parameter parsing does not destroy blocks

crates/libsyntax2/src/grammar/expressions/atom.rs

@@ -13,7 +13,7 @@ use super::*;
 //     let _ = b"e";
 //     let _ = br"f";
 // }
-const LITERAL_FIRST: TokenSet =
+pub(crate) const LITERAL_FIRST: TokenSet =
     token_set![TRUE_KW, FALSE_KW, INT_NUMBER, FLOAT_NUMBER, BYTE, CHAR,
                STRING, RAW_STRING, BYTE_STRING, RAW_BYTE_STRING];
 

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

@@ -1,7 +1,7 @@
 mod atom;
 
 use super::*;
-pub(super) use self::atom::literal;
+pub(super) use self::atom::{literal, LITERAL_FIRST};
 
 const EXPR_FIRST: TokenSet = LHS_FIRST;
 

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

@@ -250,8 +250,10 @@ fn function(p: &mut Parser, flavor: ItemFlavor) {
 
     // test fn_decl
     // trait T { fn foo(); }
-    if !p.eat(SEMI) {
+    if p.at(L_CURLY) {
         expressions::block(p);
+    } else {
+        p.expect(SEMI);
     }
 }
 

crates/libsyntax2/src/grammar/params.rs

@@ -48,6 +48,10 @@ fn list_(p: &mut Parser, flavor: Flavor) {
         opt_self_param(p);
     }
     while !p.at(EOF) && !p.at(ket) {
+        if !VALUE_PARAMETER_FIRST.contains(p.current()) {
+            p.error("expected value parameter");
+            break;
+        }
         value_parameter(p, flavor);
         if !p.at(ket) {
             p.expect(COMMA);
@@ -57,6 +61,13 @@ fn list_(p: &mut Parser, flavor: Flavor) {
     m.complete(p, PARAM_LIST);
 }
 
+
+const VALUE_PARAMETER_FIRST: TokenSet =
+    token_set_union![
+        patterns::PATTERN_FIRST,
+        types::TYPE_FIRST,
+    ];
+
 fn value_parameter(p: &mut Parser, flavor: Flavor) {
     let m = p.start();
     match flavor {

crates/libsyntax2/src/grammar/paths.rs

@@ -1,5 +1,8 @@
 use super::*;
 
+pub(super) const PATH_FIRST: TokenSet =
+    token_set![IDENT, SELF_KW, SUPER_KW, COLONCOLON, L_ANGLE];
+
 pub(super) fn is_path_start(p: &Parser) -> bool {
     match p.current() {
         IDENT | SELF_KW | SUPER_KW | COLONCOLON => true,

crates/libsyntax2/src/grammar/patterns.rs

@@ -1,5 +1,12 @@
 use super::*;
 
+pub(super) const PATTERN_FIRST: TokenSet =
+    token_set_union![
+        token_set![REF_KW, MUT_KW, L_PAREN, L_BRACK, AMP],
+        expressions::LITERAL_FIRST,
+        paths::PATH_FIRST,
+    ];
+
 pub(super) fn pattern(p: &mut Parser) {
     if let Some(lhs) = atom_pat(p) {
         // test range_pat

crates/libsyntax2/src/grammar/types.rs

@@ -1,5 +1,13 @@
 use super::*;
 
+pub(super) const TYPE_FIRST: TokenSet =
+    token_set_union![
+        token_set![
+            L_PAREN, EXCL, STAR, L_BRACK, AMP, UNDERSCORE, FN_KW, UNSAFE_KW, EXTERN_KW, FOR_KW, IMPL_KW, DYN_KW, L_ANGLE,
+        ],
+        paths::PATH_FIRST,
+    ];
+
 pub(super) fn type_(p: &mut Parser) {
     match p.current() {
         L_PAREN => paren_or_tuple_type(p),