add examples showing mixin; add examples showing passing types, macro…

…s, templates

lib/core/macros.nim

@@ -1380,9 +1380,9 @@ macro genAstOpt*(options: static set[GenAstOpt], args: varargs[untyped]): untype
       newEmptyNode()
 
   template newLitMaybe(a): untyped =
-    when type(a) is NimNode: a
-    elif compiles(newLit(a)): newLit(a)
-    else: a
+    when (a is type) or (typeof(a) is (proc | iterator | func | NimNode)):
+      a # `proc` actually also covers template, macro
+    else: newLit(a)
 
   # using `_` as workaround, see https://github.com/nim-lang/Nim/issues/2465#issuecomment-511076669
   let name = genSym(nskTemplate, "_fun")

tests/macros/mgenast.nim

@@ -41,3 +41,12 @@ macro bindme6UseExposeFalse*(): untyped =
     var ss = newStringStream("anothertext")
     writeData(ss, tst[0].addr, 2)
     discard readData(ss, tst[0].addr, 2)
+
+
+proc locafun1(): auto = "in locafun1"
+proc locafun2(): auto = "in locafun2"
+# locafun3 in caller scope only
+macro mixinExample*(): untyped =
+  genAst:
+    mixin locafun1
+    (locafun1(), locafun2(), locafun3())

tests/macros/tgenast.nim

@@ -235,3 +235,25 @@ block: # also from #11986
       let t = s
       $typeof(t)
   doAssert foo() == "set[char]"
+
+block:
+  macro foo(): untyped =
+    type Foo = object
+    template baz2(a: int): untyped = a*10
+    macro baz3(a: int): untyped = newLit 13
+    result = newStmtList()
+
+    result.add genAst(Foo, baz2, baz3) do: # shows you can pass types, templates etc
+      var x: Foo
+      $($typeof(x), baz2(3), baz3(4))
+
+    let ret = genAst() do: # shows you don't have to, since they're inject'd
+      var x: Foo
+      $($typeof(x), baz2(3), baz3(4))
+  doAssert foo() == """("Foo", 30, 13)"""
+
+block: # illustrates how symbol visiblity can be controlled precisely using `mixin`
+  proc locafun1(): auto = "in locafun1 (caller scope)" # this will be used because of `mixin locafun1` => explicit hijacking is ok
+  proc locafun2(): auto = "in locafun2 (caller scope)" # this won't be used => no hijacking
+  proc locafun3(): auto = "in locafun3 (caller scope)"
+  doAssert mixinExample() == ("in locafun1 (caller scope)", "in locafun2", "in locafun3 (caller scope)")