/
demand.rs
816 lines (771 loc) · 35.6 KB
/
demand.rs
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use crate::check::FnCtxt;
use rustc::infer::InferOk;
use rustc::traits::{ObligationCause, ObligationCauseCode};
use syntax::ast;
use syntax::util::parser::PREC_POSTFIX;
use syntax_pos::Span;
use rustc::hir;
use rustc::hir::def::Def;
use rustc::hir::Node;
use rustc::hir::{Item, ItemKind, print};
use rustc::ty::{self, Ty, AssociatedItem};
use rustc::ty::adjustment::AllowTwoPhase;
use errors::{Applicability, DiagnosticBuilder, SourceMapper};
use super::method::probe;
impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// Requires that the two types unify, and prints an error message if
// they don't.
pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
}
pub fn demand_suptype_diag(&self,
sp: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
let cause = &self.misc(sp);
match self.at(cause, self.param_env).sup(expected, actual) {
Ok(InferOk { obligations, value: () }) => {
self.register_predicates(obligations);
None
},
Err(e) => {
Some(self.report_mismatched_types(&cause, expected, actual, e))
}
}
}
pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
err.emit();
}
}
pub fn demand_eqtype_diag(&self,
sp: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
}
pub fn demand_eqtype_with_origin(&self,
cause: &ObligationCause<'tcx>,
expected: Ty<'tcx>,
actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
match self.at(cause, self.param_env).eq(expected, actual) {
Ok(InferOk { obligations, value: () }) => {
self.register_predicates(obligations);
None
}
Err(e) => {
Some(self.report_mismatched_types(cause, expected, actual, e))
}
}
}
pub fn demand_eqtype_pat(
&self,
cause_span: Span,
expected: Ty<'tcx>,
actual: Ty<'tcx>,
match_expr_span: Option<Span>,
) {
let cause = if let Some(span) = match_expr_span {
self.cause(
cause_span,
ObligationCauseCode::MatchExpressionArmPattern { span, ty: expected },
)
} else {
self.misc(cause_span)
};
self.demand_eqtype_with_origin(&cause, expected, actual).map(|mut err| err.emit());
}
pub fn demand_coerce(&self,
expr: &hir::Expr,
checked_ty: Ty<'tcx>,
expected: Ty<'tcx>,
allow_two_phase: AllowTwoPhase)
-> Ty<'tcx> {
let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
if let Some(mut err) = err {
err.emit();
}
ty
}
// Checks that the type of `expr` can be coerced to `expected`.
//
// N.B., this code relies on `self.diverges` to be accurate. In
// particular, assignments to `!` will be permitted if the
// diverges flag is currently "always".
pub fn demand_coerce_diag(&self,
expr: &hir::Expr,
checked_ty: Ty<'tcx>,
expected: Ty<'tcx>,
allow_two_phase: AllowTwoPhase)
-> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
let expected = self.resolve_type_vars_with_obligations(expected);
let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
Ok(ty) => return (ty, None),
Err(e) => e
};
let cause = self.misc(expr.span);
let expr_ty = self.resolve_type_vars_with_obligations(checked_ty);
let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
// If the expected type is an enum (Issue #55250) with any variants whose
// sole field is of the found type, suggest such variants. (Issue #42764)
if let ty::Adt(expected_adt, substs) = expected.sty {
if expected_adt.is_enum() {
let mut compatible_variants = expected_adt.variants
.iter()
.filter(|variant| variant.fields.len() == 1)
.filter_map(|variant| {
let sole_field = &variant.fields[0];
let sole_field_ty = sole_field.ty(self.tcx, substs);
if self.can_coerce(expr_ty, sole_field_ty) {
let variant_path = self.tcx.item_path_str(variant.did);
// FIXME #56861: DRYer prelude filtering
Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
} else {
None
}
}).peekable();
if compatible_variants.peek().is_some() {
let expr_text = print::to_string(print::NO_ANN, |s| s.print_expr(expr));
let suggestions = compatible_variants
.map(|v| format!("{}({})", v, expr_text));
err.span_suggestions(
expr.span,
"try using a variant of the expected type",
suggestions,
Applicability::MaybeIncorrect,
);
}
}
}
self.suggest_ref_or_into(&mut err, expr, expected, expr_ty);
(expected, Some(err))
}
pub fn get_conversion_methods(&self, span: Span, expected: Ty<'tcx>, checked_ty: Ty<'tcx>)
-> Vec<AssociatedItem> {
let mut methods = self.probe_for_return_type(span,
probe::Mode::MethodCall,
expected,
checked_ty,
ast::DUMMY_NODE_ID);
methods.retain(|m| {
self.has_no_input_arg(m) &&
self.tcx.get_attrs(m.def_id).iter()
// This special internal attribute is used to whitelist
// "identity-like" conversion methods to be suggested here.
