Use `PredicateObligation`s instead of `Predicate`s #69745

estebank · 2020-03-05T20:41:23Z

Keep more information about trait binding failures. Use more specific spans by pointing at bindings that introduce obligations.

Subset of #69709.

r? @eddyb

estebank · 2020-03-05T20:49:35Z

cc @nikomatsakis

src/test/ui/issues/issue-18919.stderr

eddyb

I need to move relevant comments from the original PR, and review the code that is different.

eddyb · 2020-03-06T03:07:59Z

src/librustc_infer/traits/wf.rs

-            .map(|pred| traits::Obligation::new(cause.clone(), self.param_env, pred))
+            .zip(predicates.spans.into_iter())
+            .map(|(pred, span)| {
+                let cause = self.cause(traits::BindingObligation(def_id, span));


Before I forget, cc @nikomatsakis on the ItemObligation vs BindingObligation split, and the name of the latter.

#69709 (comment)

Hmm, the name BindingObligation doesn't say that much to me, and the rustdoc on it is not very precise:

Like ItemObligation, but with extra detail on the source of the obligation.

I presume that it's meant to track the precise bound that caused this obligation? In which case I think the name is "decent", but I'd probably just call it WhereClause or something. I don't think the suffix "Obligation" is adding much here.

estebank

Adding some links to relevant comments in the original PR.

estebank · 2020-03-06T23:39:45Z

src/librustc_infer/traits/wf.rs

-            .map(|pred| traits::Obligation::new(cause.clone(), self.param_env, pred))
+            .zip(predicates.spans.into_iter())
+            .map(|(pred, span)| {
+                let cause = self.cause(traits::BindingObligation(def_id, span));


#69709 (comment)

src/librustc_infer/traits/util.rs

src/librustc_typeck/collect.rs

src/test/ui/derives/derives-span-Eq-struct.stderr

estebank · 2020-04-06T05:38:50Z

src/test/ui/issues/issue-21974.stderr

 LL | trait Foo {
-   | --------- required by `Foo`
+   | --------- required by this bound in `Foo`
 ...
 LL |     where &'a T : Foo,
   |                   ^^^ cannot infer type for reference `&'a T`


There are a few cases like this one where the inference error itself is already incorrect and the wording change makes them slightly worse in my eyes.

They seem rare enough that we don't need to deal with them immediately, but we should probably account for them.

estebank · 2020-04-06T05:39:01Z

src/test/ui/issues/issue-20413.stderr

  --> $DIR/issue-20413.rs:8:36
   |
 LL | trait Foo {
-   | --------- required by `Foo`
+   | --------- required by this bound in `Foo`
 ...
 LL | impl<T> Foo for T where NoData<T>: Foo {


Another case.

nikomatsakis · 2020-04-06T13:44:30Z

FYI: I plan to review this this week.

nikomatsakis

The code seems good, but I'm not sure what I think of the final output.

nikomatsakis · 2020-04-08T20:34:40Z

src/test/ui/typeck/typeck-default-trait-impl-negation-sync.stderr

@@ -3,6 +3,8 @@ error[E0277]: `MyNotSync` cannot be shared between threads safely
   |
 LL | fn is_sync<T: Sync>() {}
   |    -------    ---- required by this bound in `is_sync`
+   |    |
+   |    required by a bound in `is_sync`


I'm a bit confused by these diffs. That is -- I'm not quite sure what this label is trying to tell me. I guess what was happening before is that we had a span for is_sync but lacked more precise information, so we got no label, but now we get a label?

Nonetheless, I'm not sure this is a net improvement -- the label that tells you which bound definitely seems good, and this new label kind of distracts from that.

Would it be possible to get more precise information to help us in tracking which label is causing the problem?

This was born out of #69745 (comment), where the small separation between the two spans made @eddyb confused for a short moment. I thought that adding some label to the span might make it clearer in all cases that we're pointing at two different things. Another alternative would be to only point at the fn ident if it is in a different line to the bound.

BTW, that change is in its own commit, so you can look at the diff without it.

I have changed the second commit to check if both spans are in the same line, and if they are, to not display the span pointing at is_sync.

