Recover from missing associated item binding

Author: lowr

crates/parser/src/grammar/generic_args.rs

@@ -55,6 +55,10 @@ fn generic_arg(p: &mut Parser<'_>) -> bool {
                         // test assoc_type_eq
                         // type T = StreamingIterator<Item<'a> = &'a T>;
                         types::type_(p);
+                    } else if p.at(T![>]) || p.at(T![,]) {
+                        // test_err recover_from_missing_assoc_item_binding
+                        // fn f() -> impl Iterator<Item = , Item = > {}
+                        p.error("missing associated item binding");
                     } else {
                         // test assoc_const_eq
                         // fn foo<F: Foo<N=3>>() {}

crates/parser/test_data/parser/inline/err/0021_recover_from_missing_assoc_item_binding.rast

@@ -0,0 +1,48 @@
+SOURCE_FILE
+  FN
+    FN_KW "fn"
+    WHITESPACE " "
+    NAME
+      IDENT "f"
+    PARAM_LIST
+      L_PAREN "("
+      R_PAREN ")"
+    WHITESPACE " "
+    RET_TYPE
+      THIN_ARROW "->"
+      WHITESPACE " "
+      IMPL_TRAIT_TYPE
+        IMPL_KW "impl"
+        WHITESPACE " "
+        TYPE_BOUND_LIST
+          TYPE_BOUND
+            PATH_TYPE
+              PATH
+                PATH_SEGMENT
+                  NAME_REF
+                    IDENT "Iterator"
+                  GENERIC_ARG_LIST
+                    L_ANGLE "<"
+                    ASSOC_TYPE_ARG
+                      NAME_REF
+                        IDENT "Item"
+                      WHITESPACE " "
+                      EQ "="
+                    WHITESPACE " "
+                    COMMA ","
+                    WHITESPACE " "
+                    ASSOC_TYPE_ARG
+                      NAME_REF
+                        IDENT "Item"
+                      WHITESPACE " "
+                      EQ "="
+                    WHITESPACE " "
+                    R_ANGLE ">"
+    WHITESPACE " "
+    BLOCK_EXPR
+      STMT_LIST
+        L_CURLY "{"
+        R_CURLY "}"
+  WHITESPACE "\n"
+error 30: missing associated item binding
+error 39: missing associated item binding

crates/parser/test_data/parser/inline/err/0021_recover_from_missing_assoc_item_binding.rs

@@ -0,0 +1 @@
+fn f() -> impl Iterator<Item = , Item = > {}