fixes #7089

compiler/commands.nim

@@ -471,6 +471,16 @@ proc processSwitch(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
     processOnOffSwitch({optMemTracker}, arg, pass, info)
     if optMemTracker in gOptions: defineSymbol("memtracker")
     else: undefSymbol("memtracker")
+  of "oldnewlines":
+    case arg.normalize
+    of "on":
+      options.gOldNewlines = true
+      defineSymbol("nimOldNewlines")
+    of "off":
+      options.gOldNewlines = false
+      undefSymbol("nimOldNewlines")
+    else:
+      localError(info, errOnOrOffExpectedButXFound, arg)
   of "checks", "x": processOnOffSwitch(ChecksOptions, arg, pass, info)
   of "floatchecks":
     processOnOffSwitch({optNaNCheck, optInfCheck}, arg, pass, info)

compiler/lexer.nim

@@ -625,7 +625,15 @@ proc getEscapedChar(L: var TLexer, tok: var TToken) =
   inc(L.bufpos)               # skip '\'
   case L.buf[L.bufpos]
   of 'n', 'N':
-    if tok.tokType == tkCharLit: lexMessage(L, errNnotAllowedInCharacter)
+    if gOldNewlines:
+      if tok.tokType == tkCharLit: lexMessage(L, errNnotAllowedInCharacter)
+      add(tok.literal, tnl)
+    else:
+      add(tok.literal, '\L')
+    inc(L.bufpos)
+  of 'p', 'P':
+    if tok.tokType == tkCharLit:
+      lexMessage(L, errGenerated, "\\p not allowed in character literal")
     add(tok.literal, tnl)
     inc(L.bufpos)
   of 'r', 'R', 'c', 'C':

compiler/options.nim

@@ -114,6 +114,7 @@ proc cppDefine*(c: ConfigRef; define: string) =
 
 var
   gIdeCmd*: IdeCmd
+  gOldNewlines*: bool
 
 const
   ChecksOptions* = {optObjCheck, optFieldCheck, optRangeCheck, optNilCheck,