Keep more information about trait binding failures.

estebank · 2020-04-09T16:18:01Z

@eddyb this PR has a lot of potential to bitrot and is blocking the PR to maintain chain of obligations. @nikomatsakis signed off on the code changes but not on the new output. I think the changes in the second commit should be non-controversial.

eddyb · 2020-04-09T18:25:36Z

@bors r=nikomatsakis,eddyb

bors · 2020-04-09T18:25:37Z

📌 Commit d605a9d has been approved by nikomatsakis,eddyb

estebank · 2020-04-10T15:09:16Z

Dist extended stage1 (x86_64-apple-darwin)
Building stage1 tool cargo (x86_64-apple-darwin)
dyld: Library not loaded: /usr/lib/libcurl.4.dylib
  Referenced from: /Users/runner/runners/2.165.2/work/1/s/build/x86_64-apple-darwin/stage0/bin/cargo
  Reason: image not found
command did not execute successfully: "/Users/runner/runners/2.165.2/work/1/s/build/x86_64-apple-darwin/stage0/bin/cargo" "build" "--target" "x86_64-apple-darwin" "-Zbinary-dep-depinfo" "-j" "4" "--release" "--locked" "--color" "always" "--manifest-path" "/Users/runner/runners/2.165.2/work/1/s/src/tools/cargo/Cargo.toml" "--features" "rustc-workspace-hack/all-static" "--message-format" "json-render-diagnostics"
expected success, got: signal: 6
failed to run: /Users/runner/runners/2.165.2/work/1/s/build/bootstrap/debug/bootstrap dist
Build completed unsuccessfully in 1:11:06

@bors retry

@ghost

Rollup of 9 pull requests Successful merges: - rust-lang#69745 (Use `PredicateObligation`s instead of `Predicate`s) - rust-lang#70938 (Add ThreadSanitizer test case) - rust-lang#70973 (Use forward traversal for unconditional recursion lint) - rust-lang#70978 (compiletest: let config flags overwrite -A unused) - rust-lang#70979 (Follow up on BTreeMap comments) - rust-lang#70981 (Rearrange BTreeMap::into_iter to match range_mut.) - rust-lang#70985 (Clean up E0512 explanation) - rust-lang#70988 (Setup the `@rustbot prioritize` command) - rust-lang#70991 (fix rustc-dev-guide's url in src/librustc_codegen_ssa) Failed merges: r? @ghost

src/test/ui/traits/negative-impls/negated-auto-traits-error.stderr

rustup rust-lang/rust#69745 changelog: none

Changes: ```` Allow UUID style formatting for `inconsistent_digit_grouping` lint rustup rust-lang#70986 rustup rust-lang#69745 Rustup to rust-lang#70913 compare with the second largest instead of the smallest variant Revert "Downgrade new_ret_no_self to pedantic" Check for clone-on-copy in argument positions Check fn header along with decl when suggesting to implement trait Downgrade implicit_hasher to pedantic Move cognitive_complexity to nursery Run fmt and update test Use int assoc consts in MANUAL_SATURATING_ARITHMETIC Use int assoc consts in checked_conversions lint Use primitive type assoc consts in more tests Use integer assoc consts in more lint example code Don't import primitive type modules Use assoc const NAN for zero_div_zero lint Fix float cmp to use assoc fxx::EPSILON Fix NAN comparison lint to use assoc NAN Refine lint message. Lint on opt.as_ref().map(|x| &**x). Include OpAssign in suspicious_op_assign_impl result_map_or_into_option: fix syntax error in example result_map_or_into: fix dogfood_clippy error => {h,l}int CONTRIBUTING.md: fix broken triage link result_map_or_into_option: fix `cargo dev fmt --check` errors result_map_or_into_option: move arg checks into tuple assignment result_map_or_into_option: add `opt.map_or(None, |_| Some(y))` test result_map_or_into_option: destructure lint tuple or return early result_map_or_into_option: add good and bad examples result_map_or_into_option: explicitly note absence of known problems Downgrade new_ret_no_self to pedantic Downgrade unreadable_literal to pedantic Update CONTRIBUTING.md Rename rustc -> rustc_middle in doc links result_map_or_into_option: add lint to catch manually adpating Result -> Option Move matches test in matches module Run update_lints Make lint modules private Don't filter lints in code generation functions Build lint lists once and the reuse them to update files Get rid of Lint::is_internal method Clean up update_lints Downgrade inefficient_to_string to pedantic Downgrade trivially_copy_pass_by_ref to pedantic Downgrade let_unit_value to pedantic ```` Fixes rust-lang#70993

