use crate::{ast, attr}; use crate::edition::Edition; use crate::ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension}; use crate::ext::base::{NormalTT, TTMacroExpander}; use crate::ext::expand::{AstFragment, AstFragmentKind}; use crate::ext::tt::macro_parser::{Success, Error, Failure}; use crate::ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal}; use crate::ext::tt::macro_parser::{parse, parse_failure_msg}; use crate::ext::tt::quoted; use crate::ext::tt::transcribe::transcribe; use crate::feature_gate::Features; use crate::parse::{Directory, ParseSess}; use crate::parse::parser::Parser; use crate::parse::token::{self, NtTT}; use crate::parse::token::Token::*; use crate::symbol::Symbol; use crate::tokenstream::{DelimSpan, TokenStream, TokenTree}; use errors::FatalError; use syntax_pos::{Span, DUMMY_SP, symbol::Ident}; use log::debug; use rustc_data_structures::fx::{FxHashMap}; use std::borrow::Cow; use std::collections::hash_map::Entry; use rustc_data_structures::sync::Lrc; use errors::Applicability; const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \ `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, \ `path`, `meta`, `tt`, `item` and `vis`"; pub struct ParserAnyMacro<'a> { parser: Parser<'a>, /// Span of the expansion site of the macro this parser is for site_span: Span, /// The ident of the macro we're parsing macro_ident: ast::Ident, arm_span: Span, } impl<'a> ParserAnyMacro<'a> { pub fn make(mut self: Box>, kind: AstFragmentKind) -> AstFragment { let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self; let fragment = panictry!(parser.parse_ast_fragment(kind, true).map_err(|mut e| { if parser.token == token::Eof && e.message().ends_with(", found ``") { if !e.span.is_dummy() { // early end of macro arm (#52866) e.replace_span_with(parser.sess.source_map().next_point(parser.span)); } let msg = &e.message[0]; e.message[0] = ( format!( "macro expansion ends with an incomplete expression: {}", msg.0.replace(", found ``", ""), ), msg.1, ); } if e.span.is_dummy() { // Get around lack of span in error (#30128) e.replace_span_with(site_span); if parser.sess.source_map().span_to_filename(arm_span).is_real() { e.span_label(arm_span, "in this macro arm"); } } else if !parser.sess.source_map().span_to_filename(parser.span).is_real() { e.span_label(site_span, "in this macro invocation"); } e })); // We allow semicolons at the end of expressions -- e.g., the semicolon in // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`, // but `m!()` is allowed in expression positions (cf. issue #34706). if kind == AstFragmentKind::Expr && parser.token == token::Semi { parser.bump(); } // Make sure we don't have any tokens left to parse so we don't silently drop anything. let path = ast::Path::from_ident(macro_ident.with_span_pos(site_span)); parser.ensure_complete_parse(&path, kind.name(), site_span); fragment } } struct MacroRulesMacroExpander { name: ast::Ident, lhses: Vec, rhses: Vec, valid: bool, } impl TTMacroExpander for MacroRulesMacroExpander { fn expand<'cx>( &self, cx: &'cx mut ExtCtxt<'_>, sp: Span, input: TokenStream, def_span: Option, ) -> Box { if !self.valid { return DummyResult::any(sp); } generic_extension(cx, sp, def_span, self.name, input, &self.lhses, &self.rhses) } } fn trace_macros_note(cx: &mut ExtCtxt<'_>, sp: Span, message: String) { let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp); cx.expansions.entry(sp).or_default().push(message); } /// Given `lhses` and `rhses`, this is the new macro we create fn generic_extension<'cx>(cx: &'cx mut ExtCtxt<'_>, sp: Span, def_span: Option, name: ast::Ident, arg: TokenStream, lhses: &[quoted::TokenTree], rhses: &[quoted::TokenTree]) -> Box { if cx.trace_macros() { trace_macros_note(cx, sp, format!