fix #6583, fix #14376, index+search now generated for all projects, many bug fixes with nim doc (#14324)

* refs #6583 fix nim doc output
* changelog
* change default for outDir when unspecified
* cleanups
* --project implies --index

compiler/nimpaths.nim

@@ -0,0 +1,44 @@
+##[
+Represents absolute paths, but using a symbolic variables (eg $nimr) which can be
+resolved at runtime; this avoids hardcoding at compile time absolute paths so
+that the project root can be relocated.
+
+xxx consider some refactoring with $nim/testament/lib/stdtest/specialpaths.nim;
+specialpaths is simpler because it doesn't need variables to be relocatable at
+runtime (eg for use in testament)
+
+interpolation variables:
+  $nimr: such that `$nimr/lib/system.nim` exists (avoids confusion with $nim binary)
+         in compiler, it's obtainable via getPrefixDir(); for other tools (eg koch),
+        this could be getCurrentDir() or getAppFilename().parentDir.parentDir,
+        depending on use case
+
+Unstable API
+]##
+
+import std/[os,strutils]
+
+const
+  docCss* = "$nimr/doc/nimdoc.css"
+  docHackNim* = "$nimr/tools/dochack/dochack.nim"
+  docHackJs* = docHackNim.changeFileExt("js")
+  docHackJsFname* = docHackJs.lastPathPart
+  theindexFname* = "theindex.html"
+  nimdocOutCss* = "nimdoc.out.css"
+    # `out` to make it easier to use with gitignore in user's repos
+  htmldocsDirname* = "htmldocs"
+
+proc interp*(path: string, nimr: string): string =
+  result = path % ["nimr", nimr]
+  doAssert '$' notin result, $(path, nimr, result) # avoids un-interpolated variables in output
+
+proc getDocHacksJs*(nimr: string, nim = getCurrentCompilerExe(), forceRebuild = false): string =
+  ## return absolute path to dochhack.js, rebuilding if it doesn't exist or if
+  ## `forceRebuild`.
+  let docHackJs2 = docHackJs.interp(nimr = nimr)
+  if forceRebuild or not docHackJs2.fileExists:
+    let cmd =  "$nim js $file" % ["nim", nim.quoteShell, "file", docHackNim.interp(nimr = nimr).quoteShell]
+    echo "getDocHacksJs: cmd: " & cmd
+    doAssert execShellCmd(cmd) == 0, $(cmd)
+  doAssert docHackJs2.fileExists
+  result = docHackJs2