% The Manifest Format
# The `[package]` section
The first section in a `Cargo.toml` is `[package]`.
```toml
[package]
name = "hello_world" # the name of the package
version = "0.1.0" # the current version, obeying semver
authors = ["you@example.com"]
```
All three of these fields are mandatory.
## The `version` field
Cargo bakes in the concept of [Semantic
Versioning](http://semver.org/), so make sure you follow some basic rules:
* Before you reach 1.0.0, anything goes.
* After 1.0.0, only make breaking changes when you increment the major version.
In Rust, breaking changes include adding fields to structs or variants to
enums. Don’t break the build.
* After 1.0.0, don’t add any new public API (no new `pub` anything) in tiny
versions. Always increment the minor version if you add any new `pub` structs,
traits, fields, types, functions, methods or anything else.
* Use version numbers with three numeric parts such as 1.0.0 rather than 1.0.
## The `build` field (optional)
This field specifies a file in the repository which is a [build script][1] for
building native code. More information can be found in the build script
[guide][1].
[1]: build-script.html
```toml
[package]
# ...
build = "build.rs"
```
## The `exclude` and `include` fields (optional)
You can explicitly specify to Cargo that a set of [globs][globs] should be
ignored or included for the purposes of packaging and rebuilding a package. The
globs specified in the `exclude` field identify a set of files that are not
included when a package is published as well as ignored for the purposes of
detecting when to rebuild a package, and the globs in `include` specify files
that are explicitly included.
If a VCS is being used for a package, the `exclude` field will be seeded with
the VCS’ ignore settings (`.gitignore` for git for example).
```toml
[package]
# ...
exclude = ["build/**/*.o", "doc/**/*.html"]
```
```toml
[package]
# ...
include = ["src/**/*", "Cargo.toml"]
```
The options are mutually exclusive: setting `include` will override an
`exclude`. Note that `include` must be an exhaustive list of files as otherwise
necessary source files may not be included.
[globs]: http://doc.rust-lang.org/glob/glob/struct.Pattern.html
## The `publish` field (optional)
The `publish` field can be used to prevent a package from being published to a
repository by mistake.
```toml
[package]
# ...
publish = false
```
## The `workspace` field (optional)
The `workspace` field can be used to configure the workspace that this package
will be a member of. If not specified this will be inferred as the first
Cargo.toml with `[workspace]` upwards in the filesystem.
```toml
[package]
# ...
workspace = "path/to/root"
```
For more information, see the documentation for the workspace table below.
## Package metadata
There are a number of optional metadata fields also accepted under the
`[package]` section:
```toml
[package]
# ...
# A short blurb about the package. This is not rendered in any format when
# uploaded to crates.io (aka this is not markdown).
description = "..."
# These URLs point to more information about the repository.
documentation = "..."
homepage = "..."
repository = "..."
# This points to a file in the repository (relative to this `Cargo.toml`). The
# contents of this file are stored and indexed in the registry.
readme = "..."
# This is a small list of keywords used to categorize and search for this
# package.
keywords = ["...", "..."]
# This is a string description of the license for this package. Currently
# crates.io will validate the license provided against a whitelist of known
# license identifiers from http://spdx.org/licenses/. Multiple licenses can be
# separated with a `/`.
license = "..."
# If a project is using a nonstandard license, then this key may be specified in
# lieu of the above key and must point to a file relative to this manifest
# (similar to the readme key).
license-file = "..."
```
The [crates.io](https://crates.io) registry will render the description, display
the license, link to the three URLs and categorize by the keywords. These keys
provide useful information to users of the registry and also influence the
search ranking of a crate. It is highly discouraged to omit everything in a
published crate.
## The `metadata` table (optional)
Cargo by default will warn about unused keys in `Cargo.toml` to assist in
detecting typos and such. The `package.metadata` table, however, is completely
ignored by Cargo and will not be warned about. This section can be used for
tools which would like to store project configuration in `Cargo.toml`. For
example:
```toml
[package]
name = "..."
# ...
# Metadata used when generating an Android APK, for example.
[package.metadata.android]
package-name = "my-awesome-android-app"
assets = "path/to/static"
```
# Dependency sections
See the [specifying dependencies page](specifying-dependencies.html) for
information on the `[dependencies]`, `[dev-dependencies]`, and target-specific
`[target.*.dependencies]` sections.
