start item recovery

crates/libsyntax2/src/grammar/items/mod.rs

@@ -24,6 +24,10 @@ pub(super) enum ItemFlavor {
     Mod, Trait
 }
 
+const ITEM_RECOVERY_SET: TokenSet =
+    token_set![FN_KW, STRUCT_KW, ENUM_KW, IMPL_KW, TRAIT_KW, CONST_KW, STATIC_KW, LET_KW,
+               MOD_KW, PUB_KW, CRATE_KW];
+
 pub(super) fn item_or_macro(p: &mut Parser, stop_on_r_curly: bool, flavor: ItemFlavor) {
     let m = p.start();
     match maybe_item(p, flavor) {
@@ -231,7 +235,7 @@ fn fn_def(p: &mut Parser, flavor: ItemFlavor) {
     assert!(p.at(FN_KW));
     p.bump();
 
-    name(p);
+    name_r(p, ITEM_RECOVERY_SET);
     // test function_type_params
     // fn foo<T: Clone + Copy>(){}
     type_params::opt_type_param_list(p);

crates/libsyntax2/src/grammar/items/structs.rs

@@ -4,7 +4,7 @@ pub(super) fn struct_def(p: &mut Parser) {
     assert!(p.at(STRUCT_KW));
     p.bump();
 
-    name(p);
+    name_r(p, ITEM_RECOVERY_SET);
     type_params::opt_type_param_list(p);
     match p.current() {
         WHERE_KW => {
@@ -41,7 +41,7 @@ pub(super) fn struct_def(p: &mut Parser) {
 pub(super) fn enum_def(p: &mut Parser) {
     assert!(p.at(ENUM_KW));
     p.bump();
-    name(p);
+    name_r(p, ITEM_RECOVERY_SET);
     type_params::opt_type_param_list(p);
     type_params::opt_where_clause(p);
     if p.at(L_CURLY) {

crates/libsyntax2/src/grammar/items/traits.rs

@@ -5,7 +5,7 @@
 pub(super) fn trait_def(p: &mut Parser) {
     assert!(p.at(TRAIT_KW));
     p.bump();
-    name(p);
+    name_r(p, ITEM_RECOVERY_SET);
     type_params::opt_type_param_list(p);
     if p.at(COLON) {
         type_params::bounds(p);

crates/libsyntax2/src/grammar/mod.rs

@@ -129,16 +129,20 @@ fn opt_fn_ret_type(p: &mut Parser) -> bool {
     }
 }
 
-fn name(p: &mut Parser) {
+fn name_r(p: &mut Parser, recovery: TokenSet) {
     if p.at(IDENT) {
         let m = p.start();
         p.bump();
         m.complete(p, NAME);
     } else {
-        p.err_and_bump("expected a name");
+        p.err_recover("expected a name", recovery);
     }
 }
 
+fn name(p: &mut Parser) {
+    name_r(p, TokenSet::EMPTY)
+}
+
 fn name_ref(p: &mut Parser) {
     if p.at(IDENT) {
         let m = p.start();

crates/libsyntax2/src/parser_api.rs

@@ -12,7 +12,7 @@ fn mask(kind: SyntaxKind) -> u128 {
 }
 
 impl TokenSet {
-    const EMPTY: TokenSet = TokenSet(0);
+    pub const EMPTY: TokenSet = TokenSet(0);
 
     pub fn contains(&self, kind: SyntaxKind) -> bool {
         self.0 & mask(kind) != 0
@@ -145,10 +145,10 @@ pub(crate) fn err_and_bump(&mut self, message: &str) {
     }
 
     /// Create an error node and consume the next token.
-    pub(crate) fn err_recover(&mut self, message: &str, recovery_set: TokenSet) {
+    pub(crate) fn err_recover(&mut self, message: &str, recovery: TokenSet) {
         if self.at(SyntaxKind::L_CURLY)
             || self.at(SyntaxKind::R_CURLY)
-            || recovery_set.contains(self.current()) {
+            || recovery.contains(self.current()) {
             self.error(message);
         } else {
             let m = self.start();

crates/libsyntax2/tests/data/parser/err/0020_fn_recover.rs

@@ -0,0 +1,3 @@
+fn
+
+fn foo() {}

crates/libsyntax2/tests/data/parser/err/0020_fn_recover.txt

@@ -0,0 +1,20 @@
+ROOT@[0; 16)
+  FN_DEF@[0; 2)
+    FN_KW@[0; 2)
+    err: `expected a name`
+    err: `expected function arguments`
+    err: `expected a block`
+  WHITESPACE@[2; 4)
+  FN_DEF@[4; 15)
+    FN_KW@[4; 6)
+    WHITESPACE@[6; 7)
+    NAME@[7; 10)
+      IDENT@[7; 10) "foo"
+    PARAM_LIST@[10; 12)
+      L_PAREN@[10; 11)
+      R_PAREN@[11; 12)
+    WHITESPACE@[12; 13)
+    BLOCK@[13; 15)
+      L_CURLY@[13; 14)
+      R_CURLY@[14; 15)
+  WHITESPACE@[15; 16)