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pat.rs
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pat.rs
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use crate::check::FnCtxt;
use rustc_ast as ast;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::pat_util::EnumerateAndAdjustIterator;
use rustc_hir::{HirId, Pat, PatKind};
use rustc_infer::infer;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_middle::ty::subst::GenericArg;
use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeFoldable};
use rustc_span::hygiene::DesugaringKind;
use rustc_span::lev_distance::find_best_match_for_name;
use rustc_span::source_map::{Span, Spanned};
use rustc_span::symbol::Ident;
use rustc_span::{BytePos, DUMMY_SP};
use rustc_trait_selection::traits::{ObligationCause, Pattern};
use ty::VariantDef;
use std::cmp;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use super::report_unexpected_variant_res;
const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
this type has no compile-time size. Therefore, all accesses to trait types must be through \
pointers. If you encounter this error you should try to avoid dereferencing the pointer.
You can read more about trait objects in the Trait Objects section of the Reference: \
https://doc.rust-lang.org/reference/types.html#trait-objects";
/// Information about the expected type at the top level of type checking a pattern.
///
/// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
#[derive(Copy, Clone)]
struct TopInfo<'tcx> {
/// The `expected` type at the top level of type checking a pattern.
expected: Ty<'tcx>,
/// Was the origin of the `span` from a scrutinee expression?
///
/// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
origin_expr: bool,
/// The span giving rise to the `expected` type, if one could be provided.
///
/// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
///
/// - `match scrutinee { ... }`
/// - `let _ = scrutinee;`
///
/// This is used to point to add context in type errors.
/// In the following example, `span` corresponds to the `a + b` expression:
///
/// ```text
/// error[E0308]: mismatched types
/// --> src/main.rs:L:C
/// |
/// L | let temp: usize = match a + b {
/// | ----- this expression has type `usize`
/// L | Ok(num) => num,
/// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
/// |
/// = note: expected type `usize`
/// found type `std::result::Result<_, _>`
/// ```
span: Option<Span>,
/// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
/// ```text
/// error[E0308]: mismatched types
/// --> $DIR/const-in-struct-pat.rs:8:17
/// |
/// L | struct f;
/// | --------- unit struct defined here
/// ...
/// L | let Thing { f } = t;
/// | ^
/// | |
/// | expected struct `std::string::String`, found struct `f`
/// | `f` is interpreted as a unit struct, not a new binding
/// | help: bind the struct field to a different name instead: `f: other_f`
/// ```
parent_pat: Option<&'tcx Pat<'tcx>>,
}
impl<'tcx> FnCtxt<'_, 'tcx> {
fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
self.cause(cause_span, code)
}
fn demand_eqtype_pat_diag(
&self,
cause_span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Option<DiagnosticBuilder<'tcx>> {
self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
}
fn demand_eqtype_pat(
&self,
cause_span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
ti: TopInfo<'tcx>,
) {
if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
err.emit();
}
}
}
const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
/// Mode for adjusting the expected type and binding mode.
enum AdjustMode {
/// Peel off all immediate reference types.
Peel,
/// Reset binding mode to the initial mode.
Reset,
/// Pass on the input binding mode and expected type.
Pass,
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Type check the given top level pattern against the `expected` type.
///
/// If a `Some(span)` is provided and `origin_expr` holds,
/// then the `span` represents the scrutinee's span.
/// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
///
/// Otherwise, `Some(span)` represents the span of a type expression
/// which originated the `expected` type.
pub fn check_pat_top(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
span: Option<Span>,
origin_expr: bool,
) {
let info = TopInfo { expected, origin_expr, span, parent_pat: None };
self.check_pat(pat, expected, INITIAL_BM, info);
}
/// Type check the given `pat` against the `expected` type
/// with the provided `def_bm` (default binding mode).
///
/// Outside of this module, `check_pat_top` should always be used.
/// Conversely, inside this module, `check_pat_top` should never be used.
