koch: add --localdocs to allow building only local docs (#14783)

* koch: add --localdocs to allow building only local docs

This flag also make koch doc use the passed arguments when building
the offline docs.

This is useful when generating nightlies as we would want to use
--doccmd:skip and also skipping a pass of docgen speed things up
drastically (for non-native targets).

This flag superseded the undocumented --docslocal.

* kochdocs: filter google analytics code from the arg list instead

This commit introduce a small PEG expression to filter out the google
analytics code before building local docs when --localdocs is not
specified. This lets us keep any arguments unrelated to google analytics
when building local docs, useful for use with --doccmd:skip

tools/kochdocs.nim

@@ -1,6 +1,6 @@
 ## Part of 'koch' responsible for the documentation generation.
 
-import os, strutils, osproc, sets, pathnorm
+import os, strutils, osproc, sets, pathnorm, pegs
 from std/private/globs import nativeToUnixPath, walkDirRecFilter, PathEntry
 import "../compiler/nimpaths"
 
@@ -182,7 +182,7 @@ lib/system/iterators.nim
 lib/system/dollars.nim
 lib/system/widestrs.nim
 """.splitWhitespace()
-  
+
   proc follow(a: PathEntry): bool =
     a.path.lastPathPart notin ["nimcache", "htmldocs", "includes", "deprecated", "genode"]
   for entry in walkDirRecFilter("lib", follow = follow):
@@ -318,6 +318,19 @@ proc buildDocsDir*(args: string, dir: string) =
   buildDocPackages(args, dir)
   copyFile(docHackJsSource, dir / docHackJsSource.lastPathPart)
 
-proc buildDocs*(args: string) =
-  buildDocsDir(args, webUploadOutput / NimVersion)
-  buildDocsDir("", docHtmlOutput) # no `args` to avoid offline docs containing the 'gaCode'!
+proc buildDocs*(args: string, localOnly = false, localOutDir = "") =
+  let localOutDir =
+    if localOutDir.len == 0:
+      docHtmlOutput
+    else:
+      localOutDir
+
+  var args = args
+
+  if not localOnly:
+    buildDocsDir(args, webUploadOutput / NimVersion)
+
+    let gaFilter = peg"@( y'--doc.googleAnalytics:' @(\s / $) )"
+    args = args.replace(gaFilter)
+
+  buildDocsDir(args, localOutDir)