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use crate::base::ExtCtxt;
use crate::errors::{
CountRepetitionMisplaced, MetaVarExprUnrecognizedVar, MetaVarsDifSeqMatchers, MustRepeatOnce,
NoSyntaxVarsExprRepeat, VarStillRepeating,
};
use crate::mbe::macro_parser::{MatchedNonterminal, MatchedSeq, MatchedTokenTree, NamedMatch};
use crate::mbe::{self, MetaVarExpr};
use rustc_ast::mut_visit::{self, MutVisitor};
use rustc_ast::token::{self, Delimiter, Token, TokenKind};
use rustc_ast::tokenstream::{DelimSpan, Spacing, TokenStream, TokenTree};
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{pluralize, PResult};
use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
use rustc_span::hygiene::{LocalExpnId, Transparency};
use rustc_span::symbol::{sym, Ident, MacroRulesNormalizedIdent};
use rustc_span::Span;
use smallvec::{smallvec, SmallVec};
use std::mem;
// A Marker adds the given mark to the syntax context.
struct Marker(LocalExpnId, Transparency);
impl MutVisitor for Marker {
const VISIT_TOKENS: bool = true;
fn visit_span(&mut self, span: &mut Span) {
*span = span.apply_mark(self.0.to_expn_id(), self.1)
}
}
/// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
enum Frame<'a> {
Delimited { tts: &'a [mbe::TokenTree], idx: usize, delim: Delimiter, span: DelimSpan },
Sequence { tts: &'a [mbe::TokenTree], idx: usize, sep: Option<Token> },
}
impl<'a> Frame<'a> {
/// Construct a new frame around the delimited set of tokens.
fn new(src: &'a mbe::Delimited, span: DelimSpan) -> Frame<'a> {
Frame::Delimited { tts: &src.tts, idx: 0, delim: src.delim, span }
}
}
impl<'a> Iterator for Frame<'a> {
type Item = &'a mbe::TokenTree;
fn next(&mut self) -> Option<&'a mbe::TokenTree> {
match self {
Frame::Delimited { tts, idx, .. } | Frame::Sequence { tts, idx, .. } => {
let res = tts.get(*idx);
*idx += 1;
res
}
}
}
}
/// This can do Macro-By-Example transcription.
/// - `interp` is a map of meta-variables to the tokens (non-terminals) they matched in the
/// invocation. We are assuming we already know there is a match.
/// - `src` is the RHS of the MBE, that is, the "example" we are filling in.
///
/// For example,
///
/// ```rust
/// macro_rules! foo {
/// ($id:ident) => { println!("{}", stringify!($id)); }
/// }
///
/// foo!(bar);
/// ```
///
/// `interp` would contain `$id => bar` and `src` would contain `println!("{}", stringify!($id));`.
///
/// `transcribe` would return a `TokenStream` containing `println!("{}", stringify!(bar));`.
///
/// Along the way, we do some additional error checking.
pub(super) fn transcribe<'a>(
cx: &ExtCtxt<'a>,
interp: &FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
src: &mbe::Delimited,
src_span: DelimSpan,
transparency: Transparency,
) -> PResult<'a, TokenStream> {
// Nothing for us to transcribe...
if src.tts.is_empty() {
return Ok(TokenStream::default());
}
// We descend into the RHS (`src`), expanding things as we go. This stack contains the things
// we have yet to expand/are still expanding. We start the stack off with the whole RHS.
let mut stack: SmallVec<[Frame<'_>; 1]> = smallvec![Frame::new(&src, src_span)];
// As we descend in the RHS, we will need to be able to match nested sequences of matchers.
// `repeats` keeps track of where we are in matching at each level, with the last element being
// the most deeply nested sequence. This is used as a stack.
let mut repeats = Vec::new();
// `result` contains resulting token stream from the TokenTree we just finished processing. At
// the end, this will contain the full result of transcription, but at arbitrary points during
// `transcribe`, `result` will contain subsets of the final result.
//
// Specifically, as we descend into each TokenTree, we will push the existing results onto the
// `result_stack` and clear `results`. We will then produce the results of transcribing the
// TokenTree into `results`. Then, as we unwind back out of the `TokenTree`, we will pop the
// `result_stack` and append `results` too it to produce the new `results` up to that point.
