src/librustc_infer/infer/error_reporting/need_type_info.rs

   1 use crate::infer::type_variable::TypeVariableOriginKind;
   2 use crate::infer::InferCtxt;
   3 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
   4 use rustc_hir as hir;
   5 use rustc_hir::def::{DefKind, Namespace};
   6 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
   7 use rustc_hir::{Body, Expr, ExprKind, FnRetTy, HirId, Local, Pat};
   8 use rustc_middle::hir::map::Map;
   9 use rustc_middle::ty::print::Print;
  10 use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
  11 use rustc_middle::ty::{self, DefIdTree, Ty};
  12 use rustc_span::source_map::DesugaringKind;
  13 use rustc_span::symbol::kw;
  14 use rustc_span::Span;
  15 use std::borrow::Cow;
  16
  17 struct FindHirNodeVisitor<'a, 'tcx> {
  18     infcx: &'a InferCtxt<'a, 'tcx>,
  19     target: GenericArg<'tcx>,
  20     found_node_ty: Option<Ty<'tcx>>,
  21     found_local_pattern: Option<&'tcx Pat<'tcx>>,
  22     found_arg_pattern: Option<&'tcx Pat<'tcx>>,
  23     found_closure: Option<&'tcx Expr<'tcx>>,
  24     found_method_call: Option<&'tcx Expr<'tcx>>,
  25 }
  26
  27 impl<'a, 'tcx> FindHirNodeVisitor<'a, 'tcx> {
  28     fn new(infcx: &'a InferCtxt<'a, 'tcx>, target: GenericArg<'tcx>) -> Self {
  29         Self {
  30             infcx,
  31             target,
  32             found_node_ty: None,
  33             found_local_pattern: None,
  34             found_arg_pattern: None,
  35             found_closure: None,
  36             found_method_call: None,
  37         }
  38     }
  39
  40     fn node_ty_contains_target(&mut self, hir_id: HirId) -> Option<Ty<'tcx>> {
  41         let ty_opt =
  42             self.infcx.in_progress_tables.and_then(|tables| tables.borrow().node_type_opt(hir_id));
  43         match ty_opt {
  44             Some(ty) => {
  45                 let ty = self.infcx.resolve_vars_if_possible(&ty);
  46                 if ty.walk().any(|inner| {
  47                     inner == self.target
  48                         || match (inner.unpack(), self.target.unpack()) {
  49                             (GenericArgKind::Type(inner_ty), GenericArgKind::Type(target_ty)) => {
  50                                 match (&inner_ty.kind, &target_ty.kind) {
  51                                     (
  52                                         &ty::Infer(ty::TyVar(a_vid)),
  53                                         &ty::Infer(ty::TyVar(b_vid)),
  54                                     ) => self
  55                                         .infcx
  56                                         .inner
  57                                         .borrow_mut()
  58                                         .type_variables
  59                                         .sub_unified(a_vid, b_vid),
  60                                     _ => false,
  61                                 }
  62                             }
  63                             _ => false,
  64                         }
  65                 }) {
  66                     Some(ty)
  67                 } else {
  68                     None
  69                 }
  70             }
  71             None => None,
  72         }
  73     }
  74 }
  75
  76 impl<'a, 'tcx> Visitor<'tcx> for FindHirNodeVisitor<'a, 'tcx> {
  77     type Map = Map<'tcx>;
  78
  79     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  80         NestedVisitorMap::OnlyBodies(self.infcx.tcx.hir())
  81     }
  82
  83     fn visit_local(&mut self, local: &'tcx Local<'tcx>) {
  84         if let (None, Some(ty)) =
  85             (self.found_local_pattern, self.node_ty_contains_target(local.hir_id))
  86         {
  87             self.found_local_pattern = Some(&*local.pat);
  88             self.found_node_ty = Some(ty);
  89         }
  90         intravisit::walk_local(self, local);
  91     }
  92
  93     fn visit_body(&mut self, body: &'tcx Body<'tcx>) {
  94         for param in body.params {
  95             if let (None, Some(ty)) =
  96                 (self.found_arg_pattern, self.node_ty_contains_target(param.hir_id))
  97             {
  98                 self.found_arg_pattern = Some(&*param.pat);
  99                 self.found_node_ty = Some(ty);
 100             }
 101         }
 102         intravisit::walk_body(self, body);
 103     }
 104
 105     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
 106         if self.node_ty_contains_target(expr.hir_id).is_some() {
 107             match expr.kind {
 108                 ExprKind::Closure(..) => self.found_closure = Some(&expr),
 109                 ExprKind::MethodCall(..) => self.found_method_call = Some(&expr),
 110                 _ => {}
 111             }
 112         }
 113         intravisit::walk_expr(self, expr);
 114     }
 115 }
 116
 117 /// Suggest giving an appropriate return type to a closure expression.
