add support for ES6 rest parameter syntax

[drsm]

instead of the arguments object, which is useless in case we going to support other es6+ features.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters

[xeioex]

Hi @drsm,

Please try the patch below

# HG changeset patch
# User Alexander Pyshchev <yftuls@gmail.com>
# Date 1545073982 -7200
#      Mon Dec 17 21:13:02 2018 +0200
# Node ID 59bd0ebbaa60517ec8269bef11dfa09a6a757881
# Parent  0709c3d38212df011229fccb2e7a9e7f23263cce
Added the rest parameters support.

diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/njs_function.c
--- a/njs/njs_function.c	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/njs_function.c	Mon Dec 17 21:13:02 2018 +0200
@@ -168,6 +168,40 @@
 
 
+njs_ret_t
+njs_function_rest_parameters_init(njs_vm_t *vm, njs_native_frame_t *frame)
+{
+    nxt_uint_t   nargs, n, i;
+    njs_array_t  *array;
+    njs_value_t  *rest_arguments;
+
+    nargs = frame->nargs;
+    n = frame->function->u.lambda->nargs;
+
+    array = njs_array_alloc(vm, (nargs < n) ? 0 : (nargs - n + 1), 0);
+    if (nxt_slow_path(array == NULL)) {
+        return NXT_ERROR;
+    }
+
+    if (nxt_fast_path(nargs >= n)) {
+        i = 0;
+        while (n <= nargs) {
+            /* GC: retain. */ 
+            array->start[i++] = frame->arguments[n++];
+        }
+    }
+
+    rest_arguments = &frame->arguments[frame->function->u.lambda->nargs];
+
+    /* GC: retain. */
+    rest_arguments->type = NJS_ARRAY;
+    rest_arguments->data.u.array = array;
+    rest_arguments->data.truth = 1;
+
+    return NXT_OK;
+}
+
+
 njs_ret_t
 njs_function_arguments_thrower(njs_vm_t *vm, njs_value_t *value,
     njs_value_t *setval, njs_value_t *retval)
 {
@@ -482,6 +516,13 @@
         }
     }
 
+    if (lambda->rest_parameters) {
+        ret = njs_function_rest_parameters_init(vm, &frame->native);
+        if (nxt_slow_path(ret != NXT_OK)) {
+            return NXT_ERROR;
+        }
+    }
+
     vm->active_frame = frame;
 
     return NJS_APPLIED;
diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/njs_function.h
--- a/njs/njs_function.h	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/njs_function.h	Mon Dec 17 21:13:02 2018 +0200
@@ -31,6 +31,7 @@
     uint8_t                        block_closures;    /* 4 bits */
 
     uint8_t                        arguments_object;  /* 1 bit */
+    uint8_t                        rest_parameters;   /* 1 bit */
 
     /* Initial values of local scope. */
     njs_value_t                    *local_scope;
@@ -151,6 +152,8 @@
 njs_native_frame_t *njs_function_frame_alloc(njs_vm_t *vm, size_t size);
 njs_ret_t njs_function_arguments_object_init(njs_vm_t *vm,
     njs_native_frame_t *frame);
+njs_ret_t njs_function_rest_parameters_init(njs_vm_t *vm,
+    njs_native_frame_t *frame);
 njs_ret_t njs_function_arguments_thrower(njs_vm_t *vm, njs_value_t *value,
     njs_value_t *setval, njs_value_t *retval);
 njs_ret_t njs_function_prototype_create(njs_vm_t *vm, njs_value_t *value,
diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/njs_lexer.c
--- a/njs/njs_lexer.c	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/njs_lexer.c	Mon Dec 17 21:13:02 2018 +0200
@@ -326,6 +326,15 @@
         case NJS_TOKEN_DOT:
             p = lexer->start;
 
+            if (((p + 1) < lexer->end)
+                && NJS_TOKEN_DOT == njs_tokens[*(p)]
+                && NJS_TOKEN_DOT == njs_tokens[*(p + 1)])
+            {
+                lexer->text.length = 2 + p - lexer->text.start;
+                lexer->start += 2;
+                return NJS_TOKEN_ELLIPSIS;
+            }
+
             if (p == lexer->end || njs_tokens[*p] != NJS_TOKEN_DIGIT) {
                 lexer->text.length = p - lexer->text.start;
                 return NJS_TOKEN_DOT;
diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/njs_parser.c
--- a/njs/njs_parser.c	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/njs_parser.c	Mon Dec 17 21:13:02 2018 +0200
@@ -629,6 +629,19 @@
 
     while (token != NJS_TOKEN_CLOSE_PARENTHESIS) {
 
+        if (nxt_slow_path(1 == lambda->rest_parameters)) {
+            return NJS_TOKEN_ILLEGAL;
+        }
+
+        if (nxt_slow_path(token == NJS_TOKEN_ELLIPSIS)) {
+            lambda->rest_parameters = 1;
+
+            token = njs_parser_token(parser);
+            if (nxt_slow_path(token <= NJS_TOKEN_ILLEGAL)) {
+                return NJS_TOKEN_ILLEGAL;
+            }
+        }
+
         if (nxt_slow_path(token != NJS_TOKEN_NAME)) {
             return NJS_TOKEN_ILLEGAL;
         }
diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/njs_parser.h
--- a/njs/njs_parser.h	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/njs_parser.h	Mon Dec 17 21:13:02 2018 +0200
@@ -29,6 +29,7 @@
 
     NJS_TOKEN_COMMA,
     NJS_TOKEN_DOT,
+    NJS_TOKEN_ELLIPSIS,
     NJS_TOKEN_SEMICOLON,
 
     NJS_TOKEN_COLON,
diff -r 0709c3d38212 -r 59bd0ebbaa60 njs/test/njs_unit_test.c
--- a/njs/test/njs_unit_test.c	Fri Dec 07 18:58:27 2018 +0300
+++ b/njs/test/njs_unit_test.c	Mon Dec 17 21:13:02 2018 +0200
@@ -6063,6 +6063,34 @@
                  "[concat('.',1,2,3), concat('+',1,2,3,4)]"),
       nxt_string("1.2.3,1+2+3+4") },
 
+    { nxt_string("function myFoo(a,b,...other) { return other };"
+                 "myFoo(1,2,3,4,5);" ),
+      nxt_string("3,4,5") },
+
+    { nxt_string("function myFoo(a,b,...other, c) { return other };"),
+      nxt_string("SyntaxError: Unexpected token \"c\" in 1") },
+
+    { nxt_string("function sum(a, b, c, ...other) { return a+b+c+other[2] };"
+                 "sum(\"one \",2,\" three \",\"four \",\"five \",\"the long enough sixth argument \");"),
+      nxt_string("one 2 three the long enough sixth argument ") },
+
+    { nxt_string("function myFoo1(a,...other) { return other };"
+                 "function myFoo2(a,b,...other) { return other };"
+                 "myFoo1(1,2,3,4,5,myFoo2(1,2,3,4));"),
+      nxt_string("2,3,4,5,3,4") },
+
+    { nxt_string("function myFoo(...other) { return (other instanceof Array) };"
+                 "myFoo(1);" ),
+      nxt_string("true") },
+
+    { nxt_string("function myFoo(a,...other) { return other.length };"
+                 "myFoo(1,2,3,4,5);" ),
+      nxt_string("4") },
+
+    { nxt_string("function myFoo(a,b,...other) { return other };"
+                 "myFoo(1,2);" ),
+      nxt_string("") },
+
     /* Scopes. */
 
     { nxt_string("function f(x) { a = x } var a; f(5); a"),

[drsm]

Hi @xeioex,
the patch works for me, thanks!
except one minor issue:

>> (function(...xs) {}).length
1
>> (function(x, ...xs) {}).length
2

should be 0, 1 according to the spec:
https://tc39.github.io/ecma262/#sec-functioninitialize
https://tc39.github.io/ecma262/#sec-function-definitions-static-semantics-expectedargumentcount

[drsm]

found another one:

>> var v = function(x, ...x) { console.log(x); };
undefined
>> v(1,2,3,4)
[2,3,4]

there should be a SyntaxError.

[xeioex]

there should be a SyntaxError.

The same is for ordinary functions. The argument' names are not checked for duplicates.

[drsm]

The argument' names are not checked for duplicates.

This is allowed in non-strict mode, but not for the rest parameter:

$ node
> var x = function(a,b,a) { console.log(arguments); };
undefined
> x(1,3,4)
[Arguments] { '0': 1, '1': 3, '2': 4 }
undefined
> var x = function(a, ...a) {};
var x = function(a, ...a) {};
                       ^

SyntaxError: Duplicate parameter name not allowed in this context
>

[xeioex]

We aim to support only the strict mode, so we can consider this as an error even for ordinary functions.