/
expr.rs
1989 lines (1843 loc) · 77.9 KB
/
expr.rs
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//! Type checking expressions.
//!
//! See `mod.rs` for more context on type checking in general.
use crate::astconv::AstConv as _;
use crate::check::cast;
use crate::check::coercion::CoerceMany;
use crate::check::fatally_break_rust;
use crate::check::method::{probe, MethodError, SelfSource};
use crate::check::report_unexpected_variant_res;
use crate::check::BreakableCtxt;
use crate::check::Diverges;
use crate::check::Expectation::{self, ExpectCastableToType, ExpectHasType, NoExpectation};
use crate::check::FnCtxt;
use crate::check::Needs;
use crate::check::TupleArgumentsFlag::DontTupleArguments;
use crate::errors::{
FieldMultiplySpecifiedInInitializer, FunctionalRecordUpdateOnNonStruct,
YieldExprOutsideOfGenerator,
};
use crate::type_error_struct;
use crate::errors::{AddressOfTemporaryTaken, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive};
use rustc_ast as ast;
use rustc_ast::util::lev_distance::find_best_match_for_name;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::ErrorReported;
use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_hir::{ExprKind, QPath};
use rustc_infer::infer;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_middle::ty;
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
use rustc_middle::ty::Ty;
use rustc_middle::ty::TypeFoldable;
use rustc_middle::ty::{AdtKind, Visibility};
use rustc_span::hygiene::DesugaringKind;
use rustc_span::source_map::Span;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_trait_selection::traits::{self, ObligationCauseCode, SelectionContext};
use std::fmt::Display;
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
fn check_expr_eq_type(&self, expr: &'tcx hir::Expr<'tcx>, expected: Ty<'tcx>) {
let ty = self.check_expr_with_hint(expr, expected);
self.demand_eqtype(expr.span, expected, ty);
}
pub fn check_expr_has_type_or_error(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Ty<'tcx>,
extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
) -> Ty<'tcx> {
self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
}
fn check_expr_meets_expectation_or_error(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
extend_err: impl Fn(&mut DiagnosticBuilder<'_>),
) -> Ty<'tcx> {
let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
let mut ty = self.check_expr_with_expectation(expr, expected);
// While we don't allow *arbitrary* coercions here, we *do* allow
// coercions from ! to `expected`.
if ty.is_never() {
assert!(
!self.typeck_results.borrow().adjustments().contains_key(expr.hir_id),
"expression with never type wound up being adjusted"
);
let adj_ty = self.next_diverging_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::AdjustmentType,
span: expr.span,
});
self.apply_adjustments(
expr,
vec![Adjustment { kind: Adjust::NeverToAny, target: adj_ty }],
);
ty = adj_ty;
}
if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
let expr = expr.peel_drop_temps();
self.suggest_deref_ref_or_into(&mut err, expr, expected_ty, ty, None);
extend_err(&mut err);
// Error possibly reported in `check_assign` so avoid emitting error again.
err.emit_unless(self.is_assign_to_bool(expr, expected_ty));
}
ty
}
pub(super) fn check_expr_coercable_to_type(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Ty<'tcx>,
expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
) -> Ty<'tcx> {
let ty = self.check_expr_with_hint(expr, expected);
// checks don't need two phase
self.demand_coerce(expr, ty, expected, expected_ty_expr, AllowTwoPhase::No)
}
pub(super) fn check_expr_with_hint(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Ty<'tcx>,
) -> Ty<'tcx> {
self.check_expr_with_expectation(expr, ExpectHasType(expected))
}
fn check_expr_with_expectation_and_needs(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
needs: Needs,
) -> Ty<'tcx> {
let ty = self.check_expr_with_expectation(expr, expected);
// If the expression is used in a place whether mutable place is required
// e.g. LHS of assignment, perform the conversion.
if let Needs::MutPlace = needs {
self.convert_place_derefs_to_mutable(expr);
}
ty
}
pub(super) fn check_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
self.check_expr_with_expectation(expr, NoExpectation)
}
pub(super) fn check_expr_with_needs(
&self,
expr: &'tcx hir::Expr<'tcx>,
needs: Needs,
) -> Ty<'tcx> {
self.check_expr_with_expectation_and_needs(expr, NoExpectation, needs)
}
/// Invariant:
/// If an expression has any sub-expressions that result in a type error,
/// inspecting that expression's type with `ty.references_error()` will return
/// true. Likewise, if an expression is known to diverge, inspecting its
/// type with `ty::type_is_bot` will return true (n.b.: since Rust is
/// strict, _|_ can appear in the type of an expression that does not,
/// itself, diverge: for example, fn() -> _|_.)