//
// Thus, if we try to pop the `result_stack` and it is empty, we have reached the top-level
// again, and we are done transcribing.
let mut result: Vec<TokenTree> = Vec::new();
let mut result_stack = Vec::new();
let mut marker = Marker(cx.current_expansion.id, transparency);
loop {
// Look at the last frame on the stack.
// If it still has a TokenTree we have not looked at yet, use that tree.
let Some(tree) = stack.last_mut().unwrap().next() else {
// This else-case never produces a value for `tree` (it `continue`s or `return`s).
// Otherwise, if we have just reached the end of a sequence and we can keep repeating,
// go back to the beginning of the sequence.
if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
*repeat_idx += 1;
if repeat_idx < repeat_len {
*idx = 0;
if let Some(sep) = sep {
result.push(TokenTree::Token(sep.clone(), Spacing::Alone));
}
continue;
}
}
// We are done with the top of the stack. Pop it. Depending on what it was, we do
// different things. Note that the outermost item must be the delimited, wrapped RHS
// that was passed in originally to `transcribe`.
match stack.pop().unwrap() {
// Done with a sequence. Pop from repeats.
Frame::Sequence { .. } => {
repeats.pop();
}
// We are done processing a Delimited. If this is the top-level delimited, we are
// done. Otherwise, we unwind the result_stack to append what we have produced to
// any previous results.
Frame::Delimited { delim, span, .. } => {
if result_stack.is_empty() {
// No results left to compute! We are back at the top-level.
return Ok(TokenStream::new(result));
}
// Step back into the parent Delimited.
let tree = TokenTree::Delimited(span, delim, TokenStream::new(result));
result = result_stack.pop().unwrap();
result.push(tree);
}
}
continue;
};
// At this point, we know we are in the middle of a TokenTree (the last one on `stack`).
// `tree` contains the next `TokenTree` to be processed.
match tree {
// We are descending into a sequence. We first make sure that the matchers in the RHS
// and the matches in `interp` have the same shape. Otherwise, either the caller or the
// macro writer has made a mistake.
seq @ mbe::TokenTree::Sequence(_, delimited) => {
match lockstep_iter_size(&seq, interp, &repeats) {
LockstepIterSize::Unconstrained => {
return Err(cx.create_err(NoSyntaxVarsExprRepeat { span: seq.span() }));
}
LockstepIterSize::Contradiction(msg) => {
// FIXME: this really ought to be caught at macro definition time... It
// happens when two meta-variables are used in the same repetition in a
// sequence, but they come from different sequence matchers and repeat
// different amounts.
return Err(cx.create_err(MetaVarsDifSeqMatchers { span: seq.span(), msg }));
}
LockstepIterSize::Constraint(len, _) => {
// We do this to avoid an extra clone above. We know that this is a
// sequence already.
let mbe::TokenTree::Sequence(sp, seq) = seq else { unreachable!() };
// Is the repetition empty?
if len == 0 {
if seq.kleene.op == mbe::KleeneOp::OneOrMore {
// FIXME: this really ought to be caught at macro definition
// time... It happens when the Kleene operator in the matcher and
// the body for the same meta-variable do not match.
return Err(cx.create_err(MustRepeatOnce { span: sp.entire() }));
}
} else {
// 0 is the initial counter (we have done 0 repetitions so far). `len`
// is the total number of repetitions we should generate.
repeats.push((0, len));
// The first time we encounter the sequence we push it to the stack. It
// then gets reused (see the beginning of the loop) until we are done
// repeating.
stack.push(Frame::Sequence {
idx: 0,
sep: seq.separator.clone(),
tts: &delimited.tts,
});
}
}
}
}
// Replace the meta-var with the matched token tree from the invocation.
mbe::TokenTree::MetaVar(mut sp, mut original_ident) => {
// Find the matched nonterminal from the macro invocation, and use it to replace
// the meta-var.
let ident = MacroRulesNormalizedIdent::new(original_ident);
if let Some(cur_matched) = lookup_cur_matched(ident, interp, &repeats) {
match cur_matched {
MatchedTokenTree(tt) => {
// `tt`s are emitted into the output stream directly as "raw tokens",
// without wrapping them into groups.
result.push(tt.clone());
}
MatchedNonterminal(nt) => {
// Other variables are emitted into the output stream as groups with
// `Delimiter::Invisible` to maintain parsing priorities.
