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, kw, sym};
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<ParserAnyMacro<'a>>, 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 `<eof>`") {
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 `<eof>`", ""),
),
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<quoted::TokenTree>,
rhses: Vec<quoted::TokenTree>,
valid: bool,
}
impl TTMacroExpander for MacroRulesMacroExpander {
fn expand<'cx>(
&self,
cx: &'cx mut ExtCtxt<'_>,
sp: Span,
input: TokenStream,
def_span: Option<Span>,
) -> Box<dyn MacResult+'cx> {
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<Span>,
name: ast::Ident,
arg: TokenStream,
lhses: &[quoted::TokenTree],
rhses: &[quoted::TokenTree])
-> Box<dyn MacResult+'cx> {
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::<Vec<_>>();
// rhs has holes ( `$id` and `$(...)` that need filled)
let mut tts = transcribe(cx, &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, None);
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::from_str("lhs").gensym();
let rhs_nm = ast::Ident::from_str("rhs").gensym();
// 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::<Vec<quoted::TokenTree>>()
}
_ => 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::<Vec<quoted::TokenTree>>()
}
_ => 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, sym::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::<Vec<Symbol>>().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![sym::allow_internal_unstable_backcompat_hack].into()
})
);
let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);
let mut local_inner_macros = false;
if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
if let Some(l) = macro_export.meta_item_list() {
local_inner_macros = attr::list_contains_name(&l, sym::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, sym::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 == sym::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<Ident, Span>,
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<Span, Option<TokenSet>>,
}
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<quoted::TokenTree>,
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!("`${name}:{frag}` {may_be} followed by `{next}`, which \
is not allowed for `{frag}` fragments",
name=name,
frag=frag_spec,
next=quoted_tt_to_string(next_token),
may_be=may_be),
);
err.span_label(
sp,
format!("not allowed after `{}` fragments", frag_spec),
);
let msg = "allowed there are: ";
match &possible[..] {
&[] => {}
&[t] => {
err.note(&format!(
"only {} is allowed after `{}` fragments",
t,
frag_spec,
));
}
ts => {
err.note(&format!(
"{}{} or {}",
msg,
ts[..ts.len() - 1].iter().map(|s| *s)
.collect::<Vec<_>>().join(", "),
ts[ts.len() - 1],
));
}
}
err.emit();
}
}
}
}
}
}
last
}
fn token_can_be_followed_by_any(tok: "ed::TokenTree) -> bool {
if let quoted::TokenTree::MetaVarDecl(_, _, frag_spec) = *tok {
frag_can_be_followed_by_any(&frag_spec.as_str())
} else {
// (Non NT's can always be followed by anthing in matchers.)
true
}
}
/// Returns `true` if a fragment of type `frag` can be followed by any sort of
/// token. We use this (among other things) as a useful approximation
/// for when `frag` can be followed by a repetition like `$(...)*` 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 == kw::If ||
i.name == kw::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 == kw::As ||
i.name == kw::Where => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
},
TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::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 != kw::Priv =>
IsInFollow::Yes,
ref tok => if tok.can_begin_type() {
IsInFollow::Yes
} else {
IsInFollow::No(tokens)
}
},
TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::ident
|| frag.name == sym::ty
|| frag.name == sym::path =>
IsInFollow::Yes,
_ => IsInFollow::No(tokens),
}
},
"" => IsInFollow::Yes, // kw::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"),
}
}