1 use super::IsMethodCall;
3 AstConv, CreateSubstsForGenericArgsCtxt, ExplicitLateBound, GenericArgCountMismatch,
4 GenericArgCountResult, GenericArgPosition,
6 use crate::errors::AssocTypeBindingNotAllowed;
7 use crate::structured_errors::{GenericArgsInfo, StructuredDiagnostic, WrongNumberOfGenericArgs};
8 use rustc_ast::ast::ParamKindOrd;
9 use rustc_errors::{struct_span_err, Applicability, Diagnostic, MultiSpan};
11 use rustc_hir::def::{DefKind, Res};
12 use rustc_hir::def_id::DefId;
13 use rustc_hir::GenericArg;
14 use rustc_middle::ty::{
15 self, subst, subst::SubstsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty, TyCtxt,
17 use rustc_session::lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS;
18 use rustc_span::{symbol::kw, Span};
19 use smallvec::SmallVec;
21 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
22 /// Report an error that a generic argument did not match the generic parameter that was
24 fn generic_arg_mismatch_err(
27 param: &GenericParamDef,
28 possible_ordering_error: bool,
32 let mut err = struct_span_err!(
36 "{} provided when a {} was expected",
41 if let GenericParamDefKind::Const { .. } = param.kind {
42 if matches!(arg, GenericArg::Type(hir::Ty { kind: hir::TyKind::Infer, .. })) {
43 err.help("const arguments cannot yet be inferred with `_`");
44 if sess.is_nightly_build() {
46 "add `#![feature(generic_arg_infer)]` to the crate attributes to enable",
52 let add_braces_suggestion = |arg: &GenericArg<'_>, err: &mut Diagnostic| {
53 let suggestions = vec![
54 (arg.span().shrink_to_lo(), String::from("{ ")),
55 (arg.span().shrink_to_hi(), String::from(" }")),
57 err.multipart_suggestion(
58 "if this generic argument was intended as a const parameter, \
59 surround it with braces",
61 Applicability::MaybeIncorrect,
65 // Specific suggestion set for diagnostics
66 match (arg, ¶m.kind) {
68 GenericArg::Type(hir::Ty {
69 kind: hir::TyKind::Path(rustc_hir::QPath::Resolved(_, path)),
72 GenericParamDefKind::Const { .. },
75 add_braces_suggestion(arg, &mut err);
76 err.set_primary_message(
77 "unresolved item provided when a constant was expected",
82 Res::Def(DefKind::TyParam, src_def_id) => {
83 if let Some(param_local_id) = param.def_id.as_local() {
84 let param_name = tcx.hir().ty_param_name(param_local_id);
85 let param_type = tcx.type_of(param.def_id);
86 if param_type.is_suggestable(tcx, false) {
88 tcx.def_span(src_def_id),
89 "consider changing this type parameter to be a `const` generic",
90 format!("const {}: {}", param_name, param_type),
91 Applicability::MaybeIncorrect,
96 _ => add_braces_suggestion(arg, &mut err),
99 GenericArg::Type(hir::Ty { kind: hir::TyKind::Path(_), .. }),
100 GenericParamDefKind::Const { .. },
101 ) => add_braces_suggestion(arg, &mut err),
103 GenericArg::Type(hir::Ty { kind: hir::TyKind::Array(_, len), .. }),
104 GenericParamDefKind::Const { .. },
105 ) if tcx.type_of(param.def_id) == tcx.types.usize => {
106 let snippet = sess.source_map().span_to_snippet(tcx.hir().span(len.hir_id()));
107 if let Ok(snippet) = snippet {
110 "array type provided where a `usize` was expected, try",
111 format!("{{ {} }}", snippet),
112 Applicability::MaybeIncorrect,
116 (GenericArg::Const(cnst), GenericParamDefKind::Type { .. }) => {
117 let body = tcx.hir().body(cnst.value.body);
118 if let rustc_hir::ExprKind::Path(rustc_hir::QPath::Resolved(_, path)) =
121 if let Res::Def(DefKind::Fn { .. }, id) = path.res {
123 "`{}` is a function item, not a type",
126 err.help("function item types cannot be named directly");
133 let kind_ord = param.kind.to_ord();
134 let arg_ord = arg.to_ord();
136 // This note is only true when generic parameters are strictly ordered by their kind.