@Dylan-DPC

submodules: update clippy from d342cee to af5940b Changes: ```` Allow UUID style formatting for `inconsistent_digit_grouping` lint rustup rust-lang#70986 rustup rust-lang#69745 Rustup to rust-lang#70913 compare with the second largest instead of the smallest variant Revert "Downgrade new_ret_no_self to pedantic" Check for clone-on-copy in argument positions Check fn header along with decl when suggesting to implement trait Downgrade implicit_hasher to pedantic Move cognitive_complexity to nursery Run fmt and update test Use int assoc consts in MANUAL_SATURATING_ARITHMETIC Use int assoc consts in checked_conversions lint Use primitive type assoc consts in more tests Use integer assoc consts in more lint example code Don't import primitive type modules Use assoc const NAN for zero_div_zero lint Fix float cmp to use assoc fxx::EPSILON Fix NAN comparison lint to use assoc NAN Refine lint message. Lint on opt.as_ref().map(|x| &**x). Include OpAssign in suspicious_op_assign_impl result_map_or_into_option: fix syntax error in example result_map_or_into: fix dogfood_clippy error => {h,l}int CONTRIBUTING.md: fix broken triage link result_map_or_into_option: fix `cargo dev fmt --check` errors result_map_or_into_option: move arg checks into tuple assignment result_map_or_into_option: add `opt.map_or(None, |_| Some(y))` test result_map_or_into_option: destructure lint tuple or return early result_map_or_into_option: add good and bad examples result_map_or_into_option: explicitly note absence of known problems Downgrade new_ret_no_self to pedantic Downgrade unreadable_literal to pedantic Update CONTRIBUTING.md Rename rustc -> rustc_middle in doc links result_map_or_into_option: add lint to catch manually adpating Result -> Option Move matches test in matches module Run update_lints Make lint modules private Don't filter lints in code generation functions Build lint lists once and the reuse them to update files Get rid of Lint::is_internal method Clean up update_lints Downgrade inefficient_to_string to pedantic Downgrade trivially_copy_pass_by_ref to pedantic Downgrade let_unit_value to pedantic ```` Fixes rust-lang#70993 r? @Dylan-DPC

ecstatic-morse · 2020-04-17T22:15:42Z

FYI, this seems to have slowed down clean check builds of the futures crate by 8%.

eddyb · 2020-04-17T22:50:30Z

Oh dear, it makes the stress test for #65510 way worse. That test isn't entirely artificial btw.
It's simulating a set of real-world situations where traits and associated types are heavily used.

Also, 5% on serde itself would be enough to warrant a look.

eddyb · 2020-04-17T22:51:03Z

src/librustc_infer/infer/outlives/verify.rs

+                .into_iter()
+                .map(|o| o.predicate)
+                .collect::<Vec<_>>(),


Ahh I wonder if it's stuff like this - this is very wasteful and unlikely to be needed.

eddyb · 2020-04-17T22:52:04Z

src/librustc_infer/traits/util.rs

+    let obligations: Vec<_> =
+        predicates.into_iter().map(|predicate| predicate_obligation(predicate, None)).collect();


Again, this is Vec -> Vec, which we should avoid ever doing. I wish I spotted this earlier, oof.

eddyb · 2020-04-17T22:55:36Z

src/librustc_trait_selection/traits/wf.rs

-            let predicates = obligations.iter().map(|obligation| obligation.predicate).collect();
-            let implied_obligations = traits::elaborate_predicates(tcx, predicates);
-            let implied_obligations = implied_obligations.map(|pred| {
+            let implied_obligations = traits::util::elaborate_obligations(tcx, obligations.clone());


At a glance this seems wasteful but it's not worse than it was before. Presumably we can avoid this clone altogether, but I haven't checked.

The only reason I didn't strip them outright was because of retain calls in elaborate_predicates, but if we can change all cases of Vec<Pred> argument types into impl Iterator<Item = Pred>, we should be faster than before.

eddyb · 2020-04-17T22:56:42Z

src/librustc_trait_selection/traits/mod.rs

-        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec()).collect();
+        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.to_vec())
+            .map(|obligation| obligation.predicate)
+            .collect();


Tempted to try and find every allocation in the trait system and rewrite it.

Are you going to be doing it or should I try and do some of it now?

If you want to play around with it, feel free to! I was mostly considering taking this over in case you don't have time for it.

