fix varargs forwarding for templates; fixes #5455 (#5505)

* fix varargs forwarding for templates; fixes #5455
* document the macros' varargs change in the news for 0.16.2

compiler/sigmatch.nim

@@ -1651,7 +1651,7 @@ proc matchesAux(c: PContext, n, nOrig: PNode,
     if a >= formalLen-1 and formal != nil and formal.typ.isVarargsUntyped:
       incl(marker, formal.position)
       if container.isNil:
-        container = newNodeIT(nkBracket, n.sons[a].info, arrayConstr(c, n.info))
+        container = newNodeIT(nkArgList, n.sons[a].info, arrayConstr(c, n.info))
         setSon(m.call, formal.position + 1, container)
       else:
         incrIndexType(container.typ)
@@ -1739,7 +1739,7 @@ proc matchesAux(c: PContext, n, nOrig: PNode,
 
         if formal.typ.isVarargsUntyped:
           if container.isNil:
-            container = newNodeIT(nkBracket, n.sons[a].info, arrayConstr(c, n.info))
+            container = newNodeIT(nkArgList, n.sons[a].info, arrayConstr(c, n.info))
             setSon(m.call, formal.position + 1, container)
           else:
             incrIndexType(container.typ)

tests/overload/tparam_forwarding.nim

@@ -0,0 +1,37 @@
+discard """
+output: '''baz
+10
+100
+1000
+a
+b
+c
+'''
+"""
+
+type
+  Foo = object
+    x: int
+
+proc stringVarargs*(strings: varargs[string, `$`]): void =
+  for s in strings: echo s
+
+proc fooVarargs*(foos: varargs[Foo]) =
+  for f in foos: echo f.x
+
+template templateForwarding*(callable: untyped,
+                             condition: bool,
+                             forwarded: varargs[untyped]): untyped =
+  if condition:
+    callable(forwarded)
+
+proc procForwarding(args: varargs[string]) =
+  stringVarargs(args)
+
+templateForwarding stringVarargs, 17 + 4 < 21, "foo", "bar", 100
+templateForwarding stringVarargs, 10 < 21, "baz"
+
+templateForwarding fooVarargs, "test".len > 3, Foo(x: 10), Foo(x: 100), Foo(x: 1000)
+
+procForwarding "a", "b", "c"
+

web/news/e031_version_0_16_2.rst

@@ -23,6 +23,9 @@ Changes affecting backwards compatibility
   pointer. Now the hash is calculated from the contents of the string, assuming
   ``cstring`` is a null-terminated string. Equal ``string`` and ``cstring``
   values produce an equal hash value.
+- Macros accepting `varargs` arguments will now receive a node having the
+  `nkArgList` node kind. Previous code expecting the node kind to be `nkBracket`
+  may have to be updated.
 - ``memfiles.open`` now closes file handleds/fds by default.  Passing
   ``allowRemap=true`` to ``memfiles.open`` recovers the old behavior.  The old
   behavior is only needed to call ``mapMem`` on the resulting ``MemFile``.