//
// FIXME (#46459 and #46460): ideally
// `std::convert::Into::into` and `std::borrow:ToOwned` would
// also be `#[rustc_conversion_suggestion]`, if not for
// method-probing false-positives and -negatives (respectively).
//
// FIXME? Other potential candidate methods: `as_ref` and
// `as_mut`?
.find(|a| a.check_name("rustc_conversion_suggestion")).is_some()
});
methods
}
// This function checks if the method isn't static and takes other arguments than `self`.
fn has_no_input_arg(&self, method: &AssociatedItem) -> bool {
match method.def() {
Def::Method(def_id) => {
self.tcx.fn_sig(def_id).inputs().skip_binder().len() == 1
}
_ => false,
}
}
/// Identify some cases where `as_ref()` would be appropriate and suggest it.
///
/// Given the following code:
/// ```
/// struct Foo;
/// fn takes_ref(_: &Foo) {}
/// let ref opt = Some(Foo);
///
/// opt.map(|arg| takes_ref(arg));
/// ```
/// Suggest using `opt.as_ref().map(|arg| takes_ref(arg));` instead.
///
/// It only checks for `Option` and `Result` and won't work with
/// ```
/// opt.map(|arg| { takes_ref(arg) });
/// ```
fn can_use_as_ref(&self, expr: &hir::Expr) -> Option<(Span, &'static str, String)> {
if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = expr.node {
if let hir::def::Def::Local(id) = path.def {
let parent = self.tcx.hir().get_parent_node(id);
if let Some(Node::Expr(hir::Expr {
id,
node: hir::ExprKind::Closure(_, decl, ..),
..
})) = self.tcx.hir().find(parent) {
let parent = self.tcx.hir().get_parent_node(*id);
if let (Some(Node::Expr(hir::Expr {
node: hir::ExprKind::MethodCall(path, span, expr),
..
})), 1) = (self.tcx.hir().find(parent), decl.inputs.len()) {
let self_ty = self.tables.borrow().node_type(expr[0].hir_id);
let self_ty = format!("{:?}", self_ty);
let name = path.ident.as_str();
let is_as_ref_able = (
self_ty.starts_with("&std::option::Option") ||
self_ty.starts_with("&std::result::Result") ||
self_ty.starts_with("std::option::Option") ||
self_ty.starts_with("std::result::Result")
) && (name == "map" || name == "and_then");
if is_as_ref_able {
return Some((span.shrink_to_lo(),
"consider using `as_ref` instead",
"as_ref().".into()));
}
}
}
}
}
None
}
/// This function is used to determine potential "simple" improvements or users' errors and
/// provide them useful help. For example:
///
/// ```
/// fn some_fn(s: &str) {}
///
/// let x = "hey!".to_owned();
/// some_fn(x); // error
/// ```
///
/// No need to find every potential function which could make a coercion to transform a
/// `String` into a `&str` since a `&` would do the trick!