// `Interpolated` is currently used for such groups in rustc parser.
marker.visit_span(&mut sp);
result
.push(TokenTree::token_alone(token::Interpolated(nt.clone()), sp));
}
MatchedSeq(..) => {
// We were unable to descend far enough. This is an error.
return Err(cx.create_err(VarStillRepeating { span: sp, ident }));
}
}
} else {
// If we aren't able to match the meta-var, we push it back into the result but
// with modified syntax context. (I believe this supports nested macros).
marker.visit_span(&mut sp);
marker.visit_ident(&mut original_ident);
result.push(TokenTree::token_alone(token::Dollar, sp));
result.push(TokenTree::Token(
Token::from_ast_ident(original_ident),
Spacing::Alone,
));
}
}
// Replace meta-variable expressions with the result of their expansion.
mbe::TokenTree::MetaVarExpr(sp, expr) => {
transcribe_metavar_expr(cx, expr, interp, &mut marker, &repeats, &mut result, &sp)?;
}
// If we are entering a new delimiter, we push its contents to the `stack` to be
// processed, and we push all of the currently produced results to the `result_stack`.
// We will produce all of the results of the inside of the `Delimited` and then we will
// jump back out of the Delimited, pop the result_stack and add the new results back to
// the previous results (from outside the Delimited).
mbe::TokenTree::Delimited(mut span, delimited) => {
mut_visit::visit_delim_span(&mut span, &mut marker);
stack.push(Frame::Delimited {
tts: &delimited.tts,
delim: delimited.delim,
idx: 0,
span,
});
result_stack.push(mem::take(&mut result));
}
// Nothing much to do here. Just push the token to the result, being careful to
// preserve syntax context.
mbe::TokenTree::Token(token) => {
let mut token = token.clone();
mut_visit::visit_token(&mut token, &mut marker);
let tt = TokenTree::Token(token, Spacing::Alone);
result.push(tt);
}
// There should be no meta-var declarations in the invocation of a macro.
mbe::TokenTree::MetaVarDecl(..) => panic!("unexpected `TokenTree::MetaVarDecl`"),
}
}
}
/// Lookup the meta-var named `ident` and return the matched token tree from the invocation using
/// the set of matches `interpolations`.
///
/// See the definition of `repeats` in the `transcribe` function. `repeats` is used to descend
/// into the right place in nested matchers. If we attempt to descend too far, the macro writer has
/// made a mistake, and we return `None`.
fn lookup_cur_matched<'a>(
ident: MacroRulesNormalizedIdent,
interpolations: &'a FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
repeats: &[(usize, usize)],
) -> Option<&'a NamedMatch> {
interpolations.get(&ident).map(|mut matched| {
for &(idx, _) in repeats {
match matched {
MatchedTokenTree(_) | MatchedNonterminal(_) => break,
MatchedSeq(ads) => matched = ads.get(idx).unwrap(),
}
}
matched
})
}
/// An accumulator over a TokenTree to be used with `fold`. During transcription, we need to make
/// sure that the size of each sequence and all of its nested sequences are the same as the sizes
/// of all the matched (nested) sequences in the macro invocation. If they don't match, somebody
/// has made a mistake (either the macro writer or caller).
#[derive(Clone)]
enum LockstepIterSize {
/// No constraints on length of matcher. This is true for any TokenTree variants except a
/// `MetaVar` with an actual `MatchedSeq` (as opposed to a `MatchedNonterminal`).
Unconstrained,
/// A `MetaVar` with an actual `MatchedSeq`. The length of the match and the name of the
/// meta-var are returned.
Constraint(usize, MacroRulesNormalizedIdent),
/// Two `Constraint`s on the same sequence had different lengths. This is an error.
Contradiction(String),
}
impl LockstepIterSize {
/// Find incompatibilities in matcher/invocation sizes.
/// - `Unconstrained` is compatible with everything.
/// - `Contradiction` is incompatible with everything.
