284 lines
9.9 KiB
Rust
284 lines
9.9 KiB
Rust
/// This module takes a (parsed) definition of `macro_rules` invocation, a
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/// `tt::TokenTree` representing an argument of macro invocation, and produces a
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/// `tt::TokenTree` for the result of the expansion.
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use rustc_hash::FxHashMap;
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use ra_syntax::SmolStr;
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use tt::TokenId;
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use crate::ExpandError;
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use crate::tt_cursor::TtCursor;
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pub(crate) fn expand(
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rules: &crate::MacroRules,
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input: &tt::Subtree,
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) -> Result<tt::Subtree, ExpandError> {
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rules.rules.iter().find_map(|it| expand_rule(it, input).ok()).ok_or(ExpandError::NoMatchingRule)
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}
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fn expand_rule(rule: &crate::Rule, input: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
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let mut input = TtCursor::new(input);
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let bindings = match_lhs(&rule.lhs, &mut input)?;
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if !input.is_eof() {
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return Err(ExpandError::UnexpectedToken);
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}
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expand_subtree(&rule.rhs, &bindings, &mut Vec::new())
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}
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/// The actual algorithm for expansion is not too hard, but is pretty tricky.
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/// `Bindings` structure is the key to understanding what we are doing here.
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///
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/// On the high level, it stores mapping from meta variables to the bits of
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/// syntax it should be substituted with. For example, if `$e:expr` is matched
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/// with `1 + 1` by macro_rules, the `Binding` will store `$e -> 1 + 1`.
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///
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/// The tricky bit is dealing with repetitions (`$()*`). Consider this example:
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///
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/// ```not_rust
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/// macro_rules! foo {
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/// ($($ i:ident $($ e:expr),*);*) => {
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/// $(fn $ i() { $($ e);*; })*
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/// }
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/// }
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/// foo! { foo 1,2,3; bar 4,5,6 }
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/// ```
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///
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/// Here, the `$i` meta variable is matched first with `foo` and then with
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/// `bar`, and `$e` is matched in turn with `1`, `2`, `3`, `4`, `5`, `6`.
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///
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/// To represent such "multi-mappings", we use a recursive structures: we map
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/// variables not to values, but to *lists* of values or other lists (that is,
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/// to the trees).
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///
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/// For the above example, the bindings would store
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///
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/// ```not_rust
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/// i -> [foo, bar]
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/// e -> [[1, 2, 3], [4, 5, 6]]
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/// ```
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///
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/// We construct `Bindings` in the `match_lhs`. The interesting case is
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/// `TokenTree::Repeat`, where we use `push_nested` to create the desired
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/// nesting structure.
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///
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/// The other side of the puzzle is `expand_subtree`, where we use the bindings
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/// to substitute meta variables in the output template. When expanding, we
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/// maintain a `nesting` stack of indices which tells us which occurrence from
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/// the `Bindings` we should take. We push to the stack when we enter a
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/// repetition.
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///
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/// In other words, `Bindings` is a *multi* mapping from `SmolStr` to
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/// `tt::TokenTree`, where the index to select a particular `TokenTree` among
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/// many is not a plain `usize`, but an `&[usize]`.
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#[derive(Debug, Default)]
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struct Bindings {
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inner: FxHashMap<SmolStr, Binding>,
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}
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#[derive(Debug)]
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enum Binding {
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Simple(tt::TokenTree),
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Nested(Vec<Binding>),
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}
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impl Bindings {
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fn get(&self, name: &SmolStr, nesting: &[usize]) -> Result<&tt::TokenTree, ExpandError> {
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let mut b = self
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.inner
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.get(name)
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.ok_or(ExpandError::BindingError(format!("could not find binding `{}`", name)))?;
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for &idx in nesting.iter() {
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b = match b {
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Binding::Simple(_) => break,
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Binding::Nested(bs) => bs.get(idx).ok_or(ExpandError::BindingError(format!(
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"could not find nested binding `{}`",
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name
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)))?,
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};
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}
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match b {
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Binding::Simple(it) => Ok(it),
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Binding::Nested(_) => Err(ExpandError::BindingError(format!(
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"expected simple binding, found nested binding `{}`",
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name
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))),
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}
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}
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fn push_nested(&mut self, nested: Bindings) -> Result<(), ExpandError> {
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for (key, value) in nested.inner {
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if !self.inner.contains_key(&key) {
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self.inner.insert(key.clone(), Binding::Nested(Vec::new()));
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}
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match self.inner.get_mut(&key) {
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Some(Binding::Nested(it)) => it.push(value),
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_ => {
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return Err(ExpandError::BindingError(format!(
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"could not find binding `{}`",
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key
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)));
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}
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}
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}
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Ok(())
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}
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}
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fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Result<Bindings, ExpandError> {
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let mut res = Bindings::default();
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for pat in pattern.token_trees.iter() {
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match pat {
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crate::TokenTree::Leaf(leaf) => match leaf {
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crate::Leaf::Var(crate::Var { text, kind }) => {
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let kind = kind.clone().ok_or(ExpandError::UnexpectedToken)?;
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match kind.as_str() {
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"ident" => {
