetime(id, span, hir::LifetimeName::Error)
     }
 
@@ -2429,12 +2416,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &'s mut self,
         span: Span,
         count: usize,
-        param_mode: ParamMode,
     ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
-        (0..count).map(move |_| self.elided_path_lifetime(span, param_mode))
+        (0..count).map(move |_| self.elided_path_lifetime(span))
     }
 
-    fn elided_path_lifetime(&mut self, span: Span, param_mode: ParamMode) -> hir::Lifetime {
+    fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
         match self.anonymous_lifetime_mode {
             AnonymousLifetimeMode::CreateParameter => {
                 // We should have emitted E0726 when processing this path above
@@ -2450,7 +2436,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // lifetime. Instead, we simply create an implicit lifetime, which will be checked
             // later, at which point a suitable error will be emitted.
             AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
-                self.new_implicit_lifetime(span, param_mode == ParamMode::Explicit)
+                self.new_implicit_lifetime(span)
             }
         }
     }
@@ -2493,11 +2479,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         r
     }
 
-    fn new_implicit_lifetime(&mut self, span: Span, missing: bool) -> hir::Lifetime {
+    fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
         hir::Lifetime {
             hir_id: self.next_id(),
             span: self.lower_span(span),
-            name: hir::LifetimeName::Implicit(missing),
+            name: hir::LifetimeName::Implicit,
         }
     }
 }
@@ -2600,7 +2586,7 @@ fn lifetimes_from_impl_trait_bounds(
 
         fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
             let name = match lifetime.name {
-                hir::LifetimeName::Implicit(_) | hir::LifetimeName::Underscore => {
+                hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
                     if self.collect_elided_lifetimes {
                         // Use `'_` for both implicit and underscore lifetimes in
                         // `type Foo<'_> = impl SomeTrait<'_>;`.

compiler/rustc_ast_lowering/src/path.rs

@@ -290,47 +290,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 generic_args.span.with_lo(generic_args.span.lo() + BytePos(1)).shrink_to_lo()
             };
             generic_args.args = self
-                .elided_path_lifetimes(elided_lifetime_span, expected_lifetimes, param_mode)
+                .elided_path_lifetimes(elided_lifetime_span, expected_lifetimes)
                 .map(GenericArg::Lifetime)
                 .chain(generic_args.args.into_iter())
                 .collect();
-            // In create-parameter mode we error here because we don't want to support
-            // deprecated impl elision in new features like impl elision and `async fn`,
-            // both of which work using the `CreateParameter` mode:
-            //
-            //     impl Foo for std::cell::Ref<u32> // note lack of '_
-            //     async fn foo(_: std::cell::Ref<u32>) { ... }
             if let (ParamMode::Explicit, AnonymousLifetimeMode::CreateParameter) =
                 (param_mode, self.anonymous_lifetime_mode)
             {
-                let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
-                let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
-                let no_bindings = generic_args.bindings.is_empty();
-                let (incl_angl_brckt, suggestion) = if no_non_lt_args && no_bindings {
-                    // If there are no generic args, our suggestion can include the angle brackets.
-                    (true, format!("<{}>", anon_lt_suggestion))
-                } else {
-                    // Otherwise we'll insert a `'_, ` right after the opening bracket.
-                    (false, format!("{}, ", anon_lt_suggestion))
-                };
-                let insertion_sp = elided_lifetime_span.shrink_to_hi();
-                let mut err = struct_span_err!(
-                    self.sess,
-                    path_span,
-                    E0726,
-                    "implicit elided lifetime not allowed here"
-                );
-                rustc_errors::add_elided_lifetime_in_path_suggestion(
-                    &self.sess.source_map(),
-                    &mut err,
-                    expected_lifetimes,
-                    path_span,
-                    incl_angl_brckt,
-                    insertion_sp,
-                    suggestion,
-                );
-                err.note("assuming a `'static` lifetime...");
-                err.emit();
+                // Late resolver should have issued the error.
+                self.sess
+                    .delay_span_bug(elided_lifetime_span, "implicit lifetime not allowed here");
             }
         }
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -91,16 +91,18 @@ impl<'a> AstValidator<'a> {
         self.is_impl_trait_banned = old;
     }
 
-    fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
-        let old = mem::replace(&mut self.is_tilde_const_allowed, true);
+    fn with_tilde_const(&mut self, allowed: bool, f: impl FnOnce(&mut Self)) {
+        let old = mem::replace(&mut self.is_tilde_const_allowed, allowed);
         f(self);
         self.is_tilde_const_allowed = old;
     }
 
