Introduce dedicated AST node for union

Although structs and unions have the same syntax and differ only in
the keyword, re-using the single syntax node for both of them leads to
confusion in practice, and propagates further down the hir in an
upleasent way.

Moreover, static and consts also share syntax, but we use different
nodes for them.

crates/ra_parser/src/grammar/items.rs

@@ -1,13 +1,13 @@
 //! FIXME: write short doc here
 
 mod consts;
-mod nominal;
+mod adt;
 mod traits;
 mod use_item;
 
 pub(crate) use self::{
     expressions::{match_arm_list, record_field_list},
-    nominal::{enum_variant_list, record_field_def_list},
+    adt::{enum_variant_list, record_field_def_list},
     traits::{impl_item_list, trait_item_list},
     use_item::use_tree_list,
 };
@@ -247,7 +247,7 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             //     a: i32,
             //     b: f32,
             // }
-            nominal::struct_def(p, m, T![struct]);
+            adt::struct_def(p, m);
         }
         IDENT if p.at_contextual_kw("union") && p.nth(1) == IDENT => {
             // test union_items
@@ -256,9 +256,9 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             //     a: i32,
             //     b: f32,
             // }
-            nominal::struct_def(p, m, T![union]);
+            adt::union_def(p, m);
         }
-        T![enum] => nominal::enum_def(p, m),
+        T![enum] => adt::enum_def(p, m),
         T![use] => use_item::use_item(p, m),
         T![const] if (la == IDENT || la == T![_] || la == T![mut]) => consts::const_def(p, m),
         T![static] => consts::static_def(p, m),

crates/ra_parser/src/grammar/items/adt.rs

@@ -2,10 +2,19 @@
 
 use super::*;
 
-pub(super) fn struct_def(p: &mut Parser, m: Marker, kind: SyntaxKind) {
-    assert!(p.at(T![struct]) || p.at_contextual_kw("union"));
-    p.bump_remap(kind);
+pub(super) fn struct_def(p: &mut Parser, m: Marker) {
+    assert!(p.at(T![struct]));
+    p.bump(T![struct]);
+    struct_or_union(p, m, T![struct], STRUCT_DEF);
+}
 
+pub(super) fn union_def(p: &mut Parser, m: Marker) {
+    assert!(p.at_contextual_kw("union"));
+    p.bump_remap(T![union]);
+    struct_or_union(p, m, T![union], UNION_DEF);
+}
+
+fn struct_or_union(p: &mut Parser, m: Marker, kw: SyntaxKind, def: SyntaxKind) {
     name_r(p, ITEM_RECOVERY_SET);
     type_params::opt_type_param_list(p);
     match p.current() {
@@ -22,11 +31,11 @@ pub(super) fn struct_def(p: &mut Parser, m: Marker, kind: SyntaxKind) {
                 }
             }
         }
-        T![;] if kind == T![struct] => {
+        T![;] if kw == T![struct] => {
             p.bump(T![;]);
         }
         T!['{'] => record_field_def_list(p),
-        T!['('] if kind == T![struct] => {
+        T!['('] if kw == T![struct] => {
             tuple_field_def_list(p);
             // test tuple_struct_where
             // struct Test<T>(T) where T: Clone;
@@ -34,14 +43,14 @@ pub(super) fn struct_def(p: &mut Parser, m: Marker, kind: SyntaxKind) {
             type_params::opt_where_clause(p);
             p.expect(T![;]);
         }
-        _ if kind == T![struct] => {
+        _ if kw == T![struct] => {
             p.error("expected `;`, `{`, or `(`");
         }
         _ => {
             p.error("expected `{`");
         }
     }
-    m.complete(p, STRUCT_DEF);
+    m.complete(p, def);
 }
 
 pub(super) fn enum_def(p: &mut Parser, m: Marker) {

crates/ra_parser/src/syntax_kind/generated.rs

@@ -122,6 +122,7 @@ pub enum SyntaxKind {
     R_DOLLAR,
     SOURCE_FILE,
     STRUCT_DEF,
+    UNION_DEF,
     ENUM_DEF,
     FN_DEF,
     RET_TYPE,