5 files changed, 144 insertions, 89 deletions

diff --git a/crates/hir_expand/src/builtin_macro.rs b/crates/hir_expand/src/builtin_macro.rs
index 57bc6fbd7..6fbb9570a 100644
--- a/crates/hir_expand/src/builtin_macro.rs
+++ b/crates/hir_expand/src/builtin_macro.rs
@@ -6,7 +6,7 @@ use crate::{
 
 use base_db::{AnchoredPath, FileId};
 use either::Either;
-use mbe::{parse_to_token_tree, ExpandResult};
+use mbe::{parse_exprs_with_sep, parse_to_token_tree, ExpandResult};
 use parser::FragmentKind;
 use syntax::ast::{self, AstToken};
 
@@ -238,35 +238,21 @@ fn format_args_expand(
     // ])
     // ```,
     // which is still not really correct, but close enough for now
-    let mut args = Vec::new();
-    let mut current = Vec::new();
-    for tt in tt.token_trees.iter().cloned() {
-        match tt {
-            tt::TokenTree::Leaf(tt::Leaf::Punct(p)) if p.char == ',' => {
-                args.push(current);
-                current = Vec::new();
-            }
-            _ => {
-                current.push(tt);
-            }
-        }
-    }
-    if !current.is_empty() {
-        args.push(current);
-    }
+    let mut args = parse_exprs_with_sep(tt, ',');
+
     if args.is_empty() {
         return ExpandResult::only_err(mbe::ExpandError::NoMatchingRule);
     }
     for arg in &mut args {
         // Remove `key =`.
-        if matches!(arg.get(1), Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p))) if p.char == '=' && p.spacing != tt::Spacing::Joint)
+        if matches!(arg.token_trees.get(1), Some(tt::TokenTree::Leaf(tt::Leaf::Punct(p))) if p.char == '=' && p.spacing != tt::Spacing::Joint)
         {
-            arg.drain(..2);
+            arg.token_trees.drain(..2);
         }
     }
     let _format_string = args.remove(0);
     let arg_tts = args.into_iter().flat_map(|arg| {
-        quote! { std::fmt::ArgumentV1::new(&(##arg), std::fmt::Display::fmt), }
+        quote! { std::fmt::ArgumentV1::new(&(#arg), std::fmt::Display::fmt), }
     }.token_trees).collect::<Vec<_>>();
     let expanded = quote! {
         std::fmt::Arguments::new_v1(&[], &[##arg_tts])
@@ -720,6 +706,25 @@ mod tests {
     }
 
     #[test]
+    fn test_format_args_expand_with_comma_exprs() {
+        let expanded = expand_builtin_macro(
+            r#"
+            #[rustc_builtin_macro]
+            macro_rules! format_args {
+                ($fmt:expr) => ({ /* compiler built-in */ });
+                ($fmt:expr, $($args:tt)*) => ({ /* compiler built-in */ })
+            }
+            format_args!("{} {:?}", a::<A,B>(), b);
+            "#,
+        );
+
+        assert_eq!(
+            expanded,
+            r#"std::fmt::Arguments::new_v1(&[], &[std::fmt::ArgumentV1::new(&(a::<A,B>()),std::fmt::Display::fmt),std::fmt::ArgumentV1::new(&(b),std::fmt::Display::fmt),])"#
+        );
+    }
+
+    #[test]
     fn test_include_bytes_expand() {
         let expanded = expand_builtin_macro(
             r#"
diff --git a/crates/mbe/src/expander/matcher.rs b/crates/mbe/src/expander/matcher.rs
index 800931cd1..e3bd4c09a 100644
--- a/crates/mbe/src/expander/matcher.rs
+++ b/crates/mbe/src/expander/matcher.rs
@@ -3,15 +3,13 @@
 use crate::{
     expander::{Binding, Bindings, Fragment},
     parser::{Op, RepeatKind, Separator},
-    subtree_source::SubtreeTokenSource,
     tt_iter::TtIter,
     ExpandError, MetaTemplate,
 };
 
 use super::ExpandResult;
-use parser::{FragmentKind::*, TreeSink};
-use syntax::{SmolStr, SyntaxKind};
-use tt::buffer::{Cursor, TokenBuffer};
+use parser::FragmentKind::*;
+use syntax::SmolStr;
 
 impl Bindings {
     fn push_optional(&mut self, name: &SmolStr) {
@@ -409,68 +407,6 @@ impl<'a> TtIter<'a> {
         .into())
     }
 