 118 fn closure_return_type_suggestion(
 119     span: Span,
 120     err: &mut DiagnosticBuilder<'_>,
 121     output: &FnRetTy<'_>,
 122     body: &Body<'_>,
 123     descr: &str,
 124     name: &str,
 125     ret: &str,
 126     parent_name: Option<String>,
 127     parent_descr: Option<&str>,
 128 ) {
 129     let (arrow, post) = match output {
 130         FnRetTy::DefaultReturn(_) => ("-> ", " "),
 131         _ => ("", ""),
 132     };
 133     let suggestion = match body.value.kind {
 134         ExprKind::Block(..) => vec![(output.span(), format!("{}{}{}", arrow, ret, post))],
 135         _ => vec![
 136             (output.span(), format!("{}{}{}{{ ", arrow, ret, post)),
 137             (body.value.span.shrink_to_hi(), " }".to_string()),
 138         ],
 139     };
 140     err.multipart_suggestion(
 141         "give this closure an explicit return type without `_` placeholders",
 142         suggestion,
 143         Applicability::HasPlaceholders,
 144     );
 145     err.span_label(span, InferCtxt::missing_type_msg(&name, &descr, parent_name, parent_descr));
 146 }
 147
 148 /// Given a closure signature, return a `String` containing a list of all its argument types.
 149 fn closure_args(fn_sig: &ty::PolyFnSig<'_>) -> String {
 150     fn_sig
 151         .inputs()
 152         .skip_binder()
 153         .iter()
 154         .next()
 155         .map(|args| args.tuple_fields().map(|arg| arg.to_string()).collect::<Vec<_>>().join(", "))
 156         .unwrap_or_default()
 157 }
 158
 159 pub enum TypeAnnotationNeeded {
 160     E0282,
 161     E0283,
 162     E0284,
 163 }
 164
 165 impl Into<rustc_errors::DiagnosticId> for TypeAnnotationNeeded {
 166     fn into(self) -> rustc_errors::DiagnosticId {
 167         match self {
 168             Self::E0282 => rustc_errors::error_code!(E0282),
 169             Self::E0283 => rustc_errors::error_code!(E0283),
 170             Self::E0284 => rustc_errors::error_code!(E0284),
 171         }
 172     }
 173 }
 174
 175 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 176     pub fn extract_type_name(
 177         &self,
 178         ty: Ty<'tcx>,
 179         highlight: Option<ty::print::RegionHighlightMode>,
 180     ) -> (String, Option<Span>, Cow<'static, str>, Option<String>, Option<&'static str>) {
 181         if let ty::Infer(ty::TyVar(ty_vid)) = ty.kind {
 182             let ty_vars = &self.inner.borrow().type_variables;
 183             let var_origin = ty_vars.var_origin(ty_vid);
 184             if let TypeVariableOriginKind::TypeParameterDefinition(name, def_id) = var_origin.kind {
 185                 let parent_def_id = def_id.and_then(|def_id| self.tcx.parent(def_id));
 186                 let (parent_name, parent_desc) = if let Some(parent_def_id) = parent_def_id {
 187                     let parent_name = self
 188                         .tcx
 189                         .def_key(parent_def_id)
 190                         .disambiguated_data
 191                         .data
 192                         .get_opt_name()
 193                         .map(|parent_symbol| parent_symbol.to_string());
 194
 195                     let type_parent_desc = self
 196                         .tcx
 197                         .def_kind(parent_def_id)
 198                         .map(|parent_def_kind| parent_def_kind.descr(parent_def_id));
 199
 200                     (parent_name, type_parent_desc)
 201                 } else {
 202                     (None, None)
 203                 };
 204
 205                 if name != kw::SelfUpper {
 206                     return (
 207                         name.to_string(),
 208                         Some(var_origin.span),
 209                         "type parameter".into(),
 210                         parent_name,
 211                         parent_desc,
 212                     );
 213                 }
 214             }
 215         }
 216
 217         let mut s = String::new();
 218         let mut printer = ty::print::FmtPrinter::new(self.tcx, &mut s, Namespace::TypeNS);
 219         if let Some(highlight) = highlight {
 220             printer.region_highlight_mode = highlight;
 221         }
 222         let _ = ty.print(printer);
 223         (s, None, ty.prefix_string(), None, None)
 224     }
 225
 226     // FIXME(eddyb) generalize all of this to handle `ty::Const` inference variables as well.
