Diesel stops building with nightly-2025-12-10

@rustbot

Code

I tried this code:

git clone https://github.com/diesel-rs/diesel
cd diesel
cargo check -F postgres --all-targets -p diesel_tests

I expected to see this happen: Code builds without errors
Instead, this happened: Compilation fails with errors

Version it worked on

It most recently worked on:

Version with regression

rustc --version --verbose:

rustc 1.94.0-nightly (c61a3a44d 2025-12-09)
binary: rustc
commit-hash: c61a3a44d1a5bee35914cada6c788a05e0808f5b
commit-date: 2025-12-09
host: x86_64-unknown-linux-gnu
release: 1.94.0-nightly
LLVM version: 21.1.5

bisec-rustc points to c61a3a4 (so #147984) for the commit/PR that introduced this regression.

The error message points to #114095
Unfortunately I see no meaningful way for diesel to address this without doing a significant breaking change. To address this without breaking change on our side it would be required to have tooling that lets us import only from a specific namespace (type, function, etc) if several items with the same name exists.

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged

The actual error message as taken from https://github.com/diesel-rs/diesel/actions/runs/20098057029/job/57661673455?pr=4900:

Details

error[E0252]: the name `max` is defined multiple times
   --> diesel_tests/tests/select_by.rs:170:9
    |
169 |     use diesel::dsl::{count_star, max, CountStar};
    |                                   --- previous import of the type `max` here
170 |     use diesel::helper_types::max;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^ `max` reimported here
    |
    = note: `max` must be defined only once in the type namespace of this block

error: `max` is ambiguous
   --> diesel_tests/tests/group_by.rs:33:22
    |
 33 |     use diesel::dsl::max;
    |                      ^^^ ambiguous name
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #114095 <https://github.com/rust-lang/rust/issues/114095>
    = note: ambiguous because of multiple glob imports of a name in the same module
note: `max` could refer to the type alias defined here
   --> /home/runner/work/diesel/diesel/diesel/src/lib.rs:341:13
    |
341 |     pub use crate::helper_types::*;
    |             ^^^^^^^^^^^^^^^^^^^
note: `max` could also refer to the type alias defined here
   --> /home/runner/work/diesel/diesel/diesel/src/lib.rs:344:13
    |
344 |     pub use crate::expression::dsl::*;
    |             ^^^^^^^^^^^^^^^^^^^^^^
    = note: `#[deny(ambiguous_glob_imports)]` (part of `#[deny(future_incompatible)]`) on by default

error: `max` is ambiguous
   --> diesel_tests/tests/select.rs:519:35
    |
519 |     use diesel::dsl::{count_star, max};
   --> /home/runner/work/diesel/diesel/diesel/src/lib.rs:344:13
    |
344 |     pub use crate::expression::dsl::*;
    |             ^^^^^^^^^^^^^^^^^^^^^^

error: `nth_value` is ambiguous
   --> diesel_derives/tests/auto_type.rs:722:9
    |
722 |         nth_value(users::id, 1_i32).over(),
    |         ^^^^^^^^^ ambiguous name
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #114095 <https://github.com/rust-lang/rust/issues/114095>
    = note: ambiguous because of multiple glob imports of a name in the same module
note: `nth_value` could refer to the type alias defined here
   --> /home/runner/work/diesel/diesel/diesel/src/lib.rs:341:13
    |
341 |     pub use crate::helper_types::*;
    |             ^^^^^^^^^^^^^^^^^^^
note: `nth_value` could also refer to the type alias defined here
   --> /home/runner/work/diesel/diesel/diesel/src/lib.rs:344:13
    |
344 |     pub use crate::expression::dsl::*;
    |             ^^^^^^^^^^^^^^^^^^^^^^

warning: unused import: `diesel::helper_types::*`
 --> diesel_derives/tests/auto_type.rs:3:5
  |
3 | use diesel::helper_types::*;
  |     ^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

warning: `diesel_derives` (test "tests") generated 1 warning
error: could not compile `diesel_derives` (test "tests") due to 26 previous errors; 1 warning emitted
warning: build failed, waiting for other jobs to finish...
For more information about this error, try `rustc --explain E0252`.
warning: `diesel_tests` (test "integration_tests") generated 1 warning
error: could not compile `diesel_tests` (test "integration_tests") due to 9 previous errors; 1 warning emitted

@petrochenkov

cc @petrochenkov on that bisection

From 74 regressions in #147984 (comment) (due to ambiguous_glob_imports being deny-by-default) a significant part is indeed from depending on diesel diesel::dsl::{max,sum,/*etc*/}.

I wondered why this hazard in diesel wasn't detected before, and it turns out it was, but diesel does #[allow(ambiguous_glob_reexports)] to ignore it.

