src/librustc_passes/ast_validation.rs

   1 // Validate AST before lowering it to HIR
   2 //
   3 // This pass is supposed to catch things that fit into AST data structures,
   4 // but not permitted by the language. It runs after expansion when AST is frozen,
   5 // so it can check for erroneous constructions produced by syntax extensions.
   6 // This pass is supposed to perform only simple checks not requiring name resolution
   7 // or type checking or some other kind of complex analysis.
   8
   9 use std::mem;
  10 use rustc::lint;
  11 use rustc::session::Session;
  12 use syntax::ast::*;
  13 use syntax::attr;
  14 use syntax::source_map::Spanned;
  15 use syntax::symbol::keywords;
  16 use syntax::ptr::P;
  17 use syntax::visit::{self, Visitor};
  18 use syntax_ext::proc_macro_decls::is_proc_macro_attr;
  19 use syntax_pos::Span;
  20 use errors;
  21 use errors::Applicability;
  22
  23 struct AstValidator<'a> {
  24     session: &'a Session,
  25     has_proc_macro_decls: bool,
  26     has_global_allocator: bool,
  27
  28     // Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
  29     // Nested `impl Trait` _is_ allowed in associated type position,
  30     // e.g `impl Iterator<Item=impl Debug>`
  31     outer_impl_trait: Option<Span>,
  32
  33     // Used to ban `impl Trait` in path projections like `<impl Iterator>::Item`
  34     // or `Foo::Bar<impl Trait>`
  35     is_impl_trait_banned: bool,
  36 }
  37
  38 impl<'a> AstValidator<'a> {
  39     fn with_banned_impl_trait(&mut self, f: impl FnOnce(&mut Self)) {
  40         let old = mem::replace(&mut self.is_impl_trait_banned, true);
  41         f(self);
  42         self.is_impl_trait_banned = old;
  43     }
  44
  45     fn with_impl_trait(&mut self, outer_impl_trait: Option<Span>, f: impl FnOnce(&mut Self)) {
  46         let old = mem::replace(&mut self.outer_impl_trait, outer_impl_trait);
  47         f(self);
  48         self.outer_impl_trait = old;
  49     }
  50
  51     // Mirrors visit::walk_ty, but tracks relevant state
  52     fn walk_ty(&mut self, t: &'a Ty) {
  53         match t.node {
  54             TyKind::ImplTrait(..) => {
  55                 self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t))
  56             }
  57             TyKind::Path(ref qself, ref path) => {
  58                 // We allow these:
  59                 //  - `Option<impl Trait>`
  60                 //  - `option::Option<impl Trait>`
  61                 //  - `option::Option<T>::Foo<impl Trait>
  62                 //
  63                 // But not these:
  64                 //  - `<impl Trait>::Foo`
  65                 //  - `option::Option<impl Trait>::Foo`.
  66                 //
  67                 // To implement this, we disallow `impl Trait` from `qself`
  68                 // (for cases like `<impl Trait>::Foo>`)
  69                 // but we allow `impl Trait` in `GenericArgs`
  70                 // iff there are no more PathSegments.
  71                 if let Some(ref qself) = *qself {
  72                     // `impl Trait` in `qself` is always illegal
  73                     self.with_banned_impl_trait(|this| this.visit_ty(&qself.ty));
  74                 }
  75
  76                 // Note that there should be a call to visit_path here,
  77                 // so if any logic is added to process `Path`s a call to it should be
  78                 // added both in visit_path and here. This code mirrors visit::walk_path.
