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docs/uucore_macros ~ improve commentary/documentation

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This commit is contained in:
Roy Ivy III 2020-05-06 12:59:53 -05:00
parent c32ff9e8bb
commit cf2fcd8dc1
1 changed files with 24 additions and 24 deletions
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48
src/uucore/src/uucore_procs/src/lib.rs
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@ -1,9 +1,10 @@
extern crate proc_macro;
// spell-checker:ignore () sigpipe uucore uumain
// spell-checker:ignore () SIGPIPE uucore uumain uutils
// 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>
//## rust proc-macro background info
//* 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,
@ -17,30 +18,29 @@ impl syn::parse::Parse for Tokens {
}
}
// main!( EXPR )
// generates a `main()` function for utilities within the uutils group
// EXPR == syn::Expr::Lit::String | syn::Expr::Path::Ident ~ EXPR contains the location of the utility `uumain()` function
//* for future use of "eager" macros and more generic use, EXPR may be in either STRING or IDENT form
//* for ease-of-use, the trailing "::uumain" is optional and will be added if needed
#[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);
// match EXPR as a string literal or an ident path, o/w panic!()
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()
syn::Expr::Lit(expr) => match expr.lit {
syn::Lit::Str(ref lit) => {
let mut s = lit.value();
if !s.ends_with("::uumain") {
s += "::uumain";
}
_ => panic!(),
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 {
@ -50,13 +50,13 @@ pub fn main(stream: proc_macro::TokenStream) -> proc_macro::TokenStream {
_ => panic!(),
};
let f = quote::quote! { #expr(uucore::args().collect()) };
// eprintln!("f = {:?}", f);
// generate a uutils utility `main()` function, tailored for the calling utility
let result = quote::quote! {
fn main() {
use std::io::Write;
uucore::panic::mute_sigpipe_panic();
let code = #f;
std::io::stdout().flush().expect("could not flush stdout");
uucore::panic::mute_sigpipe_panic(); // suppress extraneous error output for SIGPIPE failures/panics
let code = #f; // execute utility code
std::io::stdout().flush().expect("could not flush stdout"); // (defensively) flush stdout for utility prior to exit; see <https://github.com/rust-lang/rust/issues/23818>
std::process::exit(code);
}
};