fix: avoid panic when parsing extern block

crates/parser/src/grammar/items.rs

@@ -93,6 +93,7 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
     };
 
     let mut has_mods = false;
+    let mut has_extern = false;
 
     // modifiers
     if p.at(T![const]) && p.nth(1) != T!['{'] {
@@ -102,7 +103,7 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
 
     // test_err async_without_semicolon
     // fn foo() { let _ = async {} }
-    if p.at(T![async]) && p.nth(1) != T!['{'] && p.nth(1) != T![move] && p.nth(1) != T![|] {
+    if p.at(T![async]) && !matches!(p.nth(1), T!['{'] | T![move] | T![|]) {
         p.eat(T![async]);
         has_mods = true;
     }
@@ -114,7 +115,8 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
         has_mods = true;
     }
 
-    if p.at(T![extern]) && p.nth(1) != T!['{'] && (p.nth(1) != STRING || p.nth(2) != T!['{']) {
+    if p.at(T![extern]) {
+        has_extern = true;
         has_mods = true;
         abi(p);
     }
@@ -211,25 +213,24 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             type_alias(p, m);
         }
 
+        // test extern_block
         // unsafe extern "C" {}
-        T![extern] => {
-            abi(p);
+        // extern {}
+        T!['{'] if has_extern => {
             extern_item_list(p);
             m.complete(p, EXTERN_BLOCK);
         }
 
-        _ => {
-            if !has_visibility && !has_mods {
-                return Err(m);
+        _ if has_visibility || has_mods => {
+            if has_mods {
+                p.error("expected existential, fn, trait or impl");
             } else {
-                if has_mods {
-                    p.error("expected existential, fn, trait or impl");
-                } else {
-                    p.error("expected an item");
-                }
-                m.complete(p, ERROR);
+                p.error("expected an item");
             }
+            m.complete(p, ERROR);
         }
+
+        _ => return Err(m),
     }
     Ok(())
 }
@@ -240,10 +241,11 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
         // test extern_crate
         // extern crate foo;
         T![extern] if la == T![crate] => extern_crate(p, m),
-        T![type] => {
-            type_alias(p, m);
-        }
+        T![use] => use_item::use_(p, m),
         T![mod] => mod_item(p, m),
+
+        T![type] => type_alias(p, m),
+
         T![struct] => {
             // test struct_items
             // struct Foo;
@@ -256,14 +258,7 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             // }
             adt::strukt(p, m);
         }
-        // test pub_macro_def
-        // pub macro m($:ident) {}
-        T![macro] => {
-            macro_def(p, m);
-        }
-        IDENT if p.at_contextual_kw("macro_rules") && p.nth(1) == BANG => {
-            macro_rules(p, m);
-        }
+        T![enum] => adt::enum_(p, m),
         IDENT if p.at_contextual_kw("union") && p.nth(1) == IDENT => {
             // test union_items
             // union Foo {}
@@ -273,17 +268,19 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             // }
             adt::union(p, m);
         }
-        T![enum] => adt::enum_(p, m),
-        T![use] => use_item::use_(p, m),
+
+        // test pub_macro_def
+        // pub macro m($:ident) {}
+        T![macro] => {
+            macro_def(p, m);
+        }
+        IDENT if p.at_contextual_kw("macro_rules") && p.nth(1) == BANG => {
+            macro_rules(p, m);
+        }
+
         T![const] if (la == IDENT || la == T![_] || la == T![mut]) => consts::konst(p, m),
         T![static] => consts::static_(p, m),
-        // test extern_block
-        // extern {}
-        T![extern] if la == T!['{'] || (la == STRING && p.nth(2) == T!['{']) => {
-            abi(p);
-            extern_item_list(p);
-            m.complete(p, EXTERN_BLOCK);
-        }
+
         _ => return Err(m),
     };
     Ok(())
@@ -292,6 +289,7 @@ fn items_without_modifiers(p: &mut Parser, m: Marker) -> Result<(), Marker> {
 fn extern_crate(p: &mut Parser, m: Marker) {
     assert!(p.at(T![extern]));
     p.bump(T![extern]);
+
     assert!(p.at(T![crate]));
     p.bump(T![crate]);
 

crates/syntax/test_data/parser/err/0048_repated_extern_modifier.rast

@@ -0,0 +1,15 @@
+SOURCE_FILE@0..22
+  ERROR@0..10
+    ABI@0..10
+      EXTERN_KW@0..6 "extern"
+      WHITESPACE@6..7 " "
+      STRING@7..10 "\"C\""
+  WHITESPACE@10..11 " "
+  ERROR@11..21
+    ABI@11..21
+      EXTERN_KW@11..17 "extern"
+      WHITESPACE@17..18 " "
+      STRING@18..21 "\"C\""
+  WHITESPACE@21..22 "\n"
+error 10..10: expected existential, fn, trait or impl
+error 21..21: expected existential, fn, trait or impl

crates/syntax/test_data/parser/err/0048_repated_extern_modifier.rs

@@ -0,0 +1 @@
+extern "C" extern "C"

crates/syntax/test_data/parser/inline/ok/0010_extern_block.rast

@@ -1,9 +1,21 @@
-SOURCE_FILE@0..10
-  EXTERN_BLOCK@0..9
-    ABI@0..6
-      EXTERN_KW@0..6 "extern"
+SOURCE_FILE@0..31
+  EXTERN_BLOCK@0..20
+    UNSAFE_KW@0..6 "unsafe"
     WHITESPACE@6..7 " "
-    EXTERN_ITEM_LIST@7..9
-      L_CURLY@7..8 "{"
-      R_CURLY@8..9 "}"
-  WHITESPACE@9..10 "\n"
+    ABI@7..17
+      EXTERN_KW@7..13 "extern"
+      WHITESPACE@13..14 " "
+      STRING@14..17 "\"C\""
+    WHITESPACE@17..18 " "
+    EXTERN_ITEM_LIST@18..20
+      L_CURLY@18..19 "{"
+      R_CURLY@19..20 "}"
+  WHITESPACE@20..21 "\n"
+  EXTERN_BLOCK@21..30
+    ABI@21..27
+      EXTERN_KW@21..27 "extern"
+    WHITESPACE@27..28 " "
+    EXTERN_ITEM_LIST@28..30
+      L_CURLY@28..29 "{"
+      R_CURLY@29..30 "}"
+  WHITESPACE@30..31 "\n"

crates/syntax/test_data/parser/inline/ok/0010_extern_block.rs

@@ -1 +1,2 @@
+unsafe extern "C" {}
 extern {}