 227     pub fn need_type_info_err(
 228         &self,
 229         body_id: Option<hir::BodyId>,
 230         span: Span,
 231         ty: Ty<'tcx>,
 232         error_code: TypeAnnotationNeeded,
 233     ) -> DiagnosticBuilder<'tcx> {
 234         let ty = self.resolve_vars_if_possible(&ty);
 235         let (name, name_sp, descr, parent_name, parent_descr) = self.extract_type_name(&ty, None);
 236
 237         let mut local_visitor = FindHirNodeVisitor::new(&self, ty.into());
 238         let ty_to_string = |ty: Ty<'tcx>| -> String {
 239             let mut s = String::new();
 240             let mut printer = ty::print::FmtPrinter::new(self.tcx, &mut s, Namespace::TypeNS);
 241             let ty_vars = &self.inner.borrow().type_variables;
 242             let getter = move |ty_vid| {
 243                 let var_origin = ty_vars.var_origin(ty_vid);
 244                 if let TypeVariableOriginKind::TypeParameterDefinition(name, _) = var_origin.kind {
 245                     return Some(name.to_string());
 246                 }
 247                 None
 248             };
 249             printer.name_resolver = Some(Box::new(&getter));
 250             let _ = ty.print(printer);
 251             s
 252         };
 253
 254         if let Some(body_id) = body_id {
 255             let expr = self.tcx.hir().expect_expr(body_id.hir_id);
 256             local_visitor.visit_expr(expr);
 257         }
 258         let err_span = if let Some(pattern) = local_visitor.found_arg_pattern {
 259             pattern.span
 260         } else if let Some(span) = name_sp {
 261             // `span` here lets us point at `sum` instead of the entire right hand side expr:
 262             // error[E0282]: type annotations needed
 263             //  --> file2.rs:3:15
 264             //   |
 265             // 3 |     let _ = x.sum() as f64;
 266             //   |               ^^^ cannot infer type for `S`
 267             span
 268         } else if let Some(ExprKind::MethodCall(_, call_span, _)) =
 269             local_visitor.found_method_call.map(|e| &e.kind)
 270         {
 271             // Point at the call instead of the whole expression:
 272             // error[E0284]: type annotations needed
 273             //  --> file.rs:2:5
 274             //   |
 275             // 2 |     vec![Ok(2)].into_iter().collect()?;
 276             //   |                             ^^^^^^^ cannot infer type
 277             //   |
 278             //   = note: cannot resolve `<_ as std::ops::Try>::Ok == _`
 279             if span.contains(*call_span) { *call_span } else { span }
 280         } else {
 281             span
 282         };
 283
 284         let is_named_and_not_impl_trait = |ty: Ty<'_>| {
 285             &ty.to_string() != "_" &&
 286                 // FIXME: Remove this check after `impl_trait_in_bindings` is stabilized. #63527
 287                 (!ty.is_impl_trait() || self.tcx.features().impl_trait_in_bindings)
 288         };
 289
 290         let ty_msg = match local_visitor.found_node_ty {
 291             Some(ty::TyS { kind: ty::Closure(_, substs), .. }) => {
 292                 let fn_sig = substs.as_closure().sig();
 293                 let args = closure_args(&fn_sig);
 294                 let ret = fn_sig.output().skip_binder().to_string();
 295                 format!(" for the closure `fn({}) -> {}`", args, ret)
 296             }
 297             Some(ty) if is_named_and_not_impl_trait(ty) => {
 298                 let ty = ty_to_string(ty);
 299                 format!(" for `{}`", ty)
 300             }
 301             _ => String::new(),
 302         };
 303
 304         // When `name` corresponds to a type argument, show the path of the full type we're
 305         // trying to infer. In the following example, `ty_msg` contains
 306         // " in `std::result::Result<i32, E>`":
 307         // ```
 308         // error[E0282]: type annotations needed for `std::result::Result<i32, E>`
 309         //  --> file.rs:L:CC
 310         //   |
 311         // L |     let b = Ok(4);
 312         //   |         -   ^^ cannot infer type for `E` in `std::result::Result<i32, E>`
 313         //   |         |
 314         //   |         consider giving `b` the explicit type `std::result::Result<i32, E>`, where
 315         //   |         the type parameter `E` is specified
 316         // ```
 317         let error_code = error_code.into();
 318         let mut err = self.tcx.sess.struct_span_err_with_code(
 319             err_span,
 320             &format!("type annotations needed{}", ty_msg),
 321             error_code,
 322         );
 323
 324         let suffix = match local_visitor.found_node_ty {
 325             Some(ty::TyS { kind: ty::Closure(_, substs), .. }) => {
 326                 let fn_sig = substs.as_closure().sig();
 327                 let ret = fn_sig.output().skip_binder().to_string();
 328
 329                 let closure_decl_and_body_id =
 330                     local_visitor.found_closure.and_then(|closure| match &closure.kind {
 331                         ExprKind::Closure(_, decl, body_id, ..) => Some((decl, *body_id)),
 332                         _ => None,
 333                     });
 334
 335                 if let Some((decl, body_id)) = closure_decl_and_body_id {
 336                     closure_return_type_suggestion(
 337                         span,
 338                         &mut err,
 339                         &decl.output,
 340                         self.tcx.hir().body(body_id),
 341                         &descr,
 342                         &name,
 343                         &ret,
 344                         parent_name,
 345                         parent_descr,
 346                     );
 347                     // We don't want to give the other suggestions when the problem is the
 348                     // closure return type.
 349                     return err;
 350                 }
 351
 352                 // This shouldn't be reachable, but just in case we leave a reasonable fallback.
 353                 let args = closure_args(&fn_sig);
 354                 // This suggestion is incomplete, as the user will get further type inference
 355                 // errors due to the `_` placeholders and the introduction of `Box`, but it does
 356                 // nudge them in the right direction.
 357                 format!("a boxed closure type like `Box<dyn Fn({}) -> {}>`", args, ret)
 358             }
 359             Some(ty) if is_named_and_not_impl_trait(ty) && name == "_" => {
 360                 let ty = ty_to_string(ty);
 361                 format!("the explicit type `{}`, with the type parameters specified", ty)
 362             }
 363             Some(ty) if is_named_and_not_impl_trait(ty) && ty.to_string() != name => {
 364                 let ty = ty_to_string(ty);
 365                 format!(
 366                     "the explicit type `{}`, where the type parameter `{}` is specified",
 367                     ty, name,
 368                 )
 369             }
 370             _ => "a type".to_string(),
 371         };
 372
 373         if let Some(pattern) = local_visitor.found_arg_pattern {
 374             // We don't want to show the default label for closures.
 375             //
 376             // So, before clearing, the output would look something like this:
 377             // ```
 378             // let x = |_| {  };
 379             //          -  ^^^^ cannot infer type for `[_; 0]`
 380             //          |
 381             //          consider giving this closure parameter a type
 382             // ```
 383             //
 384             // After clearing, it looks something like this:
 385             // ```
 386             // let x = |_| {  };
 387             //          ^ consider giving this closure parameter the type `[_; 0]`
 388             //            with the type parameter `_` specified
 389             // ```
 390             err.span_label(
 391                 pattern.span,
 392                 format!("consider giving this closure parameter {}", suffix),
 393             );
 394         } else if let Some(pattern) = local_visitor.found_local_pattern {
 395             let msg = if let Some(simple_ident) = pattern.simple_ident() {
 396                 match pattern.span.desugaring_kind() {
 397                     None => format!("consider giving `{}` {}", simple_ident, suffix),
 398                     Some(DesugaringKind::ForLoop) => {
 399                         "the element type for this iterator is not specified".to_string()
 400                     }
 401                     _ => format!("this needs {}", suffix),
 402                 }
 403             } else {
 404                 format!("consider giving this pattern {}", suffix)
 405             };
 406             err.span_label(pattern.span, msg);
 407         } else if let Some(e) = local_visitor.found_method_call {
 408             if let ExprKind::MethodCall(segment, ..) = &e.kind {
 409                 // Suggest specifying type params or point out the return type of the call:
 410                 //
 411                 // error[E0282]: type annotations needed
 412                 //   --> $DIR/type-annotations-needed-expr.rs:2:39
 413                 //    |
 414                 // LL |     let _ = x.into_iter().sum() as f64;
 415                 //    |                           ^^^
 416                 //    |                           |
 417                 //    |                           cannot infer type for `S`
 418                 //    |                           help: consider specifying the type argument in
 419                 //    |                           the method call: `sum::<S>`
 420                 //    |
 421                 //    = note: type must be known at this point
 422                 //
 423                 // or
 424                 //
 425                 // error[E0282]: type annotations needed
 426                 //   --> $DIR/issue-65611.rs:59:20
 427                 //    |
 428                 // LL |     let x = buffer.last().unwrap().0.clone();
 429                 //    |             -------^^^^--
 430                 //    |             |      |
 431                 //    |             |      cannot infer type for `T`
 432                 //    |             this method call resolves to `std::option::Option<&T>`
 433                 //    |
 434                 //    = note: type must be known at this point
 435                 self.annotate_method_call(segment, e, &mut err);
 436             }
 437         }
 438         // Instead of the following:
 439         // error[E0282]: type annotations needed
 440         //  --> file2.rs:3:15
 441         //   |
 442         // 3 |     let _ = x.sum() as f64;
 443         //   |             --^^^--------- cannot infer type for `S`
 444         //   |
 445         //   = note: type must be known at this point
 446         // We want:
 447         // error[E0282]: type annotations needed
 448         //  --> file2.rs:3:15
 449         //   |
 450         // 3 |     let _ = x.sum() as f64;
 451         //   |               ^^^ cannot infer type for `S`
 452         //   |
 453         //   = note: type must be known at this point
 454         let span = name_sp.unwrap_or(err_span);
 455         if !err
 456             .span
 457             .span_labels()
 458             .iter()
 459             .any(|span_label| span_label.label.is_some() && span_label.span == span)
 460             && local_visitor.found_arg_pattern.is_none()
 461         {
 462             // Avoid multiple labels pointing at `span`.
