rocket_codegen 0.3.0

Code generation for the Rocket web framework. failed to build rocket_codegen-0.3.0
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Rocket - Code Generation

This crate implements the code generation portions of Rocket. This includes custom derives, custom attributes, procedural macros, and lints. The documentation here is purely technical. The code generation facilities are documented thoroughly in the Rocket programming guide.

Custom Attributes

This crate implements the following custom attributes:

  • route
  • get
  • put
  • post
  • delete
  • head
  • patch
  • options
  • error

The grammar for all route attributes, including route, get, put, post, delete, head, patch, and options is defined as:

Note that the route attribute takes a method as its first argument, while the remaining do not. That is, route looks like:

#[route(GET, path = "/hello")]

while the equivalent using get looks like:


The syntax for the error attribute is:

A use of the error attribute looks like:


Custom Derives

This crate implements the following custom derives:

  • FromForm


The FromForm derive can be applied to structures with named fields:

struct MyStruct {
    field: usize,
    other: String

Each field's type is required to implement FromFormValue. The derive accepts one field attribute: form, with the following syntax:

When applied, the attribute looks as follows:

struct MyStruct {
    field: usize,
    #[form(field = "renamed_field")]
    other: String

The derive generates an implementation for the FromForm trait. The implementation parses a form whose field names match the field names of the structure on which the derive was applied. Each field's value is parsed with the FromFormValue implementation of the field's type. The FromForm implementation succeeds only when all of the field parses succeed.

The form field attribute can be used to direct that a different incoming field name is expected. In this case, the attribute's field name is used instead of the structure's field name when parsing a form.

Procedural Macros

This crate implements the following procedural macros:

  • routes
  • errors

The syntax for both of these is defined as:


This crate implements the following lints:

  • unmounted_route: defaults to warn

    emits a warning when a declared route is not mounted

  • unmanaged_state: defaults to warn

    emits a warning when a State<T> request guest is used in a mounted route without managing a value for T

Debugging Codegen

When the ROCKET_CODEGEN_DEBUG environment variable is set, this crate logs the items it has generated to the console at compile-time. For example, you might run the following to build a Rocket application with codegen logging enabled: