Rather disgusting hack to build without log dependencies

- Unfortunately there's a dependency on log via syntex_errors, so we
don't get rid of it all
- I can't find a more sensible way to set dependencies based on whether
you're building the lib or bin
- So `--no-default-features` means you need to know what you're doing,
as only the lib will build without the logging crates for now
- The replacement log macros are pretty gross too, but they show a proof
of concept ;-)

Cargo.toml

@@ -26,12 +26,18 @@ cfg-if = "0.1.0"
 clang-sys = "0.8.0"
 lazy_static = "0.1.*"
 libc = "0.2"
-log = "0.3"
-env_logger = "0.3"
 rustc-serialize = "0.3.19"
 syntex_syntax = "0.44"
 regex = "0.1"
 
+[dependencies.log]
+version = "0.3"
+optional = true
+
+[dependencies.env_logger]
+version = "0.3"
+optional = true
+
 [dependencies.aster]
 features = ["with-syntex"]
 version = "0.28"
@@ -45,6 +51,8 @@ features = ["with-syntex"]
 version = "0.20"
 
 [features]
+default = ["logging"]
+logging = ["log", "env_logger"]
 llvm_stable = []
 static = []
 # This feature only exists for CI -- don't use it!

src/lib.rs

@@ -31,10 +31,46 @@ extern crate clang_sys;
 extern crate libc;
 extern crate regex;
 #[macro_use]
-extern crate log;
-#[macro_use]
 extern crate lazy_static;
 
+cfg_if! {
+    if #[cfg(feature = "logging")] {
+#[macro_use]
+extern crate log;
+    } else {
+        macro_rules! log {
+            (target: $target:expr, $($arg:tt)+) => (
+                let _ = format_args!($($arg)+);
+            );
+            ($($arg:tt)+) => (log!(target: module_path!(), $($arg)+))
+        }
+        macro_rules! debug {
+            (target: $target:expr, $($arg:tt)*) => (
+                log!(target: $target, $($arg)*);
+            );
+            ($($arg:tt)*) => (
+                log!($($arg)*);
+            )
+        }
+        macro_rules! warn {
+            (target: $target:expr, $($arg:tt)*) => (
+                log!(target: $target, $($arg)*);
+            );
+            ($($arg:tt)*) => (
+                log!($($arg)*);
+            )
+        }
+        macro_rules! error {
+            (target: $target:expr, $($arg:tt)*) => (
+                log!(target: $target, $($arg)*);
+            );
+            ($($arg:tt)*) => (
+                log!($($arg)*);
+            )
+        }
+    }
+}
+
 // A macro to declare an internal module for which we *must* provide
 // documentation for. If we are building with the "_docs" feature, then the
 // module is declared public, and our `#![deny(missing_docs)]` pragma applies to