even more strict isNil handling for strings/seqs in order to detect bugs

lib/pure/os.nim

@@ -233,7 +233,7 @@ proc fileNewer*(a, b: string): bool {.rtl, extern: "nos$1".} =
   ## modification time is later than `b`'s.
   when defined(posix):
     # If we don't have access to nanosecond resolution, use '>='
-    when not StatHasNanoseconds:  
+    when not StatHasNanoseconds:
       result = getLastModificationTime(a) >= getLastModificationTime(b)
     else:
       result = getLastModificationTime(a) > getLastModificationTime(b)
@@ -1343,16 +1343,21 @@ elif defined(windows):
   # is always the same -- independent of the used C compiler.
   var
     ownArgv {.threadvar.}: seq[string]
+    ownParsedArgv {.threadvar.}: bool
 
   proc paramCount*(): int {.rtl, extern: "nos$1", tags: [ReadIOEffect].} =
     # Docstring in nimdoc block.
-    if isNil(ownArgv): ownArgv = parseCmdLine($getCommandLine())
+    if not ownParsedArgv:
+      ownArgv = parseCmdLine($getCommandLine())
+      ownParsedArgv = true
     result = ownArgv.len-1
 
   proc paramStr*(i: int): TaintedString {.rtl, extern: "nos$1",
     tags: [ReadIOEffect].} =
     # Docstring in nimdoc block.
-    if isNil(ownArgv): ownArgv = parseCmdLine($getCommandLine())
+    if not ownParsedArgv:
+      ownArgv = parseCmdLine($getCommandLine())
+      ownParsedArgv = true
     if i < ownArgv.len and i >= 0: return TaintedString(ownArgv[i])
     raise newException(IndexError, "invalid index")