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use super::IsMethodCall;
use crate::astconv::{
errors::prohibit_assoc_ty_binding, CreateSubstsForGenericArgsCtxt, ExplicitLateBound,
GenericArgCountMismatch, GenericArgCountResult, GenericArgPosition,
};
use crate::structured_errors::{GenericArgsInfo, StructuredDiagnostic, WrongNumberOfGenericArgs};
use rustc_ast::ast::ParamKindOrd;
use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::GenericArg;
use rustc_middle::ty::{
self, GenericArgsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty, TyCtxt,
};
use rustc_session::lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS;
use rustc_span::{symbol::kw, Span};
use smallvec::SmallVec;
/// Report an error that a generic argument did not match the generic parameter that was
/// expected.
fn generic_arg_mismatch_err(
tcx: TyCtxt<'_>,
arg: &GenericArg<'_>,
param: &GenericParamDef,
possible_ordering_error: bool,
help: Option<String>,
) -> ErrorGuaranteed {
let sess = tcx.sess;
let mut err = struct_span_err!(
sess,
arg.span(),
E0747,
"{} provided when a {} was expected",
arg.descr(),
param.kind.descr(),
);
if let GenericParamDefKind::Const { .. } = param.kind {
if matches!(arg, GenericArg::Type(hir::Ty { kind: hir::TyKind::Infer, .. })) {
err.help("const arguments cannot yet be inferred with `_`");
if sess.is_nightly_build() {
err.help("add `#![feature(generic_arg_infer)]` to the crate attributes to enable");
}
}
}
let add_braces_suggestion = |arg: &GenericArg<'_>, err: &mut Diagnostic| {
let suggestions = vec![
(arg.span().shrink_to_lo(), String::from("{ ")),
(arg.span().shrink_to_hi(), String::from(" }")),
];
err.multipart_suggestion(
"if this generic argument was intended as a const parameter, \
surround it with braces",
suggestions,
Applicability::MaybeIncorrect,
);
};
// Specific suggestion set for diagnostics
match (arg, ¶m.kind) {
(
GenericArg::Type(hir::Ty {
kind: hir::TyKind::Path(rustc_hir::QPath::Resolved(_, path)),
..
}),
GenericParamDefKind::Const { .. },
) => match path.res {
Res::Err => {
add_braces_suggestion(arg, &mut err);
return err
.set_primary_message("unresolved item provided when a constant was expected")
.emit();
}
Res::Def(DefKind::TyParam, src_def_id) => {
if let Some(param_local_id) = param.def_id.as_local() {
let param_name = tcx.hir().ty_param_name(param_local_id);
let param_type = tcx.type_of(param.def_id).instantiate_identity();
if param_type.is_suggestable(tcx, false) {
err.span_suggestion(
tcx.def_span(src_def_id),
"consider changing this type parameter to a const parameter",
format!("const {param_name}: {param_type}"),
Applicability::MaybeIncorrect,
);
};
}
}
_ => add_braces_suggestion(arg, &mut err),
},
(
GenericArg::Type(hir::Ty { kind: hir::TyKind::Path(_), .. }),
GenericParamDefKind::Const { .. },
) => add_braces_suggestion(arg, &mut err),
(
GenericArg::Type(hir::Ty { kind: hir::TyKind::Array(_, len), .. }),
GenericParamDefKind::Const { .. },
) if tcx.type_of(param.def_id).skip_binder() == tcx.types.usize => {
let snippet = sess.source_map().span_to_snippet(tcx.hir().span(len.hir_id()));
if let Ok(snippet) = snippet {
err.span_suggestion(
arg.span(),
"array type provided where a `usize` was expected, try",
format!("{{ {snippet} }}"),
Applicability::MaybeIncorrect,
);
}
}
(GenericArg::Const(cnst), GenericParamDefKind::Type { .. }) => {
let body = tcx.hir().body(cnst.value.body);
if let rustc_hir::ExprKind::Path(rustc_hir::QPath::Resolved(_, path)) = body.value.kind
{
if let Res::Def(DefKind::Fn { .. }, id) = path.res {
err.help(format!("`{}` is a function item, not a type", tcx.item_name(id)));
err.help("function item types cannot be named directly");
}
}
}
_ => {}
}
let kind_ord = param.kind.to_ord();
let arg_ord = arg.to_ord();
// This note is only true when generic parameters are strictly ordered by their kind.
