compiler/rustc_builtin_macros/src/util.rs

use rustc_ast::tokenstream::TokenStream;
use rustc_ast::{self as ast, AttrStyle, Attribute, MetaItem, attr, token};
use rustc_attr_parsing::{AttributeTemplate, validate_attr};
use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt};
use rustc_expand::expand::AstFragment;
use rustc_lint_defs::builtin::DUPLICATE_MACRO_ATTRIBUTES;
use rustc_parse::{exp, parser};
use rustc_session::diagnostics::report_lit_error;
use rustc_span::{BytePos, Span, Symbol};

use crate::diagnostics;

pub(crate) fn check_builtin_macro_attribute(ecx: &ExtCtxt<'_>, meta_item: &MetaItem, name: Symbol) {
    // All the built-in macro attributes are "words" at the moment.
    let template = AttributeTemplate { word: true, ..Default::default() };
    validate_attr::check_builtin_meta_item(
        &ecx.sess.psess,
        meta_item,
        AttrStyle::Outer,
        name,
        template,
        true,
    );
}

/// Emit a warning if the item is annotated with the given attribute. This is used to diagnose when
/// an attribute may have been mistakenly duplicated.
pub(crate) fn warn_on_duplicate_attribute(ecx: &ExtCtxt<'_>, item: &Annotatable, name: Symbol) {
    let attrs: Option<&[Attribute]> = match item {
        Annotatable::Item(item) => Some(&item.attrs),
        Annotatable::AssocItem(item, _) => Some(&item.attrs),
        Annotatable::ForeignItem(item) => Some(&item.attrs),
        Annotatable::Expr(expr) => Some(&expr.attrs),
        Annotatable::Arm(arm) => Some(&arm.attrs),
        Annotatable::ExprField(field) => Some(&field.attrs),
        Annotatable::PatField(field) => Some(&field.attrs),
        Annotatable::GenericParam(param) => Some(&param.attrs),
        Annotatable::Param(param) => Some(&param.attrs),
        Annotatable::FieldDef(def) => Some(&def.attrs),
        Annotatable::Variant(variant) => Some(&variant.attrs),
        _ => None,
    };
    if let Some(attrs) = attrs {
        if let Some(attr) = attr::find_by_name(attrs, name) {
            ecx.psess().buffer_lint(
                DUPLICATE_MACRO_ATTRIBUTES,
                attr.span,
                ecx.current_expansion.lint_node_id,
                diagnostics::DuplicateMacroAttribute,
            );
        }
    }
}

/// `Ok` represents successfully retrieving the string literal at the correct
/// position, e.g., `println("abc")`.
pub(crate) type ExprToSpannedStringResult<'a> = Result<ExprToSpannedString, UnexpectedExprKind<'a>>;

pub(crate) struct ExprToSpannedString {
    pub symbol: Symbol,
    pub style: ast::StrStyle,
    pub span: Span,
    /// The raw string literal, with no escaping or processing.
    ///
    /// Generally only useful for lints that care about the raw bytes the user wrote.
    pub uncooked_symbol: (ast::token::LitKind, Symbol),
}

/// - `Ok` is returned when the conversion to a string literal is unsuccessful,
/// but another type of expression is obtained instead.
/// - `Err` is returned when the conversion process fails.
type UnexpectedExprKind<'a> = Result<(Diag<'a>, bool /* has_suggestions */), ErrorGuaranteed>;

/// Extracts a string literal from the macro expanded version of `expr`,
/// returning a diagnostic error of `err_msg` if `expr` is not a string literal.
/// The returned bool indicates whether an applicable suggestion has already been
/// added to the diagnostic to avoid emitting multiple suggestions. `Err(Err(ErrorGuaranteed))`
/// indicates that an ast error was encountered.
pub(crate) fn expr_to_spanned_string<'a>(
    cx: &'a mut ExtCtxt<'_>,
    expr: Box<ast::Expr>,
    err_msg: &'static str,
) -> ExpandResult<ExprToSpannedStringResult<'a>, ()> {
    if !cx.force_mode
        && let ast::ExprKind::MacCall(m) = &expr.kind
        && cx.resolver.macro_accessible(cx.current_expansion.id, &m.path).is_err()
    {
        return ExpandResult::Retry(());
    }

    // Perform eager expansion on the expression.
    // We want to be able to handle e.g., `concat!("foo", "bar")`.
    let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();

    ExpandResult::Ready(Err(match expr.kind {
        ast::ExprKind::Lit(token_lit) => match ast::LitKind::from_token_lit(token_lit) {
            Ok(ast::LitKind::Str(s, style)) => {
                return ExpandResult::Ready(Ok(ExprToSpannedString {
                    symbol: s,
                    style,
                    span: expr.span,
                    uncooked_symbol: (token_lit.kind, token_lit.symbol),
                }));
            }
            Ok(ast::LitKind::ByteStr(..)) => {
                let mut err = cx.dcx().struct_span_err(expr.span, err_msg);
                let span = expr.span.shrink_to_lo();
                err.span_suggestion(
                    span.with_hi(span.lo() + BytePos(1)),
                    "consider removing the leading `b`",
                    "",
                    Applicability::MaybeIncorrect,
                );
                Ok((err, true))
            }
            Ok(ast::LitKind::Err(guar)) => Err(guar),
            Err(err) => Err(report_lit_error(&cx.sess.psess, err, token_lit, expr.span)),
            _ => Ok((cx.dcx().struct_span_err(expr.span, err_msg), false)),
        },
        ast::ExprKind::Err(guar) => Err(guar),
        ast::ExprKind::Dummy => {
            cx.dcx().span_bug(expr.span, "tried to get a string literal from `ExprKind::Dummy`")
        }
        _ => Ok((cx.dcx().struct_span_err(expr.span, err_msg), false)),
    }))
}