#[instrument(level = "debug", skip(self, ti))]
fn check_pat(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
def_bm: BindingMode,
ti: TopInfo<'tcx>,
) {
let path_res = match &pat.kind {
PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
_ => None,
};
let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
let ty = match pat.kind {
PatKind::Wild => expected,
PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
PatKind::Binding(ba, var_id, _, sub) => {
self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
}
PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
}
PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
PatKind::Struct(ref qpath, fields, etc) => {
self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, ti)
}
PatKind::Or(pats) => {
let parent_pat = Some(pat);
for pat in pats {
self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
}
expected
}
PatKind::Tuple(elements, ddpos) => {
self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
}
PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
PatKind::Ref(inner, mutbl) => {
self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
}
PatKind::Slice(before, slice, after) => {
self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
}
};
self.write_ty(pat.hir_id, ty);
// (note_1): In most of the cases where (note_1) is referenced
// (literals and constants being the exception), we relate types
// using strict equality, even though subtyping would be sufficient.
// There are a few reasons for this, some of which are fairly subtle
// and which cost me (nmatsakis) an hour or two debugging to remember,
// so I thought I'd write them down this time.
//
// 1. There is no loss of expressiveness here, though it does
// cause some inconvenience. What we are saying is that the type
// of `x` becomes *exactly* what is expected. This can cause unnecessary
// errors in some cases, such as this one:
//
// ```
// fn foo<'x>(x: &'x i32) {
// let a = 1;
// let mut z = x;
// z = &a;
// }
// ```
//
// The reason we might get an error is that `z` might be
// assigned a type like `&'x i32`, and then we would have
// a problem when we try to assign `&a` to `z`, because
// the lifetime of `&a` (i.e., the enclosing block) is
// shorter than `'x`.
//
// HOWEVER, this code works fine. The reason is that the
// expected type here is whatever type the user wrote, not
// the initializer's type. In this case the user wrote
// nothing, so we are going to create a type variable `Z`.
// Then we will assign the type of the initializer (`&'x i32`)
// as a subtype of `Z`: `&'x i32 <: Z`. And hence we
// will instantiate `Z` as a type `&'0 i32` where `'0` is
// a fresh region variable, with the constraint that `'x : '0`.
// So basically we're all set.
//
// Note that there are two tests to check that this remains true
// (`regions-reassign-{match,let}-bound-pointer.rs`).
//
// 2. Things go horribly wrong if we use subtype. The reason for
// THIS is a fairly subtle case involving bound regions. See the
// `givens` field in `region_constraints`, as well as the test
// `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
// for details. Short version is that we must sometimes detect
// relationships between specific region variables and regions
// bound in a closure signature, and that detection gets thrown
// off when we substitute fresh region variables here to enable
// subtyping.
}
/// Compute the new expected type and default binding mode from the old ones
/// as well as the pattern form we are currently checking.
fn calc_default_binding_mode(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
def_bm: BindingMode,
adjust_mode: AdjustMode,
) -> (Ty<'tcx>, BindingMode) {
match adjust_mode {
AdjustMode::Pass => (expected, def_bm),
AdjustMode::Reset => (expected, INITIAL_BM),
AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
}
}
/// How should the binding mode and expected type be adjusted?
///
/// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
// When we perform destructuring assignment, we disable default match bindings, which are
// unintuitive in this context.
if !pat.default_binding_modes {
return AdjustMode::Reset;
}
match &pat.kind {
// Type checking these product-like types successfully always require
// that the expected type be of those types and not reference types.
PatKind::Struct(..)
| PatKind::TupleStruct(..)
| PatKind::Tuple(..)
| PatKind::Box(_)
| PatKind::Range(..)
| PatKind::Slice(..) => AdjustMode::Peel,
// String and byte-string literals result in types `&str` and `&[u8]` respectively.
// All other literals result in non-reference types.
// As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
PatKind::Lit(lt) => match self.check_expr(lt).kind() {
ty::Ref(..) => AdjustMode::Pass,
_ => AdjustMode::Peel,
},
PatKind::Path(_) => match opt_path_res.unwrap() {
// These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
// Peeling the reference types too early will cause type checking failures.
// Although it would be possible to *also* peel the types of the constants too.
Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
// In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
// could successfully compile. The former being `Self` requires a unit struct.
// In either case, and unlike constants, the pattern itself cannot be
// a reference type wherefore peeling doesn't give up any expressivity.
_ => AdjustMode::Peel,
},
// When encountering a `& mut? pat` pattern, reset to "by value".
// This is so that `x` and `y` here are by value, as they appear to be:
//
// ```
// match &(&22, &44) {
// (&x, &y) => ...
// }
// ```
//
// See issue #46688.