# The `[profile.*]` sections
Cargo supports custom configuration of how rustc is invoked through profiles at
the top level. Any manifest may declare a profile, but only the top level
project’s profiles are actually read. All dependencies’ profiles will be
overridden. This is done so the top-level project has control over how its
dependencies are compiled.
There are five currently supported profile names, all of which have the same
configuration available to them. Listed below is the configuration available,
along with the defaults for each profile.
```toml
# The development profile, used for `cargo build`.
[profile.dev]
opt-level = 0 # controls the `--opt-level` the compiler builds with
debug = true # controls whether the compiler passes `-g`
rpath = false # controls whether the compiler passes `-C rpath`
lto = false # controls `-C lto` for binaries and staticlibs
debug-assertions = true # controls whether debug assertions are enabled
codegen-units = 1 # controls whether the compiler passes `-C codegen-units`
# `codegen-units` is ignored when `lto = true`
panic = 'unwind' # panic strategy (`-C panic=...`), can also be 'abort'
# The release profile, used for `cargo build --release`.
[profile.release]
opt-level = 3
debug = false
rpath = false
lto = false
debug-assertions = false
codegen-units = 1
panic = 'unwind'
# The testing profile, used for `cargo test`.
[profile.test]
opt-level = 0
debug = true
rpath = false
lto = false
debug-assertions = true
codegen-units = 1
panic = 'unwind'
# The benchmarking profile, used for `cargo bench`.
[profile.bench]
opt-level = 3
debug = false
rpath = false
lto = false
debug-assertions = false
codegen-units = 1
panic = 'unwind'
# The documentation profile, used for `cargo doc`.
[profile.doc]
opt-level = 0
debug = true
rpath = false
lto = false
debug-assertions = true
codegen-units = 1
panic = 'unwind'
```
# The `[features]` section
Cargo supports features to allow expression of:
* conditional compilation options (usable through `cfg` attributes);
* optional dependencies, which enhance a package, but are not required; and
* clusters of optional dependencies, such as `postgres`, that would include the
`postgres` package, the `postgres-macros` package, and possibly other packages
(such as development-time mocking libraries, debugging tools, etc.).
A feature of a package is either an optional dependency, or a set of other
features. The format for specifying features is:
```toml
[package]
name = "awesome"
[features]
# The default set of optional packages. Most people will want to use these
# packages, but they are strictly optional. Note that `session` is not a package
# but rather another feature listed in this manifest.
default = ["jquery", "uglifier", "session"]
# A feature with no dependencies is used mainly for conditional compilation,
# like `#[cfg(feature = "go-faster")]`.
go-faster = []
# The `secure-password` feature depends on the bcrypt package. This aliasing
# will allow people to talk about the feature in a higher-level way and allow
# this package to add more requirements to the feature in the future.
secure-password = ["bcrypt"]
# Features can be used to reexport features of other packages. The `session`
# feature of package `awesome` will ensure that the `session` feature of the
# package `cookie` is also enabled.
session = ["cookie/session"]
[dependencies]
# These packages are mandatory and form the core of this package’s distribution.
cookie = "1.2.0"
oauth = "1.1.0"
route-recognizer = "=2.1.0"
# A list of all of the optional dependencies, some of which are included in the
# above `features`. They can be opted into by apps.
jquery = { version = "1.0.2", optional = true }
uglifier = { version = "1.5.3", optional = true }
bcrypt = { version = "*", optional = true }
civet = { version = "*", optional = true }
```
To use the package `awesome`:
```toml
[dependencies.awesome]
version = "1.3.5"
default-features = false # do not include the default features, and optionally
# cherry-pick individual features
features = ["secure-password", "civet"]
```
## Rules
The usage of features is subject to a few rules:
* Feature names must not conflict with other package names in the manifest. This
is because they are opted into via `features = [...]`, which only has a single
namespace.
* With the exception of the `default` feature, all features are opt-in. To opt
out of the default feature, use `default-features = false` and cherry-pick
individual features.
* Feature groups are not allowed to cyclically depend on one another.
* Dev-dependencies cannot be optional.
* Features groups can only reference optional dependencies.
* When a feature is selected, Cargo will call `rustc` with `--cfg
feature="${feature_name}"`. If a feature group is included, it and all of its
individual features will be included. This can be tested in code via
`#[cfg(feature = "foo")]`.
