Crate rocket_codegen [] [src]

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:

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

route := METHOD? '(' ('path' '=')? path (',' kv_param)* ')'

path := URI_SEG
      | '?' DYNAMIC_PARAM
      | path '/' path
      (string literal)

kv_param := 'rank' '=' INTEGER
          | 'format' '=' STRING
          | 'data' '=' DYNAMIC_PARAM

INTEGER := isize, as defined by Rust
STRING := UTF-8 string literal, as defined by Rust
IDENT := valid identifier, as defined by Rust

URI_SEG := valid HTTP URI Segment
DYNAMIC_PARAM := '<' IDENT '..'? '>' (string literal)

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:

error := INTEGER

A use of the error attribute looks like:


Custom Derives

This crate implements the following custom derives:


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:

form := 'field' '=' '"' IDENT '"'

IDENT := valid identifier, as defined by Rust

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:

The syntax for both of these is defined as:

macro := PATH (',' macro)*

PATH := a path, as defined by Rust


This crate implements the following lints:

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:




Compiler hook for Rust to register plugins.