PatKind::Ref(..) => AdjustMode::Reset,
// A `_` pattern works with any expected type, so there's no need to do anything.
PatKind::Wild
// Bindings also work with whatever the expected type is,
// and moreover if we peel references off, that will give us the wrong binding type.
// Also, we can have a subpattern `binding @ pat`.
// Each side of the `@` should be treated independently (like with OR-patterns).
| PatKind::Binding(..)
// An OR-pattern just propagates to each individual alternative.
// This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
// In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
| PatKind::Or(_) => AdjustMode::Pass,
}
}
/// Peel off as many immediately nested `& mut?` from the expected type as possible
/// and return the new expected type and binding default binding mode.
/// The adjustments vector, if non-empty is stored in a table.
fn peel_off_references(
&self,
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
mut def_bm: BindingMode,
) -> (Ty<'tcx>, BindingMode) {
let mut expected = self.resolve_vars_with_obligations(&expected);
// Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
// for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
// the `Some(5)` which is not of type Ref.
//
// For each ampersand peeled off, update the binding mode and push the original
// type into the adjustments vector.
//
// See the examples in `ui/match-defbm*.rs`.
let mut pat_adjustments = vec![];
while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
debug!("inspecting {:?}", expected);
debug!("current discriminant is Ref, inserting implicit deref");
// Preserve the reference type. We'll need it later during THIR lowering.
pat_adjustments.push(expected);
expected = inner_ty;
def_bm = ty::BindByReference(match def_bm {
// If default binding mode is by value, make it `ref` or `ref mut`
// (depending on whether we observe `&` or `&mut`).
ty::BindByValue(_) |
// When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
// Once a `ref`, always a `ref`.
// This is because a `& &mut` cannot mutate the underlying value.
ty::BindByReference(m @ hir::Mutability::Not) => m,
});
}
if !pat_adjustments.is_empty() {
debug!("default binding mode is now {:?}", def_bm);
self.inh
.typeck_results
.borrow_mut()
.pat_adjustments_mut()
.insert(pat.hir_id, pat_adjustments);
}
(expected, def_bm)
}
fn check_pat_lit(
&self,
span: Span,
lt: &hir::Expr<'tcx>,
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
// We've already computed the type above (when checking for a non-ref pat),
// so avoid computing it again.
let ty = self.node_ty(lt.hir_id);
// Byte string patterns behave the same way as array patterns
// They can denote both statically and dynamically-sized byte arrays.
let mut pat_ty = ty;
if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
let expected = self.structurally_resolved_type(span, expected);
if let ty::Ref(_, inner_ty, _) = expected.kind() {
if matches!(inner_ty.kind(), ty::Slice(_)) {
let tcx = self.tcx;
trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
self.typeck_results
.borrow_mut()
.treat_byte_string_as_slice
.insert(lt.hir_id.local_id);
pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
}
}
}
// Somewhat surprising: in this case, the subtyping relation goes the
// opposite way as the other cases. Actually what we really want is not
// a subtyping relation at all but rather that there exists a LUB
// (so that they can be compared). However, in practice, constants are
// always scalars or strings. For scalars subtyping is irrelevant,
// and for strings `ty` is type is `&'static str`, so if we say that
//
// &'static str <: expected
//
// then that's equivalent to there existing a LUB.
let cause = self.pattern_cause(ti, span);
if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
err.emit_unless(
ti.span
.filter(|&s| {
// In the case of `if`- and `while`-expressions we've already checked
// that `scrutinee: bool`. We know that the pattern is `true`,
// so an error here would be a duplicate and from the wrong POV.
s.is_desugaring(DesugaringKind::CondTemporary)
})
.is_some(),
);
}
pat_ty
}
fn check_pat_range(
&self,
span: Span,
lhs: Option<&'tcx hir::Expr<'tcx>>,
rhs: Option<&'tcx hir::Expr<'tcx>>,
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
None => (None, None),
Some(expr) => {
let ty = self.check_expr(expr);
// Check that the end-point is of numeric or char type.
let fail = !(ty.is_numeric() || ty.is_char() || ty.references_error());
(Some(ty), Some((fail, ty, expr.span)))
}
};
let (lhs_ty, lhs) = calc_side(lhs);
let (rhs_ty, rhs) = calc_side(rhs);
if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
// There exists a side that didn't meet our criteria that the end-point
// be of a numeric or char type, as checked in `calc_side` above.