if possible_ordering_error && kind_ord.cmp(&arg_ord) != core::cmp::Ordering::Equal {
let (first, last) = if kind_ord < arg_ord {
(param.kind.descr(), arg.descr())
} else {
(arg.descr(), param.kind.descr())
};
err.note(format!("{first} arguments must be provided before {last} arguments"));
if let Some(help) = help {
err.help(help);
}
}
err.emit()
}
/// Creates the relevant generic arguments
/// corresponding to a set of generic parameters. This is a
/// rather complex function. Let us try to explain the role
/// of each of its parameters:
///
/// To start, we are given the `def_id` of the thing whose generic
/// parameters we are instantiating, and a partial set of
/// arguments `parent_args`. In general, the generic arguments
/// for an item begin with arguments for all the "parents" of
/// that item -- e.g., for a method it might include the
/// parameters from the impl.
///
/// Therefore, the method begins by walking down these parents,
/// starting with the outermost parent and proceed inwards until
/// it reaches `def_id`. For each parent `P`, it will check `parent_args`
/// first to see if the parent's arguments are listed in there. If so,
/// we can append those and move on. Otherwise, it invokes the
/// three callback functions:
///
/// - `args_for_def_id`: given the `DefId` `P`, supplies back the
/// generic arguments that were given to that parent from within
/// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
/// might refer to the trait `Foo`, and the arguments might be
/// `[T]`. The boolean value indicates whether to infer values
/// for arguments whose values were not explicitly provided.
/// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
/// instantiate a `GenericArg`.
/// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
/// creates a suitable inference variable.
pub fn create_args_for_parent_generic_args<'tcx, 'a>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
parent_args: &[ty::GenericArg<'tcx>],
has_self: bool,
self_ty: Option<Ty<'tcx>>,
arg_count: &GenericArgCountResult,
ctx: &mut impl CreateSubstsForGenericArgsCtxt<'a, 'tcx>,
) -> GenericArgsRef<'tcx> {
// Collect the segments of the path; we need to substitute arguments
// for parameters throughout the entire path (wherever there are
// generic parameters).
let mut parent_defs = tcx.generics_of(def_id);
let count = parent_defs.count();
let mut stack = vec![(def_id, parent_defs)];
while let Some(def_id) = parent_defs.parent {
parent_defs = tcx.generics_of(def_id);
stack.push((def_id, parent_defs));
}
// We manually build up the generic arguments, rather than using convenience
// methods in `subst.rs`, so that we can iterate over the arguments and
// parameters in lock-step linearly, instead of trying to match each pair.
let mut args: SmallVec<[ty::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
// Iterate over each segment of the path.
while let Some((def_id, defs)) = stack.pop() {
let mut params = defs.params.iter().peekable();
// If we have already computed the generic arguments for parents,
// we can use those directly.
while let Some(¶m) = params.peek() {
if let Some(&kind) = parent_args.get(param.index as usize) {
args.push(kind);
params.next();
} else {
break;
}
}
// `Self` is handled first, unless it's been handled in `parent_args`.
if has_self {
if let Some(¶m) = params.peek() {
if param.index == 0 {
if let GenericParamDefKind::Type { .. } = param.kind {
args.push(
self_ty
.map(|ty| ty.into())
.unwrap_or_else(|| ctx.inferred_kind(None, param, true)),
);
params.next();
}
}
}
}
// Check whether this segment takes generic arguments and the user has provided any.
let (generic_args, infer_args) = ctx.args_for_def_id(def_id);
let args_iter = generic_args.iter().flat_map(|generic_args| generic_args.args.iter());
let mut args_iter = args_iter.clone().peekable();
// If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
// If we later encounter a lifetime, we know that the arguments were provided in the
// wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
// inferred, so we can use it for diagnostics later.
let mut force_infer_lt = None;
loop {
// We're going to iterate through the generic arguments that the user
// provided, matching them with the generic parameters we expect.
