An option to disable default-features crate and workspace wide

[jaskij]

Problem

I see value in minimizing the dependency tree - only bring in what I actually use.

The problem is that, between me using workspaces and features being additive, this creates a lot of noise in my manifest files, making them much harder to read.

As an example:

A small project I'm working on now, a set of three connected libraries in a workspace. There is a total of seven external non-dev dependencies, plus one or two intra-workspace ones. A total of around three thousand lines of Rust. default-features = false is found an astonishing twenty six times among the four manifest files.

I am most definitely not the only person doing this, as cargo-deny has a ban for default-features

To show what it looks like:

[dependencies]
bytes = { workspace = true, default-features = false }
num_enum = { workspace = true, default-features = false }
thiserror = { workspace = true, default-features = false }

futures = { workspace = true, default-features = false, optional = true }
tokio = { workspace = true, default-features = false, features = ["macros"], optional = true }
tokio-util = { workspace = true, default-features = false, optional = true }
valuable = { workspace = true, default-features = false, optional = true }

Proposed Solution

I would like an option that would allow me to, in one place, set default-feature = false for every dependency in the file manifest. Ideally, this would be three switches: separately for regular, dev and build dependencies.

The big issue I see with such an addition is that it does not fit within the existing structure of the manifest file - the obvious place to put it would be under dependencies, but that would create a precedent of Cargo itself reserving crate names, which I do not think is a good idea.

Other top level keys have their own roles, and adding this feature to them would not be suitable.

Just about the only option I see is adding a new top-level key to the manifest, perhaps one generally involved with governing default features. This option would be added under it.

Notes

#3126 may be relevant to this discussion.

[Nemo157]

I've long wanted this ability too, syntax I've considered in the past was

[dependencies]
"*" = { default-features = false }

* is not a XID compatible identifier so shouldn't cause any conflicts, and should be relatively obvious (though it doesn't look great with the quoting).