self.emit_err_pat_range(span, lhs, rhs);
return self.tcx.ty_error();
}
// Now that we know the types can be unified we find the unified type
// and use it to type the entire expression.
let common_type = self.resolve_vars_if_possible(lhs_ty.or(rhs_ty).unwrap_or(expected));
// Subtyping doesn't matter here, as the value is some kind of scalar.
let demand_eqtype = |x, y| {
if let Some((_, x_ty, x_span)) = x {
if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
if let Some((_, y_ty, y_span)) = y {
self.endpoint_has_type(&mut err, y_span, y_ty);
}
err.emit();
};
}
};
demand_eqtype(lhs, rhs);
demand_eqtype(rhs, lhs);
common_type
}
fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
if !ty.references_error() {
err.span_label(span, &format!("this is of type `{}`", ty));
}
}
fn emit_err_pat_range(
&self,
span: Span,
lhs: Option<(bool, Ty<'tcx>, Span)>,
rhs: Option<(bool, Ty<'tcx>, Span)>,
) {
let span = match (lhs, rhs) {
(Some((true, ..)), Some((true, ..))) => span,
(Some((true, _, sp)), _) => sp,
(_, Some((true, _, sp))) => sp,
_ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
};
let mut err = struct_span_err!(
self.tcx.sess,
span,
E0029,
"only `char` and numeric types are allowed in range patterns"
);
let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
err.span_label(first_span, &msg(first_ty));
if let Some((_, ty, sp)) = second {
self.endpoint_has_type(&mut err, sp, ty);
}
};
match (lhs, rhs) {
(Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
err.span_label(lhs_sp, &msg(lhs_ty));
err.span_label(rhs_sp, &msg(rhs_ty));
}
(Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
(lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
_ => span_bug!(span, "Impossible, verified above."),
}
if self.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(
"In a match expression, only numbers and characters can be matched \
against a range. This is because the compiler checks that the range \
is non-empty at compile-time, and is unable to evaluate arbitrary \
comparison functions. If you want to capture values of an orderable \
type between two end-points, you can use a guard.",
);
}
err.emit();
}
fn check_pat_ident(
&self,
pat: &'tcx Pat<'tcx>,
ba: hir::BindingAnnotation,
var_id: HirId,
sub: Option<&'tcx Pat<'tcx>>,
expected: Ty<'tcx>,
def_bm: BindingMode,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
// Determine the binding mode...
let bm = match ba {
hir::BindingAnnotation::Unannotated => def_bm,
_ => BindingMode::convert(ba),
};
// ...and store it in a side table:
self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
let eq_ty = match bm {
ty::BindByReference(mutbl) => {
// If the binding is like `ref x | ref mut x`,
// then `x` is assigned a value of type `&M T` where M is the
// mutability and T is the expected type.
//
// `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
// is required. However, we use equality, which is stronger.
// See (note_1) for an explanation.
self.new_ref_ty(pat.span, mutbl, expected)
}
// Otherwise, the type of x is the expected type `T`.
ty::BindByValue(_) => {
// As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
expected
}
};
self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
// If there are multiple arms, make sure they all agree on
// what the type of the binding `x` ought to be.
if var_id != pat.hir_id {
self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
}
if let Some(p) = sub {
self.check_pat(&p, expected, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
}
local_ty
}
fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
let var_ty = self.local_ty(span, var_id).decl_ty;
if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
let hir = self.tcx.hir();
let var_ty = self.resolve_vars_with_obligations(var_ty);
let msg = format!("first introduced with type `{}` here", var_ty);
err.span_label(hir.span(var_id), msg);
let in_match = hir.parent_iter(var_id).any(|(_, n)| {
matches!(
n,
hir::Node::Expr(hir::Expr {
kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
..