("expanding `{}! {{ {} }}`", name, arg)); } // Which arm's failure should we report? (the one furthest along) let mut best_fail_spot = DUMMY_SP; let mut best_fail_tok = None; let mut best_fail_text = None; for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers let lhs_tt = match *lhs { quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..], _ => cx.span_bug(sp, "malformed macro lhs") }; match TokenTree::parse(cx, lhs_tt, arg.clone()) { Success(named_matches) => { let rhs = match rhses[i] { // ignore delimiters quoted::TokenTree::Delimited(_, ref delimed) => delimed.tts.clone(), _ => cx.span_bug(sp, "malformed macro rhs"), }; let arm_span = rhses[i].span(); let rhs_spans = rhs.iter().map(|t| t.span()).collect::>(); // rhs has holes ( `$id` and `$(...)` that need filled) let mut tts = transcribe(cx, Some(named_matches), rhs); // Replace all the tokens for the corresponding positions in the macro, to maintain // proper positions in error reporting, while maintaining the macro_backtrace. if rhs_spans.len() == tts.len() { tts = tts.map_enumerated(|i, mut tt| { let mut sp = rhs_spans[i]; sp = sp.with_ctxt(tt.span().ctxt()); tt.set_span(sp); tt }); } if cx.trace_macros() { trace_macros_note(cx, sp, format!("to `{}`", tts)); } let directory = Directory { path: Cow::from(cx.current_expansion.module.directory.as_path()), ownership: cx.current_expansion.directory_ownership, }; let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false); p.root_module_name = cx.current_expansion.module.mod_path.last() .map(|id| id.as_str().to_string()); p.process_potential_macro_variable(); // Let the context choose how to interpret the result. // Weird, but useful for X-macros. return Box::new(ParserAnyMacro { parser: p, // Pass along the original expansion site and the name of the macro // so we can print a useful error message if the parse of the expanded // macro leaves unparsed tokens. site_span: sp, macro_ident: name, arm_span, }) } Failure(sp, tok, t) => if sp.lo() >= best_fail_spot.lo() { best_fail_spot = sp; best_fail_tok = Some(tok); best_fail_text = Some(t); }, Error(err_sp, ref msg) => { cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..]) } } } let best_fail_msg = parse_failure_msg(best_fail_tok.expect("ran no matchers")); let span = best_fail_spot.substitute_dummy(sp); let mut err = cx.struct_span_err(span, &best_fail_msg); err.span_label(span, best_fail_text.unwrap_or(&best_fail_msg)); if let Some(sp) = def_span { if cx.source_map().span_to_filename(sp).is_real() && !sp.is_dummy() { err.span_label(cx.source_map().def_span(sp), "when calling this macro"); } } // Check whether there's a missing comma in this macro call, like `println!("{}" a);` if let Some((arg, comma_span)) = arg.add_comma() { for lhs in lhses { // try each arm's matchers let lhs_tt = match *lhs { quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..], _ => continue, }; match TokenTree::parse(cx, lhs_tt, arg.clone()) { Success(_) => { if comma_span.is_dummy() { err.note("you might be missing a comma"); } else { err.span_suggestion_short( comma_span, "missing comma here", ", ".to_string(), Applicability::MachineApplicable, ); } } _ => {} } } } err.emit(); cx.trace_macros_diag(); DummyResult::any(sp) } // Note that macro-by-example's input is also matched against a token tree: // $( $lhs:tt => $rhs:tt );+ // // Holy self-referential! /// Converts a `macro_rules!` invocation into a syntax extension. pub fn compile( sess: &ParseSess, features: &Features, def: &ast::Item, edition: Edition ) -> SyntaxExtension { let lhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("lhs")); let rhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("rhs")); // Parse the macro_rules! invocation let body = match def.node { ast::ItemKind::MacroDef(ref body) => body, _ => unreachable!