Auto merge of #15682 - Veykril:param-list-recov, r=Veykril

Recover better on missing parameter in param list

We should do the same for argument lists, but that is more tricky to fix.

crates/parser/src/grammar/params.rs

@@ -7,6 +7,9 @@ use super::*;
 // fn b(x: i32) {}
 // fn c(x: i32, ) {}
 // fn d(x: i32, y: ()) {}
+
+// test_err empty_param_slot
+// fn f(y: i32, ,t: i32) {}
 pub(super) fn param_list_fn_def(p: &mut Parser<'_>) {
     list_(p, Flavor::FnDef);
 }
@@ -71,7 +74,11 @@ fn list_(p: &mut Parser<'_>, flavor: Flavor) {
         if !p.at_ts(PARAM_FIRST.union(ATTRIBUTE_FIRST)) {
             p.error("expected value parameter");
             m.abandon(p);
-            break;
+            if p.eat(T![,]) {
+                continue;
+            } else {
+                break;
+            }
         }
         param(p, m, flavor);
         if !p.at(T![,]) {

crates/parser/test_data/parser/inline/err/0023_empty_param_slot.rast

@@ -0,0 +1,41 @@
+SOURCE_FILE
+  FN
+    FN_KW "fn"
+    WHITESPACE " "
+    NAME
+      IDENT "f"
+    PARAM_LIST
+      L_PAREN "("
+      PARAM
+        IDENT_PAT
+          NAME
+            IDENT "y"
+        COLON ":"
+        WHITESPACE " "
+        PATH_TYPE
+          PATH
+            PATH_SEGMENT
+              NAME_REF
+                IDENT "i32"
+      COMMA ","
+      WHITESPACE " "
+      COMMA ","
+      PARAM
+        IDENT_PAT
+          NAME
+            IDENT "t"
+        COLON ":"
+        WHITESPACE " "
+        PATH_TYPE
+          PATH
+            PATH_SEGMENT
+              NAME_REF
+                IDENT "i32"
+      R_PAREN ")"
+    WHITESPACE " "
+    BLOCK_EXPR
+      STMT_LIST
+        L_CURLY "{"
+        R_CURLY "}"
+  WHITESPACE "\n"
+error 12: expected value parameter

crates/parser/test_data/parser/inline/err/0023_empty_param_slot.rs

@@ -0,0 +1 @@
+fn f(y: i32, ,t: i32) {}