Implement --to-clipboard for macOS

* The pasteboard crate has been added to Cargo.toml.
* In src/bin, use of this crate is conditional on target_os = "macOS"
* The implementation of dump_image_to_clipboard is exactly like the linux one, except instead of shelling out to xclip, we call the unsafe function:

Pasteboard::Image.copy(temp.path().to_str().unwrap());

Hat tip to @segeljakt for pasteboard :)

Cargo.toml

@@ -19,6 +19,7 @@ tempfile = "3.1.0"
 conv = "0.3.3"
 euclid = "0.20"
 log = "0.4.8"
+pasteboard = "0.1.1"
 
 [lib]
 name = "silicon"

src/bin.rs

@@ -12,6 +12,8 @@ use syntect::easy::HighlightLines;
 use syntect::util::LinesWithEndings;
 #[cfg(target_os = "linux")]
 use {image::ImageOutputFormat, std::process::Command};
+#[cfg(target_os = "macos")]
+use {image::ImageOutputFormat, pasteboard::Pasteboard};
 
 pub mod blur;
 pub mod config;
@@ -37,7 +39,17 @@ pub fn dump_image_to_clipboard(image: &DynamicImage) -> Result<(), Error> {
     Ok(())
 }
 
-#[cfg(not(target_os = "linux"))]
+#[cfg(target_os = "macos")]
+pub fn dump_image_to_clipboard(image: &DynamicImage) -> Result<(), Error> {
+    let mut temp = tempfile::NamedTempFile::new()?;
+    image.write_to(&mut temp, ImageOutputFormat::PNG)?;
+    unsafe {
+        Pasteboard::Image.copy(temp.path().to_str().unwrap());
+    }
+    Ok(())
+}
+
+#[cfg(not(any(target_os = "linux", target_os = "macos")))]
 pub fn dump_image_to_clipboard(_image: &DynamicImage) -> Result<(), Error> {
     Err(format_err!(
         "This feature hasn't been implemented for your system"