  79                 for (i, segment) in path.segments.iter().enumerate() {
  80                     // Allow `impl Trait` iff we're on the final path segment
  81                     if i == path.segments.len() - 1 {
  82                         self.visit_path_segment(path.span, segment);
  83                     } else {
  84                         self.with_banned_impl_trait(|this| {
  85                             this.visit_path_segment(path.span, segment)
  86                         });
  87                     }
  88                 }
  89             }
  90             _ => visit::walk_ty(self, t),
  91         }
  92     }
  93
  94     fn err_handler(&self) -> &errors::Handler {
  95         &self.session.diagnostic()
  96     }
  97
  98     fn check_lifetime(&self, ident: Ident) {
  99         let valid_names = [keywords::UnderscoreLifetime.name(),
 100                            keywords::StaticLifetime.name(),
 101                            keywords::Invalid.name()];
 102         if !valid_names.contains(&ident.name) && ident.without_first_quote().is_reserved() {
 103             self.err_handler().span_err(ident.span, "lifetimes cannot use keyword names");
 104         }
 105     }
 106
 107     fn check_label(&self, ident: Ident) {
 108         if ident.without_first_quote().is_reserved() {
 109             self.err_handler()
 110                 .span_err(ident.span, &format!("invalid label name `{}`", ident.name));
 111         }
 112     }
 113
 114     fn invalid_non_exhaustive_attribute(&self, variant: &Variant) {
 115         let has_non_exhaustive = attr::contains_name(&variant.node.attrs, "non_exhaustive");
 116         if has_non_exhaustive {
 117             self.err_handler().span_err(variant.span,
 118                                         "#[non_exhaustive] is not yet supported on variants");
 119         }
 120     }
 121
 122     fn invalid_visibility(&self, vis: &Visibility, note: Option<&str>) {
 123         if let VisibilityKind::Inherited = vis.node {
 124             return
 125         }
 126
 127         let mut err = struct_span_err!(self.session,
 128                                         vis.span,
 129                                         E0449,
 130                                         "unnecessary visibility qualifier");
 131         if vis.node.is_pub() {
 132             err.span_label(vis.span, "`pub` not permitted here because it's implied");
 133         }
 134         if let Some(note) = note {
 135             err.note(note);
 136         }
 137         err.emit();
 138     }
 139
 140     fn check_decl_no_pat<ReportFn: Fn(Span, bool)>(&self, decl: &FnDecl, report_err: ReportFn) {
 141         for arg in &decl.inputs {
 142             match arg.pat.node {
 143                 PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), _, None) |
 144                 PatKind::Wild => {}
 145                 PatKind::Ident(BindingMode::ByValue(Mutability::Mutable), _, None) =>
 146                     report_err(arg.pat.span, true),
 147                 _ => report_err(arg.pat.span, false),
 148             }
 149         }
 150     }
 151
 152     fn check_trait_fn_not_async(&self, span: Span, asyncness: IsAsync) {
 153         if asyncness.is_async() {
 154             struct_span_err!(self.session, span, E0706,
 155                              "trait fns cannot be declared `async`").emit()
 156         }
 157     }
 158
 159     fn check_trait_fn_not_const(&self, constness: Spanned<Constness>) {
 160         if constness.node == Constness::Const {
 161             struct_span_err!(self.session, constness.span, E0379,
 162                              "trait fns cannot be declared const")
 163                 .span_label(constness.span, "trait fns cannot be const")
 164                 .emit();
 165         }
 166     }
 167
 168     fn no_questions_in_bounds(&self, bounds: &GenericBounds, where_: &str, is_trait: bool) {
 169         for bound in bounds {
 170             if let GenericBound::Trait(ref poly, TraitBoundModifier::Maybe) = *bound {
 171                 let mut err = self.err_handler().struct_span_err(poly.span,
 172                     &format!("`?Trait` is not permitted in {}", where_));
 173                 if is_trait {
 174                     err.note(&format!("traits are `?{}` by default", poly.trait_ref.path));
 175                 }
 176                 err.emit();
 177             }
 178         }
 179     }
 180
 181     /// matches '-' lit | lit (cf. parser::Parser::parse_literal_maybe_minus),
 182     /// or path for ranges.
 183     ///
 184     /// FIXME: do we want to allow expr -> pattern conversion to create path expressions?
 185     /// That means making this work:
 186     ///
 187     /// ```rust,ignore (FIXME)
 188     ///     struct S;
 189     ///     macro_rules! m {
 190     ///         ($a:expr) => {
 191     ///             let $a = S;
 192     ///         }
 193     ///     }
 194     ///     m!(S);
 195     /// ```
 196     fn check_expr_within_pat(&self, expr: &Expr, allow_paths: bool) {
 197         match expr.node {
 198             ExprKind::Lit(..) => {}
 199             ExprKind::Path(..) if allow_paths => {}
 200             ExprKind::Unary(UnOp::Neg, ref inner)
 201                 if match inner.node { ExprKind::Lit(_) => true, _ => false } => {}
 202             _ => self.err_handler().span_err(expr.span, "arbitrary expressions aren't allowed \
 203                                                          in patterns")
 204         }
 205     }
 206
 207     fn check_late_bound_lifetime_defs(&self, params: &[GenericParam]) {
 208         // Check only lifetime parameters are present and that the lifetime
 209         // parameters that are present have no bounds.
