1 files changed, 160 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/mbe/src/tt_iter.rs b/src/tools/rust-analyzer/crates/mbe/src/tt_iter.rs
new file mode 100644
index 000000000..7aceb676c
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/mbe/src/tt_iter.rs
@@ -0,0 +1,160 @@
+//! A "Parser" structure for token trees. We use this when parsing a declarative
+//! macro definition into a list of patterns and templates.
+
+use syntax::SyntaxKind;
+use tt::buffer::TokenBuffer;
+
+use crate::{to_parser_input::to_parser_input, ExpandError, ExpandResult};
+
+#[derive(Debug, Clone)]
+pub(crate) struct TtIter<'a> {
+    pub(crate) inner: std::slice::Iter<'a, tt::TokenTree>,
+}
+
+impl<'a> TtIter<'a> {
+    pub(crate) fn new(subtree: &'a tt::Subtree) -> TtIter<'a> {
+        TtIter { inner: subtree.token_trees.iter() }
+    }
+
+    pub(crate) fn expect_char(&mut self, char: char) -> Result<(), ()> {
+        match self.next() {
+            Some(&tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: c, .. }))) if c == char => {
+                Ok(())
+            }
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_any_char(&mut self, chars: &[char]) -> Result<(), ()> {
+        match self.next() {
+            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: c, .. })))
+                if chars.contains(c) =>
+            {
+                Ok(())
+            }
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_subtree(&mut self) -> Result<&'a tt::Subtree, ()> {
+        match self.next() {
+            Some(tt::TokenTree::Subtree(it)) => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_leaf(&mut self) -> Result<&'a tt::Leaf, ()> {
+        match self.next() {
+            Some(tt::TokenTree::Leaf(it)) => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_ident(&mut self) -> Result<&'a tt::Ident, ()> {
+        match self.expect_leaf()? {
+            tt::Leaf::Ident(it) if it.text != "_" => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_ident_or_underscore(&mut self) -> Result<&'a tt::Ident, ()> {
+        match self.expect_leaf()? {
+            tt::Leaf::Ident(it) => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_literal(&mut self) -> Result<&'a tt::Leaf, ()> {
+        let it = self.expect_leaf()?;
+        match it {
+            tt::Leaf::Literal(_) => Ok(it),
+            tt::Leaf::Ident(ident) if ident.text == "true" || ident.text == "false" => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_u32_literal(&mut self) -> Result<u32, ()> {
+        match self.expect_literal()? {
+            tt::Leaf::Literal(lit) => lit.text.parse().map_err(drop),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_punct(&mut self) -> Result<&'a tt::Punct, ()> {
+        match self.expect_leaf()? {
+            tt::Leaf::Punct(it) => Ok(it),
+            _ => Err(()),
+        }
+    }
+
+    pub(crate) fn expect_fragment(
+        &mut self,
+        entry_point: parser::PrefixEntryPoint,
+    ) -> ExpandResult<Option<tt::TokenTree>> {
+        let buffer = TokenBuffer::from_tokens(self.inner.as_slice());
+        let parser_input = to_parser_input(&buffer);
+        let tree_traversal = entry_point.parse(&parser_input);
+
+        let mut cursor = buffer.begin();
+        let mut error = false;
+        for step in tree_traversal.iter() {
+            match step {
+                parser::Step::Token { kind, mut n_input_tokens } => {
+                    if kind == SyntaxKind::LIFETIME_IDENT {
+                        n_input_tokens = 2;
+                    }
+                    for _ in 0..n_input_tokens {
+                        cursor = cursor.bump_subtree();
+                    }
+                }
+                parser::Step::Enter { .. } | parser::Step::Exit => (),
+                parser::Step::Error { .. } => error = true,
+            }
+        }
+
+        let err = if error || !cursor.is_root() {
+            Some(ExpandError::binding_error(format!("expected {entry_point:?}")))
+        } else {
+            None
+        };
+
+        let mut curr = buffer.begin();
+        let mut res = vec![];
+
+        if cursor.is_root() {
+            while curr != cursor {
+                if let Some(token) = curr.token_tree() {
+                    res.push(token);
+                }
+                curr = curr.bump();
+            }
+        }
+        self.inner = self.inner.as_slice()[res.len()..].iter();
+        let res = match res.len() {
+            1 => Some(res[0].cloned()),
+            0 => None,
+            _ => Some(tt::TokenTree::Subtree(tt::Subtree {
+                delimiter: None,
+                token_trees: res.into_iter().map(|it| it.cloned()).collect(),
+            })),
+        };
+        ExpandResult { value: res, err }
+    }
+
+    pub(crate) fn peek_n(&self, n: usize) -> Option<&tt::TokenTree> {
+        self.inner.as_slice().get(n)
+    }
+}
+
+impl<'a> Iterator for TtIter<'a> {
+    type Item = &'a tt::TokenTree;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<'a> std::iter::ExactSizeIterator for TtIter<'a> {}