fix nim-lang#6583 nim doc now outputs again in $projdir, like the oth…

…er commands

changelog.md

@@ -172,6 +172,8 @@ proc mydiv(a, b): int {.raises: [].} =
   (likewise with other hints and warnings), which is consistent with all other bool flags.
   (since 1.3.3).
 - `nim doc -r main` and `nim rst2html -r main` now call openDefaultBrowser
+- `nim doc foo/main` now outputs to `foo/main.html`, consistently with other commands. Use
+  `--usenimcache` for example to output instead under $nimcache.
 
 ## Tool changes
 

compiler/main.nim

@@ -189,10 +189,7 @@ proc mainCommand*(graph: ModuleGraph) =
   conf.searchPaths.add(conf.libpath)
   setId(100)
 
-  ## Calling `setOutDir(conf)` unconditionally would fix regression
-  ## https://github.com/nim-lang/Nim/issues/6583#issuecomment-625711125
-  when false: setOutDir(conf)
-  if optUseNimcache in conf.globalOptions: setOutDir(conf)
+  setOutDir(conf)
 
   template handleBackend(backend2: TBackend) =
     conf.backend = backend2

compiler/options.nim

@@ -542,6 +542,7 @@ proc getOutFile*(conf: ConfigRef; filename: RelativeFile, ext: string): Absolute
   # explains regression https://github.com/nim-lang/Nim/issues/6583#issuecomment-625711125
   # Yet another reason why "" should not mean ".";  `""/something` should raise
   # instead of implying "" == "." as it's bug prone.
+  doAssert conf.outDir.string.len > 0
   result = conf.outDir / changeFileExt(filename, ext)
 
 proc absOutFile*(conf: ConfigRef): AbsoluteFile =