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let ident =
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input.eat_ident().ok_or(ExpandError::UnexpectedToken)?.clone();
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res.inner.insert(
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text.clone(),
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Binding::Simple(tt::Leaf::from(ident).into()),
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);
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}
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_ => return Err(ExpandError::UnexpectedToken),
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}
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}
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crate::Leaf::Punct(punct) => {
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if input.eat_punct() != Some(punct) {
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return Err(ExpandError::UnexpectedToken);
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}
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}
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crate::Leaf::Ident(ident) => {
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if input.eat_ident().map(|i| &i.text) != Some(&ident.text) {
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return Err(ExpandError::UnexpectedToken);
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}
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}
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_ => return Err(ExpandError::UnexpectedToken),
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},
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crate::TokenTree::Repeat(crate::Repeat { subtree, kind: _, separator }) => {
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while let Ok(nested) = match_lhs(subtree, input) {
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res.push_nested(nested)?;
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if let Some(separator) = *separator {
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if !input.is_eof() {
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if input.eat_punct().map(|p| p.char) != Some(separator) {
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return Err(ExpandError::UnexpectedToken);
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}
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}
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}
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}
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}
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_ => {}
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}
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}
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Ok(res)
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}
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fn expand_subtree(
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template: &crate::Subtree,
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bindings: &Bindings,
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nesting: &mut Vec<usize>,
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) -> Result<tt::Subtree, ExpandError> {
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let token_trees = template
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.token_trees
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.iter()
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.map(|it| expand_tt(it, bindings, nesting))
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.collect::<Result<Vec<_>, ExpandError>>()?;
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Ok(tt::Subtree { token_trees, delimiter: template.delimiter })
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}
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fn expand_tt(
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template: &crate::TokenTree,
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bindings: &Bindings,
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nesting: &mut Vec<usize>,
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) -> Result<tt::TokenTree, ExpandError> {
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let res: tt::TokenTree = match template {
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crate::TokenTree::Subtree(subtree) => expand_subtree(subtree, bindings, nesting)?.into(),
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crate::TokenTree::Repeat(repeat) => {
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let mut token_trees = Vec::new();
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nesting.push(0);
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while let Ok(t) = expand_subtree(&repeat.subtree, bindings, nesting) {
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let idx = nesting.pop().unwrap();
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nesting.push(idx + 1);
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token_trees.push(t.into())
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}
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nesting.pop().unwrap();
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tt::Subtree { token_trees, delimiter: tt::Delimiter::None }.into()
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}
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crate::TokenTree::Leaf(leaf) => match leaf {
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crate::Leaf::Ident(ident) => {
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tt::Leaf::from(tt::Ident { text: ident.text.clone(), id: TokenId::unspecified() })
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.into()
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}
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crate::Leaf::Punct(punct) => tt::Leaf::from(punct.clone()).into(),
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crate::Leaf::Var(v) => bindings.get(&v.text, nesting)?.clone(),
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crate::Leaf::Literal(l) => tt::Leaf::from(tt::Literal { text: l.text.clone() }).into(),
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},
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};
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Ok(res)
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}
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#[cfg(test)]
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mod tests {
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use ra_syntax::{ast, AstNode};
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use super::*;
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use crate::ast_to_token_tree;
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#[test]
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fn test_expand_rule() {
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assert_err(
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"($i:ident) => ($j)",
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"foo!{a}",
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ExpandError::BindingError(String::from("could not find binding `j`")),
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);
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assert_err(
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"($($i:ident);*) => ($i)",
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"foo!{a}",
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ExpandError::BindingError(String::from(
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"expected simple binding, found nested binding `i`",
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)),
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);
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assert_err("($i) => ($i)", "foo!{a}", ExpandError::UnexpectedToken);
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assert_err("($i:) => ($i)", "foo!{a}", ExpandError::UnexpectedToken);
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}
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fn assert_err(macro_body: &str, invocation: &str, err: ExpandError) {
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assert_eq!(expand_first(&create_rules(&format_macro(macro_body)), invocation), Err(err));
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}
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fn format_macro(macro_body: &str) -> String {
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format!(
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"
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macro_rules! foo {{
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{}
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}}
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",
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macro_body
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)
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}
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fn create_rules(macro_definition: &str) -> crate::MacroRules {
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let source_file = ast::SourceFile::parse(macro_definition);
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let macro_definition =
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source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
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let (definition_tt, _) = ast_to_token_tree(macro_definition.token_tree().unwrap()).unwrap();
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crate::MacroRules::parse(&definition_tt).unwrap()
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}
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fn expand_first(
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rules: &crate::MacroRules,
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invocation: &str,
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) -> Result<tt::Subtree, ExpandError> {
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let source_file = ast::SourceFile::parse(invocation);
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let macro_invocation =
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source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
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let (invocation_tt, _) = ast_to_token_tree(macro_invocation.token_tree().unwrap()).unwrap();
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expand_rule(&rules.rules[0], &invocation_tt)
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}
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}
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