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Don't display default generic parameters in diagnostics that compare …
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…types.

Fixes #52097
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@glandium
glandium committed Jul 12, 2018
1 parent 5336df7 commit b5c2b79
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Showing 2 changed files with 87 additions and 31 deletions.
70 changes: 63 additions & 7 deletions src/librustc/infer/error_reporting/mod.rs
View file
Expand Up @@ -60,13 +60,13 @@ use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePa
use super::region_constraints::GenericKind;
use super::lexical_region_resolve::RegionResolutionError;

use std::fmt;
use std::{cmp, fmt};
use hir;
use hir::map as hir_map;
use hir::def_id::DefId;
use middle::region;
use traits::{ObligationCause, ObligationCauseCode};
use ty::{self, Region, Ty, TyCtxt, TypeFoldable, TypeVariants};
use ty::{self, subst::Subst, Region, Ty, TyCtxt, TypeFoldable, TypeVariants};
use ty::error::TypeError;
use syntax::ast::DUMMY_NODE_ID;
use syntax_pos::{Pos, Span};
Expand Down Expand Up @@ -672,6 +672,43 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
}
}

/// For generic types with parameters with defaults, remove the parameters corresponding to
/// the defaults. This repeats a lot of the logic found in `PrintContext::parameterized`.
fn strip_generic_default_params(
&self,
def_id: DefId,
substs: &ty::subst::Substs<'tcx>
) -> &'tcx ty::subst::Substs<'tcx> {
let generics = self.tcx.generics_of(def_id);
let mut num_supplied_defaults = 0;
let mut type_params = generics.params.iter().rev().filter_map(|param| match param.kind {
ty::GenericParamDefKind::Lifetime => None,
ty::GenericParamDefKind::Type { has_default, .. } => {
Some((param.def_id, has_default))
}
}).peekable();
let has_default = {
let has_default = type_params.peek().map(|(_, has_default)| has_default);
*has_default.unwrap_or(&false)
};
if has_default {
let types = substs.types().rev();
for ((def_id, has_default), actual) in type_params.zip(types) {
if !has_default {
break;
}
if self.tcx.type_of(def_id).subst(self.tcx, substs) != actual {
break;
}
num_supplied_defaults += 1;
}
}
let len = generics.params.len();
let mut generics = generics.clone();
generics.params.truncate(len - num_supplied_defaults);
substs.truncate_to(self.tcx, &generics)
}

/// Compare two given types, eliding parts that are the same between them and highlighting
/// relevant differences, and return two representation of those types for highlighted printing.
fn cmp(&self, t1: Ty<'tcx>, t2: Ty<'tcx>) -> (DiagnosticStyledString, DiagnosticStyledString) {
Expand Down Expand Up @@ -713,6 +750,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {

match (&t1.sty, &t2.sty) {
(&ty::TyAdt(def1, sub1), &ty::TyAdt(def2, sub2)) => {
let sub_no_defaults_1 = self.strip_generic_default_params(def1.did, sub1);
let sub_no_defaults_2 = self.strip_generic_default_params(def2.did, sub2);
let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
let path1 = self.tcx.item_path_str(def1.did.clone());
let path2 = self.tcx.item_path_str(def2.did.clone());
Expand All @@ -728,8 +767,19 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
values.0.push_normal(path1);
values.1.push_normal(path2);

// Avoid printing out default generic parameters that are common to both
// types.
let len1 = sub_no_defaults_1.len();
let len2 = sub_no_defaults_2.len();
let common_len = cmp::min(len1, len2);
let remainder1: Vec<_> = sub1.types().skip(common_len).collect();
let remainder2: Vec<_> = sub2.types().skip(common_len).collect();
let common_default_params =
remainder1.iter().rev().zip(remainder2.iter().rev())
.filter(|(a, b)| a == b).count();
let len = sub1.len() - common_default_params;

// Only draw `<...>` if there're lifetime/type arguments.
let len = sub1.len();
if len > 0 {
values.0.push_normal("<");
values.1.push_normal("<");
Expand Down Expand Up @@ -774,7 +824,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
// ^ elided type as this type argument was the same in both sides
let type_arguments = sub1.types().zip(sub2.types());
let regions_len = sub1.regions().collect::<Vec<_>>().len();
for (i, (ta1, ta2)) in type_arguments.enumerate() {
for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() {
let i = i + regions_len;
if ta1 == ta2 {
values.0.push_normal("_");
Expand Down Expand Up @@ -804,7 +854,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
&mut values.0,
&mut values.1,
path1.clone(),
sub1,
sub_no_defaults_1,
path2.clone(),
&t2,
).is_some()
Expand All @@ -816,8 +866,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
// Bar<Qux>
// Foo<Bar<Qux>>
// ------- this type argument is exactly the same as the other type
if self.cmp_type_arg(&mut values.1, &mut values.0, path2, sub2, path1, &t1)
.is_some()
if self.cmp_type_arg(
&mut values.1,
&mut values.0,
path2,
sub_no_defaults_2,
path1,
&t1,
).is_some()
{
return values;
}
Expand Down
48 changes: 24 additions & 24 deletions src/test/ui/type-mismatch.stderr
View file
Expand Up @@ -112,7 +112,7 @@ error[E0308]: mismatched types
LL | want::<Foo<foo>>(f); //~ ERROR mismatched types
| ^ expected struct `Foo`, found struct `foo`
|
= note: expected type `Foo<foo, A, B>`
= note: expected type `Foo<foo>`
found type `foo`