/// Extracts a string literal from the macro expanded version of `expr`,
/// emitting `err_msg` if `expr` is not a string literal. This does not stop
/// compilation on error, merely emits a non-fatal error and returns `Err`.
pub(crate) fn expr_to_string(
    cx: &mut ExtCtxt<'_>,
    expr: Box<ast::Expr>,
    err_msg: &'static str,
) -> ExpandResult<Result<(Symbol, ast::StrStyle), ErrorGuaranteed>, ()> {
    expr_to_spanned_string(cx, expr, err_msg).map(|res| {
        res.map_err(|err| match err {
            Ok((err, _)) => err.emit(),
            Err(guar) => guar,
        })
        .map(|ExprToSpannedString { symbol, style, .. }| (symbol, style))
    })
}

/// Non-fatally assert that `tts` is empty. Note that this function
/// returns even when `tts` is non-empty, macros that *need* to stop
/// compilation should call `cx.diagnostic().abort_if_errors()`
/// (this should be done as rarely as possible).
pub(crate) fn check_zero_tts(cx: &ExtCtxt<'_>, span: Span, tts: TokenStream, name: &str) {
    if !tts.is_empty() {
        cx.dcx().emit_err(diagnostics::TakesNoArguments { span, name });
    }
}

/// Parse an expression. On error, emit it, advancing to `Eof`, and return `Err`.
pub(crate) fn parse_expr(p: &mut parser::Parser<'_>) -> Result<Box<ast::Expr>, ErrorGuaranteed> {
    let guar = match p.parse_expr() {
        Ok(expr) => return Ok(expr),
        Err(err) => err.emit(),
    };
    while p.token != token::Eof {
        p.bump();
    }
    Err(guar)
}

/// Interpreting `tts` as a comma-separated sequence of expressions,
/// expect exactly one string literal, or emit an error and return `Err`.
pub(crate) fn get_single_str_from_tts(
    cx: &mut ExtCtxt<'_>,
    span: Span,
    tts: TokenStream,
    name: &str,
) -> ExpandResult<Result<Symbol, ErrorGuaranteed>, ()> {
    get_single_str_spanned_from_tts(cx, span, tts, name).map(|res| res.map(|(s, _)| s))
}

pub(crate) fn get_single_str_spanned_from_tts(
    cx: &mut ExtCtxt<'_>,
    span: Span,
    tts: TokenStream,
    name: &str,
) -> ExpandResult<Result<(Symbol, Span), ErrorGuaranteed>, ()> {
    let ExpandResult::Ready(ret) = get_single_expr_from_tts(cx, span, tts, name) else {
        return ExpandResult::Retry(());
    };
    let ret = match ret {
        Ok(ret) => ret,
        Err(e) => return ExpandResult::Ready(Err(e)),
    };
    expr_to_spanned_string(cx, ret, "argument must be a string literal").map(|res| {
        res.map_err(|err| match err {
            Ok((err, _)) => err.emit(),
            Err(guar) => guar,
        })
        .map(|ExprToSpannedString { symbol, span, .. }| (symbol, span))
    })
}

/// Interpreting `tts` as a comma-separated sequence of expressions,
/// expect exactly one expression, or emit an error and return `Err`.
pub(crate) fn get_single_expr_from_tts(
    cx: &mut ExtCtxt<'_>,
    span: Span,
    tts: TokenStream,
    name: &str,
) -> ExpandResult<Result<Box<ast::Expr>, ErrorGuaranteed>, ()> {
    let mut p = cx.new_parser_from_tts(tts);
    if p.token == token::Eof {
        let guar = cx.dcx().emit_err(diagnostics::OnlyOneArgument { span, name });
        return ExpandResult::Ready(Err(guar));
    }
    let ret = match parse_expr(&mut p) {
        Ok(ret) => ret,
        Err(guar) => return ExpandResult::Ready(Err(guar)),
    };
    let _ = p.eat(exp!(Comma));

    if p.token != token::Eof {
        cx.dcx().emit_err(diagnostics::OnlyOneArgument { span, name });
    }
    ExpandResult::Ready(Ok(ret))
}

/// Extracts comma-separated expressions from `tts`.
/// On error, emit it, and return `Err`.
pub(crate) fn get_exprs_from_tts(
    cx: &mut ExtCtxt<'_>,
    tts: TokenStream,
) -> ExpandResult<Result<Vec<Box<ast::Expr>>, ErrorGuaranteed>, ()> {
    let mut p = cx.new_parser_from_tts(tts);
    let mut es = Vec::new();
    while p.token != token::Eof {
        let expr = match parse_expr(&mut p) {
            Ok(expr) => expr,
            Err(guar) => return ExpandResult::Ready(Err(guar)),
        };
        if !cx.force_mode
            && let ast::ExprKind::MacCall(m) = &expr.kind
            && cx.resolver.macro_accessible(cx.current_expansion.id, &m.path).is_err()
        {
            return ExpandResult::Retry(());
        }

        // Perform eager expansion on the expression.
        // We want to be able to handle e.g., `concat!("foo", "bar")`.
        let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();

        es.push(expr);
        if p.eat(exp!(Comma)) {
            continue;
        }
        if p.token != token::Eof {
            let guar = cx.dcx().emit_err(diagnostics::ExpectedCommaInList { span: p.token.span });
            return ExpandResult::Ready(Err(guar));
        }
    }
    ExpandResult::Ready(Ok(es))
}