/// Note that inspecting a type's structure *directly* may expose the fact
/// that there are actually multiple representations for `Error`, so avoid
/// that when err needs to be handled differently.
pub(super) fn check_expr_with_expectation(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
debug!(">> type-checking: expr={:?} expected={:?}", expr, expected);
// True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
// without the final expr (e.g. `try { return; }`). We don't want to generate an
// unreachable_code lint for it since warnings for autogenerated code are confusing.
let is_try_block_generated_unit_expr = match expr.kind {
ExprKind::Call(_, ref args) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {
args.len() == 1 && args[0].span.is_desugaring(DesugaringKind::TryBlock)
}
_ => false,
};
// Warn for expressions after diverging siblings.
if !is_try_block_generated_unit_expr {
self.warn_if_unreachable(expr.hir_id, expr.span, "expression");
}
// Hide the outer diverging and has_errors flags.
let old_diverges = self.diverges.replace(Diverges::Maybe);
let old_has_errors = self.has_errors.replace(false);
let ty = ensure_sufficient_stack(|| self.check_expr_kind(expr, expected));
// Warn for non-block expressions with diverging children.
match expr.kind {
ExprKind::Block(..) | ExprKind::Loop(..) | ExprKind::Match(..) => {}
// If `expr` is a result of desugaring the try block and is an ok-wrapped
// diverging expression (e.g. it arose from desugaring of `try { return }`),
// we skip issuing a warning because it is autogenerated code.
ExprKind::Call(..) if expr.span.is_desugaring(DesugaringKind::TryBlock) => {}
ExprKind::Call(ref callee, _) => {
self.warn_if_unreachable(expr.hir_id, callee.span, "call")
}
ExprKind::MethodCall(_, ref span, _, _) => {
self.warn_if_unreachable(expr.hir_id, *span, "call")
}
_ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
}
// Any expression that produces a value of type `!` must have diverged
if ty.is_never() {
self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
}
// Record the type, which applies it effects.
// We need to do this after the warning above, so that
// we don't warn for the diverging expression itself.
self.write_ty(expr.hir_id, ty);
// Combine the diverging and has_error flags.
self.diverges.set(self.diverges.get() | old_diverges);
self.has_errors.set(self.has_errors.get() | old_has_errors);
debug!("type of {} is...", self.tcx.hir().node_to_string(expr.hir_id));
debug!("... {:?}, expected is {:?}", ty, expected);
ty
}
fn check_expr_kind(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
debug!("check_expr_kind(expr={:?}, expected={:?})", expr, expected);
let tcx = self.tcx;
match expr.kind {
ExprKind::Box(ref subexpr) => self.check_expr_box(subexpr, expected),
ExprKind::Lit(ref lit) => self.check_lit(&lit, expected),
ExprKind::Binary(op, ref lhs, ref rhs) => self.check_binop(expr, op, lhs, rhs),
ExprKind::Assign(ref lhs, ref rhs, ref span) => {
self.check_expr_assign(expr, expected, lhs, rhs, span)
}
ExprKind::AssignOp(op, ref lhs, ref rhs) => self.check_binop_assign(expr, op, lhs, rhs),
ExprKind::Unary(unop, ref oprnd) => self.check_expr_unary(unop, oprnd, expected, expr),
ExprKind::AddrOf(kind, mutbl, ref oprnd) => {
self.check_expr_addr_of(kind, mutbl, oprnd, expected, expr)
}
ExprKind::Path(QPath::LangItem(lang_item, _)) => {
self.check_lang_item_path(lang_item, expr)
}
ExprKind::Path(ref qpath) => self.check_expr_path(qpath, expr),
ExprKind::InlineAsm(asm) => self.check_expr_asm(asm),
ExprKind::LlvmInlineAsm(ref asm) => {
for expr in asm.outputs_exprs.iter().chain(asm.inputs_exprs.iter()) {
self.check_expr(expr);
}
tcx.mk_unit()
}
ExprKind::Break(destination, ref expr_opt) => {
self.check_expr_break(destination, expr_opt.as_deref(), expr)
}
ExprKind::Continue(destination) => {
if destination.target_id.is_ok() {
tcx.types.never
} else {
// There was an error; make type-check fail.
