Adding diagnostic code 0621 for lifetime errors with one named, one anonymous lifetime parameter #42669

gaurikholkar-zz · 2017-06-15T06:52:00Z

This is a fix for #42517
Note that this only handles the above case for function declarations and traits.
impl items and closures will be handled in a later PR.
Example

fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
    if x > y { x } else { y }
}

now displays the following error message. ui tests have been added for the same.

error[E0611]: explicit lifetime required in the type of `x`
11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
   |                     ^ consider changing the type of `x` to `&'a i32`
12 |     if x > y { x } else { y }
   |                  - lifetime `'a` required

#42516
r? @nikomatsakis

rust-highfive · 2017-06-15T06:52:13Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

nikomatsakis · 2017-06-15T09:09:21Z

I wonder if we should change the role of primary (^) vs secondary (-). It just seems a bit surprising to have ^ have the label "consider"; but I'm not sure if we want to put stronger wording, given that it may indeed be the function body that is at fault, not the signature.

nikomatsakis · 2017-06-15T09:09:35Z

Also, something else just occurred to me -- we are already avoiding giving this message in closures, but we may want to be careful in trait impls too. Specifically, if the impl is of a trait, then the signature is sometimes specified by the trait:

trait Foo {
    fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32;
}

impl Foo for () {
    fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
        if x > y { x } else { y }
    }
}

In this event, the user is not (necessarily) at liberty to change the signature. It's a bit tricky to judge, because the user may be able to change the trait. It's also a bit tricky because sometimes the trait signature is stricter than the one in the impl (we allow that, for better or worse):

trait Foo {
    fn foo<'a>(x: &'a i32, y: &'a i32) -> &'a i32;
}

impl Foo for () {
    fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
        // adding a `'a` to `x` would be legal here...
        y
    }
}

So there are kind of three scenarios in the case of a function in a trait impl (none of this applies to inherent impls):

user may be able to change the trait (e.g., because it is within the same crate and private)
user cannot change the trait (e.g., because it's in another crate or has been published and others are relying on it)
user has written a more permissive impl than the trait specifies, and hence could make changes

We can't really tell the difference between the first two. The final one we can detect, with some more effort. For the time being, we might want to either turn off the error for impl items (and file an issue to detect the remaining cases and handle them better), or else change the wording.

gaurikholkar-zz · 2017-06-15T14:04:32Z

@nikomatsakis Added a new commit that is not considering impl of traits for now.

nikomatsakis · 2017-06-15T18:52:52Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+
+ if let Some(simple_name) = var.pat.simple_name() {
+ struct_span_err!(self.tcx.sess,
+ var.pat.span,


to swap the role of ^ etc, just change this to span

gaurikholkar-zz · 2017-06-15T21:10:30Z

This is how the error message now looks

error[E0611]: explicit lifetime required in the type of `y`
  --> $DIR/ex1-return-one-existing-name-if-else.rs:12:27
   |
11 | fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
   |                        - consider changing the type of `y` to `&'a i32`
12 |     if x > y { x } else { y }
   |                           ^ lifetime `'a` required

bors · 2017-06-16T12:20:57Z

☔ The latest upstream changes (presumably #41840) made this pull request unmergeable. Please resolve the merge conflicts.

nikomatsakis · 2017-06-16T12:45:58Z

@gaurikholkar can you rebase instead of merging? I think this branch is probably ready to land, although I Was thinking that I might like to try and make test cases for more scenarios. Maybe a good idea to do that before hand, so that then we can land follow-up PRs targeting each one (sort of like we did for closures).

gaurikholkar-zz · 2017-06-16T13:23:52Z

@nikomatsakis I agree, we should make more test cases for the same. Currently it's only closures and trait impl. Rebased.

nikomatsakis

Left some comments.

nikomatsakis · 2017-06-16T18:04:21Z

src/librustc/infer/error_reporting/mod.rs

- ConcreteFailure(origin, sub, sup) => {
- self.report_concrete_failure(origin, sub, sup).emit();
- }
+ // If ConcreteFailure does not have an anonymous region


Nit: indentation

Honestly, though, I think I'd remove this comment. Maybe replace it with:

// These errors could indicate all manner of different // problems with many different solutions. Rather // than generate a "one size fits all" error, what we // attempt to do is go through a number of specific // scenarios and try to find the best way to present // the error. If all of these fails, we fall back to a rather // general bit of code that displays the error information.