137 if possible_ordering_error && kind_ord.cmp(&arg_ord) != core::cmp::Ordering::Equal {
138 let (first, last) = if kind_ord < arg_ord {
139 (param.kind.descr(), arg.descr())
141 (arg.descr(), param.kind.descr())
143 err.note(&format!("{} arguments must be provided before {} arguments", first, last));
144 if let Some(help) = help {
152 /// Creates the relevant generic argument substitutions
153 /// corresponding to a set of generic parameters. This is a
154 /// rather complex function. Let us try to explain the role
155 /// of each of its parameters:
157 /// To start, we are given the `def_id` of the thing we are
158 /// creating the substitutions for, and a partial set of
159 /// substitutions `parent_substs`. In general, the substitutions
160 /// for an item begin with substitutions for all the "parents" of
161 /// that item -- e.g., for a method it might include the
162 /// parameters from the impl.
164 /// Therefore, the method begins by walking down these parents,
165 /// starting with the outermost parent and proceed inwards until
166 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
167 /// first to see if the parent's substitutions are listed in there. If so,
168 /// we can append those and move on. Otherwise, it invokes the
169 /// three callback functions:
171 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
172 /// generic arguments that were given to that parent from within
173 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
174 /// might refer to the trait `Foo`, and the arguments might be
175 /// `[T]`. The boolean value indicates whether to infer values
176 /// for arguments whose values were not explicitly provided.
177 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
178 /// instantiate a `GenericArg`.
179 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
180 /// creates a suitable inference variable.
181 pub fn create_substs_for_generic_args<'a>(
184 parent_substs: &[subst::GenericArg<'tcx>],
186 self_ty: Option<Ty<'tcx>>,
187 arg_count: &GenericArgCountResult,
188 ctx: &mut impl CreateSubstsForGenericArgsCtxt<'a, 'tcx>,
189 ) -> SubstsRef<'tcx> {
190 // Collect the segments of the path; we need to substitute arguments
191 // for parameters throughout the entire path (wherever there are
192 // generic parameters).
193 let mut parent_defs = tcx.generics_of(def_id);
194 let count = parent_defs.count();
195 let mut stack = vec![(def_id, parent_defs)];
196 while let Some(def_id) = parent_defs.parent {
197 parent_defs = tcx.generics_of(def_id);
198 stack.push((def_id, parent_defs));
201 // We manually build up the substitution, rather than using convenience
202 // methods in `subst.rs`, so that we can iterate over the arguments and
203 // parameters in lock-step linearly, instead of trying to match each pair.
204 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
205 // Iterate over each segment of the path.
206 while let Some((def_id, defs)) = stack.pop() {
207 let mut params = defs.params.iter().peekable();
209 // If we have already computed substitutions for parents, we can use those directly.
210 while let Some(¶m) = params.peek() {
211 if let Some(&kind) = parent_substs.get(param.index as usize) {
219 // `Self` is handled first, unless it's been handled in `parent_substs`.
221 if let Some(¶m) = params.peek() {
222 if param.index == 0 {
223 if let GenericParamDefKind::Type { .. } = param.kind {
227 .unwrap_or_else(|| ctx.inferred_kind(None, param, true)),
235 // Check whether this segment takes generic arguments and the user has provided any.
236 let (generic_args, infer_args) = ctx.args_for_def_id(def_id);
238 let args_iter = generic_args.iter().flat_map(|generic_args| generic_args.args.iter());
239 let mut args = args_iter.clone().peekable();
241 // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
242 // If we later encounter a lifetime, we know that the arguments were provided in the
243 // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
244 // inferred, so we can use it for diagnostics later.
245 let mut force_infer_lt = None;
248 // We're going to iterate through the generic arguments that the user
249 // provided, matching them with the generic parameters we expect.
250 // Mismatches can occur as a result of elided lifetimes, or for malformed
251 // input. We try to handle both sensibly.
252 match (args.peek(), params.peek()) {
253 (Some(&arg), Some(¶m)) => {
254 match (arg, ¶m.kind, arg_count.explicit_late_bound) {
255 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
257 GenericArg::Type(_) | GenericArg::Infer(_),
258 GenericParamDefKind::Type { .. },
262 GenericArg::Const(_) | GenericArg::Infer(_),
263 GenericParamDefKind::Const { .. },
266 substs.push(ctx.provided_kind(param, arg));
271 GenericArg::Infer(_) | GenericArg::Type(_) | GenericArg::Const(_),
272 GenericParamDefKind::Lifetime,
275 // We expected a lifetime argument, but got a type or const
276 // argument. That means we're inferring the lifetimes.
277 substs.push(ctx.inferred_kind(None, param, infer_args));
278 force_infer_lt = Some((arg, param));
281 (GenericArg::Lifetime(_), _, ExplicitLateBound::Yes) => {
282 // We've come across a lifetime when we expected something else in
283 // the presence of explicit late bounds. This is most likely
284 // due to the presence of the explicit bound so we're just going to
289 // We expected one kind of parameter, but the user provided
290 // another. This is an error. However, if we already know that
291 // the arguments don't match up with the parameters, we won't issue
292 // an additional error, as the user already knows what's wrong.