-    fn expect_fragment(
-        &mut self,
-        fragment_kind: parser::FragmentKind,
-    ) -> ExpandResult<Option<tt::TokenTree>> {
-        struct OffsetTokenSink<'a> {
-            cursor: Cursor<'a>,
-            error: bool,
-        }
-
-        impl<'a> TreeSink for OffsetTokenSink<'a> {
-            fn token(&mut self, kind: SyntaxKind, mut n_tokens: u8) {
-                if kind == SyntaxKind::LIFETIME_IDENT {
-                    n_tokens = 2;
-                }
-                for _ in 0..n_tokens {
-                    self.cursor = self.cursor.bump_subtree();
-                }
-            }
-            fn start_node(&mut self, _kind: SyntaxKind) {}
-            fn finish_node(&mut self) {}
-            fn error(&mut self, _error: parser::ParseError) {
-                self.error = true;
-            }
-        }
-
-        let buffer = TokenBuffer::from_tokens(&self.inner.as_slice());
-        let mut src = SubtreeTokenSource::new(&buffer);
-        let mut sink = OffsetTokenSink { cursor: buffer.begin(), error: false };
-
-        parser::parse_fragment(&mut src, &mut sink, fragment_kind);
-
-        let mut err = None;
-        if !sink.cursor.is_root() || sink.error {
-            err = Some(err!("expected {:?}", fragment_kind));
-        }
-
-        let mut curr = buffer.begin();
-        let mut res = vec![];
-
-        if sink.cursor.is_root() {
-            while curr != sink.cursor {
-                if let Some(token) = curr.token_tree() {
-                    res.push(token);
-                }
-                curr = curr.bump();
-            }
-        }
-        self.inner = self.inner.as_slice()[res.len()..].iter();
-        if res.len() == 0 && err.is_none() {
-            err = Some(err!("no tokens consumed"));
-        }
-        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 }
-    }
-
     fn eat_vis(&mut self) -> Option<tt::TokenTree> {
         let mut fork = self.clone();
         match fork.expect_fragment(Visibility) {
diff --git a/crates/mbe/src/lib.rs b/crates/mbe/src/lib.rs
index 6b4a4eb53..4c298f85f 100644
--- a/crates/mbe/src/lib.rs
+++ b/crates/mbe/src/lib.rs
@@ -65,8 +65,8 @@ impl fmt::Display for ExpandError {
 }
 
 pub use crate::syntax_bridge::{
-    ast_to_token_tree, parse_to_token_tree, syntax_node_to_token_tree, token_tree_to_syntax_node,
-    TokenMap,
+    ast_to_token_tree, parse_exprs_with_sep, parse_to_token_tree, syntax_node_to_token_tree,
+    token_tree_to_syntax_node, TokenMap,
 };
 
 /// This struct contains AST for a single `macro_rules` definition. What might
diff --git a/crates/mbe/src/syntax_bridge.rs b/crates/mbe/src/syntax_bridge.rs
index 0cdc175be..5a91781fc 100644
--- a/crates/mbe/src/syntax_bridge.rs
+++ b/crates/mbe/src/syntax_bridge.rs
@@ -10,8 +10,8 @@ use syntax::{
 };
 use tt::buffer::{Cursor, TokenBuffer};
 
-use crate::subtree_source::SubtreeTokenSource;
 use crate::ExpandError;
+use crate::{subtree_source::SubtreeTokenSource, tt_iter::TtIter};
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
 pub enum TokenTextRange {
@@ -112,6 +112,43 @@ pub fn parse_to_token_tree(text: &str) -> Option<(tt::Subtree, TokenMap)> {
     Some((subtree, conv.id_alloc.map))
 }
 