///
/// In addition of this check, it also checks between references mutability state. If the
/// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
/// `&mut`!".
pub fn check_ref(&self,
expr: &hir::Expr,
checked_ty: Ty<'tcx>,
expected: Ty<'tcx>)
-> Option<(Span, &'static str, String)> {
let cm = self.sess().source_map();
// Use the callsite's span if this is a macro call. #41858
let sp = cm.call_span_if_macro(expr.span);
if !cm.span_to_filename(sp).is_real() {
return None;
}
match (&expected.sty, &checked_ty.sty) {
(&ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.sty, &check.sty) {
(&ty::Str, &ty::Array(arr, _)) |
(&ty::Str, &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
if let hir::ExprKind::Lit(_) = expr.node {
if let Ok(src) = cm.span_to_snippet(sp) {
if src.starts_with("b\"") {
return Some((sp,
"consider removing the leading `b`",
src[1..].to_string()));
}
}
}
},
(&ty::Array(arr, _), &ty::Str) |
(&ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
if let hir::ExprKind::Lit(_) = expr.node {
if let Ok(src) = cm.span_to_snippet(sp) {
if src.starts_with("\"") {
return Some((sp,
"consider adding a leading `b`",
format!("b{}", src)));
}
}
}
}
_ => {}
},
(&ty::Ref(_, _, mutability), _) => {
// Check if it can work when put into a ref. For example:
//
// ```
// fn bar(x: &mut i32) {}
//
// let x = 0u32;
// bar(&x); // error, expected &mut
// ```
let ref_ty = match mutability {
hir::Mutability::MutMutable => self.tcx.mk_mut_ref(
self.tcx.mk_region(ty::ReStatic),
checked_ty),
hir::Mutability::MutImmutable => self.tcx.mk_imm_ref(
self.tcx.mk_region(ty::ReStatic),
checked_ty),
};
if self.can_coerce(ref_ty, expected) {
if let Ok(src) = cm.span_to_snippet(sp) {
let needs_parens = match expr.node {
// parenthesize if needed (Issue #46756)
hir::ExprKind::Cast(_, _) |
hir::ExprKind::Binary(_, _, _) => true,
// parenthesize borrows of range literals (Issue #54505)
_ if self.is_range_literal(expr) => true,
_ => false,
};
let sugg_expr = if needs_parens {
format!("({})", src)
} else {
src
};
if let Some(sugg) = self.can_use_as_ref(expr) {
return Some(sugg);
}
return Some(match mutability {
hir::Mutability::MutMutable => {
(sp, "consider mutably borrowing here", format!("&mut {}",
sugg_expr))
}
hir::Mutability::MutImmutable => {
(sp, "consider borrowing here", format!("&{}", sugg_expr))
}
});
}
}
}
(_, &ty::Ref(_, checked, _)) => {
// We have `&T`, check if what was expected was `T`. If so,
// we may want to suggest adding a `*`, or removing
// a `&`.
//
// (But, also check the `expn_info()` to see if this is
// a macro; if so, it's hard to extract the text and make a good
// suggestion, so don't bother.)
if self.infcx.can_sub(self.param_env, checked, &expected).is_ok() &&
sp.ctxt().outer().expn_info().is_none() {
match expr.node {
// Maybe remove `&`?
hir::ExprKind::AddrOf(_, ref expr) => {
if !cm.span_to_filename(expr.span).is_real() {
return None;
}
if let Ok(code) = cm.span_to_snippet(expr.span) {
return Some((sp, "consider removing the borrow", code));
}
}
// Maybe add `*`? Only if `T: Copy`.
_ => {
if self.infcx.type_is_copy_modulo_regions(self.param_env,
checked,
sp) {
// do not suggest if the span comes from a macro (#52783)
if let (Ok(code),
true) = (cm.span_to_snippet(sp), sp == expr.span) {
return Some((
sp,
"consider dereferencing the borrow",
format!("*{}", code),
));
}
}
}
}
}
}
_ => {}
}
None
}
/// This function checks if the specified expression is a built-in range literal.