nikomatsakis · 2017-06-16T18:06:35Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ // Currently only the case where the function declaration consists of
+ // one named region and one anonymous region is handled.
+ // Consider the example `fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32`
+ // Here, the `y` and the `Ty` of `y` is returned after being substituted


I'd say: Here, we would return the hir::Arg for y, and we return the type &'a i32, which is the type of y but with the anonymous region replaced with 'a.

nikomatsakis · 2017-06-16T18:10:27Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ _ => return false, // inapplicable
+ };
+
+ let (named, (var, new_ty)) =


let's rename var to arg, for consistency. Probably a good idea to put a comment before this block of code, too:

// Determine whether the `sub` and `sup` consist of one named region (`'a`) // and one anonymous (elided) region. If so, find the parameter `arg` where the // anonymous region appears (there must always be one; we only introduced // anonymous regions in parameters) as well as a version `new_ty` of its type // where the anonymous region is replaced with the named one.

nikomatsakis · 2017-06-16T18:19:41Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ } else {
+ return false; // inapplicable
+ };
+


So, per our conversation earlier, I think we want to watch out for the case where the anonymous region appeared in the function return type as well and not try to handle that (that would be #42703 now). To do this check is a bit of a pain though. I think we need to do something like this:

extract the free_region.scope from the anonymous region (just as we do in find_arg_with_anonymous_region()); let's call that scope_def_id,

lookup the type ty associated with scope_def_id, using tcx.type_of(scope_def_id)

since we are only matching functions, this will be a TyFnDef (we can just return for other types)

that is the type of a named function like fn foo()

if we do match ty.sty { ty::TyFnDef(_, _, sig) => ... } we can extract the function signature sig (it is a PolyFnSig)

we can extract the return type ret_ty by doing this incantation (I can explain more on gitter): tcx.liberate_late_bound_regions(scope_def_id, sig.output())

then we can search ret_ty for the anonymous region as we did before (something like ret_ty.walk().flat_map(|t| t.regions()).any(|r| r == anon_region)

nikomatsakis · 2017-06-16T18:21:52Z

src/librustc/infer/error_reporting/util.rs

+ }
+
+ // This method returns whether the given Region is Anonymous
+ pub fn is_anonymous_region(&self, region: Region<'tcx>) -> bool {


I think we should change this function to return Option<DefId>, where the def-id is free_region.scope. We can call it something like anonymous_region_binding_scope. Then we can test if something is an anonymous region but also extract its scope at the same time.

nikomatsakis · 2017-06-16T18:22:12Z

src/librustc/infer/error_reporting/util.rs

+ match *region {
+ ty::ReFree(ref free_region) => {
+ match free_region.bound_region {
+ ty::BrAnon(..) => {


i.e., here we would return Some(free_region.scope)

nikomatsakis · 2017-06-16T18:23:24Z

src/librustc/infer/error_reporting/util.rs

+ ty::BrAnon(..) => {
+ let id = free_region.scope;
+ let node_id = self.tcx.hir.as_local_node_id(id).unwrap();
+ match self.tcx.hir.find(node_id) {


let's move this logic out into the "named vs anonymous" function, it seems more appropriate there to me. I'll put a comment there.

nikomatsakis · 2017-06-16T18:23:49Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ // Consider the example `fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32`
+ // Here, the `y` and the `Ty` of `y` is returned after being substituted
+ // by that of the named region.
+ pub fn find_arg_with_anonymous_region(&self,


This does not need to be public, you can just make this fn

nikomatsakis · 2017-06-16T18:24:09Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ // This method generates the error message for the case when
+ // the function arguments consist of a named region and an anonymous
+ // region and corresponds to `ConcreteFailure(..)`
+ pub fn report_named_anon_conflict(&self, error: &RegionResolutionError<'tcx>) -> bool {


Let's call this try_report_named_anon_conflict

nikomatsakis · 2017-06-16T18:31:46Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ (sup, self.find_arg_with_anonymous_region(sub, sup).unwrap())
+ } else {
+ return false; // inapplicable
+ };


Somewhere in here I think we should get the scope of the anonymous region and check that it is defined on something suitable. Something like:

let scope_node_id = self.tcx.hir.as_local_node_id(scope_def_id).unwrap(); match self.tcx.hir.find(scope_node_id) { Some(hir_map::NodeItem(..)) | Some(hir_map::NodeTraitItem(..)) => { /* proceed ahead */ } Some(hir_map::NodeImplItem(..)) => { if tcx.impl_trait_ref(scope_def_id).is_some() { // For now, we do not try to target impls of traits. This is // because this message is going to suggest that the user // change the fn signature, but they may not be free to do so, // since the signature must match the trait. // // FIXME(#42706) -- in some cases, we could do better here. return false; } } _ => return false, // inapplicable; we target only top-level functions, not closures }

This code currently lives in is_anonymous_region.