(), }; // The pattern that macro_rules matches. // The grammar for macro_rules! is: // $( $lhs:tt => $rhs:tt );+ // ...quasiquoting this would be nice. // These spans won't matter, anyways let argument_gram = vec![ quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition { tts: vec![ quoted::TokenTree::MetaVarDecl(DUMMY_SP, lhs_nm, ast::Ident::from_str("tt")), quoted::TokenTree::Token(DUMMY_SP, token::FatArrow), quoted::TokenTree::MetaVarDecl(DUMMY_SP, rhs_nm, ast::Ident::from_str("tt")), ], separator: Some(if body.legacy { token::Semi } else { token::Comma }), op: quoted::KleeneOp::OneOrMore, num_captures: 2, })), // to phase into semicolon-termination instead of semicolon-separation quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition { tts: vec![quoted::TokenTree::Token(DUMMY_SP, token::Semi)], separator: None, op: quoted::KleeneOp::ZeroOrMore, num_captures: 0 })), ]; let argument_map = match parse(sess, body.stream(), &argument_gram, None, true) { Success(m) => m, Failure(sp, tok, t) => { let s = parse_failure_msg(tok); let sp = sp.substitute_dummy(def.span); let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s); err.span_label(sp, t); err.emit(); FatalError.raise(); } Error(sp, s) => { sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise(); } }; let mut valid = true; // Extract the arguments: let lhses = match *argument_map[&lhs_nm] { MatchedSeq(ref s, _) => { s.iter().map(|m| { if let MatchedNonterminal(ref nt) = *m { if let NtTT(ref tt) = **nt { let tt = quoted::parse( tt.clone().into(), true, sess, features, &def.attrs, edition, def.id, ) .pop() .unwrap(); valid &= check_lhs_nt_follows(sess, features, &def.attrs, &tt); return tt; } } sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs") }).collect::>() } _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs") }; let rhses = match *argument_map[&rhs_nm] { MatchedSeq(ref s, _) => { s.iter().map(|m| { if let MatchedNonterminal(ref nt) = *m { if let NtTT(ref tt) = **nt { return quoted::parse( tt.clone().into(), false, sess, features, &def.attrs, edition, def.id, ).pop() .unwrap(); } } sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs") }).collect::>() } _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs") }; for rhs in &rhses { valid &= check_rhs(sess, rhs); } // don't abort iteration early, so that errors for multiple lhses can be reported for lhs in &lhses { valid &= check_lhs_no_empty_seq(sess, &[lhs.clone()]); valid &= check_lhs_duplicate_matcher_bindings( sess, &[lhs.clone()], &mut FxHashMap::default(), def.id ); } let expander: Box<_> = Box::new(MacroRulesMacroExpander { name: def.ident, lhses, rhses, valid, }); if body.legacy { let allow_internal_unstable = attr::find_by_name(&def.attrs, "allow_internal_unstable") .map(|attr| attr .meta_item_list() .map(|list| list.iter() .filter_map(|it| { let name = it.ident().map(|ident| ident.name); if name.is_none() { sess.span_diagnostic.span_err(it.span(), "allow internal unstable expects feature names") } name }) .collect::>().into() ) .unwrap_or_else(|| { sess.span_diagnostic.span_warn( attr.span, "allow_internal_unstable expects list of feature names. In the \ future this will become a hard error. Please use `allow_internal_unstable(\ foo, bar)` to only allow the `foo` and `bar` features", ); vec![Symbol::intern("allow_internal_unstable_backcompat_hack")].into() }) ); let allow_internal_unsafe = attr::contains_name(&def.attrs, "allow_internal_unsafe"); let mut local_inner_macros = false; if let Some(macro_export) = attr::find_by_name(&def.attrs, "macro_export") { if let Some(l) = macro_export.meta_item_list() { local_inner_macros = attr::list_contains_name(&l, "local_inner_macros"); } } let unstable_feature = attr::find_stability(&sess, &def.attrs, def.span).and_then(|stability| { if let attr::StabilityLevel::Unstable { issue, .. } = stability.level { Some((stability.feature, issue)) } else { None } }); NormalTT { expander, def_info: Some((def.id, def.span)), allow_internal_unstable, allow_internal_unsafe, local_inner_macros, unstable_feature, edition, } } else { let is_transparent = attr::contains_name(&def.attrs, "rustc_transparent_macro"); SyntaxExtension::DeclMacro { expander, def_info: Some((def.id, def.span)), is_transparent, edition, } } } fn check_lhs_nt_follows(sess: &ParseSess, features: &Features, attrs: &[ast::Attribute], lhs: "ed::TokenTree) -> bool { // lhs is going to be like TokenTree::Delimited(...), where the // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens. if let quoted::TokenTree::Delimited(_, ref tts) = *lhs { check_matcher(sess, features, attrs, &tts.tts) } else { let msg = "invalid macro matcher; matchers must be contained in balanced delimiters"; sess.span_diagnostic.span_err(lhs.span(), msg); false } // we don't abort on errors on rejection, the driver will do that for us // after parsing/expansion. we can report every error in every macro this way. } /// Checks that the lhs contains no repetition which could match an empty token /// tree, because then the matcher would hang indefinitely. fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[quoted::TokenTree]) -> bool { use quoted::TokenTree; for tt in tts { match *tt { TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (), TokenTree::Delimited(_, ref del) => if !check_lhs_no_empty_seq(sess, &del.tts) { return false; }, TokenTree::Sequence(span, ref seq) => { if seq.separator.is_none() && seq.tts.iter().all(|seq_tt| { match *seq_tt { TokenTree::MetaVarDecl(_, _, id) => id.name == "vis", TokenTree::Sequence(_, ref sub_seq) => sub_seq.op == quoted::KleeneOp::ZeroOrMore || sub_seq.op == quoted::KleeneOp::ZeroOrOne, _ => false, } }) { let sp = span.entire(); sess.span_diagnostic.span_err(sp, "repetition matches empty token tree"); return false; } if !check_lhs_no_empty_seq(sess, &seq.tts) { return false; } } } } true } /// Check that the LHS contains no duplicate matcher bindings. e.g. `$a:expr, $a:expr` would be /// illegal, since it would be ambiguous which `$a` to use if we ever needed to. fn check_lhs_duplicate_matcher_bindings( sess: &ParseSess, tts: &[quoted::TokenTree], metavar_names: &mut FxHashMap, node_id: ast::NodeId, ) -> bool { use self::quoted::TokenTree; for tt in tts { match *tt { TokenTree::MetaVarDecl(span, name, _kind) => { if let Some(&prev_span) = metavar_names.get(&name) { sess.span_diagnostic .struct_span_err(span, "duplicate matcher binding") .span_note(prev_span, "previous declaration was here") .emit(); return false; } else { metavar_names.insert(name, span); } } TokenTree::Delimited(_, ref del) => { if !check_lhs_duplicate_matcher_bindings(sess, &del.tts, metavar_names, node_id) { return false; } }, TokenTree::Sequence(_, ref seq) => { if !check_lhs_duplicate_matcher_bindings(sess, &seq.tts, metavar_names, node_id) { return false; } } _ => {} } } true } fn check_rhs(sess: &ParseSess, rhs: "ed::TokenTree) -> bool { match *rhs { quoted::TokenTree::Delimited(..) => return true, _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited") } false } fn check_matcher(sess: &ParseSess, features: &Features, attrs: &[ast::Attribute], matcher: &[quoted::TokenTree]) -> bool { let first_sets = FirstSets::new(matcher); let empty_suffix = TokenSet::empty(); let err = sess.span_diagnostic.err_count(); check_matcher_core(sess, features, attrs, &first_sets, matcher, &empty_suffix); err == sess.span_diagnostic.err_count() } // `The FirstSets` for a matcher is a mapping from subsequences in the // matcher to the FIRST set for that subsequence. // // This mapping is partially precomputed via a backwards scan over the // token trees of the matcher, which provides a mapping from each // repetition sequence to its *first* set. // // (Hypothetically, sequences should be uniquely identifiable via their // spans, though perhaps that is false, e.g., for macro-generated macros // that do not try to inject artificial span information. My plan is // to try to catch such cases ahead of time and not include them in // the precomputed mapping.) struct FirstSets { // this maps each TokenTree::Sequence `$(tt ...) SEP OP` that is uniquely identified by its // span in the original matcher to the First set for the inner sequence `tt ...