Note that it is explicitly allowed for features to not actually activate any
optional dependencies. This allows packages to internally enable/disable
features without requiring a new dependency.
## Usage in end products
One major use-case for this feature is specifying optional features in
end-products. For example, the Servo project may want to include optional
features that people can enable or disable when they build it.
In that case, Servo will describe features in its `Cargo.toml` and they can be
enabled using command-line flags:
```
$ cargo build --release --features "shumway pdf"
```
Default features could be excluded using `--no-default-features`.
## Usage in packages
In most cases, the concept of *optional dependency* in a library is best
expressed as a separate package that the top-level application depends on.
However, high-level packages, like Iron or Piston, may want the ability to
curate a number of packages for easy installation. The current Cargo system
allows them to curate a number of mandatory dependencies into a single package
for easy installation.
In some cases, packages may want to provide additional curation for optional
dependencies:
* grouping a number of low-level optional dependencies together into a single
high-level feature;
* specifying packages that are recommended (or suggested) to be included by
users of the package; and
* including a feature (like `secure-password` in the motivating example) that
will only work if an optional dependency is available, and would be difficult
to implement as a separate package (for example, it may be overly difficult to
design an IO package to be completely decoupled from OpenSSL, with opt-in via
the inclusion of a separate package).
In almost all cases, it is an antipattern to use these features outside of
high-level packages that are designed for curation. If a feature is optional, it
can almost certainly be expressed as a separate package.
# The `[workspace]` section
Projects can define a workspace which is a set of crates that will all share the
same `Cargo.lock` and output directory. The `[workspace]` table can be defined
as:
```toml
[workspace]
# Optional key, inferred if not present
members = ["path/to/member1", "path/to/member2"]
```
Workspaces were added to Cargo as part [RFC 1525] and have a number of
properties:
* A workspace can contain multiple crates where one of them is the root crate.
* The root crate's `Cargo.toml` contains the `[workspace]` table, but is not
required to have other configuration.
* Whenever any crate in the workspace is compiled, output is placed next to the
root crate's `Cargo.toml`.
* The lock file for all crates in the workspace resides next to the root crate's
`Cargo.toml`.
* The `[replace]` section in `Cargo.toml` is only recognized at the workspace
root crate, it's ignored in member crates' manifests.
[RFC 1525]: https://github.com/rust-lang/rfcs/blob/master/text/1525-cargo-workspace.md
The root crate of a workspace, indicated by the presence of `[workspace]` in
its manifest, is responsible for defining the entire workspace (listing all
members). This can be done through the `members` key, and if it is omitted then
members are implicitly included through all `path` dependencies. Note that
members of the workspaces listed explicitly will also have their path
dependencies included in the workspace.
The `package.workspace` manifest key (described above) is used in member crates
to point at a workspace's root crate. If this key is omitted then it is inferred
to be the first crate whose manifest contains `[workspace]` upwards in the
filesystem.
A crate may either specify `package.workspace` or specify `[workspace]`. That
is, a crate cannot both be a root crate in a workspace (contain `[workspace]`)
and also be a member crate of another workspace (contain `package.workspace`).
Most of the time workspaces will not need to be dealt with as `cargo new` and
`cargo init` will handle workspace configuration automatically.
# The project layout
If your project is an executable, name the main source file `src/main.rs`. If it
is a library, name the main source file `src/lib.rs`.
Cargo will also treat any files located in `src/bin/*.rs` as executables.
Your project can optionally contain folders named `examples`, `tests`, and
`benches`, which Cargo will treat as containing example executable files,
integration tests, and benchmarks respectively.
```notrust
▾ src/ # directory containing source files
lib.rs # the main entry point for libraries and packages
main.rs # the main entry point for projects producing executables
▾ bin/ # (optional) directory containing additional executables
*.rs
▾ examples/ # (optional) examples
*.rs
▾ tests/ # (optional) integration tests
*.rs
▾ benches/ # (optional) benchmarks
*.rs
```
To structure your code after you've created the files and folders for your project, you should remember to use Rust's module system, which you can read about in [the book](https://doc.rust-lang.org/book/crates-and-modules.html).
# Examples
Files located under `examples` are example uses of the functionality provided by
the library. When compiled, they are placed in the `target/examples` directory.
