master fails to compile with default-features=false

[ritchie46]

Describe the bug
Creating a new project with this Cargo.toml fails to compile:

[package]
name = "foo"
version = "0.1.0"
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
arrow = {git = "https://github.com/apache/arrow-rs", rev = "80a57be3215ed7210971a501b10664cadfd59bea", default-features=false}

Output:

error[E0432]: unresolved import `rand::prelude::StdRng`
  --> /home/ritchie46/.cargo/git/checkouts/arrow-rs-3b86e19e889d5acc/80a57be/arrow/src/util/bench_util.rs:27:5
   |
27 |     prelude::StdRng,
   |     ^^^^^^^^^^^^^^^ no `StdRng` in `prelude`

error[E0432]: unresolved import `rand::rngs::StdRng`
  --> /home/ritchie46/.cargo/git/checkouts/arrow-rs-3b86e19e889d5acc/80a57be/arrow/src/util/test_util.rs:20:12
   |
20 | use rand::{rngs::StdRng, Rng, SeedableRng};
   |            ^^^^^^^^^^^^ no `StdRng` in `rngs`

error[E0308]: mismatched types
   --> /home/ritchie46/.cargo/git/checkouts/arrow-rs-3b86e19e889d5acc/80a57be/arrow/src/util/bench_util.rs:102:35
    |
94  | pub fn create_string_array<Offset: StringOffsetSizeTrait>(
    |                            ------ this type parameter
...
102 |             if rng.gen::<f32>() < null_density {
    |                                   ^^^^^^^^^^^^ expected type parameter `Offset`, found `f32`
    |
    = note: expected type parameter `Offset`
                         found type `f32`

error[E0308]: mismatched types
   --> /home/ritchie46/.cargo/git/checkouts/arrow-rs-3b86e19e889d5acc/80a57be/arrow/src/util/bench_util.rs:123:35
    |
114 | pub fn create_binary_array<Offset: BinaryOffsetSizeTrait>(
    |                            ------ this type parameter
...
123 |             if rng.gen::<f32>() < null_density {
    |                                   ^^^^^^^^^^^^ expected type parameter `Offset`, found `f32`
    |
    = note: expected type parameter `Offset`
                         found type `f32`

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0308, E0432.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `arrow`

This is introduced in 80a57be / #488

There are quite often feature tag related bugs that could be prevented if we'd run cargo hack in CI.

Would you be willing to accept a PR that adds those checks? @alamb @jorgecarleitao @Dandandan @jhorstmann @nevi-me

[alamb]

For anyone finding this ticket, a workaround is to add the following to your Cargo dependencies:

# ensure we get the std version of rand so arrow builds without default features
rand = { version = "0.8" }

[alamb]

@ritchie46 I am not sure about cargo-hack -- would the idea be to check every combination of arguments?

Note we supposedly already have a CI check for --no-default-features here:
https://github.com/apache/arrow-rs/blob/master/.github/workflows/rust.yml#L116

But clearly that did not catch this regression

[ritchie46]

@ritchie46 I am not sure about cargo-hack -- would the idea be to check every combination of arguments?

Indeed. Running cargo hack check --each-feature --no-dev-deps would run a cargo check on all possible feature combinations.

[joshuataylor]

I'm also getting this when using:

arrow = { git = "https://github.com/apache/arrow-rs" }

and also from a local path.

Adding rand does fix this.

[alamb]

I am starting to work on this one

[alamb]

github got a little excited and closed this prior to the fix actually being merged