Rust Foundation Project Grant 2022

This repository is used to track information about my Rust Foundation Project Grant to improve error messages emitted by rustc for trait heavy crates. As part of this work I will focus on the following points:

1. Collect and categorise various examples of non-optimal error messages from the rust ecosystem. This includes error messages generated by crates like diesel, axum or nalgebra which relay heavily on complex trait bounds
2. Experiment with example cases to see which error messages could be improved by the usage of #[rustc_on_unimplemented]
3. Implement RFC-2397
4. Experiment with example cases to see which error messages could be improved by the usage of #[do_not_recommend]

Call for participation

Please submit examples of bad error messages in the context of trait heavy crates as issue or PR (with minimal example) to this repository.

Test cases

crate	test case	error type
uom	type_mismatch.rs	type mismatch
typed_builder	mismatch.rs	type mismatch + missing free standing function
easy_ml	recursion.rs	type recursion
diesel	bad_insertable_field.rs	trait not implemented + misleading wildcard impl
diesel	bad_sql_query.rs	trait not implemented
diesel	invalid_query.rs	traits not implemented + "duplicated errors"
diesel	queryable_order_mismatch.rs	trait not implemented with large types
chumsky	json.rs	associated type mismatch
bevy	system_mismatch.rs	trait not implemented + HRTB error
axum	argument_not_extractor.rs	debug_handler
axum	extract_self_mut.rs	debug_handler
axum	extract_self_ref.rs	debug_handler
axum	generics.rs	debug_handler
axum	invalid_attrs.rs	debug_handler
axum	missing_deserialize.rs	trait not implemented
axum	multiple_body_extractors.rs	debug_handler
axum	multiple_paths.rs	debug_handler
axum	not_a_function.rs	debug_handler
axum	not_async.rs	debug_handler
axum	not_send.rs	debug_handler
axum	request_not_last.rs	debug_handler
axum	too_many_extractors.rs	debug_handler
axum	wrong_return_type.rs	debug_handler
entrait	missing_impl_deep.rs	trait not implemented

uom

type_mismatch.rs <a name="uom_type_mismatch>

Versions:

version	link (code)	link (error message)	change since last version
1	type_mismatch.rs	type_mismatch.stderr

typed_builder

Typed builder generates hidden types/deprecating messages to improve its error messages

mismatch.rs

Versions:

version	link (code)	link (error message)	change since last version
1	mismatch.rs	mismatch.stderr

entrait

missing_impl_deep.rs

Versions:

version	link (code)	link (error message)	change since last version
1	missing_impl_deep.rs	missing_impl_deep.stderr

easy_ml

recursion.rs

Versions:

version	link (code)	link (error message)	change since last version
1	recursion.rs	recursion.stderr

diesel

bad_insertable_field.rs

version	link (code)	link (error message)	change since last version
1	bad_insertable_field.rs	bad_insertable_field.stderr
2	bad_insertable_field.rs	bad_insertable_field.stderr	https://github.com/diesel-rs/diesel/pull/3228 improves the spans for certain trait bounds so that compiler errors point to the corresponding struct fields instead of the derive

bad_sql_query.rs

version	link (code)	link (error message)	change since last version
1	bad_sql_query.rs	bad_sql_query.stderr
2	bad_sql_query.rs	bad_sql_query.stderr	Add a #[rustc_on_unimplemented] on the corresponding trait. https://github.com/diesel-rs/diesel/commit/958391a3e793e409d0a925e0cc2317726c2d84b2

invalid_query.rs

version	link (code)	link (error message)	change since last version
1	invalid_query.rs	invalid_query.stderr
2	invalid_query.rs	invalid_query.stderr	Add a #[rustc_on_unimplemented] on the corresponding trait. https://github.com/diesel-rs/diesel/commit/958391a3e793e409d0a925e0cc2317726c2d84b2

queryable_order_mismatch.rs

version	link (code)	link (error message)	change since last version
1	queryable_order_mismatch.rs	queryable_order_mismatch.stderr

chumsky

json.rs

version	link (code)	link (error message)	change since last version
1	json.rs	json.stderr

bevy

system_mismatch.rs

version	link (code)	link (error message)	change since last version
1	system_mismatch.rs	system_mismatch.stderr
2	system_mismatch.rs	system_mismatch.stderr	https://github.com/bevyengine/bevy/pull/5786, which introduces #[rustc_on_unimplemented] attributes in multiple locations

axum

axum provides a #[debug_handler] attribute which emits better error messages is some cases

argument_not_extractor.rs

version	link (code)	link (error message)	change since last version
1	argument_not_extractor.rs	argument_not_extractor.stderr
2	argument_not_extractor.rs	argument_not_extractor.stderr	Fixes to the error spans of #[debug_handler]
3	argument_not_extractor.rs	argument_not_extractor.stderr	Point to #[debug_handler]

extract_self_ref

version	link (code)	link (error message)	change since last version
1	extract_self_ref.rs	extract_self_ref.stderr

extract_self_mut

version	link (code)	link (error message)	change since last version
1	extract_self_mut.rs	extract_self_mut.stderr

generics

version	link (code)	link (error message)	change since last version
1	generics.rs	generics.stderr

invalid_attrs

version	link (code)	link (error message)	change since last version
1	invalid_attrs.rs	invalid_attrs.stderr

missing_deserialize.rs

version	link (code)	link (error message)	change since last version
1	missing_deserialize.rs	missing_deserialize.stderr
2	missing_deserialize.rs	missing_deserialize.stderr	Point to #[debug_handler]

multiple_body_extractors

version	link (code)	link (error message)	change since last version
1	multiple_body_extractors.rs	multiple_body_extractors.stderr
2	multiple_body_extractors.rs	multiple_body_extractors.stderr	Fixes to the error spans of #[debug_handler]
3	multiple_body_extractors.rs	multiple_body_extractors.stderr	Point to #[debug_handler]

multiple_paths

version	link (code)	link (error message)	change since last version
1	multiple_paths.rs	multiple_paths.stderr

not_a_function

version	link (code)	link (error message)	change since last version
1	not_a_function.rs	not_a_function.stderr

not_async

version	link (code)	link (error message)	change since last version
1	not_async.rs	not_async.stderr

not_send

version	link (code)	link (error message)	change since last version
1	not_send.rs	not_send.stderr

request_not_last

version	link (code)	link (error message)	change since last version
1	request_not_last.rs	request_not_last.stderr
2	request_not_last.rs	request_not_last.stderr	Fixes to the error spans of #[debug_handler]
3	request_not_last.rs	request_not_last.stderr	Point out as part of the error message, that Request always needs to be the last handler argument

too_many_extractors

version	link (code)	link (error message)	change since last version
1	too_many_extractors.rs	too_many_extractors.stderr

wrong_return_type.rs

version	link (code)	link (error message)	change since last version
1	wrong_return_type.rs	wrong_return_type.stderr