 463             err.span_label(
 464                 span,
 465                 InferCtxt::missing_type_msg(&name, &descr, parent_name, parent_descr),
 466             );
 467         }
 468
 469         err
 470     }
 471
 472     /// If the `FnSig` for the method call can be found and type arguments are identified as
 473     /// needed, suggest annotating the call, otherwise point out the resulting type of the call.
 474     fn annotate_method_call(
 475         &self,
 476         segment: &hir::PathSegment<'_>,
 477         e: &Expr<'_>,
 478         err: &mut DiagnosticBuilder<'_>,
 479     ) {
 480         if let (Some(tables), None) = (self.in_progress_tables, &segment.args) {
 481             let borrow = tables.borrow();
 482             if let Some((DefKind::AssocFn, did)) = borrow.type_dependent_def(e.hir_id) {
 483                 let generics = self.tcx.generics_of(did);
 484                 if !generics.params.is_empty() {
 485                     err.span_suggestion_verbose(
 486                         segment.ident.span.shrink_to_hi(),
 487                         &format!(
 488                             "consider specifying the type argument{} in the method call",
 489                             pluralize!(generics.params.len()),
 490                         ),
 491                         format!(
 492                             "::<{}>",
 493                             generics
 494                                 .params
 495                                 .iter()
 496                                 .map(|p| p.name.to_string())
 497                                 .collect::<Vec<String>>()
 498                                 .join(", ")
 499                         ),
 500                         Applicability::HasPlaceholders,
 501                     );
 502                 } else {
 503                     let sig = self.tcx.fn_sig(did);
 504                     let bound_output = sig.output();
 505                     let output = bound_output.skip_binder();
 506                     err.span_label(e.span, &format!("this method call resolves to `{:?}`", output));
 507                     let kind = &output.kind;
 508                     if let ty::Projection(proj) | ty::UnnormalizedProjection(proj) = kind {
 509                         if let Some(span) = self.tcx.hir().span_if_local(proj.item_def_id) {
 510                             err.span_label(span, &format!("`{:?}` defined here", output));
 511                         }
 512                     }
 513                 }
 514             }
 515         }
 516     }
 517
 518     pub fn need_type_info_err_in_generator(
 519         &self,
 520         kind: hir::GeneratorKind,
 521         span: Span,
 522         ty: Ty<'tcx>,
 523     ) -> DiagnosticBuilder<'tcx> {
 524         let ty = self.resolve_vars_if_possible(&ty);
 525         let (name, _, descr, parent_name, parent_descr) = self.extract_type_name(&ty, None);
 526
 527         let mut err = struct_span_err!(
 528             self.tcx.sess,
 529             span,
 530             E0698,
 531             "type inside {} must be known in this context",
 532             kind,
 533         );
 534         err.span_label(span, InferCtxt::missing_type_msg(&name, &descr, parent_name, parent_descr));
 535         err
 536     }
 537
 538     fn missing_type_msg(
 539         type_name: &str,
 540         descr: &str,
 541         parent_name: Option<String>,
 542         parent_descr: Option<&str>,
 543     ) -> Cow<'static, str> {
 544         if type_name == "_" {
 545             "cannot infer type".into()
 546         } else {
 547             let parent_desc = if let Some(parent_name) = parent_name {
 548                 let parent_type_descr = if let Some(parent_descr) = parent_descr {
 549                     format!(" the {}", parent_descr)
 550                 } else {
 551                     "".into()
 552                 };
 553
 554                 format!(" declared on{} `{}`", parent_type_descr, parent_name)
 555             } else {
 556                 "".to_string()
 557             };
 558
 559             format!("cannot infer type for {} `{}`{}", descr, type_name, parent_desc).into()
 560         }
 561     }
 562 }