1 files changed, 169 insertions, 0 deletions

diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
new file mode 100644
index 000000000..92ad26889
--- /dev/null
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -0,0 +1,169 @@
+use rustc_hash::FxHashMap;
+use smol_str::SmolStr;
+
+use crate::{self as mbe, tt_cursor::TtCursor};
+
+pub fn exapnd(rules: &mbe::MacroRules, input: &tt::Subtree) -> Option<tt::Subtree> {
+    rules.rules.iter().find_map(|it| expand_rule(it, input))
+}
+
+fn expand_rule(rule: &mbe::Rule, input: &tt::Subtree) -> Option<tt::Subtree> {
+    let mut input = TtCursor::new(input);
+    let bindings = match_lhs(&rule.lhs, &mut input)?;
+    expand_subtree(&rule.rhs, &bindings, &mut Vec::new())
+}
+
+#[derive(Debug, Default)]
+struct Bindings {
+    inner: FxHashMap<SmolStr, Binding>,
+}
+
+#[derive(Debug)]
+enum Binding {
+    Simple(tt::TokenTree),
+    Nested(Vec<Binding>),
+}
+
+impl Bindings {
+    fn get(&self, name: &SmolStr, nesting: &[usize]) -> Option<&tt::TokenTree> {
+        let mut b = self.inner.get(name)?;
+        for &idx in nesting.iter() {
+            b = match b {
+                Binding::Simple(_) => break,
+                Binding::Nested(bs) => bs.get(idx)?,
+            };
+        }
+        match b {
+            Binding::Simple(it) => Some(it),
+            Binding::Nested(_) => None,
+        }
+    }
+    fn push_nested(&mut self, nested: Bindings) -> Option<()> {
+        for (key, value) in nested.inner {
+            if !self.inner.contains_key(&key) {
+                self.inner.insert(key.clone(), Binding::Nested(Vec::new()));
+            }
+            match self.inner.get_mut(&key) {
+                Some(Binding::Nested(it)) => it.push(value),
+                _ => return None,
+            }
+        }
+        Some(())
+    }
+}
+
+fn match_lhs(pattern: &mbe::Subtree, input: &mut TtCursor) -> Option<Bindings> {
+    let mut res = Bindings::default();
+    for pat in pattern.token_trees.iter() {
+        match pat {
+            mbe::TokenTree::Leaf(leaf) => match leaf {
+                mbe::Leaf::Var(mbe::Var { text, kind }) => {
+                    let kind = kind.clone()?;
+                    match kind.as_str() {
+                        "ident" => {
+                            let ident = input.eat_ident()?.clone();
+                            res.inner.insert(
+                                text.clone(),
+                                Binding::Simple(tt::Leaf::from(ident).into()),
+                            );
+                        }
+                        _ => return None,
+                    }
+                }
+                mbe::Leaf::Punct(punct) => {
+                    if input.eat_punct()? != punct {
+                        return None;
+                    }
+                }
+                _ => return None,
+            },
+            mbe::TokenTree::Repeat(mbe::Repeat {
+                subtree,
+                kind: _,
+                separator,
+            }) => {
+                while let Some(nested) = match_lhs(subtree, input) {
+                    res.push_nested(nested)?;
+                    if separator.is_some() && !input.is_eof() {
+                        input.eat_punct()?;
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+    Some(res)
+}
+
+/*
+
+macro_rules! impl_froms {
+    ($e:ident: $($v:ident),*) => {
+        $(
+            impl From<$v> for $e {
+                fn from(it: $v) -> $e {
+                    $e::$v(it)
+                }
+            }
+        )*
+    }
+}
+
+impl_froms! (Foo: Bar, Baz)
+
+*/
+
+fn expand_subtree(
+    template: &mbe::Subtree,
+    bindings: &Bindings,
+    nesting: &mut Vec<usize>,
+) -> Option<tt::Subtree> {
+    let token_trees = template
+        .token_trees
+        .iter()
+        .map(|it| expand_tt(it, bindings, nesting))
+        .collect::<Option<Vec<_>>>()?;
+
+    Some(tt::Subtree {
+        token_trees,
+        delimiter: template.delimiter,
+    })
+}
+
+fn expand_tt(
+    template: &mbe::TokenTree,
+    bindings: &Bindings,
+    nesting: &mut Vec<usize>,
+) -> Option<tt::TokenTree> {
+    let res: tt::TokenTree = match template {
+        mbe::TokenTree::Subtree(subtree) => expand_subtree(subtree, bindings, nesting)?.into(),
+        mbe::TokenTree::Repeat(repeat) => {
+            let mut token_trees = Vec::new();
+            nesting.push(0);
+            while let Some(t) = expand_subtree(&repeat.subtree, bindings, nesting) {
+                let idx = nesting.pop().unwrap();
+                nesting.push(idx + 1);
+                token_trees.push(t.into())
+            }
+            nesting.pop().unwrap();
+            tt::Subtree {
+                token_trees,
+                delimiter: tt::Delimiter::None,
+            }
+            .into()
+        }
+        mbe::TokenTree::Leaf(leaf) => match leaf {
+            mbe::Leaf::Ident(ident) => tt::Leaf::from(tt::Ident {
+                text: ident.text.clone(),
+            })
+            .into(),
+            mbe::Leaf::Punct(punct) => tt::Leaf::from(punct.clone()).into(),
+            mbe::Leaf::Var(v) => bindings.get(&v.text, nesting)?.clone(),
+            mbe::Leaf::Literal(l) => tt::Leaf::from(tt::Literal {
+                text: l.text.clone(),
+            })
+            .into(),
+        },
+    };
+    Some(res)
+}