#[macro_use(info)] raise error: macro undefined: 'log!'

[Narann]

Code:

#[macro_use(info)]
extern crate log;

Error:

<log macros>:4:1: 4:4 error: macro undefined: 'log!'
<log macros>:4 log ! ( $ crate:: LogLevel:: Info , $ ( $ arg ) * ) ; )
               ^~~

I will use #[macro_use] for now but I thought it was interesting to limit the macro to import in the namespace

$rustc --version
rustc 1.1.0-dev

[Amanieu]

The info, warn, error and trace macros all use the log macro internally, so just specifying #[macro_use(info, log)] should work.

[dtolnay]

This is annoying. Is there a way this could be handled better using $crate? Have info! expand to an #[inline(always)] #[doc(hidden)] helper rather than to log!.

[sfackler]

log! needs to be a macro because it invokes file!, module_path! and line!. We could duplicate log!'s logic into info! etc which would avoid the import issue.

How many people actually selectively import log macros, though?

[dtolnay]

Relevant API guidelines issue: rust-lang/api-guidelines#68

[seanmonstar]

Rust issue: rust-lang/rust#25003

[mjkillough]

log! needs to be a macro because it invokes file!, module_path! and line!. We could duplicate log!'s logic into info! etc which would avoid the import issue.

The bulk of the log! macro could be moved into an inlined helper function which is used by the log!/error!/... macros, with each passing the output of file!/module_path!/line! in as arguments to the function. There wouldn't be much duplication, but the helper function would have to be part of the public API of the log crate, which is a little ugly.

However, I'd be tempted to just duplicate log!'s logic into the other macros. There isn't that much to it.

[richard-uk1]

This is going to come up with Rust 2018 - because you now import macros, the info! macro will fail unless you also import the log! macro.

EDIT: I don't really see any way around the problem, unless the inner macro expansion happens before the macro is expanded in the consumer crate. Otherwise it's hard to support both versions.