/// - `Constraint(len)` is only compatible with other constraints of the same length.
fn with(self, other: LockstepIterSize) -> LockstepIterSize {
match self {
LockstepIterSize::Unconstrained => other,
LockstepIterSize::Contradiction(_) => self,
LockstepIterSize::Constraint(l_len, l_id) => match other {
LockstepIterSize::Unconstrained => self,
LockstepIterSize::Contradiction(_) => other,
LockstepIterSize::Constraint(r_len, _) if l_len == r_len => self,
LockstepIterSize::Constraint(r_len, r_id) => {
let msg = format!(
"meta-variable `{}` repeats {} time{}, but `{}` repeats {} time{}",
l_id,
l_len,
pluralize!(l_len),
r_id,
r_len,
pluralize!(r_len),
);
LockstepIterSize::Contradiction(msg)
}
},
}
}
}
/// Given a `tree`, make sure that all sequences have the same length as the matches for the
/// appropriate meta-vars in `interpolations`.
///
/// Note that if `repeats` does not match the exact correct depth of a meta-var,
/// `lookup_cur_matched` will return `None`, which is why this still works even in the presence of
/// multiple nested matcher sequences.
///
/// Example: `$($($x $y)+*);+` -- we need to make sure that `x` and `y` repeat the same amount as
/// each other at the given depth when the macro was invoked. If they don't it might mean they were
/// declared at depths which weren't equal or there was a compiler bug. For example, if we have 3 repetitions of
/// the outer sequence and 4 repetitions of the inner sequence for `x`, we should have the same for
/// `y`; otherwise, we can't transcribe them both at the given depth.
fn lockstep_iter_size(
tree: &mbe::TokenTree,
interpolations: &FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
repeats: &[(usize, usize)],
) -> LockstepIterSize {
use mbe::TokenTree;
match tree {
TokenTree::Delimited(_, delimited) => {
delimited.tts.iter().fold(LockstepIterSize::Unconstrained, |size, tt| {
size.with(lockstep_iter_size(tt, interpolations, repeats))
})
}
TokenTree::Sequence(_, seq) => {
seq.tts.iter().fold(LockstepIterSize::Unconstrained, |size, tt| {
size.with(lockstep_iter_size(tt, interpolations, repeats))
})
}
TokenTree::MetaVar(_, name) | TokenTree::MetaVarDecl(_, name, _) => {
let name = MacroRulesNormalizedIdent::new(*name);
match lookup_cur_matched(name, interpolations, repeats) {
Some(matched) => match matched {
MatchedTokenTree(_) | MatchedNonterminal(_) => LockstepIterSize::Unconstrained,
MatchedSeq(ads) => LockstepIterSize::Constraint(ads.len(), name),
},
_ => LockstepIterSize::Unconstrained,
}
}
TokenTree::MetaVarExpr(_, expr) => {
let default_rslt = LockstepIterSize::Unconstrained;
let Some(ident) = expr.ident() else {
return default_rslt;
};
let name = MacroRulesNormalizedIdent::new(ident);
match lookup_cur_matched(name, interpolations, repeats) {
Some(MatchedSeq(ads)) => {
default_rslt.with(LockstepIterSize::Constraint(ads.len(), name))
}
_ => default_rslt,
}
}
TokenTree::Token(..) => LockstepIterSize::Unconstrained,
}
}
/// Used solely by the `count` meta-variable expression, counts the outer-most repetitions at a
/// given optional nested depth.
///
/// For example, a macro parameter of `$( { $( $foo:ident ),* } )*` called with `{ a, b } { c }`:
///
/// * `[ $( ${count(foo)} ),* ]` will return [2, 1] with a, b = 2 and c = 1
/// * `[ $( ${count(foo, 0)} ),* ]` will be the same as `[ $( ${count(foo)} ),* ]`
/// * `[ $( ${count(foo, 1)} ),* ]` will return an error because `${count(foo, 1)}` is
/// declared inside a single repetition and the index `1` implies two nested repetitions.
fn count_repetitions<'a>(
cx: &ExtCtxt<'a>,
depth_opt: Option<usize>,
mut matched: &NamedMatch,
repeats: &[(usize, usize)],
sp: &DelimSpan,
) -> PResult<'a, usize> {
// Recursively count the number of matches in `matched` at given depth
// (or at the top-level of `matched` if no depth is given).
