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Rollup merge of rust-lang#37658 - GuillaumeGomez:ref_suggestion, r=ni…
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…komatsakis,eddyb

Ref suggestion
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frewsxcv authored Apr 22, 2017
2 parents 1785bca + 7ce1eb7 commit e7bf524
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Showing 8 changed files with 94 additions and 27 deletions.
11 changes: 11 additions & 0 deletions src/librustc_typeck/check/coercion.rs
Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,7 @@ use errors::DiagnosticBuilder;
use syntax::abi;
use syntax::feature_gate;
use syntax::ptr::P;
use syntax_pos;

use std::collections::VecDeque;
use std::ops::Deref;
Expand Down Expand Up @@ -722,6 +723,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
Ok(target)
}

/// Same as `try_coerce()`, but without side-effects.
pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
let source = self.resolve_type_vars_with_obligations(expr_ty);
debug!("coercion::can({:?} -> {:?})", source, target);

let cause = self.cause(syntax_pos::DUMMY_SP, ObligationCauseCode::ExprAssignable);
let coerce = Coerce::new(self, cause);
self.probe(|_| coerce.coerce::<hir::Expr>(&[], source, target)).is_ok()
}

/// Given some expressions, their known unified type and another expression,
/// tries to unify the types, potentially inserting coercions on any of the
/// provided expressions and returns their LUB (aka "common supertype").
Expand Down
89 changes: 75 additions & 14 deletions src/librustc_typeck/check/demand.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,15 +10,14 @@


use check::FnCtxt;
use rustc::ty::Ty;
use rustc::infer::{InferOk};
use rustc::infer::InferOk;
use rustc::traits::ObligationCause;

use syntax::ast;
use syntax_pos::{self, Span};
use rustc::hir;
use rustc::hir::def::Def;
use rustc::ty::{self, AssociatedItem};
use rustc::ty::{self, Ty, AssociatedItem};
use errors::DiagnosticBuilder;

use super::method::probe;
Expand Down Expand Up @@ -80,18 +79,24 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
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 mode = probe::Mode::MethodCall;
let suggestions = self.probe_for_return_type(syntax_pos::DUMMY_SP,
mode,
expected,
checked_ty,
ast::DUMMY_NODE_ID);
let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
if suggestions.len() > 0 {
err.help(&format!("here are some functions which \
might fulfill your needs:\n{}",
self.get_best_match(&suggestions).join("\n")));
};
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")));
}
}
err.emit();
}
}
Expand Down Expand Up @@ -140,4 +145,60 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
_ => 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(_, _), &ty::TyRef(_, _)) => 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) {
if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
return Some(format!("try with `{}{}`",
match mutability.mutbl {
hir::Mutability::MutMutable => "&mut ",
hir::Mutability::MutImmutable => "&",
},
&src));
}
}
None
}
_ => None,
}
}
}
1 change: 0 additions & 1 deletion src/test/compile-fail/coercion-slice.rs
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,5 @@ fn main() {
let _: &[i32] = [0];
//~^ ERROR mismatched types
//~| expected type `&[i32]`
//~| found type `[{integer}; 1]`
//~| expected &[i32], found array of 1 elements
}
2 changes: 1 addition & 1 deletion src/test/compile-fail/cross-borrow-trait.rs
Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ impl Trait for Foo {}

pub fn main() {
let x: Box<Trait> = Box::new(Foo);
let _y: &Trait = x; //~ ERROR mismatched types
let _y: &Trait = x; //~ ERROR E0308
//~| expected type `&Trait`
//~| found type `std::boxed::Box<Trait>`
}
2 changes: 1 addition & 1 deletion src/test/compile-fail/issue-11374.rs
Original file line number Diff line number Diff line change
Expand Up @@ -33,5 +33,5 @@ pub fn for_stdin<'a>() -> Container<'a> {
fn main() {
let mut c = for_stdin();
let mut v = Vec::new();
c.read_to(v); //~ ERROR mismatched types
c.read_to(v); //~ ERROR E0308
}
1 change: 1 addition & 0 deletions src/test/compile-fail/issue-13058.rs
Original file line number Diff line number Diff line change
Expand Up @@ -35,4 +35,5 @@ fn check<'r, I: Iterator<Item=usize>, T: Itble<'r, usize, I>>(cont: &T) -> bool
fn main() {
check((3, 5));
//~^ ERROR mismatched types
//~| HELP try with `&(3, 5)`
}
1 change: 0 additions & 1 deletion src/test/ui/span/coerce-suggestions.rs
Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,6 @@ fn main() {
//~| NOTE types differ in mutability
//~| NOTE expected type `&mut std::string::String`
//~| NOTE found type `&std::string::String`
//~| HELP try with `&mut y`
test2(&y);
//~^ ERROR E0308
//~| NOTE types differ in mutability
Expand Down
14 changes: 5 additions & 9 deletions src/test/ui/span/coerce-suggestions.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -18,11 +18,7 @@ error[E0308]: mismatched types
|
= note: expected type `&str`
found type `std::string::String`
= help: here are some functions which might fulfill your needs:
- .as_str()
- .trim()
- .trim_left()
- .trim_right()
= help: try with `&String::new()`

error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:30:10
Expand All @@ -34,18 +30,18 @@ error[E0308]: mismatched types
found type `&std::string::String`

error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:36:11
--> $DIR/coerce-suggestions.rs:35:11
|
36 | test2(&y);
35 | test2(&y);
| ^^ types differ in mutability
|
= note: expected type `&mut i32`
found type `&std::string::String`

error[E0308]: mismatched types
--> $DIR/coerce-suggestions.rs:42:9
--> $DIR/coerce-suggestions.rs:41:9
|
42 | f = box f;
41 | f = box f;
| ^^^^^ cyclic type of infinite size
|
= note: expected type `_`
Expand Down

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