4 files changed, 32 insertions, 19 deletions

diff --git a/crates/libsyntax2/src/grammar/expressions/atom.rs b/crates/libsyntax2/src/grammar/expressions/atom.rs
index e62b16654..4f03862b1 100644
--- a/crates/libsyntax2/src/grammar/expressions/atom.rs
+++ b/crates/libsyntax2/src/grammar/expressions/atom.rs
@@ -38,7 +38,7 @@ pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<CompletedMark
         Some(m) => return Some(m),
         None => (),
     }
-    if paths::is_path_start(p) {
+    if paths::is_path_start(p) || p.at(L_ANGLE) {
         return Some(path_expr(p, r));
     }
     let la = p.nth(1);
diff --git a/crates/libsyntax2/src/grammar/expressions/mod.rs b/crates/libsyntax2/src/grammar/expressions/mod.rs
index 30a78d0c4..e56f3d30e 100644
--- a/crates/libsyntax2/src/grammar/expressions/mod.rs
+++ b/crates/libsyntax2/src/grammar/expressions/mod.rs
@@ -332,7 +332,7 @@ fn arg_list(p: &mut Parser) {
 //     let _ = format!();
 // }
 fn path_expr(p: &mut Parser, r: Restrictions) -> CompletedMarker {
-    assert!(paths::is_path_start(p));
+    assert!(paths::is_path_start(p) || p.at(L_ANGLE));
     let m = p.start();
     paths::expr_path(p);
     match p.current() {
diff --git a/crates/libsyntax2/src/grammar/paths.rs b/crates/libsyntax2/src/grammar/paths.rs
index aa5ecf4b8..97ab1880b 100644
--- a/crates/libsyntax2/src/grammar/paths.rs
+++ b/crates/libsyntax2/src/grammar/paths.rs
@@ -27,9 +27,6 @@ enum Mode {
 }
 
 fn path(p: &mut Parser, mode: Mode) {
-    if !is_path_start(p) {
-        return;
-    }
     let path = p.start();
     path_segment(p, mode, true);
     let mut qual = path.complete(p, PATH);
@@ -51,21 +48,36 @@ fn path(p: &mut Parser, mode: Mode) {
 }
 
 fn path_segment(p: &mut Parser, mode: Mode, first: bool) {
-    let segment = p.start();
-    if first {
-        p.eat(COLONCOLON);
-    }
-    match p.current() {
-        IDENT => {
-            name_ref(p);
-            path_generic_args(p, mode);
+    let m = p.start();
+    // test qual_paths
+    // type X = <A as B>::Output;
+    // fn foo() { <usize as Default>::default(); }
+    if first && p.eat(L_ANGLE) {
+        types::type_(p);
+        if p.eat(AS_KW) {
+            if is_path_start(p) {
+                types::path_type(p);
+            } else {
+                p.error("expected a trait");
+            }
         }
-        SELF_KW | SUPER_KW => p.bump(),
-        _ => {
-            p.err_and_bump("expected identifier");
+        p.expect(R_ANGLE);
+    } else {
+        if first {
+            p.eat(COLONCOLON);
         }
-    };
-    segment.complete(p, PATH_SEGMENT);
+        match p.current() {
+            IDENT => {
+                name_ref(p);
+                path_generic_args(p, mode);
+            }
+            SELF_KW | SUPER_KW => p.bump(),
+            _ => {
+                p.err_and_bump("expected identifier");
+            }
+        };
+    }
+    m.complete(p, PATH_SEGMENT);
 }
 
 fn path_generic_args(p: &mut Parser, mode: Mode) {
diff --git a/crates/libsyntax2/src/grammar/types.rs b/crates/libsyntax2/src/grammar/types.rs
index 88631fefe..f58b545c7 100644
--- a/crates/libsyntax2/src/grammar/types.rs
+++ b/crates/libsyntax2/src/grammar/types.rs
@@ -12,6 +12,7 @@ pub(super) fn type_(p: &mut Parser) {
         FOR_KW => for_type(p),
         IMPL_KW => impl_trait_type(p),
         DYN_KW => dyn_trait_type(p),
+        L_ANGLE => path_type(p),
         _ if paths::is_path_start(p) => path_type(p),
         _ => {
             p.err_and_bump("expected type");
@@ -214,7 +215,7 @@ fn dyn_trait_type(p: &mut Parser) {
 // type C = self::Foo;
 // type D = super::Foo;
 pub(super) fn path_type(p: &mut Parser) {
-    assert!(paths::is_path_start(p));
+    assert!(paths::is_path_start(p) || p.at(L_ANGLE));
     let m = p.start();
     paths::type_path(p);
     // test path_type_with_bounds