// Mismatches can occur as a result of elided lifetimes, or for malformed
// input. We try to handle both sensibly.
match (args_iter.peek(), params.peek()) {
(Some(&arg), Some(¶m)) => {
match (arg, ¶m.kind, arg_count.explicit_late_bound) {
(GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
| (
GenericArg::Type(_) | GenericArg::Infer(_),
GenericParamDefKind::Type { .. },
_,
)
| (
GenericArg::Const(_) | GenericArg::Infer(_),
GenericParamDefKind::Const { .. },
_,
) => {
args.push(ctx.provided_kind(param, arg));
args_iter.next();
params.next();
}
(
GenericArg::Infer(_) | GenericArg::Type(_) | GenericArg::Const(_),
GenericParamDefKind::Lifetime,
_,
) => {
// We expected a lifetime argument, but got a type or const
// argument. That means we're inferring the lifetimes.
args.push(ctx.inferred_kind(None, param, infer_args));
force_infer_lt = Some((arg, param));
params.next();
}
(GenericArg::Lifetime(_), _, ExplicitLateBound::Yes) => {
// We've come across a lifetime when we expected something else in
// the presence of explicit late bounds. This is most likely
// due to the presence of the explicit bound so we're just going to
// ignore it.
args_iter.next();
}
(_, _, _) => {
// We expected one kind of parameter, but the user provided
// another. This is an error. However, if we already know that
// the arguments don't match up with the parameters, we won't issue
// an additional error, as the user already knows what's wrong.
if arg_count.correct.is_ok() {
// We're going to iterate over the parameters to sort them out, and
// show that order to the user as a possible order for the parameters
let mut param_types_present = defs
.params
.iter()
.map(|param| (param.kind.to_ord(), param.clone()))
.collect::<Vec<(ParamKindOrd, GenericParamDef)>>();
param_types_present.sort_by_key(|(ord, _)| *ord);
let (mut param_types_present, ordered_params): (
Vec<ParamKindOrd>,
Vec<GenericParamDef>,
) = param_types_present.into_iter().unzip();
param_types_present.dedup();
generic_arg_mismatch_err(
tcx,
arg,
param,
!args_iter.clone().is_sorted_by_key(|arg| arg.to_ord()),
Some(format!(
"reorder the arguments: {}: `<{}>`",
param_types_present
.into_iter()
.map(|ord| format!("{ord}s"))
.collect::<Vec<String>>()
.join(", then "),
ordered_params
.into_iter()
.filter_map(|param| {
if param.name == kw::SelfUpper {
None
} else {
Some(param.name.to_string())
}
})
.collect::<Vec<String>>()
.join(", ")
)),
);
}
// We've reported the error, but we want to make sure that this
// problem doesn't bubble down and create additional, irrelevant
// errors. In this case, we're simply going to ignore the argument
// and any following arguments. The rest of the parameters will be
// inferred.
while args_iter.next().is_some() {}
}
}
}
(Some(&arg), None) => {
// We should never be able to reach this point with well-formed input.
// There are three situations in which we can encounter this issue.
//
// 1. The number of arguments is incorrect. In this case, an error
// will already have been emitted, and we can ignore it.
// 2. There are late-bound lifetime parameters present, yet the
// lifetime arguments have also been explicitly specified by the
// user.
// 3. We've inferred some lifetimes, which have been provided later (i.e.
