Crate proc_macro2 [−] [src]
A "shim crate" intended to multiplex the proc_macro
API on to stable
Rust.
Procedural macros in Rust operate over the upstream
proc_macro::TokenStream
type. This type currently is quite
conservative and exposed no internal implementation details. Nightly
compilers, however, contain a much richer interface. This richer interface
allows fine-grained inspection of the token stream which avoids
stringification/re-lexing and also preserves span information.
The upcoming APIs added to proc_macro
upstream are the foundation for
productive procedural macros in the ecosystem. To help prepare the ecosystem
for using them this crate serves to both compile on stable and nightly and
mirrors the API-to-be. The intention is that procedural macros which switch
to use this crate will be trivially able to switch to the upstream
proc_macro
crate once its API stabilizes.
In the meantime this crate also has a nightly
Cargo feature which
enables it to reimplement itself with the unstable API of proc_macro
.
This'll allow immediate usage of the beneficial upstream API, particularly
around preserving span information.
Unstable Features
proc-macro2
supports exporting some methods from proc_macro
which are
currently highly unstable, and may not be stabilized in the first pass of
proc_macro
stabilizations. These features are not exported by default.
Minor versions of proc-macro2
may make breaking changes to them at any
time.
To enable these features, the procmacro2_semver_exempt
config flag must be
passed to rustc.
RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo build
Note that this must not only be done for your crate, but for any crate that depends on your crate. This infectious nature is intentional, as it serves as a reminder that you are outside of the normal semver guarantees.
Modules
token_stream |
Public implementation details for the |
Structs
Group |
A delimited token stream. |
Ident |
A word of Rust code, which may be a keyword or legal variable name. |
LexError |
Error returned from |
Literal |
A literal string ( |
Punct |
An |
Span |
A region of source code, along with macro expansion information. |
TokenStream |
An abstract stream of tokens, or more concretely a sequence of token trees. |
Enums
Delimiter |
Describes how a sequence of token trees is delimited. |
Spacing |
Whether an |
TokenTree |
A single token or a delimited sequence of token trees (e.g. |