update examples + tests with varargs[typed]

lib/core/macros.nim

@@ -1683,16 +1683,20 @@ macro getCustomPragmaVal*(n: typed, cp: typed): untyped =
 
 macro unpackVarargs*(callee: untyped; args: varargs[untyped]): untyped =
   ## Calls `callee` with `args` unpacked as individual arguments.
-  ## This is only useful in the case where `args` can potentially be empty, due
-  ## to a compiler limitation, see examples.
+  ## This is useful in 2 cases:
+  ## * when forwarding `varargs[T]` for some typed `T`
+  ## * when forwarding `varargs[untyped]` when `args` can potentially be empty,
+  ##   due to a compiler limitation
   runnableExamples:
-    template call(fun: typed; args: varargs[untyped]): untyped =
+    template call1(fun: typed; args: varargs[untyped]): untyped =
       unpackVarargs(fun, args)
       # when varargsLen(args) > 0: fun(args) else: fun() # this would also work
+    template call2(fun: typed; args: varargs[typed]): untyped =
+      unpackVarargs(fun, args)
     proc fn1(a = 0, b = 1) = discard (a, b)
-    call(fn1, 10, 11)
-    call(fn1, 10)
-    call(fn1) # `args` is empty in this case
+    call1(fn1, 10, 11)
+    call1(fn1) # `args` is empty in this case
+    if true: call2(echo, 10, 11) # would print 1011
   result = newCall(callee)
   for i in 0 ..< args.len:
     result.add args[i]

tests/stdlib/tmacros.nim

@@ -33,10 +33,30 @@ block: # unpackVarargs
 
     proc fn1(a = 0, b = 1) = discard (a, b)
 
-    call1(fn1, 10, 11)
-    call1(fn1, 10)
     call1(fn1)
+    call1(fn1, 10)
+    call1(fn1, 10, 11)
 
-    call2(fn1, 10, 11)
-    call2(fn1, 10)
     call2(fn1)
+    call2(fn1, 10)
+    call2(fn1, 10, 11)
+
+  block:
+    template call1(fun: typed; args: varargs[typed]): untyped =
+      unpackVarargs(fun, args)
+    template call2(fun: typed; args: varargs[typed]): untyped =
+      # xxx this would give a confusing error message:
+      # required type for a: varargs[typed] [varargs] but expression '[10]' is of type: varargs[typed] [varargs]
+      when varargsLen(args) > 0: fun(args)
+      else: fun()
+    macro toString(a: varargs[typed, `$`]): string =
+      var msg = genSym(nskVar, "msg")
+      result = newStmtList()
+      result.add quote do:
+        var `msg` = ""
+      for ai in a:
+        result.add quote do: `msg`.add $`ai`
+      result.add quote do: `msg`
+    doAssert call1(toString) == ""
+    doAssert call1(toString, 10) == "10"
+    doAssert call1(toString, 10, 11) == "1011"