// after a type or const). We want to throw an error in this case.
if arg_count.correct.is_ok()
&& arg_count.explicit_late_bound == ExplicitLateBound::No
{
let kind = arg.descr();
assert_eq!(kind, "lifetime");
let (provided_arg, param) =
force_infer_lt.expect("lifetimes ought to have been inferred");
generic_arg_mismatch_err(tcx, provided_arg, param, false, None);
}
break;
}
(None, Some(¶m)) => {
// If there are fewer arguments than parameters, it means
// we're inferring the remaining arguments.
args.push(ctx.inferred_kind(Some(&args), param, infer_args));
params.next();
}
(None, None) => break,
}
}
}
tcx.mk_args(&args)
}
/// Checks that the correct number of generic arguments have been provided.
/// Used specifically for function calls.
pub fn check_generic_arg_count_for_call(
tcx: TyCtxt<'_>,
span: Span,
def_id: DefId,
generics: &ty::Generics,
seg: &hir::PathSegment<'_>,
is_method_call: IsMethodCall,
) -> GenericArgCountResult {
let empty_args = hir::GenericArgs::none();
let gen_args = seg.args.unwrap_or(&empty_args);
let gen_pos = match is_method_call {
IsMethodCall::Yes => GenericArgPosition::MethodCall,
IsMethodCall::No => GenericArgPosition::Value,
};
let has_self = generics.parent.is_none() && generics.has_self;
check_generic_arg_count(
tcx,
span,
def_id,
seg,
generics,
gen_args,
gen_pos,
has_self,
seg.infer_args,
)
}
/// Checks that the correct number of generic arguments have been provided.
/// This is used both for datatypes and function calls.
#[instrument(skip(tcx, gen_pos), level = "debug")]
pub(crate) fn check_generic_arg_count(
tcx: TyCtxt<'_>,
span: Span,
def_id: DefId,
seg: &hir::PathSegment<'_>,
gen_params: &ty::Generics,
gen_args: &hir::GenericArgs<'_>,
gen_pos: GenericArgPosition,
has_self: bool,
infer_args: bool,
) -> GenericArgCountResult {
let default_counts = gen_params.own_defaults();
let param_counts = gen_params.own_counts();
// Subtracting from param count to ensure type params synthesized from `impl Trait`
// cannot be explicitly specified.
let synth_type_param_count = gen_params
.params
.iter()
.filter(|param| matches!(param.kind, ty::GenericParamDefKind::Type { synthetic: true, .. }))
.count();
let named_type_param_count = param_counts.types - has_self as usize - synth_type_param_count;
let infer_lifetimes =
(gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();
if gen_pos != GenericArgPosition::Type && let Some(b) = gen_args.bindings.first() {
prohibit_assoc_ty_binding(tcx, b.span, None);
}
let explicit_late_bound =
prohibit_explicit_late_bound_lifetimes(tcx, gen_params, gen_args, gen_pos);
let mut invalid_args = vec![];
let mut check_lifetime_args = |min_expected_args: usize,
max_expected_args: usize,
provided_args: usize,
late_bounds_ignore: bool| {
if (min_expected_args..=max_expected_args).contains(&provided_args) {
return Ok(());
}
if late_bounds_ignore {
return Ok(());
}
if provided_args > max_expected_args {
invalid_args.extend(
gen_args.args[max_expected_args..provided_args].iter().map(|arg| arg.span()),
);
};
let gen_args_info = if provided_args > min_expected_args {
invalid_args.extend(
gen_args.args[min_expected_args..provided_args].iter().map(|arg| arg.span()),
);
let num_redundant_args = provided_args - min_expected_args;
GenericArgsInfo::ExcessLifetimes { num_redundant_args }
} else {
let num_missing_args = min_expected_args - provided_args;
GenericArgsInfo::MissingLifetimes { num_missing_args }
};
let reported = WrongNumberOfGenericArgs::new(
tcx,
gen_args_info,
seg,
gen_params,
has_self as usize,
gen_args,
def_id,
)
.diagnostic()
.emit();
Err(reported)
};
let min_expected_lifetime_args = if infer_lifetimes { 0 } else { param_counts.lifetimes };
let max_expected_lifetime_args = param_counts.lifetimes;
let num_provided_lifetime_args = gen_args.num_lifetime_params();
let lifetimes_correct = check_lifetime_args(
min_expected_lifetime_args,
max_expected_lifetime_args,
num_provided_lifetime_args,
explicit_late_bound == ExplicitLateBound::Yes,
);
let mut check_types_and_consts = |expected_min,
expected_max,
expected_max_with_synth,
provided,
params_offset,
args_offset| {
debug!(
?expected_min,
?expected_max,
?provided,
?params_offset,
?args_offset,
"check_types_and_consts"
);
if (expected_min..=expected_max).contains(&provided) {
return Ok(());
}
let num_default_params = expected_max - expected_min;
let gen_args_info = if provided > expected_max {
invalid_args.extend(
gen_args.args[args_offset + expected_max..args_offset + provided]
.iter()
.map(|arg| arg.span()),
);
let num_redundant_args = provided - expected_max;
// Provide extra note if synthetic arguments like `impl Trait` are specified.