tcx.ty_error()
}
}
ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
ExprKind::Loop(ref body, _, source) => {
self.check_expr_loop(body, source, expected, expr)
}
ExprKind::Match(ref discrim, ref arms, match_src) => {
self.check_match(expr, &discrim, arms, expected, match_src)
}
ExprKind::Closure(capture, ref decl, body_id, _, gen) => {
self.check_expr_closure(expr, capture, &decl, body_id, gen, expected)
}
ExprKind::Block(ref body, _) => self.check_block_with_expected(&body, expected),
ExprKind::Call(ref callee, ref args) => self.check_call(expr, &callee, args, expected),
ExprKind::MethodCall(ref segment, span, ref args, _) => {
self.check_method_call(expr, segment, span, args, expected)
}
ExprKind::Cast(ref e, ref t) => self.check_expr_cast(e, t, expr),
ExprKind::Type(ref e, ref t) => {
let ty = self.to_ty_saving_user_provided_ty(&t);
self.check_expr_eq_type(&e, ty);
ty
}
ExprKind::DropTemps(ref e) => self.check_expr_with_expectation(e, expected),
ExprKind::Array(ref args) => self.check_expr_array(args, expected, expr),
ExprKind::Repeat(ref element, ref count) => {
self.check_expr_repeat(element, count, expected, expr)
}
ExprKind::Tup(ref elts) => self.check_expr_tuple(elts, expected, expr),
ExprKind::Struct(ref qpath, fields, ref base_expr) => {
self.check_expr_struct(expr, expected, qpath, fields, base_expr)
}
ExprKind::Field(ref base, field) => self.check_field(expr, &base, field),
ExprKind::Index(ref base, ref idx) => self.check_expr_index(base, idx, expr),
ExprKind::Yield(ref value, ref src) => self.check_expr_yield(value, expr, src),
hir::ExprKind::Err => tcx.ty_error(),
}
}
fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx>) -> Ty<'tcx> {
let expected_inner = expected.to_option(self).map_or(NoExpectation, |ty| match ty.kind() {
ty::Adt(def, _) if def.is_box() => Expectation::rvalue_hint(self, ty.boxed_ty()),
_ => NoExpectation,
});
let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
self.tcx.mk_box(referent_ty)
}
fn check_expr_unary(
&self,
unop: hir::UnOp,
oprnd: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;
let expected_inner = match unop {
hir::UnOp::UnNot | hir::UnOp::UnNeg => expected,
hir::UnOp::UnDeref => NoExpectation,
};
let mut oprnd_t = self.check_expr_with_expectation(&oprnd, expected_inner);
if !oprnd_t.references_error() {
oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
match unop {
hir::UnOp::UnDeref => {
if let Some(ty) = self.lookup_derefing(expr, oprnd, oprnd_t) {
oprnd_t = ty;
} else {
let mut err = type_error_struct!(
tcx.sess,
expr.span,
oprnd_t,
E0614,
"type `{}` cannot be dereferenced",
oprnd_t,
);
let sp = tcx.sess.source_map().start_point(expr.span);
if let Some(sp) =
tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp)
{
tcx.sess.parse_sess.expr_parentheses_needed(&mut err, *sp, None);
}
err.emit();
oprnd_t = tcx.ty_error();
}
}
hir::UnOp::UnNot => {
let result = self.check_user_unop(expr, oprnd_t, unop);
// If it's builtin, we can reuse the type, this helps inference.
if !(oprnd_t.is_integral() || *oprnd_t.kind() == ty::Bool) {
oprnd_t = result;
}
}
hir::UnOp::UnNeg => {
let result = self.check_user_unop(expr, oprnd_t, unop);
// If it's builtin, we can reuse the type, this helps inference.
if !oprnd_t.is_numeric() {
oprnd_t = result;
}
}
}
}
oprnd_t
}
fn check_expr_addr_of(
&self,
kind: hir::BorrowKind,
mutbl: hir::Mutability,
oprnd: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
let hint = expected.only_has_type(self).map_or(NoExpectation, |ty| {
match ty.kind() {
ty::Ref(_, ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) => {
if oprnd.is_syntactic_place_expr() {
// Places may legitimately have unsized types.
