rust/compiler/rustc_parse/src/validate_attr.rs

//! Meta-syntax validation logic of attributes for post-expansion.

use crate::parse_in;

use rustc_ast::tokenstream::{DelimSpan, TokenTree};
use rustc_ast::{self as ast, Attribute, MacArgs, MacDelimiter, MetaItem, MetaItemKind};
use rustc_errors::{Applicability, FatalError, PResult};
use rustc_feature::{AttributeTemplate, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
use rustc_session::lint::builtin::ILL_FORMED_ATTRIBUTE_INPUT;
use rustc_session::parse::ParseSess;
use rustc_span::{sym, Symbol};

pub fn check_meta(sess: &ParseSess, attr: &Attribute) {
    if attr.is_doc_comment() {
        return;
    }

    let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));

    // Check input tokens for built-in and key-value attributes.
    match attr_info {
        // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
        Some(BuiltinAttribute { name, template, .. }) if *name != sym::rustc_dummy => {
            check_builtin_attribute(sess, attr, *name, *template)
        }
        _ if let MacArgs::Eq(..) = attr.get_normal_item().args => {
            // All key-value attributes are restricted to meta-item syntax.
            parse_meta(sess, attr)
                .map_err(|mut err| {
                    err.emit();
                })
                .ok();
        }
        _ => {}
    }
}

pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, MetaItem> {
    let item = attr.get_normal_item();
    Ok(MetaItem {
        span: attr.span,
        path: item.path.clone(),
        kind: match &item.args {
            MacArgs::Empty => MetaItemKind::Word,
            MacArgs::Eq(_, t) => {
                let t = TokenTree::Token(t.clone()).into();
                let v = parse_in(sess, t, "name value", |p| p.parse_unsuffixed_lit())?;
                MetaItemKind::NameValue(v)
            }
            MacArgs::Delimited(dspan, delim, t) => {
                check_meta_bad_delim(sess, *dspan, *delim, "wrong meta list delimiters");
                let nmis = parse_in(sess, t.clone(), "meta list", |p| p.parse_meta_seq_top())?;
                MetaItemKind::List(nmis)
            }
        },
    })
}

pub fn check_meta_bad_delim(sess: &ParseSess, span: DelimSpan, delim: MacDelimiter, msg: &str) {
    if let ast::MacDelimiter::Parenthesis = delim {
        return;
    }

    sess.span_diagnostic
        .struct_span_err(span.entire(), msg)
        .multipart_suggestion(
            "the delimiters should be `(` and `)`",
            vec![(span.open, "(".to_string()), (span.close, ")".to_string())],
            Applicability::MachineApplicable,
        )
        .emit();
}

/// Checks that the given meta-item is compatible with this `AttributeTemplate`.
fn is_attr_template_compatible(template: &AttributeTemplate, meta: &ast::MetaItemKind) -> bool {
    match meta {
        MetaItemKind::Word => template.word,
        MetaItemKind::List(..) => template.list.is_some(),
        MetaItemKind::NameValue(lit) if lit.kind.is_str() => template.name_value_str.is_some(),
        MetaItemKind::NameValue(..) => false,
    }
}

pub fn check_builtin_attribute(
    sess: &ParseSess,
    attr: &Attribute,
    name: Symbol,
    template: AttributeTemplate,
) {
    // Some special attributes like `cfg` must be checked
    // before the generic check, so we skip them here.
    let should_skip = |name| name == sym::cfg;

    match parse_meta(sess, attr) {
        Ok(meta) => {
            if !should_skip(name) && !is_attr_template_compatible(&template, &meta.kind) {
                emit_malformed_attribute(sess, attr, name, template);
            }
        }
        Err(mut err) => {
            err.emit();
        }
    }
}

fn emit_malformed_attribute(
    sess: &ParseSess,
    attr: &Attribute,
    name: Symbol,
    template: AttributeTemplate,
) {
    // Some of previously accepted forms were used in practice,
    // report them as warnings for now.
    let should_warn = |name| {
        matches!(name, sym::doc | sym::ignore | sym::inline | sym::link | sym::test | sym::bench)
    };

    let error_msg = format!("malformed `{}` attribute input", name);
    let mut msg = "attribute must be of the form ".to_owned();
    let mut suggestions = vec![];
    let mut first = true;
    let inner = if attr.style == ast::AttrStyle::Inner { "!" } else { "" };
    if template.word {
        first = false;
        let code = format!("#{}[{}]", inner, name);
        msg.push_str(&format!("`{}`", &code));
        suggestions.push(code);
    }
    if let Some(descr) = template.list {
        if !first {
            msg.push_str(" or ");
        }
        first = false;
        let code = format!("#{}[{}({})]", inner, name, descr);
        msg.push_str(&format!("`{}`", &code));
        suggestions.push(code);
    }
    if let Some(descr) = template.name_value_str {
        if !first {
            msg.push_str(" or ");
        }
        let code = format!("#{}[{} = \"{}\"]", inner, name, descr);
        msg.push_str(&format!("`{}`", &code));
        suggestions.push(code);
    }
    if should_warn(name) {
        sess.buffer_lint(&ILL_FORMED_ATTRIBUTE_INPUT, attr.span, ast::CRATE_NODE_ID, &msg);
    } else {
        sess.span_diagnostic
            .struct_span_err(attr.span, &error_msg)
            .span_suggestions(
                attr.span,
                if suggestions.len() == 1 {
                    "must be of the form"
                } else {
                    "the following are the possible correct uses"
                },
                suggestions.into_iter(),
                Applicability::HasPlaceholders,
            )
            .emit();
    }
}

pub fn emit_fatal_malformed_builtin_attribute(
    sess: &ParseSess,
    attr: &Attribute,
    name: Symbol,
) -> ! {
    let template = BUILTIN_ATTRIBUTE_MAP.get(&name).expect("builtin attr defined").template;
    emit_malformed_attribute(sess, attr, name, template);
    // This is fatal, otherwise it will likely cause a cascade of other errors
    // (and an error here is expected to be very rare).
    FatalError.raise()
}