They must compile as executables (with a `main()` function) and load in the
library by using `extern crate <library-name>`. They are compiled when you run
your tests to protect them from bitrotting.
You can run individual examples with the command `cargo run --example
<example-name>`.
# Tests
When you run `cargo test`, Cargo will:
* compile and run your library’s unit tests, which are in the files reachable
from `lib.rs` (naturally, any sections marked with `#[cfg(test)]` will be
considered at this stage);
* compile and run your library’s documentation tests, which are embedded inside
of documentation blocks;
* compile and run your library’s [integration tests](#integration-tests); and
* compile your library’s examples.
## Integration tests
Each file in `tests/*.rs` is an integration test. When you run `cargo test`,
Cargo will compile each of these files as a separate crate. The crate can link
to your library by using `extern crate <library-name>`, like any other code that
depends on it.
Cargo will not automatically compile files inside subdirectories of `tests`, but
an integration test can import modules from these directories as usual. For
example, if you want several integration tests to share some code, you can put
the shared code in `tests/common/mod.rs` and then put `mod common;` in each of
the test files.
# Configuring a target
All of the `[[bin]]`, `[lib]`, `[[bench]]`, `[[test]]`, and `[[example]]`
sections support similar configuration for specifying how a target should be
built. The double-bracket sections like `[[bin]]` are array-of-table of
[TOML](https://github.com/toml-lang/toml#array-of-tables), which means you can
write more than one `[[bin]]` section to make several executables in your crate.
The example below uses `[lib]`, but it also applies to all other sections
as well. All values listed are the defaults for that option unless otherwise
specified.
```toml
[package]
# ...
[lib]
# The name of a target is the name of the library that will be generated. This
# is defaulted to the name of the package or project, with any dashes replaced
# with underscores. (Rust `extern crate` declarations reference this name;
# therefore the value must be a valid Rust identifier to be usable.)
name = "foo"
# This field points at where the crate is located, relative to the `Cargo.toml`.
path = "src/lib.rs"
# A flag for enabling unit tests for this target. This is used by `cargo test`.
test = true
# A flag for enabling documentation tests for this target. This is only relevant
# for libraries, it has no effect on other sections. This is used by
# `cargo test`.
doctest = true
# A flag for enabling benchmarks for this target. This is used by `cargo bench`.
bench = true
# A flag for enabling documentation of this target. This is used by `cargo doc`.
doc = true
# If the target is meant to be a compiler plugin, this field must be set to true
# for Cargo to correctly compile it and make it available for all dependencies.
plugin = false
# If the target is meant to be a "macros 1.1" procedural macro, this field must
# be set to true.
proc-macro = false
# If set to false, `cargo test` will omit the `--test` flag to rustc, which
# stops it from generating a test harness. This is useful when the binary being
# built manages the test runner itself.
harness = true
```
# Building dynamic or static libraries
If your project produces a library, you can specify which kind of library to
build by explicitly listing the library in your `Cargo.toml`:
```toml
# ...
[lib]
name = "..."
crate-type = ["dylib"] # could be `staticlib` as well
```
The available options are `dylib`, `rlib`, `staticlib`, `cdylib`, and
`proc-macro`. You should only use this option in a project. Cargo will always
compile packages (dependencies) based on the requirements of the project that
includes them.
You can read more about the different crate types in the
[Rust Reference Manual](https://doc.rust-lang.org/reference.html#linkage)
# The `[replace]` Section
This section of Cargo.toml can be used to [override dependencies][replace] with
other copies. The syntax is similar to the `[dependencies]` section:
```toml
[replace]
"foo:0.1.0" = { git = 'https://github.com/example/foo' }
"bar:1.0.2" = { path = 'my/local/bar' }
```
Each key in the `[replace]` table is a [package id
specification](pkgid-spec.html) which allows arbitrarily choosing a node in the
dependency graph to override. The value of each key is the same as the
`[dependencies]` syntax for specifying dependencies, except that you can't
specify features. Note that when a crate is overridden the copy it's overridden
with must have both the same name and version, but it can come from a different
source (e.g. git or a local path).
More information about overriding dependencies can be found in the [overriding
dependencies][replace] section of the documentation.
[replace]: specifying-dependencies.html#overriding-dependencies