G: placeholder types

grammar.ron

@@ -109,6 +109,7 @@ Grammar(
         "ARRAY_TYPE",
         "SLICE_TYPE",
         "REFERENCE_TYPE",
+        "PLACEHOLDER_TYPE",
 
         "EXTERN_BLOCK",
         "ENUM_VARIANT",

src/parser/grammar/types.rs

@@ -7,6 +7,7 @@ pub(super) fn type_(p: &mut Parser) {
         STAR => pointer_type(p),
         L_BRACK => array_or_slice_type(p),
         AMPERSAND => reference_type(p),
+        UNDERSCORE => placeholder_type(p),
         IDENT => path_type(p),
         _ => {
             p.error("expected type");
@@ -130,6 +131,15 @@ fn reference_type(p: &mut Parser) {
     m.complete(p, REFERENCE_TYPE);
 }
 
+// test placeholder_type
+// type Placeholder = _;
+fn placeholder_type(p: &mut Parser) {
+    assert!(p.at(UNDERSCORE));
+    let m = p.start();
+    p.bump();
+    m.complete(p, PLACEHOLDER_TYPE);
+}
+
 fn path_type(p: &mut Parser) {
     assert!(p.at(IDENT));
     let m = p.start();

src/syntax_kinds.rs

@@ -107,6 +107,7 @@ pub enum SyntaxKind {
     ARRAY_TYPE,
     SLICE_TYPE,
     REFERENCE_TYPE,
+    PLACEHOLDER_TYPE,
     EXTERN_BLOCK,
     ENUM_VARIANT,
     NAMED_FIELD,
@@ -240,6 +241,7 @@ pub(crate) fn info(self) -> &'static SyntaxInfo {
             ARRAY_TYPE => &SyntaxInfo { name: "ARRAY_TYPE" },
             SLICE_TYPE => &SyntaxInfo { name: "SLICE_TYPE" },
             REFERENCE_TYPE => &SyntaxInfo { name: "REFERENCE_TYPE" },
+            PLACEHOLDER_TYPE => &SyntaxInfo { name: "PLACEHOLDER_TYPE" },
             EXTERN_BLOCK => &SyntaxInfo { name: "EXTERN_BLOCK" },
             ENUM_VARIANT => &SyntaxInfo { name: "ENUM_VARIANT" },
             NAMED_FIELD => &SyntaxInfo { name: "NAMED_FIELD" },

tests/data/parser/inline/0027_placeholder_type.rs

@@ -0,0 +1 @@
+type Placeholder = _;

tests/data/parser/inline/0027_placeholder_type.txt

@@ -0,0 +1,13 @@
+FILE@[0; 22)
+  TYPE_ITEM@[0; 22)
+    TYPE_KW@[0; 4)
+    NAME@[4; 17)
+      WHITESPACE@[4; 5)
+      IDENT@[5; 16) "Placeholder"
+      WHITESPACE@[16; 17)
+    EQ@[17; 18)
+    PLACEHOLDER_TYPE@[18; 20)
+      WHITESPACE@[18; 19)
+      UNDERSCORE@[19; 20)
+    SEMI@[20; 21)
+    WHITESPACE@[21; 22)