293 if arg_count.correct.is_ok() {
294 // We're going to iterate over the parameters to sort them out, and
295 // show that order to the user as a possible order for the parameters
296 let mut param_types_present = defs
299 .map(|param| (param.kind.to_ord(), param.clone()))
300 .collect::<Vec<(ParamKindOrd, GenericParamDef)>>();
301 param_types_present.sort_by_key(|(ord, _)| *ord);
302 let (mut param_types_present, ordered_params): (
304 Vec<GenericParamDef>,
305 ) = param_types_present.into_iter().unzip();
306 param_types_present.dedup();
308 Self::generic_arg_mismatch_err(
312 !args_iter.clone().is_sorted_by_key(|arg| arg.to_ord()),
314 "reorder the arguments: {}: `<{}>`",
317 .map(|ord| format!("{}s", ord))
318 .collect::<Vec<String>>()
322 .filter_map(|param| {
323 if param.name == kw::SelfUpper {
326 Some(param.name.to_string())
329 .collect::<Vec<String>>()
335 // We've reported the error, but we want to make sure that this
336 // problem doesn't bubble down and create additional, irrelevant
337 // errors. In this case, we're simply going to ignore the argument
338 // and any following arguments. The rest of the parameters will be
340 while args.next().is_some() {}
345 (Some(&arg), None) => {
346 // We should never be able to reach this point with well-formed input.
347 // There are three situations in which we can encounter this issue.
349 // 1. The number of arguments is incorrect. In this case, an error
350 // will already have been emitted, and we can ignore it.
351 // 2. There are late-bound lifetime parameters present, yet the
352 // lifetime arguments have also been explicitly specified by the
354 // 3. We've inferred some lifetimes, which have been provided later (i.e.
355 // after a type or const). We want to throw an error in this case.
357 if arg_count.correct.is_ok()
358 && arg_count.explicit_late_bound == ExplicitLateBound::No
360 let kind = arg.descr();
361 assert_eq!(kind, "lifetime");
362 let (provided_arg, param) =
363 force_infer_lt.expect("lifetimes ought to have been inferred");
364 Self::generic_arg_mismatch_err(tcx, provided_arg, param, false, None);
370 (None, Some(¶m)) => {
371 // If there are fewer arguments than parameters, it means
372 // we're inferring the remaining arguments.
373 substs.push(ctx.inferred_kind(Some(&substs), param, infer_args));
377 (None, None) => break,
382 tcx.intern_substs(&substs)
385 /// Checks that the correct number of generic arguments have been provided.
386 /// Used specifically for function calls.
387 pub fn check_generic_arg_count_for_call(
391 generics: &ty::Generics,
392 seg: &hir::PathSegment<'_>,
393 is_method_call: IsMethodCall,
394 ) -> GenericArgCountResult {
395 let empty_args = hir::GenericArgs::none();
396 let gen_args = seg.args.unwrap_or(&empty_args);
397 let gen_pos = if is_method_call == IsMethodCall::Yes {
398 GenericArgPosition::MethodCall
400 GenericArgPosition::Value
402 let has_self = generics.parent.is_none() && generics.has_self;
404 Self::check_generic_arg_count(
417 /// Checks that the correct number of generic arguments have been provided.
418 /// This is used both for datatypes and function calls.
419 #[instrument(skip(tcx, gen_pos), level = "debug")]
420 pub(crate) fn check_generic_arg_count(
424 seg: &hir::PathSegment<'_>,
425 gen_params: &ty::Generics,
426 gen_args: &hir::GenericArgs<'_>,
427 gen_pos: GenericArgPosition,
430 ) -> GenericArgCountResult {
431 let default_counts = gen_params.own_defaults();
432 let param_counts = gen_params.own_counts();
434 // Subtracting from param count to ensure type params synthesized from `impl Trait`
435 // cannot be explicitly specified.
