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Auto merge of #48326 - RalfJung:generic-bounds, r=petrochenkov

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Warn about ignored generic bounds in `for`

This adds a new lint to fix #42181. For consistency and to avoid code duplication, I also moved the existing "bounds in type aliases are ignored" here.

Questions to the reviewer:
* Is it okay to just remove a diagnostic error code like this? Should I instead keep the warning about type aliases where it is? The old code provided a detailed explanation of what's going on when asked, that information is now lost. On the other hand, `span_warn!` seems deprecated (after this patch, it has exactly one user left!).
* Did I miss any syntactic construct that can appear as `for` in the surface syntax? I covered function types (`for<'a> fn(...)`), generic traits (`for <'a> Fn(...)`, can appear both as bounds as as trait objects) and bounds (`for<'a> F: ...`).
* For the sake of backwards compatibility, this adds a warning, not an error. @nikomatsakis suggested an error in https://github.com/rust-lang/rust/issues/42181#issuecomment-306924389, but I feel that can only happen in a new epoch -- right?

Cc @eddyb
This commit is contained in:
bors 2018-03-09 10:45:29 +00:00
commit fedce67cd2
20 changed files with 325 additions and 109 deletions
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82
src/test/ui/param-bounds-ignored.rs
View file

@ -8,13 +8,18 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// must-compile-successfully
#![allow(dead_code, non_camel_case_types)]
use std::rc::Rc;
type SVec<T: Send> = Vec<T>;
type VVec<'b, 'a: 'b> = Vec<&'a i32>;
type WVec<'b, T: 'b> = Vec<T>;
type SVec<T: Send+Send> = Vec<T>;
//~^ WARN bounds on generic parameters are ignored in type aliases
type VVec<'b, 'a: 'b+'b> = Vec<&'a i32>;
//~^ WARN bounds on generic parameters are ignored in type aliases
type WVec<'b, T: 'b+'b> = Vec<T>;
//~^ WARN bounds on generic parameters are ignored in type aliases
type W2Vec<'b, T> where T: 'b, T: 'b = Vec<T>;
//~^ WARN where clauses are ignored in type aliases
fn foo<'a>(y: &'a i32) {
// If the bounds above would matter, the code below would be rejected.
@ -26,8 +31,73 @@ fn foo<'a>(y: &'a i32) {
let mut x : WVec<'static, & 'a i32> = Vec::new();
x.push(y);
let mut x : W2Vec<'static, & 'a i32> = Vec::new();
x.push(y);
}
fn main() {
foo(&42);
fn bar1<'a, 'b>(
x: &'a i32,
y: &'b i32,
f: for<'xa, 'xb: 'xa+'xa> fn(&'xa i32, &'xb i32) -> &'xa i32)
//~^ ERROR lifetime bounds cannot be used in this context
{
// If the bound in f's type would matter, the call below would (have to)
// be rejected.
f(x, y);
}
fn bar2<'a, 'b, F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>(
//~^ ERROR lifetime bounds cannot be used in this context
x: &'a i32,
y: &'b i32,
f: F)
{
// If the bound in f's type would matter, the call below would (have to)
// be rejected.
f(x, y);
}
fn bar3<'a, 'b, F>(
x: &'a i32,
y: &'b i32,
f: F)
where F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32
//~^ ERROR lifetime bounds cannot be used in this context
{
// If the bound in f's type would matter, the call below would (have to)
// be rejected.
f(x, y);
}
fn bar4<'a, 'b, F>(
x: &'a i32,
y: &'b i32,
f: F)
where for<'xa, 'xb: 'xa> F: Fn(&'xa i32, &'xb i32) -> &'xa i32
//~^ ERROR lifetime bounds cannot be used in this context
{
// If the bound in f's type would matter, the call below would (have to)
// be rejected.
f(x, y);
}
struct S1<F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>(F);
//~^ ERROR lifetime bounds cannot be used in this context
struct S2<F>(F) where F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32;
//~^ ERROR lifetime bounds cannot be used in this context
struct S3<F>(F) where for<'xa, 'xb: 'xa> F: Fn(&'xa i32, &'xb i32) -> &'xa i32;
//~^ ERROR lifetime bounds cannot be used in this context
struct S_fnty(for<'xa, 'xb: 'xa> fn(&'xa i32, &'xb i32) -> &'xa i32);
//~^ ERROR lifetime bounds cannot be used in this context
type T1 = Box<for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>;
//~^ ERROR lifetime bounds cannot be used in this context
fn main() {
let _ : Option<for<'xa, 'xb: 'xa> fn(&'xa i32, &'xb i32) -> &'xa i32> = None;
//~^ ERROR lifetime bounds cannot be used in this context
let _ : Option<Box<for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>> = None;
//~^ ERROR lifetime bounds cannot be used in this context
}

100
src/test/ui/param-bounds-ignored.stderr
View file

@ -1,18 +1,94 @@
warning[E0122]: generic bounds are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:15:1
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:42:22
|
LL | type SVec<T: Send> = Vec<T>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | f: for<'xa, 'xb: 'xa+'xa> fn(&'xa i32, &'xb i32) -> &'xa i32)
| ^^^ ^^^
warning[E0122]: generic bounds are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:16:1
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:50:34
|
LL | type VVec<'b, 'a: 'b> = Vec<&'a i32>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | fn bar2<'a, 'b, F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>(
| ^^^
warning[E0122]: generic bounds are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:17:1
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:65:28
|
LL | type WVec<'b, T: 'b> = Vec<T>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LL | where F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:77:25
|
LL | where for<'xa, 'xb: 'xa> F: Fn(&'xa i32, &'xb i32) -> &'xa i32
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:85:28
|
LL | struct S1<F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>(F);
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:87:40
|
LL | struct S2<F>(F) where F: for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32;
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:89:37
|
LL | struct S3<F>(F) where for<'xa, 'xb: 'xa> F: Fn(&'xa i32, &'xb i32) -> &'xa i32;
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:92:29
|
LL | struct S_fnty(for<'xa, 'xb: 'xa> fn(&'xa i32, &'xb i32) -> &'xa i32);
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:95:29
|
LL | type T1 = Box<for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>;
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:99:34
|
LL | let _ : Option<for<'xa, 'xb: 'xa> fn(&'xa i32, &'xb i32) -> &'xa i32> = None;
| ^^^
error: lifetime bounds cannot be used in this context
--> $DIR/param-bounds-ignored.rs:101:38
|
LL | let _ : Option<Box<for<'xa, 'xb: 'xa> Fn(&'xa i32, &'xb i32) -> &'xa i32>> = None;
| ^^^
warning: bounds on generic parameters are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:15:14
|
LL | type SVec<T: Send+Send> = Vec<T>;
| ^^^^ ^^^^
|
= note: #[warn(ignored_generic_bounds)] on by default
warning: bounds on generic parameters are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:17:19
|
LL | type VVec<'b, 'a: 'b+'b> = Vec<&'a i32>;
| ^^ ^^
warning: bounds on generic parameters are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:19:18
|
LL | type WVec<'b, T: 'b+'b> = Vec<T>;
| ^^ ^^
warning: where clauses are ignored in type aliases
--> $DIR/param-bounds-ignored.rs:21:25
|
LL | type W2Vec<'b, T> where T: 'b, T: 'b = Vec<T>;
| ^^^^^ ^^^^^
error: aborting due to 11 previous errors