Alternatively, we could do the check in that function, but then let's move it into this file (it's now rather specific to this error message) and give it a different name, like is_suitable_anonymous_region(). That's maybe the best path.

gaurikholkar-zz · 2017-06-18T19:04:31Z

@nikomatsakis added a check for Trait Impls and anonymous region in return type

gaurikholkar-zz · 2017-06-22T09:05:43Z

@nikomatsakis added the anonymous region check for self and the ui test too

nikomatsakis · 2017-06-22T14:53:16Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ if body.arguments.iter().nth(0) == Some(&arg) {
+ is_first = true;
+ }
+ return Some((arg,


Nit: we don't need the return here, right? That is, I would either have return here, or else below, but not both.

nikomatsakis · 2017-06-22T14:54:39Z

src/librustc/infer/error_reporting/named_anon_conflict.rs

+ let body = self.tcx.hir.body(body_id);
+ body.arguments
+ .iter()
+ .filter_map(|arg| if let Some(tables) = self.in_progress_tables {


Nit: maybe we should move the if let outside of the body.arguments.iter(). Something like:

if let Some(tables) = self.in_progress_tables { body.arguments .iter() .filter_map(|arg| { ... }) .next() } else { None }

gaurikholkar-zz · 2017-06-22T20:08:19Z

@nikomatsakis made the changes

GuillaumeGomez · 2017-06-25T07:03:40Z

src/librustc/diagnostics.rs

+ if x > y { x } else { y }
+}
+
+fn main () { }


Please remove this.

GuillaumeGomez · 2017-06-25T07:03:44Z

src/librustc/diagnostics.rs

+ if x > y { x } else { y }
+}
+
+fn main() {


Please remove this.

GuillaumeGomez · 2017-06-25T07:05:39Z

Sorry to come with bad news, but I added a lot of error codes meanwhile. The current highest is E0620, so you should take E0621. Also, please add a corresponding test into the src/test/compile-fail folder (look at the other E0*.rs).

To be honest, I think it'd be better to just wait that my last two PRs get merged. Great job otherwise! :)

nikomatsakis · 2017-06-26T14:28:41Z

@GuillaumeGomez

Sorry to come with bad news, but I added a lot of error codes meanwhile.

Heh, thanks for the warning! Man I hate the way error codes are guaranteed merge conflcits. :(

nikomatsakis · 2017-06-26T15:53:02Z

Here is a proposed rewrite for the extended error description: https://gist.github.com/nikomatsakis/e9ec2091abe1b9a7a3371c6894132463

nikomatsakis · 2017-06-30T12:29:57Z

@bors r+

bors · 2017-06-30T12:29:58Z

📌 Commit 37a88f4 has been approved by nikomatsakis

@nikomatsakis

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter This is a fix for rust-lang#42517 Note that this only handles the above case for **function declarations** and **traits**. `impl items` and `closures` will be handled in a later PR. Example ``` fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { if x > y { x } else { y } } ``` now displays the following error message. ui tests have been added for the same. ``` error[E0611]: explicit lifetime required in the type of `x` 11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { | ^ consider changing the type of `x` to `&'a i32` 12 | if x > y { x } else { y } | - lifetime `'a` required ``` rust-lang#42516 r? @nikomatsakis

@nikomatsakis

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter This is a fix for rust-lang#42517 Note that this only handles the above case for **function declarations** and **traits**. `impl items` and `closures` will be handled in a later PR. Example ``` fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { if x > y { x } else { y } } ``` now displays the following error message. ui tests have been added for the same. ``` error[E0611]: explicit lifetime required in the type of `x` 11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { | ^ consider changing the type of `x` to `&'a i32` 12 | if x > y { x } else { y } | - lifetime `'a` required ``` rust-lang#42516 r? @nikomatsakis

