cleanup the api

crates/ra_mbe/src/lib.rs

@@ -24,17 +24,26 @@ use ra_syntax::SmolStr;
 
 pub use tt::{Delimiter, Punct};
 
-pub use crate::{
-    mbe_parser::parse,
-    mbe_expander::exapnd,
-    syntax_bridge::macro_call_to_tt,
-};
+pub use crate::syntax_bridge::ast_to_token_tree;
 
+/// This struct contains AST for a single `macro_rules` defenition. What might
+/// be very confusing is that AST has almost exactly the same shape as
+/// `tt::TokenTree`, but there's a crucial difference: in macro rules, `$ident`
+/// and `$()*` have special meaning (see `Var` and `Repeat` data structures)
 #[derive(Debug)]
 pub struct MacroRules {
     pub(crate) rules: Vec<Rule>,
 }
 
+impl MacroRules {
+    pub fn parse(tt: &tt::Subtree) -> Option<MacroRules> {
+        mbe_parser::parse(tt)
+    }
+    pub fn expand(&self, tt: &tt::Subtree) -> Option<tt::Subtree> {
+        mbe_expander::exapnd(self, tt)
+    }
+}
+
 #[derive(Debug)]
 pub(crate) struct Rule {
     pub(crate) lhs: Subtree,
@@ -93,3 +102,55 @@ pub(crate) struct Var {
     pub(crate) text: SmolStr,
     pub(crate) kind: Option<SmolStr>,
 }
+
+#[cfg(test)]
+mod tests {
+    use ra_syntax::{ast, AstNode};
+
+    use super::*;
+
+    #[test]
+    fn test_convert_tt() {
+        let macro_definition = r#"
+macro_rules! impl_froms {
+    ($e:ident: $($v:ident),*) => {
+        $(
+            impl From<$v> for $e {
+                fn from(it: $v) -> $e {
+                    $e::$v(it)
+                }
+            }
+        )*
+    }
+}
+"#;
+
+        let macro_invocation = r#"
+impl_froms!(TokenTree: Leaf, Subtree);
+"#;
+
+        let source_file = ast::SourceFile::parse(macro_definition);
+        let macro_definition = source_file
+            .syntax()
+            .descendants()
+            .find_map(ast::MacroCall::cast)
+            .unwrap();
+
+        let source_file = ast::SourceFile::parse(macro_invocation);
+        let macro_invocation = source_file
+            .syntax()
+            .descendants()
+            .find_map(ast::MacroCall::cast)
+            .unwrap();
+
+        let definition_tt = ast_to_token_tree(macro_definition.token_tree().unwrap()).unwrap();
+        let invocation_tt = ast_to_token_tree(macro_invocation.token_tree().unwrap()).unwrap();
+        let rules = crate::MacroRules::parse(&definition_tt).unwrap();
+        let expansion = rules.expand(&invocation_tt).unwrap();
+        assert_eq!(
+        expansion.to_string(),
+        "impl From < Leaf > for TokenTree {fn from (it : Leaf) -> TokenTree {TokenTree :: Leaf (it)}} \
+         impl From < Subtree > for TokenTree {fn from (it : Subtree) -> TokenTree {TokenTree :: Subtree (it)}}"
+    )
+    }
+}