+/// Split token tree with seperate expr: $($e:expr)SEP*
+pub fn parse_exprs_with_sep(tt: &tt::Subtree, sep: char) -> Vec<tt::Subtree> {
+    if tt.token_trees.is_empty() {
+        return Vec::new();
+    }
+
+    let mut iter = TtIter::new(tt);
+    let mut res = Vec::new();
+
+    while iter.peek_n(0).is_some() {
+        let expanded = iter.expect_fragment(FragmentKind::Expr);
+        if expanded.err.is_some() {
+            break;
+        }
+
+        res.push(match expanded.value {
+            None => break,
+            Some(tt @ tt::TokenTree::Leaf(_)) => {
+                tt::Subtree { delimiter: None, token_trees: vec![tt.into()] }
+            }
+            Some(tt::TokenTree::Subtree(tt)) => tt,
+        });
+
+        let mut fork = iter.clone();
+        if fork.expect_char(sep).is_err() {
+            break;
+        }
+        iter = fork;
+    }
+
+    if iter.peek_n(0).is_some() {
+        res.push(tt::Subtree { delimiter: None, token_trees: iter.into_iter().cloned().collect() });
+    }
+
+    res
+}
+
 impl TokenMap {
     pub fn token_by_range(&self, relative_range: TextRange) -> Option<tt::TokenId> {
         let &(token_id, _) = self.entries.iter().find(|(_, range)| match range {
diff --git a/crates/mbe/src/tt_iter.rs b/crates/mbe/src/tt_iter.rs
index 46c420718..a362d31fc 100644
--- a/crates/mbe/src/tt_iter.rs
+++ b/crates/mbe/src/tt_iter.rs
@@ -1,5 +1,20 @@
 //! FIXME: write short doc here
 
+use crate::{subtree_source::SubtreeTokenSource, ExpandError, ExpandResult};
+
+use parser::TreeSink;
+use syntax::SyntaxKind;
+use tt::buffer::{Cursor, TokenBuffer};
+
+macro_rules! err {
+    () => {
+        ExpandError::BindingError(format!(""))
+    };
+    ($($tt:tt)*) => {
+        ExpandError::BindingError(format!($($tt)*))
+    };
+}
+
 #[derive(Debug, Clone)]
 pub(crate) struct TtIter<'a> {
     pub(crate) inner: std::slice::Iter<'a, tt::TokenTree>,
@@ -56,6 +71,68 @@ impl<'a> TtIter<'a> {
         }
     }
 
+    pub(crate) fn expect_fragment(
+        &mut self,
+        fragment_kind: parser::FragmentKind,
+    ) -> ExpandResult<Option<tt::TokenTree>> {
+        struct OffsetTokenSink<'a> {
+            cursor: Cursor<'a>,
+            error: bool,
+        }
+
+        impl<'a> TreeSink for OffsetTokenSink<'a> {
+            fn token(&mut self, kind: SyntaxKind, mut n_tokens: u8) {
+                if kind == SyntaxKind::LIFETIME_IDENT {
+                    n_tokens = 2;
+                }
+                for _ in 0..n_tokens {
+                    self.cursor = self.cursor.bump_subtree();
+                }
+            }
+            fn start_node(&mut self, _kind: SyntaxKind) {}
+            fn finish_node(&mut self) {}
+            fn error(&mut self, _error: parser::ParseError) {
+                self.error = true;
+            }
+        }
+
+        let buffer = TokenBuffer::from_tokens(&self.inner.as_slice());
+        let mut src = SubtreeTokenSource::new(&buffer);
+        let mut sink = OffsetTokenSink { cursor: buffer.begin(), error: false };
+
+        parser::parse_fragment(&mut src, &mut sink, fragment_kind);
+
+        let mut err = None;
+        if !sink.cursor.is_root() || sink.error {
+            err = Some(err!("expected {:?}", fragment_kind));
+        }
+
+        let mut curr = buffer.begin();
+        let mut res = vec![];
+
+        if sink.cursor.is_root() {
+            while curr != sink.cursor {
+                if let Some(token) = curr.token_tree() {
+                    res.push(token);
+                }
+                curr = curr.bump();
+            }
+        }
+        self.inner = self.inner.as_slice()[res.len()..].iter();
+        if res.len() == 0 && err.is_none() {
+            err = Some(err!("no tokens consumed"));
+        }
+        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)
     }