// For example, dereferences of a fat pointer and
// the last field of a struct can be unsized.
ExpectHasType(ty)
} else {
Expectation::rvalue_hint(self, ty)
}
}
_ => NoExpectation,
}
});
let ty =
self.check_expr_with_expectation_and_needs(&oprnd, hint, Needs::maybe_mut_place(mutbl));
let tm = ty::TypeAndMut { ty, mutbl };
match kind {
_ if tm.ty.references_error() => self.tcx.ty_error(),
hir::BorrowKind::Raw => {
self.check_named_place_expr(oprnd);
self.tcx.mk_ptr(tm)
}
hir::BorrowKind::Ref => {
// Note: at this point, we cannot say what the best lifetime
// is to use for resulting pointer. We want to use the
// shortest lifetime possible so as to avoid spurious borrowck
// errors. Moreover, the longest lifetime will depend on the
// precise details of the value whose address is being taken
// (and how long it is valid), which we don't know yet until
// type inference is complete.
//
// Therefore, here we simply generate a region variable. The
// region inferencer will then select a suitable value.
// Finally, borrowck will infer the value of the region again,
// this time with enough precision to check that the value
// whose address was taken can actually be made to live as long
// as it needs to live.
let region = self.next_region_var(infer::AddrOfRegion(expr.span));
self.tcx.mk_ref(region, tm)
}
}
}
/// Does this expression refer to a place that either:
/// * Is based on a local or static.
/// * Contains a dereference
/// Note that the adjustments for the children of `expr` should already
/// have been resolved.
fn check_named_place_expr(&self, oprnd: &'tcx hir::Expr<'tcx>) {
let is_named = oprnd.is_place_expr(|base| {
// Allow raw borrows if there are any deref adjustments.
//
// const VAL: (i32,) = (0,);
// const REF: &(i32,) = &(0,);
//
// &raw const VAL.0; // ERROR
// &raw const REF.0; // OK, same as &raw const (*REF).0;
//
// This is maybe too permissive, since it allows
// `let u = &raw const Box::new((1,)).0`, which creates an
// immediately dangling raw pointer.
self.typeck_results.borrow().adjustments().get(base.hir_id).map_or(false, |x| {
x.iter().any(|adj| if let Adjust::Deref(_) = adj.kind { true } else { false })
})
});
if !is_named {
self.tcx.sess.emit_err(AddressOfTemporaryTaken { span: oprnd.span })
}
}
fn check_lang_item_path(
&self,
lang_item: hir::LangItem,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
self.resolve_lang_item_path(lang_item, expr.span, expr.hir_id).1
}
fn check_expr_path(&self, qpath: &hir::QPath<'_>, expr: &'tcx hir::Expr<'tcx>) -> Ty<'tcx> {
let tcx = self.tcx;
let (res, opt_ty, segs) = self.resolve_ty_and_res_ufcs(qpath, expr.hir_id, expr.span);
let ty = match res {
Res::Err => {
self.set_tainted_by_errors();
tcx.ty_error()
}
Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _) => {
report_unexpected_variant_res(tcx, res, expr.span);
tcx.ty_error()
}
_ => self.instantiate_value_path(segs, opt_ty, res, expr.span, expr.hir_id).0,
};
if let ty::FnDef(..) = ty.kind() {
let fn_sig = ty.fn_sig(tcx);
if !tcx.features().unsized_locals {
// We want to remove some Sized bounds from std functions,
// but don't want to expose the removal to stable Rust.
