5 files changed, 65 insertions, 13 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index b9f555ef6..ec2fd1eb5 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -144,8 +144,8 @@ impl_froms!(TokenTree: Leaf, Subtree);
         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 (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!(
@@ -160,7 +160,7 @@ impl_froms!(TokenTree: Leaf, Subtree);
         let macro_definition =
             source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
 
-        let definition_tt = ast_to_token_tree(macro_definition.token_tree().unwrap()).unwrap();
+        let (definition_tt, _) = ast_to_token_tree(macro_definition.token_tree().unwrap()).unwrap();
         crate::MacroRules::parse(&definition_tt).unwrap()
     }
 
@@ -169,7 +169,7 @@ impl_froms!(TokenTree: Leaf, Subtree);
         let macro_invocation =
             source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
 
-        let invocation_tt = ast_to_token_tree(macro_invocation.token_tree().unwrap()).unwrap();
+        let (invocation_tt, _) = ast_to_token_tree(macro_invocation.token_tree().unwrap()).unwrap();
 
         let expaned = rules.expand(&invocation_tt).unwrap();
         assert_eq!(expaned.to_string(), expansion);
diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
index eec713d9c..f6177f078 100644
--- a/crates/ra_mbe/src/mbe_expander.rs
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -3,6 +3,7 @@
 /// `tt::TokenTree` for the result of the expansion.
 use rustc_hash::FxHashMap;
 use ra_syntax::SmolStr;
+use tt::TokenId;
 
 use crate::tt_cursor::TtCursor;
 
@@ -185,7 +186,8 @@ fn expand_tt(
         }
         crate::TokenTree::Leaf(leaf) => match leaf {
             crate::Leaf::Ident(ident) => {
-                tt::Leaf::from(tt::Ident { text: ident.text.clone() }).into()
+                tt::Leaf::from(tt::Ident { text: ident.text.clone(), id: TokenId::unspecified() })
+                    .into()
             }
             crate::Leaf::Punct(punct) => tt::Leaf::from(punct.clone()).into(),
             crate::Leaf::Var(v) => bindings.get(&v.text, nesting)?.clone(),
diff --git a/crates/ra_mbe/src/mbe_parser.rs b/crates/ra_mbe/src/mbe_parser.rs
index 60e566ed2..58e2533f1 100644
--- a/crates/ra_mbe/src/mbe_parser.rs
+++ b/crates/ra_mbe/src/mbe_parser.rs
@@ -41,7 +41,7 @@ fn parse_subtree(tt: &tt::Subtree) -> Option<crate::Subtree> {
                     }
                 }
                 tt::Leaf::Punct(punct) => crate::Leaf::from(*punct).into(),
-                tt::Leaf::Ident(tt::Ident { text }) => {
+                tt::Leaf::Ident(tt::Ident { text, id: _ }) => {
                     crate::Leaf::from(crate::Ident { text: text.clone() }).into()
                 }
                 tt::Leaf::Literal(tt::Literal { text }) => {
diff --git a/crates/ra_mbe/src/syntax_bridge.rs b/crates/ra_mbe/src/syntax_bridge.rs
index 9a2eceaba..848c785f8 100644
--- a/crates/ra_mbe/src/syntax_bridge.rs
+++ b/crates/ra_mbe/src/syntax_bridge.rs
@@ -1,10 +1,42 @@
-use ra_syntax::{ast, AstNode, SyntaxNode, SyntaxKind::*};
+use ra_syntax::{
+    AstNode, SyntaxNode, TextRange,
+    ast, SyntaxKind::*, TextUnit
+};
 
-pub fn ast_to_token_tree(ast: &ast::TokenTree) -> Option<tt::Subtree> {
-    convert_tt(ast.syntax())
+/// Maps `tt::TokenId` to the relative range of the original token.
+#[derive(Default)]
+pub struct TokenMap {
+    /// Maps `tt::TokenId` to the *relative* source range.
+    toknes: Vec<TextRange>,
 }
 
-fn convert_tt(tt: &SyntaxNode) -> Option<tt::Subtree> {
+/// Convert the syntax tree (what user has written) to a `TokenTree` (what macro
+/// will consume).
+pub fn ast_to_token_tree(ast: &ast::TokenTree) -> Option<(tt::Subtree, TokenMap)> {
+    let mut token_map = TokenMap::default();
+    let node = ast.syntax();
+    let tt = convert_tt(&mut token_map, node.range().start(), node)?;
+    Some((tt, token_map))
+}
+
+impl TokenMap {
+    pub fn relative_range_of(&self, tt: tt::TokenId) -> Option<TextRange> {
+        let idx = tt.0 as usize;
+        self.toknes.get(idx).map(|&it| it)
+    }
+
+    fn alloc(&mut self, relative_range: TextRange) -> tt::TokenId {
+        let id = self.toknes.len();
+        self.toknes.push(relative_range);
+        tt::TokenId(id as u32)
+    }
+}
+
+fn convert_tt(
+    token_map: &mut TokenMap,
+    global_offset: TextUnit,
+    tt: &SyntaxNode,
+) -> Option<tt::Subtree> {
     let first_child = tt.first_child()?;
     let last_child = tt.last_child()?;
     let delimiter = match (first_child.kind(), last_child.kind()) {
@@ -34,10 +66,12 @@ fn convert_tt(tt: &SyntaxNode) -> Option<tt::Subtree> {
             }
         } else {
             let child: tt::TokenTree = if child.kind() == TOKEN_TREE {
-                convert_tt(child)?.into()
+                convert_tt(token_map, global_offset, child)?.into()
             } else if child.kind().is_keyword() || child.kind() == IDENT {
+                let relative_range = child.range() - global_offset;
+                let id = token_map.alloc(relative_range);
                 let text = child.leaf_text().unwrap().clone();
-                tt::Leaf::from(tt::Ident { text }).into()
+                tt::Leaf::from(tt::Ident { text, id }).into()
             } else if child.kind().is_literal() {
                 tt::Leaf::from(tt::Literal { text: child.leaf_text().unwrap().clone() }).into()
             } else {
diff --git a/crates/ra_tt/src/lib.rs b/crates/ra_tt/src/lib.rs
index df31f72f3..c1f37b889 100644
--- a/crates/ra_tt/src/lib.rs
+++ b/crates/ra_tt/src/lib.rs
@@ -1,4 +1,4 @@
-/// `tt` crate defines a `TokenTree` datastructure: this is the interface (both
+/// `tt` crate defines a `TokenTree` data structure: this is the interface (both
 /// input and output) of macros. It closely mirrors `proc_macro` crate's
 /// `TokenTree`.
 
@@ -18,6 +18,21 @@ use std::fmt;
 
 use smol_str::SmolStr;
 
+/// Represents identity of the token.
+///
+/// For hygiene purposes, we need to track which expanded tokens originated from
+/// which source tokens. We do it by assigning an distinct identity to each
+/// source token and making sure that identities are preserved during macro
+/// expansion.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct TokenId(pub u32);
+
+impl TokenId {
+    pub const fn unspecified() -> TokenId {
+        TokenId(!0)
+    }
+}
+
 #[derive(Debug, Clone)]
 pub enum TokenTree {
     Leaf(Leaf),
@@ -67,6 +82,7 @@ pub enum Spacing {
 #[derive(Debug, Clone)]
 pub struct Ident {
     pub text: SmolStr,
+    pub id: TokenId,
 }
 
 impl fmt::Display for TokenTree {