Refer to types using the local identifier #44642

estebank · Sep 17, 2017

On type errors, refer to types using the locally available name when
they have been imported into scope instead of the fully qualified path.

error[E0308]: mismatched types
 --> file.rs:7:24
  |
7 |     let y: Option<X> = Ok(());
  |                        ^^^^^^ expected enum `std::option::Option`, found enum `std::result::Result`
  |
  = note: expected type `Option<X>`
             found type `Result<(), _>`
  = help: here are some functions which might fulfill your needs:
          - .err()
          - .unwrap_err()

Re: #21934.

rust-highfive · Sep 17, 2017

r? @nikomatsakis

(rust_highfive has picked a reviewer for you, use r? to override)

bors · Sep 17, 2017

☔️ The latest upstream changes (presumably #44634) made this pull request unmergeable. Please resolve the merge conflicts.

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/ty/context.rs

@@ -1179,6 +1179,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
        self.all_crate_nums(LOCAL_CRATE)
    }

+    pub fn cstore(&self) -> &CrateStore {


I think @alexcrichton removed this for a reason.

I'm sure. This was a quick fix after rebasing against master to get the code as I had written it working. I fully intend to clean this up before attempting to merge this PR.

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

@@ -357,7 +359,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                // for imported and non-imported crates
                if exp_path == found_path
                || exp_abs_path == found_abs_path {
-                    let crate_name = self.tcx.crate_name(did1.krate);
+                    let crate_name = self.tcx.cstore().crate_name_untracked(did1.krate);


Why can't you use crate_name here?

This is a spurious change that should not have happened. I introduced it after hastily rebasing to HEAD of master when the moving of cstore from sess to tcx happened. I'll revert.

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+    full_imports: FxHashMap<String, String>,
+}
+
+impl<'a, 'gcx, 'tcx> ImportVisitor<'a, 'gcx, 'tcx> {


This looks likely to be buggy - you are reimplementing half of name resolution. Could name resolution be made to supply a types_in_scope map?

cc @jseyfried - is there a way for resolution to be called after it is complete?

I figured that was the case, but it was the closest I've been in any of my approaches to get this working. Once I saw that the suggestion machinery used a visitor it gave me enough context to get this. Having this also allowed me to identify the unit tests that would need to change. It is definitely less than ideal and fully expect there to be a way to do this using existing datastructures, but I feel it is much easier for me to point at this code and saw "this is what I want to do, is there a better way?". :)

There's not a way to do name resolution after lowering to HIR (i.e. after we drop the Resolver). A naive solution would be to keep the Resolver for longer, but that would hog memory and isn't ideal since the Resolver has needless complexity used for import resolution and is based on the AST.

@nikomatsakis and I have discussed creating and saving some name resolution structures for this purpose before destroying the Resolver, but we haven't made detailed designs.

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+struct ImportVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'gcx, 'tcx>,
+    /// All the `Item`s from other scopes visible from this `TyCtxt`, as well as their local name.
+    full_imports: FxHashMap<String, String>,


Why not an FxHashMap<DefId, String>?

This is an artifact from the exploratory way I wrote this code, as while working on this I didn't have access to DefIds from other crates. Very sensible suggestion.

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+    }
+}
+
+/// This struct knows how to print out a single type for human consumption, compare two types and


Can this replace rustc::util::ppaux?

That is my eventual objective. I have moved the type argument elision code away from TyCtxt in order to isolate as much from it as possible in order to unify it with the code in ppaux. Do you think I should strive to do it in this PR?

arielb1 · Sep 17, 2017

arielb1 reviewed Sep 17, 2017

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arielb1 · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+                s.push_str(&self.ty_str(ty_and_mut.ty));
+                s
+            }
+            _ => format!("{}", ty),


You really want to replace the entirety of ppaux here. Otherwise e.g. everything within a trait object will go back to ugly.

Yes, that is indeed true. Given how big this PR was getting I thought that it was a good idea to put it out there to get feedback before going further down this rabbit hole. That being said, this covered a big enough percentage of cases that allowed me to test this approach.

alexcrichton · Sep 17, 2017

alexcrichton reviewed Sep 17, 2017

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alexcrichton · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+                        }
+                    } else {
+                        // Importing from a different crate.
+                        for child in self.tcx.cstore().item_children_untracked(def_id,


Ah so the "untracked" here means that it's not tracked by incremental compilation, so this is something that we're going to want to handle as this is all happening after the tcx is created. If you need help turning this into a query though just let me know!

Could you point me in the right direction of a query being performed? I haven't worked in that part of the compiler yet and would appreciate having a thread to pull from to unravel that sweater.

Sure! You can check out #41417 for some more info

estebank · Sep 17, 2017

estebank reviewed Sep 17, 2017

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TL;DR: Some of the weird code is the result of hastily rebasing against master and pushing the code out without reworking it to fit the current state of the compiler, and some is the result of the exploratory way I was writing the code without going back to clean it up after the reasons for the current state were no longer there.

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

@@ -357,7 +359,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                // for imported and non-imported crates
                if exp_path == found_path
                || exp_abs_path == found_abs_path {
-                    let crate_name = self.tcx.crate_name(did1.krate);
+                    let crate_name = self.tcx.cstore().crate_name_untracked(did1.krate);


This is a spurious change that should not have happened. I introduced it after hastily rebasing to HEAD of master when the moving of cstore from sess to tcx happened. I'll revert.

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+struct ImportVisitor<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'gcx, 'tcx>,
+    /// All the `Item`s from other scopes visible from this `TyCtxt`, as well as their local name.
+    full_imports: FxHashMap<String, String>,


This is an artifact from the exploratory way I wrote this code, as while working on this I didn't have access to DefIds from other crates. Very sensible suggestion.

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+    }
+}
+
+/// This struct knows how to print out a single type for human consumption, compare two types and


That is my eventual objective. I have moved the type argument elision code away from TyCtxt in order to isolate as much from it as possible in order to unify it with the code in ppaux. Do you think I should strive to do it in this PR?

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+                s.push_str(&self.ty_str(ty_and_mut.ty));
+                s
+            }
+            _ => format!("{}", ty),


Yes, that is indeed true. Given how big this PR was getting I thought that it was a good idea to put it out there to get feedback before going further down this rabbit hole. That being said, this covered a big enough percentage of cases that allowed me to test this approach.

estebank · Sep 17, 2017

src/librustc/ty/context.rs

@@ -1179,6 +1179,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
        self.all_crate_nums(LOCAL_CRATE)
    }

+    pub fn cstore(&self) -> &CrateStore {


I'm sure. This was a quick fix after rebasing against master to get the code as I had written it working. I fully intend to clean this up before attempting to merge this PR.

estebank · Sep 17, 2017

src/test/ui/local-ident.stderr

+  --> $DIR/local-ident.rs:16:28
+   |
+16 |     let y: Option<usize> = Ok(2);
+   |                            ^^^^^ expected enum `std::option::Option`, found enum `std::result::Result`


This is an open question: Do we want to show the fully qualified path here? I don't think length is as much of an issue here as this label doesn't print the type arguments, keeping the line relatively short. Alternatively it might be jarring to have two different things being shown here...

estebank · Sep 17, 2017

src/test/ui/local-ident.stderr

+   |                            ^^^^^ expected enum `std::option::Option`, found enum `std::result::Result`
+   |
+   = note: expected type `Option<usize>`
+              found type `Result<{integer}, _>`


Should we add a note here stating Option: std::option::Option and Result: std::result::Result? This could become a very long list for cases like the one put forward in #40186.

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+                        }
+                    } else {
+                        // Importing from a different crate.
+                        for child in self.tcx.cstore().item_children_untracked(def_id,


Could you point me in the right direction of a query being performed? I haven't worked in that part of the compiler yet and would appreciate having a thread to pull from to unravel that sweater.

estebank · Sep 17, 2017

src/librustc/infer/error_reporting/mod.rs

+    full_imports: FxHashMap<String, String>,
+}
+
+impl<'a, 'gcx, 'tcx> ImportVisitor<'a, 'gcx, 'tcx> {


I figured that was the case, but it was the closest I've been in any of my approaches to get this working. Once I saw that the suggestion machinery used a visitor it gave me enough context to get this. Having this also allowed me to identify the unit tests that would need to change. It is definitely less than ideal and fully expect there to be a way to do this using existing datastructures, but I feel it is much easier for me to point at this code and saw "this is what I want to do, is there a better way?". :)

krdln · Sep 17, 2017

What about shadowing? For example:

struct Result;

fn main() {
    let res: Result = Ok(());
}

This PR produces the following note:

   = note: expected type `Result`
              found type `Result<(), _>`

(the full path for std::result::Result is present in the former part of the error message though)

alexcrichton · Sep 21, 2017

ping @estebank just want to make sure this doesn't fall off your radar!

nikomatsakis · Sep 21, 2017

r? @arielb1

Reassigning to @arielb1 since he did initial review.

arielb1 · Sep 24, 2017

Still waiting on resolution coordination with @jseyfried.

aidanhs · Oct 5, 2017

Not clear what the status here is - is there an issue that triagers can visit to see progress of any blockers? Just wondering who's 'responsible' for pushing this along :)

bors · Oct 7, 2017

☔️ The latest upstream changes (presumably #44614) made this pull request unmergeable. Please resolve the merge conflicts.

aidanhs · Oct 12, 2017

@arielb1 / @jseyfried / @estebank - can anyone clarify what/who this PR is waiting on at the moment (aside from a rebase)? I'm not sure how to triage this at the moment as I don't know what's blocking or if there's an issue we can track!

estebank · Oct 12, 2017

@aidanhs I need to rework the PR to use queries, but I haven't had time available to do so. If people prefer, I can close this PR and resubmit once I've reworked it.

aidanhs · Oct 12, 2017

@estebank ok great, thanks for clarifying! If you reckon you might get to this in the next couple of weeks then I'd be fine with keeping it open - up to you.

alexcrichton · Oct 19, 2017

Here for triage again! I'm going to go ahead and close this now to help clear out the queue, but @estebank of course feel free to resubmit once it's reworked!

rust-highfive assigned nikomatsakis Sep 17, 2017

estebank force-pushed the estebank:local-alias branch 6 times, most recently from c28a79a to 154d971 Sep 17, 2017

estebank force-pushed the estebank:local-alias branch from 154d971 to 01cbfca Sep 17, 2017

estebank force-pushed the estebank:local-alias branch from 01cbfca to 6877688 Sep 17, 2017

carols10cents added the S-waiting-on-author label Sep 18, 2017

rust-highfive assigned arielb1 and unassigned nikomatsakis Sep 21, 2017

alexcrichton closed this Oct 19, 2017

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Refer to types using the local identifier #44642

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estebank commented Sep 17, 2017 • edited

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estebank force-pushed the estebank:local-alias branch from 154d971 to 01cbfca Sep 17, 2017

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estebank commented Sep 17, 2017 •

edited

estebank force-pushed the estebank:local-alias branch 6 times, most recently from `c28a79a` to `154d971` Sep 17, 2017

estebank force-pushed the estebank:local-alias branch from `154d971` to `01cbfca` Sep 17, 2017

estebank force-pushed the estebank:local-alias branch from `01cbfca` to `6877688` Sep 17, 2017

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