# fmt.rs - source
Source of the Rust file `/home/justine/.cargo/registry/src/github.com-1ecc6299db9ec823/thiserror-impl-1.0.38/src/fmt.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::ast::Field;
    use crate::attr::{Display, Trait};
    use proc_macro2::TokenTree;
    use quote::{format_ident, quote_spanned};
    use std::collections::{BTreeSet as Set, HashMap as Map};
    use syn::ext::IdentExt;
    use syn::parse::{ParseStream, Parser};
    use syn::{Ident, Index, LitStr, Member, Result, Token};

    impl Display<'_> {
        // Transform `"error {var}"` to `"error {}", var`.
        pub fn expand_shorthand(&mut self, fields: &[Field]) {
            let raw_args = self.args.clone();
            let mut named_args = explicit_named_args.parse2(raw_args).unwrap();
            let mut member_index = Map::new();
            for (i, field) in fields.iter().enumerate() {
                member_index.insert(&field.member, i);
            }

            let span = self.fmt.span();
            let fmt = self.fmt.value();
            let mut read = fmt.as_str();
            let mut out = String::new();
            let mut args = self.args.clone();
            let mut has_bonus_display = false;
            let mut implied_bounds = Set::new();

            let mut has_trailing_comma = false;
            if let Some(TokenTree::Punct(punct)) = args.clone().into_iter().last() {
                if punct.as_char() == ',' {
                    has_trailing_comma = true;
                }
            }

            while let Some(brace) = read.find('{') {
                out += &read[..brace + 1];
                read = &read[brace + 1..];
                if read.starts_with('{') {
                    out.push('{');
                    read = &read[1..];
                    continue;
                }
                let next = match read.chars().next() {
                    Some(next) => next,
                    None => return,
                };
                let member = match next {
                    '0'..='9' => {
                        let int = take_int(&mut read);
                        let member = match int.parse::<u32>() {
                            Ok(index) => Member::Unnamed(Index { index, span }),
                            Err(_) => return,
                        };
                        if !member_index.contains_key(&member) {
                            out += &int;
                            continue;
                        }
                        member
                    }
                    'a'..='z' | 'A'..='Z' | '_' => {
                        let mut ident = take_ident(&mut read);
                        ident.set_span(span);
                        Member::Named(ident)
                    }
                    _ => continue,
                };
                if let Some(&field) = member_index.get(&member) {
                    let end_spec = match read.find('}') {
                        Some(end_spec) => end_spec,
                        None => return,
                    };
                    let bound = match read[..end_spec].chars().next_back() {
                        Some('?') => Trait::Debug,
                        Some('o') => Trait::Octal,
                        Some('x') => Trait::LowerHex,
                        Some('X') => Trait::UpperHex,
                        Some('p') => Trait::Pointer,
                        Some('b') => Trait::Binary,
                        Some('e') => Trait::LowerExp,
                        Some('E') => Trait::UpperExp,
                        Some(_) | None => Trait::Display,
                    };
                    implied_bounds.insert((field, bound));
                }
                let local = match &member {
                    Member::Unnamed(index) => format_ident!("_{}", index),
                    Member::Named(ident) => ident.clone(),
                };
                let mut formatvar = local.clone();
                if formatvar.to_string().starts_with("r#") {
                    formatvar = format_ident!("r_{}", formatvar);
                }
                if formatvar.to_string().starts_with('_') {
                    // Work around leading underscore being rejected by 1.40 and
                    // older compilers. https://github.com/rust-lang/rust/pull/66847
                    formatvar = format_ident!("field_{}", formatvar);
                }
                out += &formatvar.to_string();
                if !named_args.insert(formatvar.clone()) {
                    // Already specified in the format argument list.
                    continue;
                }
                if !has_trailing_comma {
                    args.extend(quote_spanned!(span=> ,));
                }
                args.extend(quote_spanned!(span=> #formatvar = #local));
                if read.starts_with('}') && member_index.contains_key(&member) {
                    has_bonus_display = true;
                    args.extend(quote_spanned!(span=> .as_display()));
                }
                has_trailing_comma = false;
            }

            out += read;
            self.fmt = LitStr::new(&out, self.fmt.span());
            self.args = args;
            self.has_bonus_display = has_bonus_display;
            self.implied_bounds = implied_bounds;
        }
    }

    fn explicit_named_args(input: ParseStream) -> Result<Set<Ident>> {
        let mut named_args = Set::new();

        while !input.is_empty() {
            if input.peek(Token![,]) && input.peek2(Ident::peek_any) && input.peek3(Token![=]) {
                input.parse::<Token![,]>()?;
                let ident = input.call(Ident::parse_any)?;
                input.parse::<Token![=]>()?;
                named_args.insert(ident);
            } else {
                input.parse::<TokenTree>()?;
            }
        }

        Ok(named_args)
    }

    fn take_int(read: &mut &str) -> String {
        let mut int = String::new();
        for (i, ch) in read.char_indices() {
            match ch {
                '0'..='9' => int.push(ch),
                _ => {
                    *read = &read[i..];
                    break;
                }
            }
        }
        int
    }

    fn take_ident(read: &mut &str) -> Ident {
        let mut ident = String::new();
        let raw = read.starts_with("r#");
        if raw {
            ident.push_str("r#");
            *read = &read[2..];
        }
        for (i, ch) in read.char_indices() {
            match ch {
                'a'..='z' | 'A'..='Z' | '0'..='9' | '_' => ident.push(ch),
                _ => {
                    *read = &read[i..];
                    break;
                }
            }
        }
        Ident::parse_any.parse_str(&ident).unwrap()
    }