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#![feature(extern_crate_item_prelude)]
#![feature(proc_macro_span)]
extern crate proc_macro;
use std::fmt::{self, Display, Write};
use std::iter::FromIterator;
use proc_macro::{Delimiter, Group, Ident, LineColumn, Literal, Punct, TokenStream, TokenTree};
pub trait FaithfulDisplay {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error>;
}
impl FaithfulDisplay for Ident {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
let current_span = self.span();
whitespace_adjust_span(f, prev_span, current_span.start())?;
self.fmt(f).map(|_| current_span.end())
}
}
impl FaithfulDisplay for Literal {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
let current_span = self.span();
whitespace_adjust_span(f, prev_span, current_span.start())?;
self.fmt(f).map(|_| current_span.end())
}
}
impl FaithfulDisplay for Punct {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
let current_span = self.span();
whitespace_adjust_span(f, prev_span, current_span.start())?;
f.write_char(self.as_char()).map(|_| current_span.end())
}
}
impl FaithfulDisplay for Group {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
let current_span = self.span_open();
whitespace_adjust_span(f, prev_span, current_span.start())?;
match self.delimiter() {
Delimiter::Parenthesis => {
faithful_delimited(f, '(', ')', self.stream(), current_span.end(), self.span_close().start())?;
}
Delimiter::Brace => {
faithful_delimited(f, '{', '}', self.stream(), current_span.end(), self.span_close().start())?;
}
Delimiter::Bracket => {
faithful_delimited(f, '[', ']', self.stream(), current_span.end(), self.span_close().start())?;
}
Delimiter::None => {
let line_col = self.stream().faithful_fmt(f, current_span.end())?;
whitespace_adjust_span(f, prev_span, line_col)?;
}
}
Ok(self.span_close().end())
}
}
impl FaithfulDisplay for TokenStream {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
let mut current_span = prev_span;
for tree in self.clone() {
current_span = tree.faithful_fmt(f, current_span)?;
}
Ok(current_span)
}
}
impl FaithfulDisplay for TokenTree {
fn faithful_fmt(&self, f: &mut fmt::Formatter, prev_span: LineColumn) -> Result<LineColumn, fmt::Error> {
match self {
TokenTree::Group(gr) => gr.faithful_fmt(f, prev_span),
TokenTree::Ident(ident) => ident.faithful_fmt(f, prev_span),
TokenTree::Punct(p) => p.faithful_fmt(f, prev_span),
TokenTree::Literal(lit) => lit.faithful_fmt(f, prev_span)
}
}
}
pub fn faithful_display<'a>(stream: &'a TokenStream) -> impl Display + 'a {
struct D<'a>(&'a TokenStream);
impl<'a> fmt::Display for D<'a> {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
let mut iter = self.0.clone().into_iter();
let first = iter.next();
if let Some(tree) = first {
let first_line_col = tree.span().start();
let line_col = tree.faithful_fmt(f, first_line_col)?;
TokenStream::from_iter(iter).faithful_fmt(f, line_col).map(|_| ())
} else {
Ok(())
}
}
}
D(stream)
}
fn whitespace_adjust_span(
f: &mut fmt::Formatter,
prev_span: LineColumn,
current_span: LineColumn
) -> Result<(), fmt::Error> {
if current_span.line == prev_span.line {
let nb_spaces = current_span.column - prev_span.column;
f.write_str(" ".repeat(nb_spaces).as_str())
} else {
let nb_newlines = current_span.line - prev_span.line;
let nb_spaces = current_span.column;
f.write_str("\n".repeat(nb_newlines).as_str())?;
f.write_str(" ".repeat(nb_spaces).as_str())
}
}
fn faithful_delimited(
f: &mut fmt::Formatter,
del_first: char,
del_end: char,
stream: TokenStream,
prev_span: LineColumn,
final_span: LineColumn
) -> Result<(), fmt::Error> {
f.write_char(del_first)?;
let current_span = stream.faithful_fmt(f, prev_span)?;
whitespace_adjust_span(f, current_span, final_span)?;
f.write_char(del_end)
}