1 files changed, 115 insertions, 0 deletions

diff --git a/crates/parser/src/grammar/paths.rs b/crates/parser/src/grammar/paths.rs
new file mode 100644
index 000000000..52562afa4
--- /dev/null
+++ b/crates/parser/src/grammar/paths.rs
@@ -0,0 +1,115 @@
+//! FIXME: write short doc here
+
+use super::*;
+
+pub(super) const PATH_FIRST: TokenSet =
+    token_set![IDENT, T![self], T![super], T![crate], T![:], T![<]];
+
+pub(super) fn is_path_start(p: &Parser) -> bool {
+    is_use_path_start(p) || p.at(T![<])
+}
+
+pub(super) fn is_use_path_start(p: &Parser) -> bool {
+    match p.current() {
+        IDENT | T![self] | T![super] | T![crate] => true,
+        T![:] if p.at(T![::]) => true,
+        _ => false,
+    }
+}
+
+pub(super) fn use_path(p: &mut Parser) {
+    path(p, Mode::Use)
+}
+
+pub(crate) fn type_path(p: &mut Parser) {
+    path(p, Mode::Type)
+}
+
+pub(super) fn expr_path(p: &mut Parser) {
+    path(p, Mode::Expr)
+}
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+enum Mode {
+    Use,
+    Type,
+    Expr,
+}
+
+fn path(p: &mut Parser, mode: Mode) {
+    let path = p.start();
+    path_segment(p, mode, true);
+    let mut qual = path.complete(p, PATH);
+    loop {
+        let use_tree = matches!(p.nth(2), T![*] | T!['{']);
+        if p.at(T![::]) && !use_tree {
+            let path = qual.precede(p);
+            p.bump(T![::]);
+            path_segment(p, mode, false);
+            let path = path.complete(p, PATH);
+            qual = path;
+        } else {
+            break;
+        }
+    }
+}
+
+fn path_segment(p: &mut Parser, mode: Mode, first: bool) {
+    let m = p.start();
+    // test qual_paths
+    // type X = <A as B>::Output;
+    // fn foo() { <usize as Default>::default(); }
+    if first && p.eat(T![<]) {
+        types::type_(p);
+        if p.eat(T![as]) {
+            if is_use_path_start(p) {
+                types::path_type(p);
+            } else {
+                p.error("expected a trait");
+            }
+        }
+        p.expect(T![>]);
+    } else {
+        let mut empty = true;
+        if first {
+            p.eat(T![::]);
+            empty = false;
+        }
+        match p.current() {
+            IDENT => {
+                name_ref(p);
+                opt_path_type_args(p, mode);
+            }
+            // test crate_path
+            // use crate::foo;
+            T![self] | T![super] | T![crate] => p.bump_any(),
+            _ => {
+                p.err_recover("expected identifier", items::ITEM_RECOVERY_SET);
+                if empty {
+                    // test_err empty_segment
+                    // use crate::;
+                    m.abandon(p);
+                    return;
+                }
+            }
+        };
+    }
+    m.complete(p, PATH_SEGMENT);
+}
+
+fn opt_path_type_args(p: &mut Parser, mode: Mode) {
+    match mode {
+        Mode::Use => {}
+        Mode::Type => {
+            // test path_fn_trait_args
+            // type F = Box<Fn(i32) -> ()>;
+            if p.at(T!['(']) {
+                params::param_list_fn_trait(p);
+                opt_ret_type(p);
+            } else {
+                type_args::opt_generic_arg_list(p, false)
+            }
+        }
+        Mode::Expr => type_args::opt_generic_arg_list(p, true),
+    }
+}