})
)
});
let pre = if in_match { "in the same arm, " } else { "" };
err.note(&format!("{}a binding must have the same type in all alternatives", pre));
err.emit();
}
}
fn borrow_pat_suggestion(
&self,
err: &mut DiagnosticBuilder<'_>,
pat: &Pat<'_>,
inner: &Pat<'_>,
expected: Ty<'tcx>,
) {
let tcx = self.tcx;
if let PatKind::Binding(..) = inner.kind {
let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
let binding_parent = tcx.hir().get(binding_parent_id);
debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
match binding_parent {
hir::Node::Param(hir::Param { span, .. }) => {
if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
err.span_suggestion(
*span,
&format!("did you mean `{}`", snippet),
format!(" &{}", expected),
Applicability::MachineApplicable,
);
}
}
hir::Node::Arm(_) | hir::Node::Pat(_) => {
// rely on match ergonomics or it might be nested `&&pat`
if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
err.span_suggestion(
pat.span,
"you can probably remove the explicit borrow",
snippet,
Applicability::MaybeIncorrect,
);
}
}
_ => {} // don't provide suggestions in other cases #55175
}
}
}
pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
if let PatKind::Binding(..) = inner.kind {
if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
if let ty::Dynamic(..) = mt.ty.kind() {
// This is "x = SomeTrait" being reduced from
// "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
let type_str = self.ty_to_string(expected);
let mut err = struct_span_err!(
self.tcx.sess,
span,
E0033,
"type `{}` cannot be dereferenced",
type_str
);
err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
if self.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
}
err.emit();
return false;
}
}
}
true
}
fn check_pat_struct(
&self,
pat: &'tcx Pat<'tcx>,
qpath: &hir::QPath<'_>,
fields: &'tcx [hir::PatField<'tcx>],
etc: bool,
expected: Ty<'tcx>,
def_bm: BindingMode,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
// Resolve the path and check the definition for errors.
let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
{
variant_ty
} else {
let err = self.tcx.ty_error();
for field in fields {
let ti = TopInfo { parent_pat: Some(&pat), ..ti };
self.check_pat(&field.pat, err, def_bm, ti);
}
return err;
};
// Type-check the path.
self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
// Type-check subpatterns.
if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, etc, def_bm, ti) {
pat_ty
} else {
self.tcx.ty_error()
}
}
fn check_pat_path(
&self,
pat: &Pat<'_>,
path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
expected: Ty<'tcx>,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;
// We have already resolved the path.
let (res, opt_ty, segments) = path_resolution;
match res {
Res::Err => {
self.set_tainted_by_errors();
return tcx.ty_error();
}
Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
report_unexpected_variant_res(tcx, res, pat.span);
return tcx.ty_error();
}
Res::SelfCtor(..)
| Res::Def(
DefKind::Ctor(_, CtorKind::Const)
| DefKind::Const
| DefKind::AssocConst
| DefKind::ConstParam,
_,
) => {} // OK
_ => bug!("unexpected pattern resolution: {:?}", res),
}
// Type-check the path.
let (pat_ty, pat_res) =
self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
if let Some(err) =
self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
{
self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
}
pat_ty
}
fn maybe_suggest_range_literal(
&self,
e: &mut DiagnosticBuilder<'_>,
opt_def_id: Option<hir::def_id::DefId>,
ident: Ident,
) -> bool {
match opt_def_id {
Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
Some(hir::Node::Item(hir::Item {
kind: hir::ItemKind::Const(_, body_id), ..
})) => match self.tcx.hir().get(body_id.hir_id) {
hir::Node::Expr(expr) => {
if hir::is_range_literal(expr) {
let span = self.tcx.hir().span(body_id.hir_id);
if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
e.span_suggestion_verbose(
ident.span,
"you may want to move the range into the match block",
snip,
Applicability::MachineApplicable,
);
return true;
}
}
}
_ => (),
},
_ => (),
},
_ => (),
}
false
}
fn emit_bad_pat_path(
&self,
mut e: DiagnosticBuilder<'_>,
pat_span: Span,
res: Res,
pat_res: Res,
pat_ty: Ty<'tcx>,
segments: &'b [hir::PathSegment<'b>],
parent_pat: Option<&Pat<'_>>,
) {
if let Some(span) = self.tcx.hir().res_span(pat_res) {
e.span_label(span, &format!("{} defined here", res.descr()));
if let [hir::PathSegment { ident, .. }] = &*segments {
e.span_label(
pat_span,
&format!(
"`{}` is interpreted as {} {}, not a new binding",
ident,
res.article(),
res.descr(),
),
);
match parent_pat {
Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
e.span_suggestion_verbose(
ident.span.shrink_to_hi(),
"bind the struct field to a different name instead",
format!(": other_{}", ident.as_str().to_lowercase()),
Applicability::HasPlaceholders,
);
}
_ => {
let (type_def_id, item_def_id) = match pat_ty.kind() {
Adt(def, _) => match res {
Res::Def(DefKind::Const, def_id) => (Some(def.did), Some(def_id)),
_ => (None, None),
},
_ => (None, None),
};
let ranges = &[
self.tcx.lang_items().range_struct(),
self.tcx.lang_items().range_from_struct(),
self.tcx.lang_items().range_to_struct(),
self.tcx.lang_items().range_full_struct(),
self.tcx.lang_items().range_inclusive_struct(),
self.tcx.lang_items().range_to_inclusive_struct(),
];
if type_def_id != None && ranges.contains(&type_def_id) {
if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
let msg = "constants only support matching by type, \
if you meant to match against a range of values, \
consider using a range pattern like `min ..= max` in the match block";
e.note(msg);
}
} else {
let msg = "introduce a new binding instead";
let sugg = format!("other_{}", ident.as_str().to_lowercase());
e.span_suggestion(
ident.span,
msg,
sugg,
Applicability::HasPlaceholders,
);
}
}
};
}
}
e.emit();
}
fn check_pat_tuple_struct(
&self,
pat: &'tcx Pat<'tcx>,
qpath: &'tcx hir::QPath<'tcx>,
subpats: &'tcx [&'tcx Pat<'tcx>],
ddpos: Option<usize>,
expected: Ty<'tcx>,
def_bm: BindingMode,
ti: TopInfo<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let on_error = || {
let parent_pat = Some(pat);
for pat in subpats {
self.check_pat(&pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
}
};
let report_unexpected_res = |res: Res| {
let sm = tcx.sess.source_map();
let path_str = sm
.span_to_snippet(sm.span_until_char(pat.span, '('))
.map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
let msg = format!(
"expected tuple struct or tuple variant, found {}{}",
res.descr(),
path_str
);
let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
match res {
Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
err.span_label(pat.span, "`fn` calls are not allowed in patterns");
err.help(
"for more information, visit \
https://doc.rust-lang.org/book/ch18-00-patterns.html",
);
}
_ => {
err.span_label(pat.span, "not a tuple variant or struct");
}
}
err.emit();
on_error();
};
// Resolve the path and check the definition for errors.
let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
if res == Res::Err {
self.set_tainted_by_errors();
on_error();
return self.tcx.ty_error();
}
// Type-check the path.
let (pat_ty, res) =
self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
if !pat_ty.is_fn() {
report_unexpected_res(res);
return tcx.ty_error();
}
let variant = match res {
Res::Err => {
self.set_tainted_by_errors();
on_error();
return tcx.ty_error();
}
Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
report_unexpected_res(res);
return tcx.ty_error();
}
Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
_ => bug!("unexpected pattern resolution: {:?}", res),
};
// Replace constructor type with constructed type for tuple struct patterns.
let pat_ty = pat_ty.fn_sig(tcx).output();
let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
// Type-check the tuple struct pattern against the expected type.
let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
let had_err = if let Some(mut err) = diag {
err.emit();
true
} else {
false
};
// Type-check subpatterns.
if subpats.len() == variant.fields.len()
|| subpats.len() < variant.fields.len() && ddpos.is_some()
{
let substs = match pat_ty.kind() {
ty::Adt(_, substs) => substs,
_ => bug!("unexpected pattern type {:?}", pat_ty),
};
for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
self.check_pat(&subpat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
}
} else {
// Pattern has wrong number of fields.
self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
on_error();
return tcx.ty_error();
}
pat_ty
}
fn e0023(
&self,
pat_span: Span,
res: Res,
qpath: &hir::QPath<'_>,
subpats: &'tcx [&'tcx Pat<'tcx>],
fields: &'tcx [ty::FieldDef],
expected: Ty<'tcx>,
had_err: bool,
) {
let subpats_ending = pluralize!(subpats.len());
let fields_ending = pluralize!(fields.len());
let res_span = self.tcx.def_span(res.def_id());
let mut err = struct_span_err!(
self.tcx.sess,
pat_span,
E0023,
"this pattern has {} field{}, but the corresponding {} has {} field{}",
subpats.len(),
subpats_ending,
res.descr(),
fields.len(),
fields_ending,
);
err.span_label(
pat_span,
format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
)
.span_label(res_span, format!("{} defined here", res.descr()));