Add macro to get rustc version. (#62)

Add macro to query git-describe. (#62)

Signed-off-by: Jason Volk <jason@zemos.net>

src/macros/git.rs

@@ -0,0 +1,64 @@
+use std::process::Command;
+
+use proc_macro::TokenStream;
+use quote::quote;
+
+pub(super) fn semantic(_args: TokenStream) -> TokenStream {
+	static ARGS: &[&str] = &["describe", "--tags", "--abbrev=1"];
+
+	let output = git(ARGS);
+	let output = output
+		.strip_prefix('v')
+		.map(str::to_string)
+		.unwrap_or(output);
+
+	let output = output
+		.rsplit_once('-')
+		.map(|(s, _)| s)
+		.map(str::to_string)
+		.unwrap_or(output);
+
+	let ret = quote! {
+		static GIT_SEMANTIC: &'static str = #output;
+	};
+
+	ret.into()
+}
+
+pub(super) fn commit(_args: TokenStream) -> TokenStream {
+	static ARGS: &[&str] = &["describe", "--always", "--dirty", "--abbrev=10"];
+
+	let output = git(ARGS);
+	let ret = quote! {
+		static GIT_COMMIT: &'static str = #output;
+	};
+
+	ret.into()
+}
+
+pub(super) fn describe(_args: TokenStream) -> TokenStream {
+	static ARGS: &[&str] =
+		&["describe", "--dirty", "--tags", "--always", "--broken", "--abbrev=10"];
+
+	let output = git(ARGS);
+	let ret = quote! {
+		static GIT_DESCRIBE: &'static str = #output;
+	};
+
+	ret.into()
+}
+
+fn git(args: &[&str]) -> String {
+	Command::new("git")
+		.args(args)
+		.output()
+		.map(|output| {
+			str::from_utf8(&output.stdout)
+				.map(str::trim)
+				.map(String::from)
+				.ok()
+		})
+		.ok()
+		.flatten()
+		.unwrap_or_default()
+}