6 files changed, 112 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
diff --git a/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.rs b/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.rs
new file mode 100644
index 000000000..d140692e2
--- /dev/null
+++ b/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.rs
@@ -0,0 +1,2 @@
+type X = <A as B>::Output;
+fn foo() { <usize as Default>::default(); }
diff --git a/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.txt b/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.txt
new file mode 100644
index 000000000..58b545bdd
--- /dev/null
+++ b/crates/libsyntax2/tests/data/parser/inline/0101_qual_paths.txt
@@ -0,0 +1,78 @@
+FILE@[0; 71)
+  TYPE_DEF@[0; 26)
+    TYPE_KW@[0; 4)
+    WHITESPACE@[4; 5)
+    NAME@[5; 6)
+      IDENT@[5; 6) "X"
+    WHITESPACE@[6; 7)
+    EQ@[7; 8)
+    WHITESPACE@[8; 9)
+    PATH_TYPE@[9; 25)
+      PATH@[9; 25)
+        PATH@[9; 17)
+          PATH_SEGMENT@[9; 17)
+            L_ANGLE@[9; 10)
+            PATH_TYPE@[10; 11)
+              PATH@[10; 11)
+                PATH_SEGMENT@[10; 11)
+                  NAME_REF@[10; 11)
+                    IDENT@[10; 11) "A"
+            WHITESPACE@[11; 12)
+            AS_KW@[12; 14)
+            WHITESPACE@[14; 15)
+            PATH_TYPE@[15; 16)
+              PATH@[15; 16)
+                PATH_SEGMENT@[15; 16)
+                  NAME_REF@[15; 16)
+                    IDENT@[15; 16) "B"
+            R_ANGLE@[16; 17)
+        COLONCOLON@[17; 19)
+        PATH_SEGMENT@[19; 25)
+          NAME_REF@[19; 25)
+            IDENT@[19; 25) "Output"
+    SEMI@[25; 26)
+  WHITESPACE@[26; 27)
+  FN_DEF@[27; 70)
+    FN_KW@[27; 29)
+    WHITESPACE@[29; 30)
+    NAME@[30; 33)
+      IDENT@[30; 33) "foo"
+    PARAM_LIST@[33; 35)
+      L_PAREN@[33; 34)
+      R_PAREN@[34; 35)
+    WHITESPACE@[35; 36)
+    BLOCK_EXPR@[36; 70)
+      L_CURLY@[36; 37)
+      WHITESPACE@[37; 38)
+      EXPR_STMT@[38; 68)
+        CALL_EXPR@[38; 67)
+          PATH_EXPR@[38; 65)
+            PATH@[38; 65)
+              PATH@[38; 56)
+                PATH_SEGMENT@[38; 56)
+                  L_ANGLE@[38; 39)
+                  PATH_TYPE@[39; 44)
+                    PATH@[39; 44)
+                      PATH_SEGMENT@[39; 44)
+                        NAME_REF@[39; 44)
+                          IDENT@[39; 44) "usize"
+                  WHITESPACE@[44; 45)
+                  AS_KW@[45; 47)
+                  WHITESPACE@[47; 48)
+                  PATH_TYPE@[48; 55)
+                    PATH@[48; 55)
+                      PATH_SEGMENT@[48; 55)
+                        NAME_REF@[48; 55)
+                          IDENT@[48; 55) "Default"
+                  R_ANGLE@[55; 56)
+              COLONCOLON@[56; 58)
+              PATH_SEGMENT@[58; 65)
+                NAME_REF@[58; 65)
+                  IDENT@[58; 65) "default"
+          ARG_LIST@[65; 67)
+            L_PAREN@[65; 66)
+            R_PAREN@[66; 67)
+        SEMI@[67; 68)
+      WHITESPACE@[68; 69)
+      R_CURLY@[69; 70)
+  WHITESPACE@[70; 71)