rust/compiler/rustc_builtin_macros/src/concat.rs

use rustc_ast as ast;
use rustc_ast::tokenstream::TokenStream;
use rustc_expand::base::{self, DummyResult};
use rustc_session::errors::report_lit_error;
use rustc_span::symbol::Symbol;

pub fn expand_concat(
    cx: &mut base::ExtCtxt<'_>,
    sp: rustc_span::Span,
    tts: TokenStream,
) -> Box<dyn base::MacResult + 'static> {
    let Some(es) = base::get_exprs_from_tts(cx, tts) else {
        return DummyResult::any(sp);
    };
    let mut accumulator = String::new();
    let mut missing_literal = vec![];
    let mut has_errors = false;
    for e in es {
        match e.kind {
            ast::ExprKind::Lit(token_lit) => match ast::LitKind::from_token_lit(token_lit) {
                Ok(ast::LitKind::Str(s, _) | ast::LitKind::Float(s, _)) => {
                    accumulator.push_str(s.as_str());
                }
                Ok(ast::LitKind::Char(c)) => {
                    accumulator.push(c);
                }
                Ok(ast::LitKind::Int(i, _)) => {
                    accumulator.push_str(&i.to_string());
                }
                Ok(ast::LitKind::Bool(b)) => {
                    accumulator.push_str(&b.to_string());
                }
                Ok(ast::LitKind::Byte(..) | ast::LitKind::ByteStr(..)) => {
                    cx.span_err(e.span, "cannot concatenate a byte string literal");
                    has_errors = true;
                }
                Ok(ast::LitKind::Err) => {
                    has_errors = true;
                }
                Err(err) => {
                    report_lit_error(&cx.sess.parse_sess, err, token_lit, e.span);
                    has_errors = true;
                }
            },
            // We also want to allow negative numeric literals.
            ast::ExprKind::Unary(ast::UnOp::Neg, ref expr) if let ast::ExprKind::Lit(token_lit) = expr.kind => {
                match ast::LitKind::from_token_lit(token_lit) {
                    Ok(ast::LitKind::Int(i, _)) => accumulator.push_str(&format!("-{i}")),
                    Ok(ast::LitKind::Float(f, _)) => accumulator.push_str(&format!("-{f}")),
                    Err(err) => {
                        report_lit_error(&cx.sess.parse_sess, err, token_lit, e.span);
                        has_errors = true;
                    }
                    _ => missing_literal.push(e.span),
                }
            }
            ast::ExprKind::IncludedBytes(..) => {
                cx.span_err(e.span, "cannot concatenate a byte string literal")
            }
            ast::ExprKind::Err => {
                has_errors = true;
            }
            _ => {
                missing_literal.push(e.span);
            }
        }
    }

    if !missing_literal.is_empty() {
        let mut err = cx.struct_span_err(missing_literal, "expected a literal");
        err.note("only literals (like `\"foo\"`, `-42` and `3.14`) can be passed to `concat!()`");
        err.emit();
        return DummyResult::any(sp);
    } else if has_errors {
        return DummyResult::any(sp);
    }
    let sp = cx.with_def_site_ctxt(sp);
    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&accumulator)))
}