391 lines
17 KiB
Rust
391 lines
17 KiB
Rust
use crate::base::ExtCtxt;
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use crate::mbe;
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use crate::mbe::macro_parser::{MatchedNonterminal, MatchedSeq, NamedMatch};
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use rustc_data_structures::fx::FxHashMap;
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use rustc_data_structures::sync::Lrc;
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use rustc_errors::pluralize;
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use rustc_span::hygiene::{ExpnId, Transparency};
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use rustc_span::Span;
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use syntax::ast::{Ident, Mac};
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use syntax::mut_visit::{self, MutVisitor};
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use syntax::token::{self, NtTT, Token};
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use syntax::tokenstream::{DelimSpan, TokenStream, TokenTree, TreeAndJoint};
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use smallvec::{smallvec, SmallVec};
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use std::mem;
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// A Marker adds the given mark to the syntax context.
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struct Marker(ExpnId, Transparency);
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impl MutVisitor for Marker {
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fn visit_span(&mut self, span: &mut Span) {
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*span = span.apply_mark(self.0, self.1)
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}
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fn visit_mac(&mut self, mac: &mut Mac) {
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mut_visit::noop_visit_mac(mac, self)
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}
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}
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/// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
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enum Frame {
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Delimited { forest: Lrc<mbe::Delimited>, idx: usize, span: DelimSpan },
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Sequence { forest: Lrc<mbe::SequenceRepetition>, idx: usize, sep: Option<Token> },
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}
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impl Frame {
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/// Construct a new frame around the delimited set of tokens.
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fn new(tts: Vec<mbe::TokenTree>) -> Frame {
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let forest = Lrc::new(mbe::Delimited { delim: token::NoDelim, tts });
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Frame::Delimited { forest, idx: 0, span: DelimSpan::dummy() }
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}
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}
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impl Iterator for Frame {
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type Item = mbe::TokenTree;
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fn next(&mut self) -> Option<mbe::TokenTree> {
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match *self {
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Frame::Delimited { ref forest, ref mut idx, .. } => {
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*idx += 1;
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forest.tts.get(*idx - 1).cloned()
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}
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Frame::Sequence { ref forest, ref mut idx, .. } => {
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*idx += 1;
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forest.tts.get(*idx - 1).cloned()
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}
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}
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}
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}
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/// This can do Macro-By-Example transcription.
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/// - `interp` is a map of meta-variables to the tokens (non-terminals) they matched in the
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/// invocation. We are assuming we already know there is a match.
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/// - `src` is the RHS of the MBE, that is, the "example" we are filling in.
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///
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/// For example,
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///
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/// ```rust
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/// macro_rules! foo {
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/// ($id:ident) => { println!("{}", stringify!($id)); }
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/// }
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///
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/// foo!(bar);
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/// ```
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///
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/// `interp` would contain `$id => bar` and `src` would contain `println!("{}", stringify!($id));`.
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///
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/// `transcribe` would return a `TokenStream` containing `println!("{}", stringify!(bar));`.
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///
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/// Along the way, we do some additional error checking.
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pub(super) fn transcribe(
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cx: &ExtCtxt<'_>,
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interp: &FxHashMap<Ident, NamedMatch>,
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src: Vec<mbe::TokenTree>,
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transparency: Transparency,
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) -> TokenStream {
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// Nothing for us to transcribe...
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if src.is_empty() {
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return TokenStream::default();
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}
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// We descend into the RHS (`src`), expanding things as we go. This stack contains the things
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// we have yet to expand/are still expanding. We start the stack off with the whole RHS.
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let mut stack: SmallVec<[Frame; 1]> = smallvec![Frame::new(src)];
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// As we descend in the RHS, we will need to be able to match nested sequences of matchers.
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// `repeats` keeps track of where we are in matching at each level, with the last element being
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// the most deeply nested sequence. This is used as a stack.
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let mut repeats = Vec::new();
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// `result` contains resulting token stream from the TokenTree we just finished processing. At
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// the end, this will contain the full result of transcription, but at arbitrary points during
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// `transcribe`, `result` will contain subsets of the final result.
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//
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// Specifically, as we descend into each TokenTree, we will push the existing results onto the
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// `result_stack` and clear `results`. We will then produce the results of transcribing the
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// TokenTree into `results`. Then, as we unwind back out of the `TokenTree`, we will pop the
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// `result_stack` and append `results` too it to produce the new `results` up to that point.
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//
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// Thus, if we try to pop the `result_stack` and it is empty, we have reached the top-level
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// again, and we are done transcribing.
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let mut result: Vec<TreeAndJoint> = Vec::new();
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let mut result_stack = Vec::new();
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let mut marker = Marker(cx.current_expansion.id, transparency);
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loop {
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// Look at the last frame on the stack.
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let tree = if let Some(tree) = stack.last_mut().unwrap().next() {
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// If it still has a TokenTree we have not looked at yet, use that tree.
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tree
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}
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// The else-case never produces a value for `tree` (it `continue`s or `return`s).
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else {
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// Otherwise, if we have just reached the end of a sequence and we can keep repeating,
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// go back to the beginning of the sequence.
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if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
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let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
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*repeat_idx += 1;
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if repeat_idx < repeat_len {
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*idx = 0;
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if let Some(sep) = sep {
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result.push(TokenTree::Token(sep.clone()).into());
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}
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continue;
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}
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}
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// We are done with the top of the stack. Pop it. Depending on what it was, we do
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// different things. Note that the outermost item must be the delimited, wrapped RHS
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// that was passed in originally to `transcribe`.
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match stack.pop().unwrap() {
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// Done with a sequence. Pop from repeats.
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Frame::Sequence { .. } => {
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repeats.pop();
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}
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// We are done processing a Delimited. If this is the top-level delimited, we are
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// done. Otherwise, we unwind the result_stack to append what we have produced to
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// any previous results.
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Frame::Delimited { forest, span, .. } => {
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if result_stack.is_empty() {
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// No results left to compute! We are back at the top-level.
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return TokenStream::new(result);
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}
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// Step back into the parent Delimited.
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let tree =
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TokenTree::Delimited(span, forest.delim, TokenStream::new(result).into());
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result = result_stack.pop().unwrap();
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result.push(tree.into());
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}
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}
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continue;
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};
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// At this point, we know we are in the middle of a TokenTree (the last one on `stack`).
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// `tree` contains the next `TokenTree` to be processed.
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match tree {
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// We are descending into a sequence. We first make sure that the matchers in the RHS
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// and the matches in `interp` have the same shape. Otherwise, either the caller or the
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// macro writer has made a mistake.
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seq @ mbe::TokenTree::Sequence(..) => {
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match lockstep_iter_size(&seq, interp, &repeats) {
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LockstepIterSize::Unconstrained => {
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cx.span_fatal(
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seq.span(), /* blame macro writer */
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"attempted to repeat an expression containing no syntax variables \
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matched as repeating at this depth",
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);
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}
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LockstepIterSize::Contradiction(ref msg) => {
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// FIXME: this really ought to be caught at macro definition time... It
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// happens when two meta-variables are used in the same repetition in a
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// sequence, but they come from different sequence matchers and repeat
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// different amounts.
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cx.span_fatal(seq.span(), &msg[..]);
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}
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LockstepIterSize::Constraint(len, _) => {
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// We do this to avoid an extra clone above. We know that this is a
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// sequence already.
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let (sp, seq) = if let mbe::TokenTree::Sequence(sp, seq) = seq {
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(sp, seq)
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} else {
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unreachable!()
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};
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// Is the repetition empty?
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if len == 0 {
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if seq.kleene.op == mbe::KleeneOp::OneOrMore {
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// FIXME: this really ought to be caught at macro definition
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// time... It happens when the Kleene operator in the matcher and
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// the body for the same meta-variable do not match.
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cx.span_fatal(sp.entire(), "this must repeat at least once");
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}
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} else {
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// 0 is the initial counter (we have done 0 repretitions so far). `len`
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// is the total number of reptitions we should generate.
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repeats.push((0, len));
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// The first time we encounter the sequence we push it to the stack. It
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// then gets reused (see the beginning of the loop) until we are done
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// repeating.
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stack.push(Frame::Sequence {
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idx: 0,
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sep: seq.separator.clone(),
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forest: seq,
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});
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}
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}
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}
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}
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// Replace the meta-var with the matched token tree from the invocation.
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mbe::TokenTree::MetaVar(mut sp, mut ident) => {
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// Find the matched nonterminal from the macro invocation, and use it to replace
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// the meta-var.
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if let Some(cur_matched) = lookup_cur_matched(ident, interp, &repeats) {
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if let MatchedNonterminal(ref nt) = cur_matched {
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// FIXME #2887: why do we apply a mark when matching a token tree meta-var
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// (e.g. `$x:tt`), but not when we are matching any other type of token
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// tree?
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if let NtTT(ref tt) = **nt {
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result.push(tt.clone().into());
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} else {
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marker.visit_span(&mut sp);
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let token = TokenTree::token(token::Interpolated(nt.clone()), sp);
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result.push(token.into());
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}
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} else {
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// We were unable to descend far enough. This is an error.
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cx.span_fatal(
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sp, /* blame the macro writer */
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&format!("variable '{}' is still repeating at this depth", ident),
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);
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}
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} else {
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// If we aren't able to match the meta-var, we push it back into the result but
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// with modified syntax context. (I believe this supports nested macros).
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marker.visit_span(&mut sp);
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marker.visit_ident(&mut ident);
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result.push(TokenTree::token(token::Dollar, sp).into());
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result.push(TokenTree::Token(Token::from_ast_ident(ident)).into());
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}
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}
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// If we are entering a new delimiter, we push its contents to the `stack` to be
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// processed, and we push all of the currently produced results to the `result_stack`.
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// We will produce all of the results of the inside of the `Delimited` and then we will
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// jump back out of the Delimited, pop the result_stack and add the new results back to
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// the previous results (from outside the Delimited).
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mbe::TokenTree::Delimited(mut span, delimited) => {
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mut_visit::visit_delim_span(&mut span, &mut marker);
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stack.push(Frame::Delimited { forest: delimited, idx: 0, span });
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result_stack.push(mem::take(&mut result));
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}
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// Nothing much to do here. Just push the token to the result, being careful to
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// preserve syntax context.
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mbe::TokenTree::Token(token) => {
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let mut tt = TokenTree::Token(token);
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marker.visit_tt(&mut tt);
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result.push(tt.into());
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}
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// There should be no meta-var declarations in the invocation of a macro.
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mbe::TokenTree::MetaVarDecl(..) => panic!("unexpected `TokenTree::MetaVarDecl"),
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}
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}
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}
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/// Lookup the meta-var named `ident` and return the matched token tree from the invocation using
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/// the set of matches `interpolations`.
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///
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/// See the definition of `repeats` in the `transcribe` function. `repeats` is used to descend
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/// into the right place in nested matchers. If we attempt to descend too far, the macro writer has
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/// made a mistake, and we return `None`.
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fn lookup_cur_matched<'a>(
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ident: Ident,
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interpolations: &'a FxHashMap<Ident, NamedMatch>,
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repeats: &[(usize, usize)],
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) -> Option<&'a NamedMatch> {
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interpolations.get(&ident).map(|matched| {
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let mut matched = matched;
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for &(idx, _) in repeats {
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match matched {
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MatchedNonterminal(_) => break,
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MatchedSeq(ref ads) => matched = ads.get(idx).unwrap(),
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}
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}
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matched
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})
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}
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/// An accumulator over a TokenTree to be used with `fold`. During transcription, we need to make
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/// sure that the size of each sequence and all of its nested sequences are the same as the sizes
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/// of all the matched (nested) sequences in the macro invocation. If they don't match, somebody
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/// has made a mistake (either the macro writer or caller).
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#[derive(Clone)]
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enum LockstepIterSize {
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/// No constraints on length of matcher. This is true for any TokenTree variants except a
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/// `MetaVar` with an actual `MatchedSeq` (as opposed to a `MatchedNonterminal`).
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Unconstrained,
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/// A `MetaVar` with an actual `MatchedSeq`. The length of the match and the name of the
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/// meta-var are returned.
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Constraint(usize, Ident),
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/// Two `Constraint`s on the same sequence had different lengths. This is an error.
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Contradiction(String),
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}
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impl LockstepIterSize {
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/// Find incompatibilities in matcher/invocation sizes.
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/// - `Unconstrained` is compatible with everything.
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/// - `Contradiction` is incompatible with everything.
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/// - `Constraint(len)` is only compatible with other constraints of the same length.
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fn with(self, other: LockstepIterSize) -> LockstepIterSize {
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match self {
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LockstepIterSize::Unconstrained => other,
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LockstepIterSize::Contradiction(_) => self,
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LockstepIterSize::Constraint(l_len, ref l_id) => match other {
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LockstepIterSize::Unconstrained => self,
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LockstepIterSize::Contradiction(_) => other,
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LockstepIterSize::Constraint(r_len, _) if l_len == r_len => self,
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LockstepIterSize::Constraint(r_len, r_id) => {
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let msg = format!(
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"meta-variable `{}` repeats {} time{}, but `{}` repeats {} time{}",
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l_id,
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l_len,
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pluralize!(l_len),
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r_id,
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r_len,
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pluralize!(r_len),
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);
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LockstepIterSize::Contradiction(msg)
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}
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},
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}
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}
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}
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/// Given a `tree`, make sure that all sequences have the same length as the matches for the
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/// appropriate meta-vars in `interpolations`.
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///
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/// Note that if `repeats` does not match the exact correct depth of a meta-var,
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/// `lookup_cur_matched` will return `None`, which is why this still works even in the presnece of
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/// multiple nested matcher sequences.
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fn lockstep_iter_size(
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tree: &mbe::TokenTree,
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interpolations: &FxHashMap<Ident, NamedMatch>,
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repeats: &[(usize, usize)],
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) -> LockstepIterSize {
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use mbe::TokenTree;
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match *tree {
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TokenTree::Delimited(_, ref delimed) => {
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delimed.tts.iter().fold(LockstepIterSize::Unconstrained, |size, tt| {
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size.with(lockstep_iter_size(tt, interpolations, repeats))
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})
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}
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TokenTree::Sequence(_, ref seq) => {
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seq.tts.iter().fold(LockstepIterSize::Unconstrained, |size, tt| {
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size.with(lockstep_iter_size(tt, interpolations, repeats))
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})
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}
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TokenTree::MetaVar(_, name) | TokenTree::MetaVarDecl(_, name, _) => {
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match lookup_cur_matched(name, interpolations, repeats) {
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Some(matched) => match matched {
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MatchedNonterminal(_) => LockstepIterSize::Unconstrained,
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MatchedSeq(ref ads) => LockstepIterSize::Constraint(ads.len(), name),
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},
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_ => LockstepIterSize::Unconstrained,
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}
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}
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TokenTree::Token(..) => LockstepIterSize::Unconstrained,
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}
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}
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