 210         let non_lt_param_spans: Vec<_> = params.iter().filter_map(|param| match param.kind {
 211             GenericParamKind::Lifetime { .. } => {
 212                 if !param.bounds.is_empty() {
 213                     let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
 214                     self.err_handler()
 215                         .span_err(spans, "lifetime bounds cannot be used in this context");
 216                 }
 217                 None
 218             }
 219             _ => Some(param.ident.span),
 220         }).collect();
 221         if !non_lt_param_spans.is_empty() {
 222             self.err_handler().span_err(non_lt_param_spans,
 223                 "only lifetime parameters can be used in this context");
 224         }
 225     }
 226
 227     /// With eRFC 2497, we need to check whether an expression is ambiguous and warn or error
 228     /// depending on the edition, this function handles that.
 229     fn while_if_let_ambiguity(&self, expr: &P<Expr>) {
 230         if let Some((span, op_kind)) = self.while_if_let_expr_ambiguity(&expr) {
 231             let mut err = self.err_handler().struct_span_err(
 232                 span, &format!("ambiguous use of `{}`", op_kind.to_string())
 233             );
 234
 235             err.note(
 236                 "this will be a error until the `let_chains` feature is stabilized"
 237             );
 238             err.note(
 239                 "see rust-lang/rust#53668 for more information"
 240             );
 241
 242             if let Ok(snippet) = self.session.source_map().span_to_snippet(span) {
 243                 err.span_suggestion(
 244                     span, "consider adding parentheses", format!("({})", snippet),
 245                     Applicability::MachineApplicable,
 246                 );
 247             }
 248
 249             err.emit();
 250         }
 251     }
 252
 253     /// With eRFC 2497 adding if-let chains, there is a requirement that the parsing of
 254     /// `&&` and `||` in a if-let statement be unambiguous. This function returns a span and
 255     /// a `BinOpKind` (either `&&` or `||` depending on what was ambiguous) if it is determined
 256     /// that the current expression parsed is ambiguous and will break in future.
 257     fn while_if_let_expr_ambiguity(&self, expr: &P<Expr>) -> Option<(Span, BinOpKind)> {
 258         debug!("while_if_let_expr_ambiguity: expr.node: {:?}", expr.node);
 259         match &expr.node {
 260             ExprKind::Binary(op, _, _) if op.node == BinOpKind::And || op.node == BinOpKind::Or => {
 261                 Some((expr.span, op.node))
 262             },
 263             ExprKind::Range(ref lhs, ref rhs, _) => {
 264                 let lhs_ambiguous = lhs.as_ref()
 265                     .and_then(|lhs| self.while_if_let_expr_ambiguity(lhs));
 266                 let rhs_ambiguous = rhs.as_ref()
 267                     .and_then(|rhs| self.while_if_let_expr_ambiguity(rhs));
 268
 269                 lhs_ambiguous.or(rhs_ambiguous)
 270             }
 271             _ => None,
 272         }
 273     }
 274
 275 }
 276
 277 impl<'a> Visitor<'a> for AstValidator<'a> {
 278     fn visit_expr(&mut self, expr: &'a Expr) {
 279         match expr.node {
 280             ExprKind::IfLet(_, ref expr, _, _) | ExprKind::WhileLet(_, ref expr, _, _) =>
 281                 self.while_if_let_ambiguity(&expr),
 282             ExprKind::InlineAsm(..) if !self.session.target.target.options.allow_asm => {
 283                 span_err!(self.session, expr.span, E0472, "asm! is unsupported on this target");
 284             }
 285             ExprKind::ObsoleteInPlace(ref place, ref val) => {
 286                 let mut err = self.err_handler().struct_span_err(
 287                     expr.span,
 288                     "emplacement syntax is obsolete (for now, anyway)",
 289                 );
 290                 err.note(
 291                     "for more information, see \
 292                      <https://github.com/rust-lang/rust/issues/27779#issuecomment-378416911>"
 293                 );
 294                 match val.node {
 295                     ExprKind::Lit(ref v) if v.node.is_numeric() => {
 296                         err.span_suggestion(
 297                             place.span.between(val.span),
 298                             "if you meant to write a comparison against a negative value, add a \
 299                              space in between `<` and `-`",
 300                             "< -".to_string(),
 301                             Applicability::MaybeIncorrect
 302                         );
 303                     }
 304                     _ => {}
 305                 }
 306                 err.emit();
 307             }
 308             _ => {}
 309         }
 310
 311         visit::walk_expr(self, expr)
 312     }
 313
 314     fn visit_ty(&mut self, ty: &'a Ty) {
 315         match ty.node {
 316             TyKind::BareFn(ref bfty) => {
 317                 self.check_decl_no_pat(&bfty.decl, |span, _| {
 318                     struct_span_err!(self.session, span, E0561,
 319                                      "patterns aren't allowed in function pointer types").emit();
 320                 });
 321                 self.check_late_bound_lifetime_defs(&bfty.generic_params);
 322             }
 323             TyKind::TraitObject(ref bounds, ..) => {
