lib: Add a way to override rustfmt path.

I'll need it to format some stuff on mozilla-central.

Author: emilio

src/lib.rs

@@ -1079,6 +1079,12 @@ impl Builder {
         self
     }
 
+    /// Sets an explicit path to rustfmt, to be used when rustfmt is enabled.
+    pub fn with_rustfmt<P: Into<PathBuf>>(mut self, path: P) -> Self {
+        self.options.rustfmt_path = Some(path.into());
+        self
+    }
+
     /// Generate the Rust bindings using the options built up thus far.
     pub fn generate(mut self) -> Result<Bindings, ()> {
         self.options.input_header = self.input_headers.pop();
@@ -1216,6 +1222,9 @@ struct BindgenOptions {
     /// generated code.
     opaque_types: RegexSet,
 
+    /// The explicit rustfmt path.
+    rustfmt_path: Option<PathBuf>,
+
     /// The set of types that we should have bindings for in the generated
     /// code.
     ///
@@ -1441,6 +1450,7 @@ impl Default for BindgenOptions {
             rust_features: rust_target.into(),
             blacklisted_types: Default::default(),
             opaque_types: Default::default(),
+            rustfmt_path: Default::default(),
             whitelisted_types: Default::default(),
             whitelisted_functions: Default::default(),
             whitelisted_vars: Default::default(),
@@ -1709,10 +1719,19 @@ impl Bindings {
             return Ok(Cow::Borrowed(source));
         }
 
-        let rustfmt = which::which("rustfmt")
-            .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_owned()))?;
+        let rustfmt = match self.options.rustfmt_path {
+            Some(ref p) => Cow::Borrowed(p),
+            None => {
+                let path = which::which("rustfmt")
+                    .map_err(|e| {
+                        io::Error::new(io::ErrorKind::Other, e.to_owned())
+                    })?;
+
+                Cow::Owned(path)
+            }
+        };
 
-        let mut cmd = Command::new(rustfmt);
+        let mut cmd = Command::new(&*rustfmt);
 
         cmd
             .stdin(Stdio::piped())