Build on Rust nightly fails: error[E0221]: ambiguous associated type Group in bounds of Q

[ivan]

This happens only with a recent nightly (tested with rustup on NixOS 20.09).

• nightly-2020-11-29 good
• nightly-2020-11-30 bad

at@ra:/home/at/code/rust/salsa:master# rustup default nightly
info: using existing install for 'nightly-x86_64-unknown-linux-gnu'
info: default toolchain set to 'nightly-x86_64-unknown-linux-gnu'

  nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.50.0-nightly (6645da366 2020-12-01)

at@ra:/home/at/code/rust/salsa:master# cargo test
   Compiling libc v0.2.80
   Compiling cfg-if v0.1.10
   Compiling autocfg v1.0.1
   Compiling proc-macro2 v1.0.24
   Compiling getrandom v0.1.15
   Compiling unicode-xid v0.2.1
   Compiling cfg-if v1.0.0
   Compiling memchr v2.3.4
   Compiling syn v1.0.53
   Compiling log v0.4.11
   Compiling smallvec v1.5.0
   Compiling scopeguard v1.1.0
   Compiling ppv-lite86 v0.2.10
   Compiling lazy_static v1.4.0
   Compiling unicode-segmentation v1.7.1
   Compiling regex-syntax v0.6.21
   Compiling quick-error v1.2.3
   Compiling hashbrown v0.9.1
   Compiling rustc-hash v1.1.0
   Compiling termcolor v1.1.2
   Compiling oorandom v11.1.3
   Compiling diff v0.1.12
   Compiling linked-hash-map v0.5.3
   Compiling instant v0.1.9
   Compiling lock_api v0.4.2
   Compiling thread_local v1.0.1
   Compiling humantime v1.3.0
   Compiling crossbeam-utils v0.8.1
   Compiling indexmap v1.6.0
   Compiling heck v0.3.1
   Compiling aho-corasick v0.7.15
   Compiling quote v1.0.7
   Compiling parking_lot_core v0.8.0
   Compiling atty v0.2.14
   Compiling rand_core v0.5.1
   Compiling parking_lot v0.11.1
   Compiling rand_chacha v0.2.2
   Compiling rand v0.7.3
   Compiling regex v1.4.2
   Compiling rand_distr v0.2.2
   Compiling env_logger v0.7.1
   Compiling salsa-macros v0.16.0 (/home/at/code/rust/salsa/components/salsa-macros)
   Compiling salsa v0.16.0 (/home/at/code/rust/salsa)
error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:466:57
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:478:57
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:490:57
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:512:57
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:466:57
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
466 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:478:57
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
478 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:490:57
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
490 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0221]: ambiguous associated type `Group` in bounds of `Q`
   --> src/interned.rs:512:57
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<Q::Group>>::group_storage(db);
    |                                                         ^^^^^^^^ ambiguous associated type `Group`
    |
   ::: src/lib.rs:431:5
    |
431 |     type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
    |     --------------------------------------------------------------------
    |     |
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |     ambiguous `Group` from `for<'d> QueryDb<'d>`
    |
help: use fully qualified syntax to disambiguate
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: use fully qualified syntax to disambiguate
    |
512 |             <<Q as QueryDb<'_>>::DynDb as HasQueryGroup<<Q as for<'d> QueryDb<'d>>::Group>>::group_storage(db);
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0221`.
error: could not compile `salsa`

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0221`.
error: build failed

[ivan]

No longer an issue with nightly-2020-12-03