 324                 let mut any_lifetime_bounds = false;
 325                 for bound in bounds {
 326                     if let GenericBound::Outlives(ref lifetime) = *bound {
 327                         if any_lifetime_bounds {
 328                             span_err!(self.session, lifetime.ident.span, E0226,
 329                                       "only a single explicit lifetime bound is permitted");
 330                             break;
 331                         }
 332                         any_lifetime_bounds = true;
 333                     }
 334                 }
 335                 self.no_questions_in_bounds(bounds, "trait object types", false);
 336             }
 337             TyKind::ImplTrait(_, ref bounds) => {
 338                 if self.is_impl_trait_banned {
 339                     struct_span_err!(self.session, ty.span, E0667,
 340                         "`impl Trait` is not allowed in path parameters").emit();
 341                 }
 342
 343                 if let Some(outer_impl_trait) = self.outer_impl_trait {
 344                     struct_span_err!(self.session, ty.span, E0666,
 345                                     "nested `impl Trait` is not allowed")
 346                         .span_label(outer_impl_trait, "outer `impl Trait`")
 347                         .span_label(ty.span, "nested `impl Trait` here")
 348                         .emit();
 349
 350                 }
 351                 if !bounds.iter()
 352                           .any(|b| if let GenericBound::Trait(..) = *b { true } else { false }) {
 353                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
 354                 }
 355             }
 356             _ => {}
 357         }
 358
 359         self.walk_ty(ty)
 360     }
 361
 362     fn visit_label(&mut self, label: &'a Label) {
 363         self.check_label(label.ident);
 364         visit::walk_label(self, label);
 365     }
 366
 367     fn visit_lifetime(&mut self, lifetime: &'a Lifetime) {
 368         self.check_lifetime(lifetime.ident);
 369         visit::walk_lifetime(self, lifetime);
 370     }
 371
 372     fn visit_item(&mut self, item: &'a Item) {
 373         if item.attrs.iter().any(|attr| is_proc_macro_attr(attr)  ) {
 374             self.has_proc_macro_decls = true;
 375         }
 376
 377         if attr::contains_name(&item.attrs, "global_allocator") {
 378             self.has_global_allocator = true;
 379         }
 380
 381         match item.node {
 382             ItemKind::Impl(unsafety, polarity, _, _, Some(..), ref ty, ref impl_items) => {
 383                 self.invalid_visibility(&item.vis, None);
 384                 if let TyKind::Err = ty.node {
 385                     self.err_handler()
 386                         .struct_span_err(item.span, "`impl Trait for .. {}` is an obsolete syntax")
 387                         .help("use `auto trait Trait {}` instead").emit();
 388                 }
 389                 if unsafety == Unsafety::Unsafe && polarity == ImplPolarity::Negative {
 390                     span_err!(self.session, item.span, E0198, "negative impls cannot be unsafe");
 391                 }
 392                 for impl_item in impl_items {
 393                     self.invalid_visibility(&impl_item.vis, None);
 394                     if let ImplItemKind::Method(ref sig, _) = impl_item.node {
 395                         self.check_trait_fn_not_const(sig.header.constness);
 396                         self.check_trait_fn_not_async(impl_item.span, sig.header.asyncness);
 397                     }
 398                 }
 399             }
 400             ItemKind::Impl(unsafety, polarity, defaultness, _, None, _, _) => {
 401                 self.invalid_visibility(&item.vis,
 402                                         Some("place qualifiers on individual impl items instead"));
 403                 if unsafety == Unsafety::Unsafe {
 404                     span_err!(self.session, item.span, E0197, "inherent impls cannot be unsafe");
 405                 }
 406                 if polarity == ImplPolarity::Negative {
 407                     self.err_handler().span_err(item.span, "inherent impls cannot be negative");
 408                 }
 409                 if defaultness == Defaultness::Default {
 410                     self.err_handler()
 411                         .struct_span_err(item.span, "inherent impls cannot be default")
 412                         .note("only trait implementations may be annotated with default").emit();
 413                 }
 414             }
 415             ItemKind::ForeignMod(..) => {
 416                 self.invalid_visibility(
 417                     &item.vis,
 418                     Some("place qualifiers on individual foreign items instead"),
 419                 );
 420             }
 421             ItemKind::Enum(ref def, _) => {
 422                 for variant in &def.variants {
 423                     self.invalid_non_exhaustive_attribute(variant);
 424                     for field in variant.node.data.fields() {
 425                         self.invalid_visibility(&field.vis, None);
 426                     }
 427                 }
 428             }
 429             ItemKind::Trait(is_auto, _, ref generics, ref bounds, ref trait_items) => {
 430                 if is_auto == IsAuto::Yes {
 431                     // Auto traits cannot have generics, super traits nor contain items.