`. // // If two sequences have the same span in a matcher, then map that // span to None (invalidating the mapping here and forcing the code to // use a slow path). first: FxHashMap>, } impl FirstSets { fn new(tts: &[quoted::TokenTree]) -> FirstSets { use quoted::TokenTree; let mut sets = FirstSets { first: FxHashMap::default() }; build_recur(&mut sets, tts); return sets; // walks backward over `tts`, returning the FIRST for `tts` // and updating `sets` at the same time for all sequence // substructure we find within `tts`. fn build_recur(sets: &mut FirstSets, tts: &[TokenTree]) -> TokenSet { let mut first = TokenSet::empty(); for tt in tts.iter().rev() { match *tt { TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => { first.replace_with(tt.clone()); } TokenTree::Delimited(span, ref delimited) => { build_recur(sets, &delimited.tts[..]); first.replace_with(delimited.open_tt(span.open)); } TokenTree::Sequence(sp, ref seq_rep) => { let subfirst = build_recur(sets, &seq_rep.tts[..]); match sets.first.entry(sp.entire()) { Entry::Vacant(vac) => { vac.insert(Some(subfirst.clone())); } Entry::Occupied(mut occ) => { // if there is already an entry, then a span must have collided. // This should not happen with typical macro_rules macros, // but syntax extensions need not maintain distinct spans, // so distinct syntax trees can be assigned the same span. // In such a case, the map cannot be trusted; so mark this // entry as unusable. occ.insert(None); } } // If the sequence contents can be empty, then the first // token could be the separator token itself. if let (Some(ref sep), true) = (seq_rep.separator.clone(), subfirst.maybe_empty) { first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone())); } // Reverse scan: Sequence comes before `first`. if subfirst.maybe_empty || seq_rep.op == quoted::KleeneOp::ZeroOrMore || seq_rep.op == quoted::KleeneOp::ZeroOrOne { // If sequence is potentially empty, then // union them (preserving first emptiness). first.add_all(&TokenSet { maybe_empty: true, ..subfirst }); } else { // Otherwise, sequence guaranteed // non-empty; replace first. first = subfirst; } } } } first } } // walks forward over `tts` until all potential FIRST tokens are // identified. fn first(&self, tts: &[quoted::TokenTree]) -> TokenSet { use quoted::TokenTree; let mut first = TokenSet::empty(); for tt in tts.iter() { assert!(first.maybe_empty); match *tt { TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => { first.add_one(tt.clone()); return first; } TokenTree::Delimited(span, ref delimited) => { first.add_one(delimited.open_tt(span.open)); return first; } TokenTree::Sequence(sp, ref seq_rep) => { match self.first.get(&sp.entire()) { Some(&Some(ref subfirst)) => { // If the sequence contents can be empty, then the first // token could be the separator token itself. if let (Some(ref sep), true) = (seq_rep.separator.clone(), subfirst.maybe_empty) { first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone())); } assert!(first.maybe_empty); first.add_all(subfirst); if subfirst.maybe_empty || seq_rep.op == quoted::KleeneOp::ZeroOrMore || seq_rep.op == quoted::KleeneOp::ZeroOrOne { // continue scanning for more first // tokens, but also make sure we // restore empty-tracking state first.maybe_empty = true; continue; } else { return first; } } Some(&None) => { panic!("assume all sequences have (unique) spans for now"); } None => { panic!("We missed a sequence during FirstSets construction"); } } } } } // we only exit the loop if `tts` was empty or if every // element of `tts` matches the empty sequence. assert!(first.maybe_empty); first } } // A set of `quoted::TokenTree`s, which may include `TokenTree::Match`s // (for macro-by-example syntactic variables). It also carries the // `maybe_empty` flag; that is true if and only if the matcher can // match an empty token sequence. // // The First set is computed on submatchers like `$($a:expr b),* $(c)* d`, // which has corresponding FIRST = {$a:expr, c, d}. // Likewise, `$($a:expr b),* $(c)+ d` has FIRST = {$a:expr, c}. // // (Notably, we must allow for *-op to occur zero times.) #[derive(Clone, Debug)] struct TokenSet { tokens: Vec, maybe_empty: bool, } impl TokenSet { // Returns a set for the empty sequence. fn empty() -> Self { TokenSet { tokens: Vec::new(), maybe_empty: true } } // Returns the set `{ tok }` for the single-token (and thus // non-empty) sequence [tok]. fn singleton(tok: quoted::TokenTree) -> Self { TokenSet { tokens: vec![tok], maybe_empty: false } } // Changes