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Incorrect documentation for default-features in workspace dependencies #14841

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konstin opened this issue Nov 20, 2024 · 2 comments
Open

Incorrect documentation for default-features in workspace dependencies #14841

konstin opened this issue Nov 20, 2024 · 2 comments
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A-documenting-cargo-itself Area: Cargo's documentation A-features Area: features — conditional compilation A-manifest Area: Cargo.toml issues A-workspace-inheritance Area: workspace inheritance RFC 2906 S-needs-design Status: Needs someone to work further on the design for the feature or fix. NOT YET accepted.

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@konstin
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konstin commented Nov 20, 2024

The cargo docs on workspace packages say (https://doc.rust-lang.org/nightly/cargo/reference/specifying-dependencies.html#inheriting-a-dependency-from-a-workspace):

Along with the workspace key, dependencies can also include these keys:

  • optional: Note that the[workspace.dependencies] table is not allowed to specify optional.
  • features: These are additive with the features declared in the [workspace.dependencies]

Other than optional and features, inherited dependencies cannot use any other dependency key (such as version or default-features).

Trying this out however, cargo does not seem to mind the default-features key:

[workspace]
members = ["workspace-member"]
resolver = "2"

[workspace.dependencies]
flate2 = { version = "1.0.35", default-features = false }
url = { version = "2.5.3", features = ["serde"] }
[package]
name = "workspace-member"
version = "0.1.0"
edition = "2021"

[dependencies]
flate2 = { workspace = true, default-features = true }
url = { workspace = true, default-features = false }

It's unfortunately not clear to me from the docs if default-features are inherited.
konstin added a commit to astral-sh/uv that referenced this issue Nov 20, 2024
@konstin
Unify cargo features
4b6d556 
When building only a single crate in the workspace to run its test, we often recompile a lot of other, unrelated crates. Whenever cargo has a different set of crate features, it needs to recompile. By moving some features (non-exhaustive for now) to the workspace level, we always activate them an avoid recompiling.

The cargo docs mismatch the behavior of cargo around default-deps, so I filed that upstream: rust-lang/cargo#14841

Reference script:

```python
import tomllib
from collections import defaultdict
from pathlib import Path

uv = Path("/home/konsti/projects/uv")
skip_list = ["uv-trampoline", "uv-dev", "uv-performance-flate2-backend", "uv-performance-memory-allocator"]

root_feature_map = defaultdict(set)
root_default_features = defaultdict(bool)
cargo_toml = tomllib.loads(uv.joinpath("Cargo.toml").read_text())
for dep, declaration in cargo_toml["workspace"]["dependencies"].items():
    root_default_features[dep] = root_default_features[dep] or declaration.get("default-features", True)
    root_feature_map[dep].update(declaration.get("features", []))

feature_map = defaultdict(set)
default_features = defaultdict(bool)
for crate in uv.joinpath("crates").iterdir():
    if crate.name in skip_list:
        continue
    if not crate.joinpath("Cargo.toml").is_file():
        continue
    cargo_toml = tomllib.loads(crate.joinpath("Cargo.toml").read_text())
    for dep, declaration in cargo_toml.get("dependencies", {}).items():
        # If any item uses default features, they are used everywhere
        default_features[dep] = default_features[dep] or declaration.get("default-features", True)
        feature_map[dep].update(declaration.get("features", []))

for dep, features in sorted(feature_map.items()):
    features = features - root_feature_map.get(dep, set())
    if not features and default_features[dep] == root_default_features[dep]:
        continue
    print(dep, default_features[dep], sorted(features))
```
@konstin konstin mentioned this issue Nov 20, 2024
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@weihanglo
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Documenting is hard ;(
This is something we've tried to make it clear. See https://doc.rust-lang.org/nightly/edition-guide/rust-2024/cargo-inherited-default-features.html and #12162 (comment).

Any idea how to add a succinct explanation to the doc?
cc @Muscraft

@weihanglo weihanglo added A-features Area: features — conditional compilation A-documenting-cargo-itself Area: Cargo's documentation A-manifest Area: Cargo.toml issues S-needs-design Status: Needs someone to work further on the design for the feature or fix. NOT YET accepted. A-workspace-inheritance Area: workspace inheritance RFC 2906 labels Nov 20, 2024
@konstin
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konstin commented Nov 20, 2024

Something like "A workspace member will inherit default-features = false if set in the workspace root, but it can't deactivate default features if they weren't deactivated by the workspace root". I found the table in #12162 (comment) very helpful.

konstin added a commit to astral-sh/uv that referenced this issue Nov 20, 2024
@konstin
Unify cargo features (#9267)
2f5a64a 
When building only a single crate in the workspace to run its tests, we
often recompile a lot of other, unrelated crates. Whenever cargo has a
different set of crate features, it needs to recompile. By moving some
features (non-exhaustive for now) to the workspace level, we always
activate them an avoid recompiling.

The cargo docs mismatch the behavior of cargo around default-deps, so I
filed that upstream and left most `default-features` mismatches:
rust-lang/cargo#14841.

Reference script:

```python
import tomllib
from collections import defaultdict
from pathlib import Path

uv = Path("/home/konsti/projects/uv")
skip_list = ["uv-trampoline", "uv-dev", "uv-performance-flate2-backend", "uv-performance-memory-allocator"]

root_feature_map = defaultdict(set)
root_default_features = defaultdict(bool)
cargo_toml = tomllib.loads(uv.joinpath("Cargo.toml").read_text())
for dep, declaration in cargo_toml["workspace"]["dependencies"].items():
    root_default_features[dep] = root_default_features[dep] or declaration.get("default-features", True)
    root_feature_map[dep].update(declaration.get("features", []))

feature_map = defaultdict(set)
default_features = defaultdict(bool)
for crate in uv.joinpath("crates").iterdir():
    if crate.name in skip_list:
        continue
    if not crate.joinpath("Cargo.toml").is_file():
        continue
    cargo_toml = tomllib.loads(crate.joinpath("Cargo.toml").read_text())
    for dep, declaration in cargo_toml.get("dependencies", {}).items():
        # If any item uses default features, they are used everywhere
        default_features[dep] = default_features[dep] or declaration.get("default-features", True)
        feature_map[dep].update(declaration.get("features", []))

for dep, features in sorted(feature_map.items()):
    features = features - root_feature_map.get(dep, set())
    if not features and default_features[dep] == root_default_features[dep]:
        continue
    print(dep, default_features[dep], sorted(features))
```
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A-documenting-cargo-itself Area: Cargo's documentation A-features Area: features — conditional compilation A-manifest Area: Cargo.toml issues A-workspace-inheritance Area: workspace inheritance RFC 2906 S-needs-design Status: Needs someone to work further on the design for the feature or fix. NOT YET accepted.
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