 432                     if !generics.params.is_empty() {
 433                         struct_span_err!(self.session, item.span, E0567,
 434                                         "auto traits cannot have generic parameters").emit();
 435                     }
 436                     if !bounds.is_empty() {
 437                         struct_span_err!(self.session, item.span, E0568,
 438                                         "auto traits cannot have super traits").emit();
 439                     }
 440                     if !trait_items.is_empty() {
 441                         struct_span_err!(self.session, item.span, E0380,
 442                                 "auto traits cannot have methods or associated items").emit();
 443                     }
 444                 }
 445                 self.no_questions_in_bounds(bounds, "supertraits", true);
 446                 for trait_item in trait_items {
 447                     if let TraitItemKind::Method(ref sig, ref block) = trait_item.node {
 448                         self.check_trait_fn_not_async(trait_item.span, sig.header.asyncness);
 449                         self.check_trait_fn_not_const(sig.header.constness);
 450                         if block.is_none() {
 451                             self.check_decl_no_pat(&sig.decl, |span, mut_ident| {
 452                                 if mut_ident {
 453                                     self.session.buffer_lint(
 454                                         lint::builtin::PATTERNS_IN_FNS_WITHOUT_BODY,
 455                                         trait_item.id, span,
 456                                         "patterns aren't allowed in methods without bodies");
 457                                 } else {
 458                                     struct_span_err!(self.session, span, E0642,
 459                                         "patterns aren't allowed in methods without bodies").emit();
 460                                 }
 461                             });
 462                         }
 463                     }
 464                 }
 465             }
 466             ItemKind::Mod(_) => {
 467                 // Ensure that `path` attributes on modules are recorded as used (cf. issue #35584).
 468                 attr::first_attr_value_str_by_name(&item.attrs, "path");
 469                 if attr::contains_name(&item.attrs, "warn_directory_ownership") {
 470                     let lint = lint::builtin::LEGACY_DIRECTORY_OWNERSHIP;
 471                     let msg = "cannot declare a new module at this location";
 472                     self.session.buffer_lint(lint, item.id, item.span, msg);
 473                 }
 474             }
 475             ItemKind::Union(ref vdata, _) => {
 476                 if !vdata.is_struct() {
 477                     self.err_handler().span_err(item.span,
 478                                                 "tuple and unit unions are not permitted");
 479                 }
 480                 if vdata.fields().is_empty() {
 481                     self.err_handler().span_err(item.span,
 482                                                 "unions cannot have zero fields");
 483                 }
 484             }
 485             _ => {}
 486         }
 487
 488         visit::walk_item(self, item)
 489     }
 490
 491     fn visit_foreign_item(&mut self, fi: &'a ForeignItem) {
 492         match fi.node {
 493             ForeignItemKind::Fn(ref decl, _) => {
 494                 self.check_decl_no_pat(decl, |span, _| {
 495                     struct_span_err!(self.session, span, E0130,
 496                                      "patterns aren't allowed in foreign function declarations")
 497                         .span_label(span, "pattern not allowed in foreign function").emit();
 498                 });
 499             }
 500             ForeignItemKind::Static(..) | ForeignItemKind::Ty | ForeignItemKind::Macro(..) => {}
 501         }
 502
 503         visit::walk_foreign_item(self, fi)
 504     }
 505
 506     // Mirrors visit::walk_generic_args, but tracks relevant state
 507     fn visit_generic_args(&mut self, _: Span, generic_args: &'a GenericArgs) {
 508         match *generic_args {
 509             GenericArgs::AngleBracketed(ref data) => {
 510                 walk_list!(self, visit_generic_arg, &data.args);
 511                 // Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
 512                 // are allowed to contain nested `impl Trait`.
 513                 self.with_impl_trait(None, |this| {
 514                     walk_list!(this, visit_assoc_type_binding, &data.bindings);
 515                 });
 516             }
 517             GenericArgs::Parenthesized(ref data) => {
 518                 walk_list!(self, visit_ty, &data.inputs);
 519                 if let Some(ref type_) = data.output {
 520                     // `-> Foo` syntax is essentially an associated type binding,
 521                     // so it is also allowed to contain nested `impl Trait`.
 522                     self.with_impl_trait(None, |this| visit::walk_ty(this, type_));
 523                 }
 524             }
 525         }
 526     }
 527
 528     fn visit_generics(&mut self, generics: &'a Generics) {
 529         let mut seen_non_lifetime_param = false;
 530         let mut seen_default = None;
 531         for param in &generics.params {
 532             match (&param.kind, seen_non_lifetime_param) {
 533                 (GenericParamKind::Lifetime { .. }, true) => {
 534                     self.err_handler()
 535                         .span_err(param.ident.span, "lifetime parameters must be leading");
 536                 },
 537                 (GenericParamKind::Lifetime { .. }, false) => {}
 538                 (GenericParamKind::Type { ref default, .. }, _) => {
 539                     seen_non_lifetime_param = true;
 540                     if default.is_some() {
 541                         seen_default = Some(param.ident.span);
 542                     } else if let Some(span) = seen_default {
 543                         self.err_handler()
 544                             .span_err(span, "type parameters with a default must be trailing");
 545                         break;
 546                     }
 547                 }
 548             }
 549         }
 550         for predicate in &generics.where_clause.predicates {
 551             if let WherePredicate::EqPredicate(ref predicate) = *predicate {
 552                 self.err_handler()
 553                     .span_err(predicate.span, "equality constraints are not yet \
 554                                                supported in where clauses (see #20041)");
 555             }
 556         }
 557         visit::walk_generics(self, generics)
 558     }
 559
 560     fn visit_generic_param(&mut self, param: &'a GenericParam) {
 561         if let GenericParamKind::Lifetime { .. } = param.kind {
 562             self.check_lifetime(param.ident);
 563         }
 564         visit::walk_generic_param(self, param);
 565     }
 566
 567     fn visit_pat(&mut self, pat: &'a Pat) {
 568         match pat.node {
 569             PatKind::Lit(ref expr) => {
 570                 self.check_expr_within_pat(expr, false);
 571             }
 572             PatKind::Range(ref start, ref end, _) => {
 573                 self.check_expr_within_pat(start, true);
 574                 self.check_expr_within_pat(end, true);
 575             }
 576             _ => {}
 577         }
 578
 579         visit::walk_pat(self, pat)
 580     }
 581
 582     fn visit_where_predicate(&mut self, p: &'a WherePredicate) {
 583         if let &WherePredicate::BoundPredicate(ref bound_predicate) = p {
 584             // A type binding, eg `for<'c> Foo: Send+Clone+'c`
 585             self.check_late_bound_lifetime_defs(&bound_predicate.bound_generic_params);
 586         }
 587         visit::walk_where_predicate(self, p);
 588     }
 589
 590     fn visit_poly_trait_ref(&mut self, t: &'a PolyTraitRef, m: &'a TraitBoundModifier) {
 591         self.check_late_bound_lifetime_defs(&t.bound_generic_params);
 592         visit::walk_poly_trait_ref(self, t, m);
 593     }
 594
 595     fn visit_mac(&mut self, mac: &Spanned<Mac_>) {
 596         // when a new macro kind is added but the author forgets to set it up for expansion
 597         // because that's the only part that won't cause a compiler error
 598         self.session.diagnostic()
 599             .span_bug(mac.span, "macro invocation missed in expansion; did you forget to override \
 600                                  the relevant `fold_*()` method in `PlaceholderExpander`?");
 601     }
 602 }
 603
 604 pub fn check_crate(session: &Session, krate: &Crate) -> (bool, bool) {
 605     let mut validator = AstValidator {
 606         session,
 607         has_proc_macro_decls: false,
 608         has_global_allocator: false,
 609         outer_impl_trait: None,
 610         is_impl_trait_banned: false,
 611     };
 612     visit::walk_crate(&mut validator, krate);
 613
 614     (validator.has_proc_macro_decls, validator.has_global_allocator)
 615 }