Add partial static-path.html

The existing `static-path` shortcode already satisfies most needs of
pages, but a page's inline shortcode cannot make use of the
`static-path` shortcode because Hugo does not support nested shortcodes.
Inline shortcodes can call partials though, so this commit creates a
partial with the same functionality for use from inline shortcodes.

Author: Leo3418

layouts/partials/static-path.html

@@ -0,0 +1,94 @@
+{{/*
+Based on this site's convention for organizing static files, returns the full
+relative path of a static file to the site base URL.  The returned path's value
+depends on the current page's permalink, section, kind, and draft status.
+
+This site's static files are organized in the following convention:
+- The files are organized by their types under different directories in the
+  union of all static directories, like 'static/img/' for images, and
+  'static/res/' for miscellaneous resources.
+- Under each type's directory are static files of that type for the section of
+  this site whose name is the same as the directory, such as
+  'static/img/collections/' for all images used in the 'collections' section,
+  and 'static/res/posts/' for all resources used in the 'posts' section.
+
+With respect to the basic conventions above, the exact path relative to a
+section's directory is determined as follows:
+- For each post that is not a draft: The post's date in 'YYYY-MM-DD' format,
+  followed by a hyphen, and the last element of the post's permalink with any
+  extension stripped.  e.g. '2006/01/02/lorem-ipsum.html' ->
+  'static/img/posts/2006-01-02-lorem-ipsum/'
+- For each draft post: The string 'drafts/', followed by the last element of
+  the post's permalink with any extension stripped.  e.g.
+  '2006/01/02/lorem-ipsum.html' -> 'static/img/posts/drafts/lorem-ipsum/'
+- For each page in other sections: The page's permalink relative to the root of
+  the section it is in, with any extension stripped. e.g.
+  - 'collections/hugo/shortcode.html' ->
+    'static/img/collections/hugo/shortcode/'
+  - 'collections/hugo.html' -> 'static/img/collections/hugo/'
+
+Finally, under every path derived from the above rules, a directory whose name
+is the same as a locale's language code (i.e. what '.Language.Lang' returns)
+can be optionally created to store localized static files for the locale.  Any
+static files not in such a directory are unlocalized files that may be shared
+across all multilingual variants of the site.  For example:
+- 'static/img/posts/2006-01-02-lorem-ipsum/en/' contains the post's images
+  that are localized for English
+- 'static/img/posts/2006-01-02-lorem-ipsum/' is for images that can be shared
+  among all locales
+
+The context should be a dictionary with these key-value pairs:
+- page: The page whose static file path is queried
+- type: The static file's type, such as 'img' and 'res'
+- file: The static file's base name, like 'hugo.png'; optional -- if not
+  specified, the root path to all static files of the specified type (without
+  trailing slash) is returned instead
+- l10n: Optional -- if specified and truthy, then a path to the file's
+  localized version for the current locale will be returned
+- abs: Optional -- if specified and truthy, then the absolute path to the file
+  will be returned instead of the relative path
+*/}}
+
+{{- $page := .page }}
+{{- $type := .type }}
+{{- $file := index . "file" | default "" }}
+{{- $l10n := index . "l10n" | default false }}
+{{- $abs := index . "abs" | default false }}
+
+{{- with $file }}
+    {{- $file = printf "/%s" . }}
+{{- end }}
+{{- $l10nDir := cond $l10n (printf "/%s" $page.Language.Lang) "" }}
+
+{{- $staticPath := false }}
+
+{{- with $page }}
+    {{- $path := "" }}
+    {{- $pageBaseName := path.BaseName .RelPermalink }}
+    {{- if eq .Section "posts" }}
+        {{- $path = printf "%s/posts/%s%s%s%s"
+            $type
+            (cond .Draft "drafts/" (.Date.Format "2006-01-02-"))
+            $pageBaseName
+            $l10nDir
+            $file
+        }}
+    {{- else }}
+        {{- /* Hugo starts .Page.RelPermalink with .Site.LanguagePrefix
+            and may end it with '/', which can be removed by path.Clean */}}
+        {{- $pageURLParent := replace (path.Clean .RelPermalink | path.Dir)
+            .Site.LanguagePrefix ""
+            1
+        }}
+        {{- $path = printf "%s%s/%s%s%s"
+            $type
+            $pageURLParent
+            $pageBaseName
+            $l10nDir
+            $file
+        }}
+    {{- end }}
+    {{- $staticPath = cond $abs (absURL $path) (relURL $path) }}
+{{- end -}}
+
+{{- return $staticPath }}