/
demand.rs
267 lines (248 loc) · 11.2 KB
/
demand.rs
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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use check::FnCtxt;
use rustc::infer::InferOk;
use rustc::traits::ObligationCause;
use syntax::ast;
use syntax_pos::{self, Span};
use rustc::hir;
use rustc::hir::print;
use rustc::hir::def::Def;
use rustc::ty::{self, Ty, AssociatedItem};
use errors::{DiagnosticBuilder, CodeMapper};
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_coerce(&self, expr: &hir::Expr, checked_ty: Ty<'tcx>, expected: Ty<'tcx>) {
if let Some(mut err) = self.demand_coerce_diag(expr, checked_ty, expected) {
err.emit();
}
}
// Checks that the type of `expr` can be coerced to `expected`.
//
// NB: 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>) -> Option<DiagnosticBuilder<'tcx>> {
let expected = self.resolve_type_vars_with_obligations(expected);
if let Err(e) = self.try_coerce(expr, checked_ty, self.diverges.get(), expected) {
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 with any variants whose sole
// field is of the found type, suggest such variants. See Issue
// #42764.
if let ty::TyAdt(expected_adt, substs) = expected.sty {
let mut compatible_variants = vec![];
for variant in &expected_adt.variants {
if variant.fields.len() == 1 {
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 mut variant_path = self.tcx.item_path_str(variant.did);
variant_path = variant_path.trim_left_matches("std::prelude::v1::")
.to_string();
compatible_variants.push(variant_path);
}
}
}
if !compatible_variants.is_empty() {
let expr_text = print::to_string(print::NO_ANN, |s| s.print_expr(expr));
let suggestions = compatible_variants.iter()
.map(|v| format!("{}({})", v, expr_text)).collect::<Vec<_>>();
err.span_suggestions(expr.span,
"try using a variant of the expected type",
suggestions);
}
}
if let Some(suggestion) = self.check_ref(expr,
checked_ty,
expected) {
err.help(&suggestion);
} else {
let mode = probe::Mode::MethodCall;
let suggestions = self.probe_for_return_type(syntax_pos::DUMMY_SP,
mode,
expected,
checked_ty,
ast::DUMMY_NODE_ID);
if suggestions.len() > 0 {
err.help(&format!("here are some functions which \
might fulfill your needs:\n{}",
self.get_best_match(&suggestions).join("\n")));
}
}
return Some(err);
}
None
}
fn format_method_suggestion(&self, method: &AssociatedItem) -> String {
format!("- .{}({})",
method.name,
if self.has_no_input_arg(method) {
""
} else {
"..."
})
}
fn display_suggested_methods(&self, methods: &[AssociatedItem]) -> Vec<String> {
methods.iter()
.take(5)
.map(|method| self.format_method_suggestion(&*method))
.collect::<Vec<String>>()
}
fn get_best_match(&self, methods: &[AssociatedItem]) -> Vec<String> {
let no_argument_methods: Vec<_> =
methods.iter()
.filter(|ref x| self.has_no_input_arg(&*x))
.map(|x| x.clone())
.collect();
if no_argument_methods.len() > 0 {
self.display_suggested_methods(&no_argument_methods)
} else {
self.display_suggested_methods(&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,
}
}
/// 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`!".
fn check_ref(&self,
expr: &hir::Expr,
checked_ty: Ty<'tcx>,
expected: Ty<'tcx>)
-> Option<String> {
match (&expected.sty, &checked_ty.sty) {
(&ty::TyRef(_, exp), &ty::TyRef(_, check)) => match (&exp.ty.sty, &check.ty.sty) {
(&ty::TyStr, &ty::TyArray(arr, _)) |
(&ty::TyStr, &ty::TySlice(arr)) if arr == self.tcx.types.u8 => {
if let hir::ExprLit(_) = expr.node {
let sp = self.sess().codemap().call_span_if_macro(expr.span);
if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
return Some(format!("try `{}`", &src[1..]));
}
}
None
},
(&ty::TyArray(arr, _), &ty::TyStr) |
(&ty::TySlice(arr), &ty::TyStr) if arr == self.tcx.types.u8 => {
if let hir::ExprLit(_) = expr.node {
let sp = self.sess().codemap().call_span_if_macro(expr.span);
if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
return Some(format!("try `b{}`", src));
}
}
None
}
_ => None,
},
(&ty::TyRef(_, 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.mutbl {
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) {
// Use the callsite's span if this is a macro call. #41858
let sp = self.sess().codemap().call_span_if_macro(expr.span);
if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
return Some(format!("try with `{}{}`",
match mutability.mutbl {
hir::Mutability::MutMutable => "&mut ",
hir::Mutability::MutImmutable => "&",
},
&src));
}
}
None
}
_ => None,
}
}
}