// i.e., we don't want to allow
//
// ```rust
// drop as fn(str);
// ```
//
// to work in stable even if the Sized bound on `drop` is relaxed.
for i in 0..fn_sig.inputs().skip_binder().len() {
// We just want to check sizedness, so instead of introducing
// placeholder lifetimes with probing, we just replace higher lifetimes
// with fresh vars.
let input = self
.replace_bound_vars_with_fresh_vars(
expr.span,
infer::LateBoundRegionConversionTime::FnCall,
&fn_sig.input(i),
)
.0;
self.require_type_is_sized_deferred(
input,
expr.span,
traits::SizedArgumentType(None),
);
}
}
// Here we want to prevent struct constructors from returning unsized types.
// There were two cases this happened: fn pointer coercion in stable
// and usual function call in presence of unsized_locals.
// Also, as we just want to check sizedness, instead of introducing
// placeholder lifetimes with probing, we just replace higher lifetimes
// with fresh vars.
let output = self
.replace_bound_vars_with_fresh_vars(
expr.span,
infer::LateBoundRegionConversionTime::FnCall,
&fn_sig.output(),
)
.0;
self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
}
// We always require that the type provided as the value for
// a type parameter outlives the moment of instantiation.
let substs = self.typeck_results.borrow().node_substs(expr.hir_id);
self.add_wf_bounds(substs, expr);
ty
}
fn check_expr_break(
&self,
destination: hir::Destination,
expr_opt: Option<&'tcx hir::Expr<'tcx>>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
let tcx = self.tcx;
if let Ok(target_id) = destination.target_id {
let (e_ty, cause);
if let Some(ref e) = expr_opt {
// If this is a break with a value, we need to type-check
// the expression. Get an expected type from the loop context.
let opt_coerce_to = {
// We should release `enclosing_breakables` before the `check_expr_with_hint`
// below, so can't move this block of code to the enclosing scope and share
// `ctxt` with the second `encloding_breakables` borrow below.
let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
match enclosing_breakables.opt_find_breakable(target_id) {
Some(ctxt) => ctxt.coerce.as_ref().map(|coerce| coerce.expected_ty()),
None => {
// Avoid ICE when `break` is inside a closure (#65383).
return tcx.ty_error_with_message(
expr.span,
"break was outside loop, but no error was emitted",
);
}
}
};
// If the loop context is not a `loop { }`, then break with
// a value is illegal, and `opt_coerce_to` will be `None`.
// Just set expectation to error in that case.
let coerce_to = opt_coerce_to.unwrap_or_else(|| tcx.ty_error());
// Recurse without `enclosing_breakables` borrowed.
e_ty = self.check_expr_with_hint(e, coerce_to);
cause = self.misc(e.span);
} else {
// Otherwise, this is a break *without* a value. That's
// always legal, and is equivalent to `break ()`.
e_ty = tcx.mk_unit();
cause = self.misc(expr.span);
}
// Now that we have type-checked `expr_opt`, borrow
// the `enclosing_loops` field and let's coerce the
// type of `expr_opt` into what is expected.
let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
let ctxt = match enclosing_breakables.opt_find_breakable(target_id) {
Some(ctxt) => ctxt,
None => {
// Avoid ICE when `break` is inside a closure (#65383).
return tcx.ty_error_with_message(
expr.span,
"break was outside loop, but no error was emitted",
);
}
};
if let Some(ref mut coerce) = ctxt.coerce {
if let Some(ref e) = expr_opt {
coerce.coerce(self, &cause, e, e_ty);
} else {
assert!(e_ty.is_unit());
let ty = coerce.expected_ty();
coerce.coerce_forced_unit(
self,
&cause,
&mut |mut err| {
self.suggest_mismatched_types_on_tail(
&mut err, expr, ty, e_ty, cause.span, target_id,
);
if let Some(val) = ty_kind_suggestion(ty) {
let label = destination
.label
.map(|l| format!(" {}", l.ident))
.unwrap_or_else(String::new);
err.span_suggestion(
expr.span,
"give it a value of the expected type",
format!("break{} {}", label, val),
Applicability::HasPlaceholders,
);
}
},
false,
);
}
} else {
// If `ctxt.coerce` is `None`, we can just ignore
// the type of the expression. This is because
// either this was a break *without* a value, in
// which case it is always a legal type (`()`), or
// else an error would have been flagged by the
// `loops` pass for using break with an expression
// where you are not supposed to.
assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
}
ctxt.may_break = true;
// the type of a `break` is always `!`, since it diverges
tcx.types.never
} else {
// Otherwise, we failed to find the enclosing loop;
// this can only happen if the `break` was not
// inside a loop at all, which is caught by the
// loop-checking pass.
let err = self.tcx.ty_error_with_message(
expr.span,
"break was outside loop, but no error was emitted",
);
// We still need to assign a type to the inner expression to
// prevent the ICE in #43162.
if let Some(ref e) = expr_opt {
self.check_expr_with_hint(e, err);
// ... except when we try to 'break rust;'.
// ICE this expression in particular (see #43162).
if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
if path.segments.len() == 1 && path.segments[0].ident.name == sym::rust {
fatally_break_rust(self.tcx.sess);
}
}
}
// There was an error; make type-check fail.
err
}
}
fn check_expr_return(
&self,
expr_opt: Option<&'tcx hir::Expr<'tcx>>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
if self.ret_coercion.is_none() {
self.tcx.sess.emit_err(ReturnStmtOutsideOfFnBody { span: expr.span });
} else if let Some(ref e) = expr_opt {
if self.ret_coercion_span.borrow().is_none() {
*self.ret_coercion_span.borrow_mut() = Some(e.span);
}
self.check_return_expr(e);
} else {
let mut coercion = self.ret_coercion.as_ref().unwrap().borrow_mut();
if self.ret_coercion_span.borrow().is_none() {
*self.ret_coercion_span.borrow_mut() = Some(expr.span);
}
let cause = self.cause(expr.span, ObligationCauseCode::ReturnNoExpression);
if let Some((fn_decl, _)) = self.get_fn_decl(expr.hir_id) {
coercion.coerce_forced_unit(
self,
&cause,
&mut |db| {
let span = fn_decl.output.span();
if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
db.span_label(
span,
format!("expected `{}` because of this return type", snippet),
);
}
},
true,
);
} else {
coercion.coerce_forced_unit(self, &cause, &mut |_| (), true);
}
}
self.tcx.types.never
}
pub(super) fn check_return_expr(&self, return_expr: &'tcx hir::Expr<'tcx>) {
let ret_coercion = self.ret_coercion.as_ref().unwrap_or_else(|| {
span_bug!(return_expr.span, "check_return_expr called outside fn body")
});
let ret_ty = ret_coercion.borrow().expected_ty();
let return_expr_ty = self.check_expr_with_hint(return_expr, ret_ty.clone());
ret_coercion.borrow_mut().coerce(
self,
&self.cause(return_expr.span, ObligationCauseCode::ReturnValue(return_expr.hir_id)),
return_expr,
return_expr_ty,
);
}
fn is_destructuring_place_expr(&self, expr: &'tcx hir::Expr<'tcx>) -> bool {
match &expr.kind {
ExprKind::Array(comps) | ExprKind::Tup(comps) => {
comps.iter().all(|e| self.is_destructuring_place_expr(e))
}
ExprKind::Struct(_path, fields, rest) => {
rest.as_ref().map(|e| self.is_destructuring_place_expr(e)).unwrap_or(true)
&& fields.iter().all(|f| self.is_destructuring_place_expr(&f.expr))
}
_ => expr.is_syntactic_place_expr(),
}
}
pub(crate) fn check_lhs_assignable(
&self,
lhs: &'tcx hir::Expr<'tcx>,
err_code: &'static str,
expr_span: &Span,
) {
if !lhs.is_syntactic_place_expr() {
// FIXME: Make this use SessionDiagnostic once error codes can be dynamically set.
let mut err = self.tcx.sess.struct_span_err_with_code(
*expr_span,
"invalid left-hand side of assignment",
DiagnosticId::Error(err_code.into()),
);
err.span_label(lhs.span, "cannot assign to this expression");
if self.is_destructuring_place_expr(lhs) {
err.note("destructuring assignments are not currently supported");
err.note("for more information, see https://github.com/rust-lang/rfcs/issues/372");
}
err.emit();
}
}
/// Type check assignment expression `expr` of form `lhs = rhs`.
