Attribute crate_type 

Specifies the type of a crate.

Written as an inner attribute at the top of the crate root, crate_type is used to specify the type of a crate.

#![crate_type = "lib"]

The specified crate type must be a known crate type (for the list of valid crate types, see Linkage), otherwise rustc reports an error:

error: invalid `crate_type` value
 --> typo.rs:1:17
  |
1 | #![crate_type = "dyllib"]
  |                 ^^^^^^^^ help: did you mean: `"dylib"`
  |
  = note: `#[deny(unknown_crate_types)]` on by default

In one session of compilation, the compiler can generate multiple artifacts through the use of either command line flags or the crate_type attribute. Note that the output artifacts are stackable in the sense that if multiple are specified, then the compiler will produce each form of output without having to recompile.

For example, if a crate has the following crate_type attributes:

#![crate_type = "staticlib"]
#![crate_type = "dylib"]

Then the compiler will build both a static library and a dynamic library.

If the flag --test is passed, the crate_type attributes will be ignored, and the crate will be built as a test harness.

For [lib]/[[bin]] targets Cargo passes --crate-type derived from the target ([lib] crate-type, [[bin]]); test/bench targets are compiled with --test. In all these cases the attribute is ignored.

Note that the bin type and proc-macro type cannot be mixed with any other crate type, otherwise rustc reports an error:

error: cannot mix `bin` crate type with others

error: cannot mix `proc-macro` crate type with others

In general, crate type bin and crate type lib should be sufficient for all compilation needs, and the other options are just available if more fine-grained control is desired over the output format of a crate.

For more information, see the Reference on Linkage.