fixes nim-lang#12885 [backport] (nim-lang#12895)

(cherry picked from commit 347a046)

compiler/semtempl.nim

@@ -242,6 +242,10 @@ proc addLocalDecl(c: var TemplCtx, n: var PNode, k: TSymKind) =
 
 proc semTemplSymbol(c: PContext, n: PNode, s: PSym; isField: bool): PNode =
   incl(s.flags, sfUsed)
+  # bug #12885; ideally sem'checking is performed again afterwards marking
+  # the symbol as used properly, but the nfSem mechanism currently prevents
+  # that from happening, so we mark the module as used here already:
+  markOwnerModuleAsUsed(c, s)
   # we do not call onUse here, as the identifier is not really
   # resolved here. We will fixup the used identifiers later.
   case s.kind

tests/tools/second.nim

@@ -0,0 +1,3 @@
+import tables
+
+let dataEx* = {1: 2, 3: 4}.toTable

tests/tools/tunused_imports.nim

@@ -2,14 +2,23 @@ discard """
   cmd: '''nim c --hint[Processing]:off $file'''
   nimout: '''
 tunused_imports.nim(11, 10) Warning: BEGIN [User]
-tunused_imports.nim(27, 10) Warning: END [User]
-tunused_imports.nim(25, 8) Warning: imported and not used: 'strutils' [UnusedImport]
+tunused_imports.nim(36, 10) Warning: END [User]
+tunused_imports.nim(34, 8) Warning: imported and not used: 'strutils' [UnusedImport]
 '''
   action: "compile"
 """
 
 {.warning: "BEGIN".}
 
+# bug #12885
+
+import tables, second
+
+template test(key: int): untyped =
+  `[]`(dataEx, key)
+
+echo test(1)
+
 import net, dontmentionme
 
 echo AF_UNIX