Ambiguous traits in QueryableByName derivation when two fields have same concrete type but different SQL types

[fiadliel]

Setup

Versions

• Rust: 1.80.0
• Diesel: 2.2.2
• Database: PostgreSQL
• **Operating System: ** MacOS

Feature Flags

• diesel: postgres

Problem Description

What are you trying to accomplish?

Attempting to use QueryableByName + sql_query. In this case, two fields have the same type in the struct, but different SQL types.

Example:

#[derive(QueryableByName)]
#[diesel(check_for_backend(Pg))]
struct StructWithTextAndCitext {
    #[diesel(sql_type = sql_types::Text)]
    name: String,
    #[diesel(sql_type = sql_types::Citext)]
    email: String,
}

Alternative example (this also requires the serde_json feature of diesel):

#[derive(QueryableByName)]
#[diesel(check_for_backend(Pg))]
struct StructWithJsonAndJsonb {
    #[diesel(sql_type = sql_types::Json)]
    v1: serde_json::Value,
    #[diesel(sql_type = sql_types::Jsonb)]
    v2: serde_json::Value,
}

What is the expected output?

The code compiles, and creates a useful QueryableByName trait implementation.

What is the actual output?

In the first case above, the error is:

error[E0283]: type annotations needed
   --> src/main.rs:11:10
    |
11  | #[derive(QueryableByName)]
    |          ^^^^^^^^^^^^^^^ cannot infer type
    |
    = note: cannot satisfy `String: FromSql<_, __DB>`
    = help: the following types implement trait `FromSql<A, DB>`:
              <String as FromSql<Citext, Pg>>
              <String as FromSql<ST, DB>>
note: required by a bound in `diesel::row::NamedRow::get`
   --> /xxx/.cargo/registry/src/index.crates.io-6f17d22bba15001f/diesel-2.2.2/src/row.rs:133:12
    |
131 |     fn get<ST, T>(&self, column_name: &str) -> deserialize::Result<T>
    |        --- required by a bound in this associated function
132 |     where
133 |         T: FromSql<ST, DB>;
    |            ^^^^^^^^^^^^^^^ required by this bound in `NamedRow::get`
    = note: this error originates in the derive macro `QueryableByName` (in Nightly builds, run with -Z macro-backtrace for more info)

In the second case, the error is:

error[E0283]: type annotations needed
   --> src/main.rs:11:10
    |
11  | #[derive(QueryableByName)]
    |          ^^^^^^^^^^^^^^^ cannot infer type
    |
    = note: cannot satisfy `Value: FromSql<_, __DB>`
    = help: the following types implement trait `FromSql<A, DB>`:
              <Value as FromSql<Json, Pg>>
              <Value as FromSql<Jsonb, Pg>>
note: required by a bound in `diesel::row::NamedRow::get`
   --> /xxx/.cargo/registry/src/index.crates.io-6f17d22bba15001f/diesel-2.2.2/src/row.rs:133:12
    |
131 |     fn get<ST, T>(&self, column_name: &str) -> deserialize::Result<T>
    |        --- required by a bound in this associated function
132 |     where
133 |         T: FromSql<ST, DB>;
    |            ^^^^^^^^^^^^^^^ required by this bound in `NamedRow::get`
    = note: this error originates in the derive macro `QueryableByName` (in Nightly builds, run with -Z macro-backtrace for more info)

Steps to reproduce

Write the code above, with diesel dependency, and features postgres (and serde_json in the second case). If added to src/main.rs, you should see the above compile errors.

Checklist

• I have already looked over the issue tracker and the discussion forum for similar possible closed issues.
• This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)
• This issue can be reproduced without requiring a third party crate