/// The expected type is `()` and is passsed to the function for the purposes of diagnostics.
fn check_expr_assign(
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
lhs: &'tcx hir::Expr<'tcx>,
rhs: &'tcx hir::Expr<'tcx>,
span: &Span,
) -> Ty<'tcx> {
let expected_ty = expected.coercion_target_type(self, expr.span);
if expected_ty == self.tcx.types.bool {
// The expected type is `bool` but this will result in `()` so we can reasonably
// say that the user intended to write `lhs == rhs` instead of `lhs = rhs`.
// The likely cause of this is `if foo = bar { .. }`.
let actual_ty = self.tcx.mk_unit();
let mut err = self.demand_suptype_diag(expr.span, expected_ty, actual_ty).unwrap();
let lhs_ty = self.check_expr(&lhs);
let rhs_ty = self.check_expr(&rhs);
if self.can_coerce(lhs_ty, rhs_ty) {
if !lhs.is_syntactic_place_expr() {
// Do not suggest `if let x = y` as `==` is way more likely to be the intention.
if let hir::Node::Expr(hir::Expr {
kind: ExprKind::Match(_, _, hir::MatchSource::IfDesugar { .. }),
..
}) = self.tcx.hir().get(
self.tcx.hir().get_parent_node(self.tcx.hir().get_parent_node(expr.hir_id)),
) {
// Likely `if let` intended.
err.span_suggestion_verbose(
expr.span.shrink_to_lo(),
"you might have meant to use pattern matching",
"let ".to_string(),
Applicability::MaybeIncorrect,
);
}
}
err.span_suggestion_verbose(
*span,
"you might have meant to compare for equality",
"==".to_string(),
Applicability::MaybeIncorrect,
);
} else {
// Do this to cause extra errors about the assignment.
let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
let _ = self.check_expr_coercable_to_type(&rhs, lhs_ty, Some(lhs));
}
if self.sess().if_let_suggestions.borrow().get(&expr.span).is_some() {
// We already emitted an `if let` suggestion due to an identifier not found.
err.delay_as_bug();
} else {
err.emit();
}
return self.tcx.ty_error();
}
self.check_lhs_assignable(lhs, "E0070", span);
let lhs_ty = self.check_expr_with_needs(&lhs, Needs::MutPlace);
let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty, Some(lhs));
self.require_type_is_sized(lhs_ty, lhs.span, traits::AssignmentLhsSized);
if lhs_ty.references_error() || rhs_ty.references_error() {
self.tcx.ty_error()
} else {
self.tcx.mk_unit()
}
}
fn check_expr_loop(
&self,
body: &'tcx hir::Block<'tcx>,
source: hir::LoopSource,
expected: Expectation<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
let coerce = match source {
// you can only use break with a value from a normal `loop { }`
hir::LoopSource::Loop => {
let coerce_to = expected.coercion_target_type(self, body.span);
Some(CoerceMany::new(coerce_to))
}
hir::LoopSource::While | hir::LoopSource::WhileLet | hir::LoopSource::ForLoop => None,
};
let ctxt = BreakableCtxt {
coerce,
may_break: false, // Will get updated if/when we find a `break`.
};
let (ctxt, ()) = self.with_breakable_ctxt(expr.hir_id, ctxt, || {
self.check_block_no_value(&body);
});
if ctxt.may_break {
// No way to know whether it's diverging because
// of a `break` or an outer `break` or `return`.
self.diverges.set(Diverges::Maybe);
}
// If we permit break with a value, then result type is
// the LUB of the breaks (possibly ! if none); else, it
// is nil. This makes sense because infinite loops
// (which would have type !) are only possible iff we
// permit break with a value [1].
if ctxt.coerce.is_none() && !ctxt.may_break {
// [1]
self.tcx.sess.delay_span_bug(body.span, "no coercion, but loop may not break");
}
ctxt.coerce.map(|c| c.complete(self)).unwrap_or_else(|| self.tcx.mk_unit())
}
/// Checks a method call.