fn count<'a>(
cx: &ExtCtxt<'a>,
declared_lhs_depth: usize,
depth_opt: Option<usize>,
matched: &NamedMatch,
sp: &DelimSpan,
) -> PResult<'a, usize> {
match matched {
MatchedTokenTree(_) | MatchedNonterminal(_) => {
if declared_lhs_depth == 0 {
return Err(cx.create_err(CountRepetitionMisplaced { span: sp.entire() }));
}
match depth_opt {
None => Ok(1),
Some(_) => Err(out_of_bounds_err(cx, declared_lhs_depth, sp.entire(), "count")),
}
}
MatchedSeq(named_matches) => {
let new_declared_lhs_depth = declared_lhs_depth + 1;
match depth_opt {
None => named_matches
.iter()
.map(|elem| count(cx, new_declared_lhs_depth, None, elem, sp))
.sum(),
Some(0) => Ok(named_matches.len()),
Some(depth) => named_matches
.iter()
.map(|elem| count(cx, new_declared_lhs_depth, Some(depth - 1), elem, sp))
.sum(),
}
}
}
}
// `repeats` records all of the nested levels at which we are currently
// matching meta-variables. The meta-var-expr `count($x)` only counts
// matches that occur in this "subtree" of the `NamedMatch` where we
// are currently transcribing, so we need to descend to that subtree
// before we start counting. `matched` contains the various levels of the
// tree as we descend, and its final value is the subtree we are currently at.
for &(idx, _) in repeats {
if let MatchedSeq(ads) = matched {
matched = &ads[idx];
}
}
count(cx, 0, depth_opt, matched, sp)
}
/// Returns a `NamedMatch` item declared on the LHS given an arbitrary [Ident]
fn matched_from_ident<'ctx, 'interp, 'rslt>(
cx: &ExtCtxt<'ctx>,
ident: Ident,
interp: &'interp FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
) -> PResult<'ctx, &'rslt NamedMatch>
where
'interp: 'rslt,
{
let span = ident.span;
let key = MacroRulesNormalizedIdent::new(ident);
interp.get(&key).ok_or_else(|| cx.create_err(MetaVarExprUnrecognizedVar { span, key }))
}
/// Used by meta-variable expressions when an user input is out of the actual declared bounds. For
/// example, index(999999) in an repetition of only three elements.
fn out_of_bounds_err<'a>(
cx: &ExtCtxt<'a>,
max: usize,
span: Span,
ty: &str,
) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
let msg = if max == 0 {
format!(
"meta-variable expression `{ty}` with depth parameter \
must be called inside of a macro repetition"
)
} else {
format!(
"depth parameter on meta-variable expression `{ty}` \
must be less than {max}"
)
};
cx.struct_span_err(span, msg)
}
fn transcribe_metavar_expr<'a>(
cx: &ExtCtxt<'a>,
expr: &MetaVarExpr,
interp: &FxHashMap<MacroRulesNormalizedIdent, NamedMatch>,
marker: &mut Marker,
repeats: &[(usize, usize)],
result: &mut Vec<TokenTree>,
sp: &DelimSpan,
) -> PResult<'a, ()> {
let mut visited_span = || {
let mut span = sp.entire();
marker.visit_span(&mut span);
span
};
match *expr {
MetaVarExpr::Count(original_ident, depth_opt) => {
let matched = matched_from_ident(cx, original_ident, interp)?;
let count = count_repetitions(cx, depth_opt, matched, &repeats, sp)?;
let tt = TokenTree::token_alone(
TokenKind::lit(token::Integer, sym::integer(count), None),
visited_span(),
);
result.push(tt);
}
MetaVarExpr::Ignore(original_ident) => {
// Used to ensure that `original_ident` is present in the LHS
let _ = matched_from_ident(cx, original_ident, interp)?;
}
MetaVarExpr::Index(depth) => match repeats.iter().nth_back(depth) {
Some((index, _)) => {
result.push(TokenTree::token_alone(
TokenKind::lit(token::Integer, sym::integer(*index), None),
visited_span(),
));
}
None => return Err(out_of_bounds_err(cx, repeats.len(), sp.entire(), "index")),
},
MetaVarExpr::Length(depth) => match repeats.iter().nth_back(depth) {
Some((_, length)) => {
result.push(TokenTree::token_alone(
TokenKind::lit(token::Integer, sym::integer(*length), None),
visited_span(),
));
}
None => return Err(out_of_bounds_err(cx, repeats.len(), sp.entire(), "length")),
},
}
Ok(())
}