self to be the set `{ tok }`. // Since `tok` is always present, marks self as non-empty. fn replace_with(&mut self, tok: quoted::TokenTree) { self.tokens.clear(); self.tokens.push(tok); self.maybe_empty = false; } // Changes self to be the empty set `{}`; meant for use when // the particular token does not matter, but we want to // record that it occurs. fn replace_with_irrelevant(&mut self) { self.tokens.clear(); self.maybe_empty = false; } // Adds `tok` to the set for `self`, marking sequence as non-empy. fn add_one(&mut self, tok: quoted::TokenTree) { if !self.tokens.contains(&tok) { self.tokens.push(tok); } self.maybe_empty = false; } // Adds `tok` to the set for `self`. (Leaves `maybe_empty` flag alone.) fn add_one_maybe(&mut self, tok: quoted::TokenTree) { if !self.tokens.contains(&tok) { self.tokens.push(tok); } } // Adds all elements of `other` to this. // // (Since this is a set, we filter out duplicates.) // // If `other` is potentially empty, then preserves the previous // setting of the empty flag of `self`. If `other` is guaranteed // non-empty, then `self` is marked non-empty. fn add_all(&mut self, other: &Self) { for tok in &other.tokens { if !self.tokens.contains(tok) { self.tokens.push(tok.clone()); } } if !other.maybe_empty { self.maybe_empty = false; } } } // Checks that `matcher` is internally consistent and that it // can legally by followed by a token N, for all N in `follow`. // (If `follow` is empty, then it imposes no constraint on // the `matcher`.) // // Returns the set of NT tokens that could possibly come last in // `matcher`. (If `matcher` matches the empty sequence, then // `maybe_empty` will be set to true.) // // Requires that `first_sets` is pre-computed for `matcher`; // see `FirstSets::new`. fn check_matcher_core(sess: &ParseSess, features: &Features, attrs: &[ast::Attribute], first_sets: &FirstSets, matcher: &[quoted::TokenTree], follow: &TokenSet) -> TokenSet { use quoted::TokenTree; let mut last = TokenSet::empty(); // 2. For each token and suffix [T, SUFFIX] in M: // ensure that T can be followed by SUFFIX, and if SUFFIX may be empty, // then ensure T can also be followed by any element of FOLLOW. 'each_token: for i in 0..matcher.len() { let token = &matcher[i]; let suffix = &matcher[i+1..]; let build_suffix_first = || { let mut s = first_sets.first(suffix); if s.maybe_empty { s.add_all(follow); } s }; // (we build `suffix_first` on demand below; you can tell // which cases are supposed to fall through by looking for the // initialization of this variable.) let suffix_first; // First, update `last` so that it corresponds to the set // of NT tokens that might end the sequence `... token`. match *token { TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => { let can_be_followed_by_any; if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) { let msg = format!("invalid fragment specifier `{}`", bad_frag); sess.span_diagnostic.struct_span_err(token.span(), &msg) .help(VALID_FRAGMENT_NAMES_MSG) .emit(); // (This eliminates false positives and duplicates // from error messages.) can_be_followed_by_any = true; } else { can_be_followed_by_any = token_can_be_followed_by_any(token); } if can_be_followed_by_any { // don't need to track tokens that work with any, last.replace_with_irrelevant(); // ... and don't need to check tokens that can be // followed by anything against SUFFIX. continue 'each_token; } else { last.replace_with(token.clone()); suffix_first = build_suffix_first(); } } TokenTree::Delimited(span, ref d) => { let my_suffix = TokenSet::singleton(d.close_tt(span.close)); check_matcher_core(sess, features, attrs, first_sets, &d.tts, &my_suffix); // don't track non NT tokens last.replace_with_irrelevant(); // also, we don't need to check delimited sequences // against SUFFIX continue 'each_token; } TokenTree::Sequence(sp, ref seq_rep) => { suffix_first = build_suffix_first(); // The trick here: when we check the interior, we want // to include the separator (if any) as a potential // (but not guaranteed) element of FOLLOW. So in that // case, we make a temp copy of suffix and stuff // delimiter in there. // // FIXME: Should I first scan suffix_first to see if // delimiter is already in it before I go through the // work of cloning it? But then again, this way I may // get a "tighter" span? let mut new; let my_suffix = if let Some(ref u) = seq_rep.separator { new = suffix_first.clone(); new.add_one_maybe(TokenTree::Token(sp.entire(), u.clone())); &new } else { &suffix_first }; // At this point, `suffix_first` is built, and // `my_suffix` is some TokenSet that we can use // for checking the interior of `seq_rep`. let next = check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix); if next.maybe_empty { last.add_all(&next); } else { last = next; } // the recursive call to check_matcher_core already ran the 'each_last // check below, so we can just keep going forward here. continue 'each_token; } } // (`suffix_first` guaranteed initialized once reaching here.) // Now `last` holds the complete set of NT tokens that could // end the sequence before SUFFIX. Check that every one works with `suffix`. 'each_last: for token in &last.tokens { if let TokenTree::MetaVarDecl(_, ref name, ref frag_spec) = *token { for next_token in &suffix_first.tokens { match is_in_follow(next_token, &frag_spec.as_str()) { IsInFollow::Invalid(msg, help) => { sess.span_diagnostic.struct_span_err(next_token.span(), &msg) .help(help).emit(); // don't bother reporting every source of // conflict for a particular element of `last`. continue 'each_last; } IsInFollow::Yes => {} IsInFollow::No(ref possible) => { let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1 { "is" } else { "may be" }; let sp = next_token.span(); let mut err = sess.span_diagnostic.struct_span_err( sp, &format!("`${name}:{frag}` {may_be} followed by `{next}`, which \ is not allowed for `{frag}` fragments", name=name, frag=frag_spec, next=quoted_tt_to_string(next_token), may_be=may_be), ); err.span_label( sp, format!("not allowed after `{}` fragments", frag_spec), ); let msg = "allowed there are: "; match &possible[..] { &[] => {} &[t] => { err.note(&format!( "only {} is allowed after `{}` fragments", t, frag_spec, )); } ts => { err.note(&format!( "{}{} or {}", msg, ts[..ts.len() - 1].iter().map(|s| *s) .collect::>().join(", "), ts[ts.len() - 1], )); } } err.emit(); } } } } } } last } fn token_can_be_followed_by_any(tok: "ed::TokenTree) -> bool { if let quoted::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok { frag_can_be_followed_by_any(&frag_spec.as_str()) } else { // (Non NT's can always be followed by anthing in matchers.) true } } /// Returns `true` if a fragment of type `frag` can be followed by any sort of /// token. We use this (among other things) as a useful approximation /// for when `frag` can be followed by a repetition like `$(...)*` or /// `$(...)+`. In general, these can be a bit tricky to reason about, /// so we adopt a conservative position that says that any fragment /// specifier which consumes at most one token tree can be followed by /// a fragment specifier (indeed, these fragments can be followed by /// ANYTHING without fear of future compatibility hazards). fn frag_can_be_followed_by_any(frag: &str) -> bool { match frag { "item" | // always terminated by `}` or `;` "block" | // exactly one token tree "ident" | // exactly one token tree "literal" | // exactly one token tree "meta" | // exactly one token tree "lifetime" | // exactly one token tree "tt" => // exactly one token tree true, _ => false, } } enum IsInFollow { Yes, No(Vec<&'static str>), Invalid(String, &'static str), } /// Returns `true` if `frag` can legally be followed by the token `tok`. For /// fragments that can consume an unbounded number of tokens, `tok` /// must be within a well-defined follow set. This is intended to /// guarantee future compatibility: for example, without this rule, if /// we expanded `expr` to include a new binary operator, we might /// break macros that were relying on that binary operator as a /// separator. // when changing this do not forget to update doc/book/macros.md! fn is_in_follow(tok: "ed::TokenTree, frag: &str) -> IsInFollow { use quoted::TokenTree; if let TokenTree::Token(_, token::CloseDelim(_)) = *tok { // closing a token tree can never be matched by any fragment; // iow, we always require that `(` and `)` match, etc. IsInFollow::Yes } else { match frag { "item" => { // since items *must* be followed by either a `;` or a `}`, we can // accept anything after them IsInFollow::Yes }, "block" => { // anything can follow block, the braces provide an easy boundary to // maintain IsInFollow::Yes }, "stmt" | "expr" => { let tokens = vec!["`=>`", "`,`", "`;`"]; match *tok { TokenTree::Token(_, ref tok) => match *tok { FatArrow | Comma | Semi => IsInFollow::Yes, _ => IsInFollow::No(tokens), }, _ => IsInFollow::No(tokens), } }, "pat" => { let tokens = vec!["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"]; match *tok { TokenTree::Token(_, ref tok) => match *tok { FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes, Ident(i, false) if i.name == "if" || i.name == "in" => IsInFollow::Yes, _ => IsInFollow::No(tokens), }, _ => IsInFollow::No(tokens), } }, "path" | "ty" => { let tokens = vec![ "`{`", "`[`", "`=>`", "`,`", "`>`","`=`", "`:`", "`;`", "`|`", "`as`", "`where`", ]; match *tok { TokenTree::Token(_, ref tok) => match *tok { OpenDelim(token::DelimToken::Brace) | OpenDelim(token::DelimToken::Bracket) | Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi | BinOp(token::Or) => IsInFollow::Yes, Ident(i, false) if i.name == "as" || i.name == "where" => IsInFollow::Yes, _ => IsInFollow::No(tokens), }, TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => IsInFollow::Yes, _ => IsInFollow::No(tokens), } }, "ident" | "lifetime" => { // being a single token, idents and lifetimes are harmless IsInFollow::Yes }, "literal" => { // literals may be of a single token, or two tokens (negative numbers) IsInFollow::Yes }, "meta" | "tt" => { // being either a single token or a delimited sequence, tt is // harmless IsInFollow::Yes }, "vis" => { // Explicitly disallow `priv`, on the off chance it comes back. let tokens = vec!["`,`", "an ident", "a type"]; match *tok { TokenTree::Token(_, ref tok) => match *tok { Comma => IsInFollow::Yes, Ident(i, is_raw) if is_raw || i.name != "priv" => IsInFollow::Yes, ref tok => if tok.can_begin_type() { IsInFollow::Yes } else { IsInFollow::No(tokens) } }, TokenTree::MetaVarDecl(_, _, frag) if frag.name == "ident" || frag.name == "ty" || frag.name == "path" => IsInFollow::Yes, _ => IsInFollow::No(tokens), } }, "" => IsInFollow::Yes, // keywords::Invalid _ => IsInFollow::Invalid(format!("invalid fragment specifier `{}`", frag), VALID_FRAGMENT_NAMES_MSG), } } } fn has_legal_fragment_specifier(sess: &ParseSess, features: &Features, attrs: &[ast::Attribute], tok: "ed::TokenTree) -> Result<(), String> { debug!("has_legal_fragment_specifier({:?})", tok); if let quoted::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok { let frag_name = frag_spec.as_str(); let frag_span = tok.span(); if !is_legal_fragment_specifier(sess, features, attrs, &frag_name, frag_span) { return Err(frag_name.to_string()); } } Ok(()) } fn is_legal_fragment_specifier(_sess: &ParseSess, _features: &Features, _attrs: &[ast::Attribute], frag_name: &str, _frag_span: Span) -> bool { /* * If new fragment specifiers are invented in nightly, `_sess`, * `_features`, `_attrs`, and `_frag_span` will be useful here * for checking against feature gates. See past versions of * this function. */ match frag_name { "item" | "block" | "stmt" | "expr" | "pat" | "lifetime" | "path" | "ty" | "ident" | "meta" | "tt" | "vis" | "literal" | "" => true, _ => false, } } fn quoted_tt_to_string(tt: "ed::TokenTree) -> String { match *tt { quoted::TokenTree::Token(_, ref tok) => crate::print::pprust::token_to_string(tok), quoted::TokenTree::MetaVar(_, name) => format!("${}", name), quoted::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind), _ => panic!("unexpected quoted::TokenTree::{{Sequence or Delimited}} \ in follow set checker"), } }