+    fn with_tilde_const_allowed(&mut self, f: impl FnOnce(&mut Self)) {
+        self.with_tilde_const(true, f)
+    }
+
     fn with_banned_tilde_const(&mut self, f: impl FnOnce(&mut Self)) {
-        let old = mem::replace(&mut self.is_tilde_const_allowed, false);
-        f(self);
-        self.is_tilde_const_allowed = old;
+        self.with_tilde_const(false, f)
     }
 
     fn with_let_management(
@@ -1202,12 +1204,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 }
                 self.visit_vis(&item.vis);
                 self.visit_ident(item.ident);
-                if let Const::Yes(_) = sig.header.constness {
-                    self.with_tilde_const_allowed(|this| this.visit_generics(generics));
-                } else {
-                    self.visit_generics(generics);
-                }
-                let kind = FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, body.as_deref());
+                let kind =
+                    FnKind::Fn(FnCtxt::Free, item.ident, sig, &item.vis, generics, body.as_deref());
                 self.visit_fn(kind, item.span, item.id);
                 walk_list!(self, visit_attribute, &item.attrs);
                 return; // Avoid visiting again.
@@ -1555,13 +1553,14 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             FnSig { span: sig_span, header: FnHeader { ext: Extern::Implicit, .. }, .. },
             _,
             _,
+            _,
         ) = fk
         {
             self.maybe_lint_missing_abi(*sig_span, id);
         }
 
         // Functions without bodies cannot have patterns.
-        if let FnKind::Fn(ctxt, _, sig, _, None) = fk {
+        if let FnKind::Fn(ctxt, _, sig, _, _, None) = fk {
             Self::check_decl_no_pat(&sig.decl, |span, ident, mut_ident| {
                 let (code, msg, label) = match ctxt {
                     FnCtxt::Foreign => (
@@ -1596,7 +1595,11 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             });
         }
 
-        visit::walk_fn(self, fk, span);
+        let tilde_const_allowed =
+            matches!(fk.header(), Some(FnHeader { constness: Const::Yes(_), .. }))
+                || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
+
+        self.with_tilde_const(tilde_const_allowed, |this| visit::walk_fn(this, fk, span));
     }
 
     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
@@ -1670,9 +1673,14 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             {
                 self.visit_vis(&item.vis);
                 self.visit_ident(item.ident);
-                self.with_tilde_const_allowed(|this| this.visit_generics(generics));
-                let kind =
-                    FnKind::Fn(FnCtxt::Assoc(ctxt), item.ident, sig, &item.vis, body.as_deref());
+                let kind = FnKind::Fn(
+                    FnCtxt::Assoc(ctxt),
+                    item.ident,
+                    sig,
+                    &item.vis,
+                    generics,
+                    body.as_deref(),
+                );
                 self.visit_fn(kind, item.span, item.id);
             }
             _ => self

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -575,7 +575,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                 Some(RegionNameHighlight::MatchedAdtAndSegment(lifetime_span))
             }
 
-            hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Implicit(_) => {
+            hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Implicit => {
                 // In this case, the user left off the lifetime; so
                 // they wrote something like:
                 //

compiler/rustc_errors/src/lib.rs

@@ -1511,35 +1511,17 @@ pub fn add_elided_lifetime_in_path_suggestion(
     path_span: Span,
     incl_angl_brckt: bool,
     insertion_span: Span,
-    anon_lts: String,
 ) {
-    let (replace_span, suggestion) = if incl_angl_brckt {
-        (insertion_span, anon_lts)
-    } else {
-        // When possible, prefer a suggestion that replaces the whole
-        // `Path<T>` expression with `Path<'_, T>`, rather than inserting `'_, `
-        // at a point (which makes for an ugly/confusing label)
-        if let Ok(snippet) = source_map.span_to_snippet(path_span) {
-            // But our spans can get out of whack due to macros; if the place we think
-            // we want to insert `'_` isn't even within the path expression's span, we
-            // should bail out of making any suggestion rather than panicking on a
-            // subtract-with-overflow or string-slice-out-out-bounds (!)
-            // FIXME: can we do better?
-            if insertion_span.lo().0 < path_span.lo().0 {
-                return;
-            }
-            let insertion_index = (insertion_span.lo().0 - path_span.lo().0) as usize;
-            if insertion_index > snippet.len() {
-                return;
-            }
-            let (before, after) = snippet.split_at(insertion_index);
-            (path_span, format!("{}{}{}", before, anon_lts, after))
-        } else {
-            (insertion_span, anon_lts)
-        }
-    };
-    diag.span_suggestion(
-        replace_span,
+    diag.span_label(path_span, format!("expected lifetime parameter{}", pluralize!(n)));
+    if source_map.span_to_snippet(insertion_span).is_err() {
+        // Do not try to suggest anything if generated by a proc-macro.
+        return;
+    }
+    let anon_lts = vec!["'_"; n].join(", ");
+    let suggestion =
+        if incl_angl_brckt { format!("<{}>", anon_lts) } else { format!("{}, ", anon_lts) };
+    diag.span_suggestion_verbose(
+        insertion_span.shrink_to_hi(),
         &format!("indicate the anonymous lifetime{}", pluralize!(n)),
         suggestion,
         Applicability::MachineApplicable,