/// (See: `LoweringContext::lower_expr()` in `src/librustc/hir/lowering.rs`).
fn is_range_literal(&self, expr: &hir::Expr) -> bool {
use hir::{Path, QPath, ExprKind, TyKind};
// We support `::std::ops::Range` and `::core::ops::Range` prefixes
let is_range_path = |path: &Path| {
let mut segs = path.segments.iter()
.map(|seg| seg.ident.as_str());
if let (Some(root), Some(std_core), Some(ops), Some(range), None) =
(segs.next(), segs.next(), segs.next(), segs.next(), segs.next())
{
// "{{root}}" is the equivalent of `::` prefix in Path
root == "{{root}}" && (std_core == "std" || std_core == "core")
&& ops == "ops" && range.starts_with("Range")
} else {
false
}
};
let span_is_range_literal = |span: &Span| {
// Check whether a span corresponding to a range expression
// is a range literal, rather than an explicit struct or `new()` call.
let source_map = self.tcx.sess.source_map();
let end_point = source_map.end_point(*span);
if let Ok(end_string) = source_map.span_to_snippet(end_point) {
!(end_string.ends_with("}") || end_string.ends_with(")"))
} else {
false
}
};
match expr.node {
// All built-in range literals but `..=` and `..` desugar to Structs
ExprKind::Struct(ref qpath, _, _) => {
if let QPath::Resolved(None, ref path) = **qpath {
return is_range_path(&path) && span_is_range_literal(&expr.span);
}
}
// `..` desugars to its struct path
ExprKind::Path(QPath::Resolved(None, ref path)) => {
return is_range_path(&path) && span_is_range_literal(&expr.span);
}
// `..=` desugars into `::std::ops::RangeInclusive::new(...)`
ExprKind::Call(ref func, _) => {
if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.node {
if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.node {
let call_to_new = segment.ident.as_str() == "new";
return is_range_path(&path) && span_is_range_literal(&expr.span)
&& call_to_new;
}
}
}
_ => {}
}
false
}
pub fn check_for_cast(
&self,
err: &mut DiagnosticBuilder<'tcx>,
expr: &hir::Expr,
checked_ty: Ty<'tcx>,
expected_ty: Ty<'tcx>,
) -> bool {
let parent_id = self.tcx.hir().get_parent_node(expr.id);
if let Some(parent) = self.tcx.hir().find(parent_id) {
// Shouldn't suggest `.into()` on `const`s.
if let Node::Item(Item { node: ItemKind::Const(_, _), .. }) = parent {
// FIXME(estebank): modify once we decide to suggest `as` casts
return false;
}
};
let will_truncate = "will truncate the source value";
let depending_on_isize = "will truncate or zero-extend depending on the bit width of \
`isize`";
let depending_on_usize = "will truncate or zero-extend depending on the bit width of \
`usize`";
let will_sign_extend = "will sign-extend the source value";
let will_zero_extend = "will zero-extend the source value";
// If casting this expression to a given numeric type would be appropriate in case of a type
// mismatch.
//
// We want to minimize the amount of casting operations that are suggested, as it can be a
// lossy operation with potentially bad side effects, so we only suggest when encountering
// an expression that indicates that the original type couldn't be directly changed.
//
// For now, don't suggest casting with `as`.
let can_cast = false;
let mut prefix = String::new();
if let Some(hir::Node::Expr(hir::Expr {
node: hir::ExprKind::Struct(_, fields, _),
..
})) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.id)) {
// `expr` is a literal field for a struct, only suggest if appropriate
for field in fields {
if field.expr.id == expr.id && field.is_shorthand {
// This is a field literal
prefix = format!("{}: ", field.ident);
break;
}
}
if &prefix == "" {
// Likely a field was meant, but this field wasn't found. Do not suggest anything.
