segment.rs - source
Description: Source of the Rust file `/Users/erlendbasso/.cargo/registry/src/github.com-1ecc6299db9ec823/paste-1.0.11/src/segment.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::error::{Error, Result};
    use proc_macro::{token_stream, Delimiter, Ident, Span, TokenTree};
    use std::iter::Peekable;

    pub(crate) enum Segment {
        String(LitStr),
        Apostrophe(Span),
        Env(LitStr),
        Modifier(Colon, Ident),
    }

    pub(crate) struct LitStr {
        pub value: String,
        pub span: Span,
    }

    pub(crate) struct Colon {
        pub span: Span,
    }

    pub(crate) fn parse(tokens: &mut Peekable<token_stream::IntoIter>) -> Result<Vec<Segment>> {
        let mut segments = Vec::new();
        while match tokens.peek() {
            None => false,
            Some(TokenTree::Punct(punct)) => punct.as_char() != '>',
            Some(_) => true,
        } {
            match tokens.next().unwrap() {
                TokenTree::Ident(ident) => {
                    let mut fragment = ident.to_string();
                    if fragment.starts_with("r#") {
                        fragment = fragment.split_off(2);
                    }
                    if fragment == "env"
                        && match tokens.peek() {
                            Some(TokenTree::Punct(punct)) => punct.as_char() == '!',
                            _ => false,
                        }
                    {
                        let bang = tokens.next().unwrap(); // `!`
                        let expect_group = tokens.next();
                        let parenthesized = match &expect_group {
                            Some(TokenTree::Group(group))
                                if group.delimiter() == Delimiter::Parenthesis =>
                            {
                                group
                            }
                            Some(wrong) => return Err(Error::new(wrong.span(), "expected `(`")),
                            None => {
                                return Err(Error::new2(
                                    ident.span(),
                                    bang.span(),
                                    "expected `(` after `env!`",
                                ));
                            }
                        };
                        let mut inner = parenthesized.stream().into_iter();
                        let lit = match inner.next() {
                            Some(TokenTree::Literal(lit)) => lit,
                            Some(wrong) => {
                                return Err(Error::new(wrong.span(), "expected string literal"))
                            }
                            None => {
                                return Err(Error::new2(
                                    ident.span(),
                                    parenthesized.span(),
                                    "expected string literal as argument to env! macro",
                                ))
                            }
                        };
                        let lit_string = lit.to_string();
                        if lit_string.starts_with('"')
                            && lit_string.ends_with('"')
                            && lit_string.len() >= 2
                        {
                            // TODO: maybe handle escape sequences in the string if
                            // someone has a use case.
                            segments.push(Segment::Env(LitStr {
                                value: lit_string[1..lit_string.len() - 1].to_owned(),
                                span: lit.span(),
                            }));
                        } else {
                            return Err(Error::new(lit.span(), "expected string literal"));
                        }
                        if let Some(unexpected) = inner.next() {
                            return Err(Error::new(
                                unexpected.span(),
                                "unexpected token in env! macro",
                            ));
                        }
                    } else {
                        segments.push(Segment::String(LitStr {
                            value: fragment,
                            span: ident.span(),
                        }));
                    }
                }
                TokenTree::Literal(lit) => {
                    segments.push(Segment::String(LitStr {
                        value: lit.to_string(),
                        span: lit.span(),
                    }));
                }
                TokenTree::Punct(punct) => match punct.as_char() {
                    '_' => segments.push(Segment::String(LitStr {
                        value: "_".to_owned(),
                        span: punct.span(),
                    })),
                    '\'' => segments.push(Segment::Apostrophe(punct.span())),
                    ':' => {
                        let colon_span = punct.span();
                        let colon = Colon { span: colon_span };
                        let ident = match tokens.next() {
                            Some(TokenTree::Ident(ident)) => ident,
                            wrong => {
                                let span = wrong.as_ref().map_or(colon_span, TokenTree::span);
                                return Err(Error::new(span, "expected identifier after `:`"));
                            }
                        };
                        segments.push(Segment::Modifier(colon, ident));
                    }
                    _ => return Err(Error::new(punct.span(), "unexpected punct")),
                },
                TokenTree::Group(group) => {
                    if group.delimiter() == Delimiter::None {
                        let mut inner = group.stream().into_iter().peekable();
                        let nested = parse(&mut inner)?;
                        if let Some(unexpected) = inner.next() {
                            return Err(Error::new(unexpected.span(), "unexpected token"));
                        }
                        segments.extend(nested);
                    } else {
                        return Err(Error::new(group.span(), "unexpected token"));
                    }
                }
            }
        }
        Ok(segments)
    }

    pub(crate) fn paste(segments: &[Segment]) -> Result<String> {
        let mut evaluated = Vec::new();
        let mut is_lifetime = false;

        for segment in segments {
            match segment {
                Segment::String(segment) => {
                    evaluated.push(segment.value.clone());
                }
                Segment::Apostrophe(span) => {
                    if is_lifetime {
                        return Err(Error::new(*span, "unexpected lifetime"));
                    }
                    is_lifetime = true;
                }
                Segment::Env(var) => {
                    let resolved = match std::env::var(&var.value) {
                        Ok(resolved) => resolved,
                        Err(_) => {
                            return Err(Error::new(
                                var.span,
                                &format!("no such env var: {:?}", var.value),
                            ));
                        }
                    };
                    let resolved = resolved.replace('-', "_");
                    evaluated.push(resolved);
                }
                Segment::Modifier(colon, ident) => {
                    let last = match evaluated.pop() {
                        Some(last) => last,
                        None => {
                            return Err(Error::new2(colon.span, ident.span(), "unexpected modifier"))
                        }
                    };
                    match ident.to_string().as_str() {
                        "lower" => {
                            evaluated.push(last.to_lowercase());
                        }
                        "upper" => {
                            evaluated.push(last.to_uppercase());
                        }
                        "snake" => {
                            let mut acc = String::new();
                            let mut prev = '_';
                            for ch in last.chars() {
                                if ch.is_uppercase() && prev != '_' {
                                    acc.push('_');
                                }
                                acc.push(ch);
                                prev = ch;
                            }
                            evaluated.push(acc.to_lowercase());
                        }
                        "camel" => {
                            let mut acc = String::new();
                            let mut prev = '_';
                            for ch in last.chars() {
                                if ch != '_' {
                                    if prev == '_' {
                                        for chu in ch.to_uppercase() {
                                            acc.push(chu);
                                        }
                                    } else if prev.is_uppercase() {
                                        for chl in ch.to_lowercase() {
                                            acc.push(chl);
                                        }
                                    } else {
                                        acc.push(ch);
                                    }
                                }
                                prev = ch;
                            }
                            evaluated.push(acc);
                        }
                        _ => {
                            return Err(Error::new2(
                                colon.span,
                                ident.span(),
                                "unsupported modifier",
                            ));
                        }
                    }
                }
            }
        }

        let mut pasted = evaluated.into_iter().collect::<String>();
        if is_lifetime {
            pasted.insert(0, '\'');
        }
        Ok(pasted)
    }