@nikomatsakis

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter This is a fix for rust-lang#42517 Note that this only handles the above case for **function declarations** and **traits**. `impl items` and `closures` will be handled in a later PR. Example ``` fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { if x > y { x } else { y } } ``` now displays the following error message. ui tests have been added for the same. ``` error[E0611]: explicit lifetime required in the type of `x` 11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { | ^ consider changing the type of `x` to `&'a i32` 12 | if x > y { x } else { y } | - lifetime `'a` required ``` rust-lang#42516 r? @nikomatsakis

@nikomatsakis

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter This is a fix for rust-lang#42517 Note that this only handles the above case for **function declarations** and **traits**. `impl items` and `closures` will be handled in a later PR. Example ``` fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { if x > y { x } else { y } } ``` now displays the following error message. ui tests have been added for the same. ``` error[E0611]: explicit lifetime required in the type of `x` 11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 { | ^ consider changing the type of `x` to `&'a i32` 12 | if x > y { x } else { y } | - lifetime `'a` required ``` rust-lang#42516 r? @nikomatsakis

Rollup of 6 pull requests - Successful merges: #42669, #42911, #42925, #42957, #42985, #42987 - Failed merges: #42936

@nikomatsakis

Clean up some code From #42669. r? @nikomatsakis

gaurikholkar-zz · 2017-08-14T06:13:16Z

#43851
Modifying the error message

When there's a lifetime mismatch between an argument with an anonymous lifetime being returned in a method with a return type that has a named lifetime, show specialized lifetime error pointing at argument with a hint to give it an explicit lifetime matching the return type. ``` error[E0621]: explicit lifetime required in the type of `other` --> file2.rs:21:21 | 17 | fn bar(&self, other: Foo) -> Foo<'a> { | ----- consider changing the type of `other` to `Foo<'a>` ... 21 | other | ^^^^^ lifetime `'a` required ``` Follow up to rust-lang#44124 and rust-lang#42669.

Handle anon lifetime arg being returned with named lifetime return type When there's a lifetime mismatch between an argument with an anonymous lifetime being returned in a method with a return type that has a named lifetime, show specialized lifetime error pointing at argument with a hint to give it an explicit lifetime matching the return type. ``` error[E0621]: explicit lifetime required in the type of `other` --> file2.rs:21:21 | 17 | fn bar(&self, other: Foo) -> Foo<'a> { | ----- consider changing the type of `other` to `Foo<'a>` ... 21 | other | ^^^^^ lifetime `'a` required ``` Follow up to rust-lang#44124 and rust-lang#42669. Fix rust-lang#44684.

rust-highfive assigned nikomatsakis Jun 15, 2017

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src/librustc/diagnostics.rs Outdated

if x > y { x } else { y }

}

fn main () { }

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Please remove this.

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src/librustc/diagnostics.rs Outdated

if x > y { x } else { y }

}

fn main() {

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Please remove this.

gaurikholkar-zz force-pushed the master branch from 2ad0198 to 4b73f18 Compare June 27, 2017 14:18

nikomatsakis and others added 3 commits June 29, 2017 18:02

tweak comments in E0495.rs

cb26a25

move ERROR line

a433777

rename compile-fail test

37a88f4

GuillaumeGomez mentioned this pull request Jun 30, 2017

Rollup of 4 pull requests #42989

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Rollup of 7 pull requests #42990

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Rollup of 6 pull requests #42992

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Rollup of 6 pull requests #42995

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Auto merge of #42995 - GuillaumeGomez:rollup, r=GuillaumeGomez

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Rollup of 6 pull requests - Successful merges: #42669, #42911, #42925, #42957, #42985, #42987 - Failed merges: #42936

bors merged commit 37a88f4 into rust-lang:master Jul 1, 2017

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Clean up some code #43006

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Auto merge of #43006 - GuillaumeGomez:e0611-cleanup, r=nikomatsakis

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Clean up some code From #42669. r? @nikomatsakis

gaurikholkar-zz changed the title ~~Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter~~ Adding diagnostic code 0623 for lifetime errors with one named, one anonymous lifetime parameter Aug 16, 2017

gaurikholkar-zz changed the title ~~Adding diagnostic code 0623 for lifetime errors with one named, one anonymous lifetime parameter~~ Adding diagnostic code 0621 for lifetime errors with one named, one anonymous lifetime parameter Aug 29, 2017

gaurikholkar-zz mentioned this pull request Oct 9, 2017

Code snippet is machine dependent #45149

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Handle anon lifetime arg being returned with named lifetime return type #45751

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Adding diagnostic code 0621 for lifetime errors with one named, one anonymous lifetime parameter #42669

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