error[E0308]: mismatched types
Expand All @@ -121,7 +121,7 @@ error[E0308]: mismatched types
LL | want::<Foo<foo, B>>(f); //~ ERROR mismatched types
| ^ expected struct `Foo`, found struct `foo`
|
= note: expected type `Foo<foo, B, B>`
= note: expected type `Foo<foo, B>`
found type `foo`

error[E0308]: mismatched types
Expand Down Expand Up @@ -158,7 +158,7 @@ LL | want::<foo>(f); //~ ERROR mismatched types
| ^ expected struct `foo`, found struct `Foo`
|
= note: expected type `foo`
found type `Foo<foo, A, B>`
found type `Foo<foo>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:49:17
Expand All @@ -175,44 +175,44 @@ error[E0308]: mismatched types
LL | want::<Foo<usize>>(f); //~ ERROR mismatched types
| ^ expected usize, found struct `foo`
|
= note: expected type `Foo<usize, _, _>`
found type `Foo<foo, _, _>`
= note: expected type `Foo<usize>`
found type `Foo<foo>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:51:27
|
LL | want::<Foo<usize, B>>(f); //~ ERROR mismatched types
| ^ expected usize, found struct `foo`
|
= note: expected type `Foo<usize, B, _>`
found type `Foo<foo, A, _>`
= note: expected type `Foo<usize, B>`
found type `Foo<foo, A>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:52:25
|
LL | want::<Foo<foo, B>>(f); //~ ERROR mismatched types
| ^ expected struct `B`, found struct `A`
|
= note: expected type `Foo<_, B, _>`
found type `Foo<_, A, _>`
= note: expected type `Foo<_, B>`
found type `Foo<_, A>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:53:22
|
LL | want::<Foo<bar>>(f); //~ ERROR mismatched types
| ^ expected struct `bar`, found struct `foo`
|
= note: expected type `Foo<bar, _, _>`
found type `Foo<foo, _, _>`
= note: expected type `Foo<bar>`
found type `Foo<foo>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:54:25
|
LL | want::<Foo<bar, B>>(f); //~ ERROR mismatched types
| ^ expected struct `bar`, found struct `foo`
|
= note: expected type `Foo<bar, B, _>`
found type `Foo<foo, A, _>`
= note: expected type `Foo<bar, B>`
found type `Foo<foo, A>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:55:23
Expand Down Expand Up @@ -251,7 +251,7 @@ LL | want::<foo>(f); //~ ERROR mismatched types
| ^ expected struct `foo`, found struct `Foo`
|
= note: expected type `foo`
found type `Foo<foo, B, B>`
found type `Foo<foo, B>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:62:17
Expand All @@ -268,44 +268,44 @@ error[E0308]: mismatched types
LL | want::<Foo<usize>>(f); //~ ERROR mismatched types
| ^ expected usize, found struct `foo`
|
= note: expected type `Foo<usize, A, _>`
found type `Foo<foo, B, _>`
= note: expected type `Foo<usize, A>`
found type `Foo<foo, B>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:64:27
|
LL | want::<Foo<usize, B>>(f); //~ ERROR mismatched types
| ^ expected usize, found struct `foo`
|
= note: expected type `Foo<usize, _, _>`
found type `Foo<foo, _, _>`
= note: expected type `Foo<usize, _>`
found type `Foo<foo, _>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:65:22
|
LL | want::<Foo<foo>>(f); //~ ERROR mismatched types
| ^ expected struct `A`, found struct `B`
|
= note: expected type `Foo<_, A, _>`
found type `Foo<_, B, _>`
= note: expected type `Foo<_, A>`
found type `Foo<_, B>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:66:22
|
LL | want::<Foo<bar>>(f); //~ ERROR mismatched types
| ^ expected struct `bar`, found struct `foo`
|
= note: expected type `Foo<bar, A, _>`
found type `Foo<foo, B, _>`
= note: expected type `Foo<bar, A>`
found type `Foo<foo, B>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:67:25
|
LL | want::<Foo<bar, B>>(f); //~ ERROR mismatched types
| ^ expected struct `bar`, found struct `foo`
|
= note: expected type `Foo<bar, _, _>`
found type `Foo<foo, _, _>`
= note: expected type `Foo<bar, _>`
found type `Foo<foo, _>`

error[E0308]: mismatched types
--> $DIR/type-mismatch.rs:68:23
Expand Down

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