fix #13374 nim c -r - now generates $nimcache/stdinfile (#13380) [backport]

compiler/cmdlinehelper.nim

@@ -29,10 +29,7 @@ proc initDefinesProg*(self: NimProg, conf: ConfigRef, name: string) =
 proc processCmdLineAndProjectPath*(self: NimProg, conf: ConfigRef) =
   self.processCmdLine(passCmd1, "", conf)
   if self.supportsStdinFile and conf.projectName == "-":
-    conf.projectName = "stdinfile"
+    handleStdinInput(conf)
-    conf.projectFull = AbsoluteFile "stdinfile"
-    conf.projectPath = AbsoluteDir getCurrentDir()
-    conf.projectIsStdin = true
   elif conf.projectName != "":
     try:
       conf.projectFull = canonicalizePath(conf, AbsoluteFile conf.projectName)

compiler/commands.nim

@@ -369,6 +369,14 @@ proc dynlibOverride(conf: ConfigRef; switch, arg: string, pass: TCmdLinePass, in
     expectArg(conf, switch, arg, pass, info)
     options.inclDynlibOverride(conf, arg)
 
+proc handleStdinInput*(conf: ConfigRef) =
+  conf.projectName = "stdinfile"
+  conf.projectFull = conf.projectName.AbsoluteFile
+  conf.projectPath = AbsoluteDir getCurrentDir()
+  conf.projectIsStdin = true
+  if conf.outDir.isEmpty:
+    conf.outDir = getNimcacheDir(conf)
+
 proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
                     conf: ConfigRef) =
   var
@@ -861,8 +869,8 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
       localError(conf, info, "unknown Nim version; currently supported values are: {1.0}")
   of "benchmarkvm":
     processOnOffSwitchG(conf, {optBenchmarkVM}, arg, pass, info)
-  of "":
+  of "": # comes from "-" in for example: `nim c -r -` (gets stripped from -)
-    conf.projectName = "-"
+    handleStdinInput(conf)
   else:
     if strutils.find(switch, '.') >= 0: options.setConfigVar(conf, switch, arg)
     else: invalidCmdLineOption(conf, pass, switch, info)