436 let synth_type_param_count = gen_params
440 matches!(param.kind, ty::GenericParamDefKind::Type { synthetic: true, .. })
443 let named_type_param_count =
444 param_counts.types - has_self as usize - synth_type_param_count;
445 let infer_lifetimes =
446 (gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();
448 if gen_pos != GenericArgPosition::Type && let Some(b) = gen_args.bindings.first() {
449 Self::prohibit_assoc_ty_binding(tcx, b.span);
452 let explicit_late_bound =
453 Self::prohibit_explicit_late_bound_lifetimes(tcx, gen_params, gen_args, gen_pos);
455 let mut invalid_args = vec![];
457 let mut check_lifetime_args =
458 |min_expected_args: usize,
459 max_expected_args: usize,
460 provided_args: usize,
461 late_bounds_ignore: bool| {
462 if (min_expected_args..=max_expected_args).contains(&provided_args) {
466 if late_bounds_ignore {
470 if provided_args > max_expected_args {
472 gen_args.args[max_expected_args..provided_args]
474 .map(|arg| arg.span()),
478 let gen_args_info = if provided_args > min_expected_args {
480 gen_args.args[min_expected_args..provided_args]
482 .map(|arg| arg.span()),
484 let num_redundant_args = provided_args - min_expected_args;
485 GenericArgsInfo::ExcessLifetimes { num_redundant_args }
487 let num_missing_args = min_expected_args - provided_args;
488 GenericArgsInfo::MissingLifetimes { num_missing_args }
491 let reported = WrongNumberOfGenericArgs::new(
506 let min_expected_lifetime_args = if infer_lifetimes { 0 } else { param_counts.lifetimes };
507 let max_expected_lifetime_args = param_counts.lifetimes;
508 let num_provided_lifetime_args = gen_args.num_lifetime_params();
510 let lifetimes_correct = check_lifetime_args(
511 min_expected_lifetime_args,
512 max_expected_lifetime_args,
513 num_provided_lifetime_args,
514 explicit_late_bound == ExplicitLateBound::Yes,
517 let mut check_types_and_consts = |expected_min,
519 expected_max_with_synth,
529 "check_types_and_consts"
531 if (expected_min..=expected_max).contains(&provided) {
535 let num_default_params = expected_max - expected_min;
537 let gen_args_info = if provided > expected_max {
539 gen_args.args[args_offset + expected_max..args_offset + provided]
541 .map(|arg| arg.span()),
543 let num_redundant_args = provided - expected_max;
545 // Provide extra note if synthetic arguments like `impl Trait` are specified.
546 let synth_provided = provided <= expected_max_with_synth;
548 GenericArgsInfo::ExcessTypesOrConsts {
555 let num_missing_args = expected_max - provided;
557 GenericArgsInfo::MissingTypesOrConsts {
564 debug!(?gen_args_info);
566 let reported = WrongNumberOfGenericArgs::new(
576 .emit_unless(gen_args.has_err());
582 let expected_min = if infer_args {
585 param_counts.consts + named_type_param_count
586 - default_counts.types
587 - default_counts.consts
589 debug!(?expected_min);
590 debug!(arg_counts.lifetimes=?gen_args.num_lifetime_params());
592 check_types_and_consts(
594 param_counts.consts + named_type_param_count,
595 param_counts.consts + named_type_param_count + synth_type_param_count,
596 gen_args.num_generic_params(),
597 param_counts.lifetimes + has_self as usize,
598 gen_args.num_lifetime_params(),
602 GenericArgCountResult {
604 correct: lifetimes_correct.and(args_correct).map_err(|reported| {
605 GenericArgCountMismatch { reported: Some(reported), invalid_args }
610 /// Emits an error regarding forbidden type binding associations
611 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
612 tcx.sess.emit_err(AssocTypeBindingNotAllowed { span });
615 /// Prohibits explicit lifetime arguments if late-bound lifetime parameters
616 /// are present. This is used both for datatypes and function calls.
617 pub(crate) fn prohibit_explicit_late_bound_lifetimes(
620 args: &hir::GenericArgs<'_>,
621 position: GenericArgPosition,
622 ) -> ExplicitLateBound {
623 let param_counts = def.own_counts();
624 let infer_lifetimes = position != GenericArgPosition::Type && !args.has_lifetime_params();
627 return ExplicitLateBound::No;
630 if let Some(span_late) = def.has_late_bound_regions {
631 let msg = "cannot specify lifetime arguments explicitly \
632 if late bound lifetime parameters are present";
633 let note = "the late bound lifetime parameter is introduced here";
634 let span = args.args[0].span();
636 if position == GenericArgPosition::Value
637 && args.num_lifetime_params() != param_counts.lifetimes
639 let mut err = tcx.sess.struct_span_err(span, msg);
640 err.span_note(span_late, note);
643 let mut multispan = MultiSpan::from_span(span);
644 multispan.push_span_label(span_late, note);
645 tcx.struct_span_lint_hir(
646 LATE_BOUND_LIFETIME_ARGUMENTS,
647 args.args[0].hir_id(),
654 ExplicitLateBound::Yes
656 ExplicitLateBound::No