change ~ add proc-macros module (uucore_procs) with uucore_procs::main()

- `uucore_procs::main!(UUTIL_NAME)` allows simple, consistent instantiation of `main()` for uutils

src/uucore/Cargo.toml

@@ -18,6 +18,9 @@ travis-ci = { repository = "uutils/uucore" }
 [lib]
 path="src/lib/lib.rs"
 
+[workspace]
+members=["src/uucore_procs"]
+
 [dependencies]
 dunce = "1.0.0"
 getopts = "<= 0.2.21"

src/uucore/src/uucore_procs/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "uucore_procs"
+version = "0.0.2"
+authors = []
+license = "MIT"
+description = "`uucore` proc-macros for use by various uutils projects"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0"
+quote = "1.0"
+syn = { version="1.0" } ## debug: use `features=["extra-traits"]` to add Debug traits to structs (for `println!("{:?}", ...)`)
+
+[features]
+default = []
+debug = []

src/uucore/src/uucore_procs/src/lib.rs

@@ -0,0 +1,64 @@
+extern crate proc_macro;
+
+// spell-checker:ignore () sigpipe uucore uumain
+
+// ref: <https://dev.to/naufraghi/procedural-macro-in-rust-101-k3f> @@ <http://archive.is/Vbr5e>
+// ref: [path construction from LitStr](https://oschwald.github.io/maxminddb-rust/syn/struct.LitStr.html) @@ <http://archive.is/8YDua>
+
+struct Tokens {
+    expr: syn::Expr,
+}
+
+impl syn::parse::Parse for Tokens {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        Ok(Tokens {
+            expr: input.parse()?,
+        })
+    }
+}
+
+#[proc_macro]
+pub fn main(stream: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let Tokens { expr } = syn::parse_macro_input!(stream as Tokens);
+    // eprintln!("expr={:?}", expr);
+    let expr = match expr {
+        syn::Expr::Lit(expr) => {
+            // eprintln!("found Expr::Lit => {:?}", expr);
+            match expr.lit {
+                syn::Lit::Str(ref lit) => {
+                    let mut s = lit.value();
+                    if !s.ends_with("::uumain") {
+                        s += "::uumain";
+                    }
+                    syn::LitStr::new(&s, proc_macro2::Span::call_site())
+                        .parse()
+                        .unwrap()
+                }
+                _ => panic!(),
+            }
+        }
+        syn::Expr::Path(expr) => {
+            // eprintln!("found Expr::Path => {:?}", expr);
+            // let i = &expr.path.segments.last().unwrap().ident;
+            // eprintln!("... i => {:?}", i);
+            if &expr.path.segments.last().unwrap().ident.to_string() != "uumain" {
+                syn::parse_quote!( #expr::uumain )
+            } else {
+                expr
+            }
+        }
+        _ => panic!(),
+    };
+    let f = quote::quote! { #expr(uucore::args().collect()) };
+    // eprintln!("f = {:?}", f);
+    let result = quote::quote! {
+        fn main() {
+            use std::io::Write;
+            uucore::panic::install_sigpipe_hook();
+            let code = #f;
+            std::io::stdout().flush().expect("could not flush stdout");
+            std::process::exit(code);
+        }
+    };
+    proc_macro::TokenStream::from(result)
+}