return false;
}
}
let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
let msg = format!("you can cast an `{}` to `{}`", checked_ty, expected_ty);
let cast_suggestion = format!(
"{}{}{}{} as {}",
prefix,
if needs_paren { "(" } else { "" },
src,
if needs_paren { ")" } else { "" },
expected_ty,
);
let into_suggestion = format!(
"{}{}{}{}.into()",
prefix,
if needs_paren { "(" } else { "" },
src,
if needs_paren { ")" } else { "" },
);
let literal_is_ty_suffixed = |expr: &hir::Expr| {
if let hir::ExprKind::Lit(lit) = &expr.node {
lit.node.is_suffixed()
} else {
false
}
};
let into_sugg = into_suggestion.clone();
let suggest_to_change_suffix_or_into = |err: &mut DiagnosticBuilder,
note: Option<&str>| {
let suggest_msg = if literal_is_ty_suffixed(expr) {
format!(
"change the type of the numeric literal from `{}` to `{}`",
checked_ty,
expected_ty,
)
} else {
match note {
Some(note) => format!("{}, which {}", msg, note),
_ => format!("{} in a lossless way", msg),
}
};
let suffix_suggestion = format!(
"{}{}{}{}",
if needs_paren { "(" } else { "" },
src.trim_end_matches(&checked_ty.to_string()),
expected_ty,
if needs_paren { ")" } else { "" },
);
err.span_suggestion(
expr.span,
&suggest_msg,
if literal_is_ty_suffixed(expr) {
suffix_suggestion
} else {
into_sugg
},
Applicability::MachineApplicable,
);
};
match (&expected_ty.sty, &checked_ty.sty) {
(&ty::Int(ref exp), &ty::Int(ref found)) => {
match (found.bit_width(), exp.bit_width()) {
(Some(found), Some(exp)) if found > exp => {
if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_truncate),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
}
(None, _) | (_, None) => {
if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_isize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
}
_ => {
suggest_to_change_suffix_or_into(
err,
Some(will_sign_extend),
);
}
}
true
}
(&ty::Uint(ref exp), &ty::Uint(ref found)) => {
match (found.bit_width(), exp.bit_width()) {
(Some(found), Some(exp)) if found > exp => {
if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_truncate),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
}
(None, _) | (_, None) => {
if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_usize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
}
_ => {
suggest_to_change_suffix_or_into(
err,
Some(will_zero_extend),
);
}
}
true
}
(&ty::Int(ref exp), &ty::Uint(ref found)) => {
if can_cast {
match (found.bit_width(), exp.bit_width()) {
(Some(found), Some(exp)) if found > exp - 1 => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_truncate),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
(None, None) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_truncate),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
(None, _) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_isize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
(_, None) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_usize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
_ => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_zero_extend),
cast_suggestion,
Applicability::MachineApplicable
);
}
}
}
true
}
(&ty::Uint(ref exp), &ty::Int(ref found)) => {
if can_cast {
match (found.bit_width(), exp.bit_width()) {
(Some(found), Some(exp)) if found - 1 > exp => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_truncate),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
(None, None) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_sign_extend),
cast_suggestion,
Applicability::MachineApplicable // lossy conversion
);
}
(None, _) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_usize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
(_, None) => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, depending_on_isize),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
_ => {
err.span_suggestion(
expr.span,
&format!("{}, which {}", msg, will_sign_extend),
cast_suggestion,
Applicability::MachineApplicable
);
}
}
}
true
}
(&ty::Float(ref exp), &ty::Float(ref found)) => {
if found.bit_width() < exp.bit_width() {
suggest_to_change_suffix_or_into(
err,
None,
);
} else if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, producing the closest possible value", msg),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
true
}
(&ty::Uint(_), &ty::Float(_)) | (&ty::Int(_), &ty::Float(_)) => {
if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, rounding the float towards zero", msg),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
err.warn("casting here will cause undefined behavior if the rounded value \
cannot be represented by the target integer type, including \
`Inf` and `NaN` (this is a bug and will be fixed)");
}
true
}
(&ty::Float(ref exp), &ty::Uint(ref found)) => {
// if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
if exp.bit_width() > found.bit_width().unwrap_or(256) {
err.span_suggestion(
expr.span,
&format!("{}, producing the floating point representation of the \
integer",
msg),
into_suggestion,
Applicability::MachineApplicable
);
} else if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, producing the floating point representation of the \
integer, rounded if necessary",
msg),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
true
}
(&ty::Float(ref exp), &ty::Int(ref found)) => {
// if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
if exp.bit_width() > found.bit_width().unwrap_or(256) {
err.span_suggestion(
expr.span,
&format!("{}, producing the floating point representation of the \
integer",
msg),
into_suggestion,
Applicability::MachineApplicable
);
} else if can_cast {
err.span_suggestion(
expr.span,
&format!("{}, producing the floating point representation of the \
integer, rounded if necessary",
msg),
cast_suggestion,
Applicability::MaybeIncorrect // lossy conversion
);
}
true
}
_ => false,
}
} else {
false
}
}
}