fn check_method_call(
&self,
expr: &'tcx hir::Expr<'tcx>,
segment: &hir::PathSegment<'_>,
span: Span,
args: &'tcx [hir::Expr<'tcx>],
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
let rcvr = &args[0];
let rcvr_t = self.check_expr(&rcvr);
// no need to check for bot/err -- callee does that
let rcvr_t = self.structurally_resolved_type(args[0].span, rcvr_t);
let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr) {
Ok(method) => {
// We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
// trigger this codepath causing `structuraly_resolved_type` to emit an error.
self.write_method_call(expr.hir_id, method);
Ok(method)
}
Err(error) => {
if segment.ident.name != kw::Invalid {
self.report_extended_method_error(segment, span, args, rcvr_t, error);
}
Err(())
}
};
// Call the generic checker.
self.check_method_argument_types(
span,
expr,
method,
&args[1..],
DontTupleArguments,
expected,
)
}
fn report_extended_method_error(
&self,
segment: &hir::PathSegment<'_>,
span: Span,
args: &'tcx [hir::Expr<'tcx>],
rcvr_t: Ty<'tcx>,
error: MethodError<'tcx>,
) {
let rcvr = &args[0];
let try_alt_rcvr = |err: &mut DiagnosticBuilder<'_>, new_rcvr_t| {
if let Some(new_rcvr_t) = new_rcvr_t {
if let Ok(pick) = self.lookup_probe(
span,
segment.ident,
new_rcvr_t,
rcvr,
probe::ProbeScope::AllTraits,
) {
debug!("try_alt_rcvr: pick candidate {:?}", pick);
// Make sure the method is defined for the *actual* receiver:
// we don't want to treat `Box<Self>` as a receiver if
// it only works because of an autoderef to `&self`
if pick.autoderefs == 0 {
err.span_label(
pick.item.ident.span,
&format!("the method is available for `{}` here", new_rcvr_t),
);
}
}
}
};
if let Some(mut err) = self.report_method_error(
span,
rcvr_t,
segment.ident,
SelfSource::MethodCall(rcvr),
error,
Some(args),
) {
if let ty::Adt(..) = rcvr_t.kind() {
// Try alternative arbitrary self types that could fulfill this call.
// FIXME: probe for all types that *could* be arbitrary self-types, not
// just this list.
try_alt_rcvr(&mut err, self.tcx.mk_lang_item(rcvr_t, LangItem::OwnedBox));
try_alt_rcvr(&mut err, self.tcx.mk_lang_item(rcvr_t, LangItem::Pin));
try_alt_rcvr(&mut err, self.tcx.mk_diagnostic_item(rcvr_t, sym::Arc));
try_alt_rcvr(&mut err, self.tcx.mk_diagnostic_item(rcvr_t, sym::Rc));
}
err.emit();
}
}
fn check_expr_cast(
&self,
e: &'tcx hir::Expr<'tcx>,
t: &'tcx hir::Ty<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
// Find the type of `e`. Supply hints based on the type we are casting to,
// if appropriate.
let t_cast = self.to_ty_saving_user_provided_ty(t);
let t_cast = self.resolve_vars_if_possible(&t_cast);
let t_expr = self.check_expr_with_expectation(e, ExpectCastableToType(t_cast));
let t_cast = self.resolve_vars_if_possible(&t_cast);
// Eagerly check for some obvious errors.
if t_expr.references_error() || t_cast.references_error() {
self.tcx.ty_error()
} else {
// Defer other checks until we're done type checking.
let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
match cast::CastCheck::new(self, e, t_expr, t_cast, t.span, expr.span) {
Ok(cast_check) => {
deferred_cast_checks.push(cast_check);
t_cast
}
Err(ErrorReported) => self.tcx.ty_error(),
}
}
}
fn check_expr_array(
&self,
args: &'tcx [hir::Expr<'tcx>],
expected: Expectation<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
) -> Ty<'tcx> {
let element_ty = if !args.is_empty() {
let coerce_to = expected
.to_option(self)
.and_then(|uty| match *uty.kind() {
ty::Array(ty, _) | ty::Slice(ty) => Some(ty),
_ => None,