Silence declared but unused warnings when there is no loggging code g… (

#143)

* Silence declared but unused warnings when there is no loggging code generated

* Create custom 'used' magic

* Also disable warning for eventName

chronicles.nim

@@ -159,13 +159,13 @@ else:
  else:
  proc getLogThreadId*(): int = 0
 
-template formatItIMPL*(value: any): auto =
+template formatItIMPL*(value: auto): auto =
  value
 
 template formatIt*(T: type, body: untyped) {.dirty.} =
  template formatItIMPL*(it: T): auto = body
 
-template expandItIMPL*[R](record: R, field: static string, value: any) =
+template expandItIMPL*[R](record: R, field: static string, value: auto) =
  mixin setProperty, formatItIMPL
  setProperty(record, field, formatItIMPL(value))
 
@@ -216,14 +216,18 @@ macro expandIt*(T: type, expandedProps: untyped): untyped =
  when defined(debugLogImpl):
  echo result.repr
 
+template chroniclesUsedMagic(x: untyped) =
+ # Force the compiler to mark any symbol in the x
+ # as used without actually generate any code.
+ when compiles(x): discard
+
 macro logIMPL(lineInfo: static InstInfo,
  Stream: typed,
  RecordType: type,
  eventName: static[string],
  severity: static[LogLevel],
  scopes: typed,
  logStmtBindings: varargs[untyped]): untyped =
- if not loggingEnabled: return
  clearEmptyVarargs logStmtBindings
 
  # First, we merge the lexical bindings with the additional
@@ -237,6 +241,17 @@ macro logIMPL(lineInfo: static InstInfo,
  for k, v in assignments(lexicalBindings, acLogStatement):
  finalBindings[k] = v
 
+ result = newStmtList()
+ # This statement is to silence compiler warnings
+ # `declared but not used` when there is no logging code generated.
+ # push/pop pragma pairs cannot be used in this situation
+ # because the variables are declared outside of this function.
+ result.add quote do: chroniclesUsedMagic(`eventName`)
+ for k, v in finalBindings:
+ result.add quote do: chroniclesUsedMagic(`v`)
+
+ if not loggingEnabled: return
+
  # This is the compile-time topic filtering code, which has a similar
  # logic to the generated run-time filtering code:
  var enabledTopicsMatch = enabledTopics.len == 0 and severity >= enabledLogLevel
@@ -314,7 +329,7 @@ macro logIMPL(lineInfo: static InstInfo,
  code.add newCall("logAllDynamicProperties", Stream, record)
  code.add newCall("flushRecord", record)
 
- result = quote do:
+ result.add quote do:
  try:
  block `chroniclesBlockName`:
  `code`