I won't have time to look at elaborate_obligations, which is the one that might have the biggest impact, but I can have a small PR shortly where I'm replacing a bunch of these arguments with impl Iterator<Item = PredicateObligation> so that it becomes clearer where we're collecting multiple times.

Looking at this in closer detail, I think I might be able to simplify this a bit.

estebank · 2020-04-18T17:25:46Z

@eddyb @ecstatic-morse #71268 seems to get us closer to the previous baseline but I also found a couple of other improvements I might be able to make.

@eddyb

…ikomatsakis Maintain chain of derived obligations When evaluating the derived obligations from super traits, maintain a reference to the original obligation in order to give more actionable context in the output. Continuation (and built on) rust-lang#69745, subset of rust-lang#69709. r? @eddyb

@eddyb

Remove some `Vec` allocations to improve performance This claws back most of the performance lost in rust-lang#69745. r? @eddyb

Changes: ```` Allow UUID style formatting for `inconsistent_digit_grouping` lint rustup rust-lang/rust#70986 rustup rust-lang/rust#69745 Rustup to rust-lang/rust#70913 compare with the second largest instead of the smallest variant Revert "Downgrade new_ret_no_self to pedantic" Check for clone-on-copy in argument positions Check fn header along with decl when suggesting to implement trait Downgrade implicit_hasher to pedantic Move cognitive_complexity to nursery Run fmt and update test Use int assoc consts in MANUAL_SATURATING_ARITHMETIC Use int assoc consts in checked_conversions lint Use primitive type assoc consts in more tests Use integer assoc consts in more lint example code Don't import primitive type modules Use assoc const NAN for zero_div_zero lint Fix float cmp to use assoc fxx::EPSILON Fix NAN comparison lint to use assoc NAN Refine lint message. Lint on opt.as_ref().map(|x| &**x). Include OpAssign in suspicious_op_assign_impl result_map_or_into_option: fix syntax error in example result_map_or_into: fix dogfood_clippy error => {h,l}int CONTRIBUTING.md: fix broken triage link result_map_or_into_option: fix `cargo dev fmt --check` errors result_map_or_into_option: move arg checks into tuple assignment result_map_or_into_option: add `opt.map_or(None, |_| Some(y))` test result_map_or_into_option: destructure lint tuple or return early result_map_or_into_option: add good and bad examples result_map_or_into_option: explicitly note absence of known problems Downgrade new_ret_no_self to pedantic Downgrade unreadable_literal to pedantic Update CONTRIBUTING.md Rename rustc -> rustc_middle in doc links result_map_or_into_option: add lint to catch manually adpating Result -> Option Move matches test in matches module Run update_lints Make lint modules private Don't filter lints in code generation functions Build lint lists once and the reuse them to update files Get rid of Lint::is_internal method Clean up update_lints Downgrade inefficient_to_string to pedantic Downgrade trivially_copy_pass_by_ref to pedantic Downgrade let_unit_value to pedantic ```` Fixes #70993

rust-highfive assigned eddyb Mar 5, 2020

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Maintain predicate obligation chain for more detailed diagnostics #69709

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Maintain chain of derived obligations #69793

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Remove duplicated code in trait selection #70641

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estebank added 2 commits April 8, 2020 14:40

Use PredicateObligations instead of Predicates

bd7ea54

Keep more information about trait binding failures.

Small tweaks to required bound span

d605a9d

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Rollup of 9 pull requests #70994

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rustup rust-lang/rust#69745

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rustup rust-lang/rust#69745

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Auto merge of #5450 - matthiaskrgr:rustup_41, r=phansch

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rustup rust-lang/rust#69745 changelog: none

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Auto merge of #5450 - matthiaskrgr:rustup_41, r=phansch

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Remove some Vec allocations to improve performance #71268

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Regression in spacing of left margin in diagnostics #71363

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Auto merge of rust-lang#71268 - estebank:devectorize, r=eddyb

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Remove some `Vec` allocations to improve performance This claws back most of the performance lost in rust-lang#69745. r? @eddyb

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Separate projection bounds and predicates #73905

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		let obligations: Vec<_> =
		predicates.into_iter().map(\|predicate\| predicate_obligation(predicate, None)).collect();

Use PredicateObligations instead of Predicates #69745

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Use `PredicateObligation`s instead of `Predicate`s #69745

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