let synth_provided = provided <= expected_max_with_synth;
GenericArgsInfo::ExcessTypesOrConsts {
num_redundant_args,
num_default_params,
args_offset,
synth_provided,
}
} else {
let num_missing_args = expected_max - provided;
GenericArgsInfo::MissingTypesOrConsts {
num_missing_args,
num_default_params,
args_offset,
}
};
debug!(?gen_args_info);
let reported = WrongNumberOfGenericArgs::new(
tcx,
gen_args_info,
seg,
gen_params,
params_offset,
gen_args,
def_id,
)
.diagnostic()
.emit_unless(gen_args.has_err());
Err(reported)
};
let args_correct = {
let expected_min = if infer_args {
0
} else {
param_counts.consts + named_type_param_count
- default_counts.types
- default_counts.consts
};
debug!(?expected_min);
debug!(arg_counts.lifetimes=?gen_args.num_lifetime_params());
check_types_and_consts(
expected_min,
param_counts.consts + named_type_param_count,
param_counts.consts + named_type_param_count + synth_type_param_count,
gen_args.num_generic_params(),
param_counts.lifetimes + has_self as usize,
gen_args.num_lifetime_params(),
)
};
GenericArgCountResult {
explicit_late_bound,
correct: lifetimes_correct
.and(args_correct)
.map_err(|reported| GenericArgCountMismatch { reported: Some(reported), invalid_args }),
}
}
/// Prohibits explicit lifetime arguments if late-bound lifetime parameters
/// are present. This is used both for datatypes and function calls.
pub(crate) fn prohibit_explicit_late_bound_lifetimes(
tcx: TyCtxt<'_>,
def: &ty::Generics,
args: &hir::GenericArgs<'_>,
position: GenericArgPosition,
) -> ExplicitLateBound {
let param_counts = def.own_counts();
let infer_lifetimes = position != GenericArgPosition::Type && !args.has_lifetime_params();
if infer_lifetimes {
return ExplicitLateBound::No;
}
if let Some(span_late) = def.has_late_bound_regions {
let msg = "cannot specify lifetime arguments explicitly \
if late bound lifetime parameters are present";
let note = "the late bound lifetime parameter is introduced here";
let span = args.args[0].span();
if position == GenericArgPosition::Value
&& args.num_lifetime_params() != param_counts.lifetimes
{
let mut err = struct_span_err!(tcx.sess, span, E0794, "{}", msg);
err.span_note(span_late, note);
err.emit();
} else {
let mut multispan = MultiSpan::from_span(span);
multispan.push_span_label(span_late, note);
tcx.struct_span_lint_hir(
LATE_BOUND_LIFETIME_ARGUMENTS,
args.args[0].hir_id(),
multispan,
msg,
|lint| lint,
);
}
ExplicitLateBound::Yes
} else {
ExplicitLateBound::No
}
}