1 files changed, 153 insertions, 0 deletions

diff --git a/crates/parser/src/grammar/items/traits.rs b/crates/parser/src/grammar/items/traits.rs
new file mode 100644
index 000000000..751ce65f2
--- /dev/null
+++ b/crates/parser/src/grammar/items/traits.rs
@@ -0,0 +1,153 @@
+//! FIXME: write short doc here
+
+use super::*;
+
+// test trait_item
+// trait T<U>: Hash + Clone where U: Copy {}
+// trait X<U: Debug + Display>: Hash + Clone where U: Copy {}
+pub(super) fn trait_def(p: &mut Parser) {
+    assert!(p.at(T![trait]));
+    p.bump(T![trait]);
+    name_r(p, ITEM_RECOVERY_SET);
+    type_params::opt_type_param_list(p);
+    // test trait_alias
+    // trait Z<U> = T<U>;
+    // trait Z<U> = T<U> where U: Copy;
+    // trait Z<U> = where Self: T<U>;
+    if p.eat(T![=]) {
+        type_params::bounds_without_colon(p);
+        type_params::opt_where_clause(p);
+        p.expect(T![;]);
+        return;
+    }
+    if p.at(T![:]) {
+        type_params::bounds(p);
+    }
+    type_params::opt_where_clause(p);
+    if p.at(T!['{']) {
+        trait_item_list(p);
+    } else {
+        p.error("expected `{`");
+    }
+}
+
+// test trait_item_list
+// impl F {
+//     type A: Clone;
+//     const B: i32;
+//     fn foo() {}
+//     fn bar(&self);
+// }
+pub(crate) fn trait_item_list(p: &mut Parser) {
+    assert!(p.at(T!['{']));
+    let m = p.start();
+    p.bump(T!['{']);
+    while !p.at(EOF) && !p.at(T!['}']) {
+        if p.at(T!['{']) {
+            error_block(p, "expected an item");
+            continue;
+        }
+        item_or_macro(p, true);
+    }
+    p.expect(T!['}']);
+    m.complete(p, ASSOC_ITEM_LIST);
+}
+
+// test impl_def
+// impl Foo {}
+pub(super) fn impl_def(p: &mut Parser) {
+    assert!(p.at(T![impl]));
+    p.bump(T![impl]);
+    if choose_type_params_over_qpath(p) {
+        type_params::opt_type_param_list(p);
+    }
+
+    // FIXME: never type
+    // impl ! {}
+
+    // test impl_def_neg
+    // impl !Send for X {}
+    p.eat(T![!]);
+    impl_type(p);
+    if p.eat(T![for]) {
+        impl_type(p);
+    }
+    type_params::opt_where_clause(p);
+    if p.at(T!['{']) {
+        impl_item_list(p);
+    } else {
+        p.error("expected `{`");
+    }
+}
+
+// test impl_item_list
+// impl F {
+//     type A = i32;
+//     const B: i32 = 92;
+//     fn foo() {}
+//     fn bar(&self) {}
+// }
+pub(crate) fn impl_item_list(p: &mut Parser) {
+    assert!(p.at(T!['{']));
+    let m = p.start();
+    p.bump(T!['{']);
+    // test impl_inner_attributes
+    // enum F{}
+    // impl F {
+    //      //! This is a doc comment
+    //      #![doc("This is also a doc comment")]
+    // }
+    attributes::inner_attributes(p);
+
+    while !p.at(EOF) && !p.at(T!['}']) {
+        if p.at(T!['{']) {
+            error_block(p, "expected an item");
+            continue;
+        }
+        item_or_macro(p, true);
+    }
+    p.expect(T!['}']);
+    m.complete(p, ASSOC_ITEM_LIST);
+}
+
+// test impl_type_params
+// impl<const N: u32> Bar<N> {}
+fn choose_type_params_over_qpath(p: &Parser) -> bool {
+    // There's an ambiguity between generic parameters and qualified paths in impls.
+    // If we see `<` it may start both, so we have to inspect some following tokens.
+    // The following combinations can only start generics,
+    // but not qualified paths (with one exception):
+    //     `<` `>` - empty generic parameters
+    //     `<` `#` - generic parameters with attributes
+    //     `<` `const` - const generic parameters
+    //     `<` (LIFETIME|IDENT) `>` - single generic parameter
+    //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
+    //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
+    //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
+    // The only truly ambiguous case is
+    //     `<` IDENT `>` `::` IDENT ...
+    // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
+    // because this is what almost always expected in practice, qualified paths in impls
+    // (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
+    if !p.at(T![<]) {
+        return false;
+    }
+    if p.nth(1) == T![#] || p.nth(1) == T![>] || p.nth(1) == CONST_KW {
+        return true;
+    }
+    (p.nth(1) == LIFETIME || p.nth(1) == IDENT)
+        && (p.nth(2) == T![>] || p.nth(2) == T![,] || p.nth(2) == T![:] || p.nth(2) == T![=])
+}
+
+// test_err impl_type
+// impl Type {}
+// impl Trait1 for T {}
+// impl impl NotType {}
+// impl Trait2 for impl NotType {}
+pub(crate) fn impl_type(p: &mut Parser) {
+    if p.at(T![impl]) {
+        p.error("expected trait or type");
+        return;
+    }
+    types::type_(p);
+}