I'm trying to understand what's going on, but it's hard because diesel uses proc macros to generate code.

Why do both crate::helper_types::* and crate::expression::dsl::* contain fn max, but different ones?
The compiler doesn't know which one to choose -> ambiguous_glob_imports is reported, this is a legitimate error.
Which one is supposed to be chosen?

it would be required to have tooling that lets us import only from a specific namespace (type, function, etc) if several items with the same name exists

FWIW, the tooling exists, it's just not pretty.
I could make a fix if I understood what's going on there.

Upd: the correct fix is below - #149845 (comment).

Possible fix (at least the reproducer command line passes).
Single imports can be used to explicitly disambiguate the crate::helper_types::* vs crate::expression::dsl::* situation.

diff --git i/diesel/src/lib.rs w/diesel/src/lib.rs
index d6e26dc52..2dba34a76 100644
--- i/diesel/src/lib.rs
+++ w/diesel/src/lib.rs
@@ -339,6 +339,7 @@ pub mod dsl {

     #[doc(inline)]
     pub use crate::helper_types::*;
+    pub use crate::helper_types::{max, array_append};

     #[doc(inline)]
     pub use crate::expression::dsl::*;
diff --git i/diesel_tests/tests/select_by.rs w/diesel_tests/tests/select_by.rs
index 6adaf9717..554f5f27b 100644
--- i/diesel_tests/tests/select_by.rs
+++ w/diesel_tests/tests/select_by.rs
@@ -167,7 +167,6 @@ fn select_can_be_called_on_query_that_is_valid_subselect_but_invalid_query() {
 fn selecting_multiple_aggregate_expressions_without_group_by() {
     use self::users::dsl::*;
     use diesel::dsl::{count_star, max, CountStar};
-    use diesel::helper_types::max;

     #[derive(Queryable)]
     struct CountAndMax {

Thanks for pointing out how to fix it in diesel. I will try to verify this tomorrow.

Based on the diff I unfortunately guess that this might exactly be the thing I called breaking change above, as it requires also to change the calling side as demonstrated by the changes to diesel_tests.

As for the questions around what the code actually expands to: The diesel documentation shows expanded code for the relevant macro: https://docs.diesel.rs/main/diesel/expression/functions/attr.declare_sql_function.html#expanded-code-1

If that is not sufficient I can try to provide more details tomorrow, I'm currently occupied with other tasks.

The FCP set it to a deny-by-default lint, not a hard error. It can be set to a warn-by-default lint instead, yes (by introducing a new lint, because the old one is shared with other cases). I'll have the bandwidth after the holidays (around next week).

Implemented in #151074.

We talked about this in today's @rust-lang/lang meeting. For simplicity's sake, rather than splitting out the external vs intra-crate lint, we'd like to temporarily downgrade the existing lint (covering the use site) to warn-by-default, and wait one release before re-upgrading it, to give an extra six weeks for this to get fixed in the ecosystem.

(Also, if it's not yet warn-in-deps, please go ahead and make it warn-in-deps.)

We talked about this in today's @rust-lang/lang meeting. For simplicity's sake, rather than splitting out the external vs intra-crate lint, we'd like to temporarily downgrade the existing lint (covering the use site) to warn-by-default, and wait one release before re-upgrading it, to give an extra six weeks for this to get fixed in the ecosystem.

(Also, if it's not yet warn-in-deps, please go ahead and make it warn-in-deps.)

Implemented in #151130.

Rollup merge of rust-lang#151130 - diesel2, r=lqd

Unrolled build for #151130

Add an additional help note to the ambiguity lint error

I would like to thank you all for giving me a bit more time. That's really appropriated. I opened #151198 to add an additional note to the error message to ask users to update their dependencies to resolve this particular issues. Hopefully that's helpful.

Add an additional help note to the ambiguity lint error

Rollup merge of rust-lang#151198 - ambiguity_fix_help, r=petrochenkov

Unrolled build for #151198

Add an additional help note to the ambiguity lint error

Navigation Menu

Repository navigation

Diesel stops building with nightly-2025-12-10 #149845

Code

Version it worked on

Version with regression

35 remaining items

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Diesel stops building with nightly-2025-12-10 #149845

Description

Code

Version it worked on

Version with regression

Activity

bjorn3 commented on Dec 10, 2025

lqd commented on Dec 10, 2025

petrochenkov commented on Dec 10, 2025

petrochenkov commented on Dec 10, 2025

petrochenkov commented on Dec 10, 2025

weiznich commented on Dec 10, 2025

35 remaining items

petrochenkov commented on Jan 13, 2026

joshtriplett commented on Jan 14, 2026

petrochenkov commented on Jan 14, 2026

weiznich commented on Jan 16, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions