HTML export: Fix linking to targets in external files

Dan Davison writes:

> Bug report
> ==========
> If I have this:
>
> A [[file:zz.org::#mytarget][link]] to a target with a custom ID
>
> and export it to HTML, I get
>
> A <a href="zz.html##mytarget">link</a> to a target with a custom ID
>
> which (in firefox on linux) links to the file but does not jump to the
> target. However, if I change the '##' to '#' then firefox jumps to the
> correct location. Is this an org bug?
>
> Very tentatively proposed patch
> ===============================
> I've investigated a bit (notes below), resulting in this proposed patch:
>
> --8<---------------cut here---------------start------------->8---
> diff --git a/lisp/org-html.el b/lisp/org-html.el
> index aa70408..5ee5b19 100644
> --- a/lisp/org-html.el
> +++ b/lisp/org-html.el
> @@ -1110,7 +1110,7 @@ lang=\"%s\" xml:lang=\"%s\">
>                     (abs-p (file-name-absolute-p filename))
>                     thefile file-is-image-p search)
>                (save-match-data
> -                 (if (string-match "::\\(.*\\)" filename)
> +                 (if (string-match "::#?\\(.*\\)" filename)
>                      (setq search (match-string 1 filename)
>                            filename (replace-match "" t nil filename)))
>                  (setq valid
> --8<---------------cut here---------------end--------------->8---
>
> Doc patch
> =========
> The link above (file:zz.org::#mytarget) was created by C-c l on a
> heading with a CUSTOM_ID property. However, I couldn't see where in the
> manual links of this form are documented. Do we need to add this link
> type to section 4.7 "Search options in file links", e.g.
>
> --8<---------------cut here---------------start------------->8---
> diff --git a/doc/org.texi b/doc/org.texi
> index f49f056..c8cc1a5 100644
> --- a/doc/org.texi
> +++ b/doc/org.texi
> @@ -3116,6 +3116,7 @@ link, together with an explanation:
> [[file:~/code/main.c::255]]
> [[file:~/xx.org::My Target]]
> [[file:~/xx.org::*My Target]]
> +[[file:~/xx.org::#my-custom-id]]
> [[file:~/xx.org::/regexp/]]
> @end example
>
> @@ -3130,6 +3131,8 @@ link will become an HTML reference to the corresponding named anchor in
> the linked file.
> @item *My Target
> In an Org file, restrict search to headlines.
> +@item #my-custom-id
> +Link to a heading with a @code{CUSTOM_ID} property
> @item /regexp/
> Do a regular expression search for @code{regexp}.  This uses the Emacs
> command @code{occur} to list all matches in a separate window.  If the
> --8<---------------cut here---------------end--------------->8---
>
> Notes
> =====
> At line 1134 of org-html.el there is
>
> 			(setq thefile (concat thefile "#"
> 					      (org-solidify-link-text
> 					       (org-link-unescape search)))))
>
> during evaluation of which 'search is bound to "#mytarget", which
> suggested that the problem might be in the regexp parsing creating
> 'search.

doc/org.texi

@@ -3116,6 +3116,7 @@ link, together with an explanation:
 [[file:~/code/main.c::255]]
 [[file:~/xx.org::My Target]]
 [[file:~/xx.org::*My Target]]
+[[file:~/xx.org::#my-custom-id]]
 [[file:~/xx.org::/regexp/]]
 @end example
 
@@ -3130,6 +3131,8 @@ link will become an HTML reference to the corresponding named anchor in
 the linked file.
 @item *My Target
 In an Org file, restrict search to headlines.
+@item #my-custom-id
+Link to a heading with a @code{CUSTOM_ID} property
 @item /regexp/
 Do a regular expression search for @code{regexp}.  This uses the Emacs
 command @code{occur} to list all matches in a separate window.  If the

lisp/ChangeLog

@@ -1,5 +1,7 @@
 2010-03-19  Carsten Dominik  <carsten.dominik@gmail.com>
 
+	* org-html.el (org-export-as-html): Avoid double # in href.
+
 	* org.el (org-refile-get-location): Catch an invalid target
 	specification.
 

lisp/org-html.el

@@ -1131,9 +1131,11 @@ lang=\"%s\" xml:lang=\"%s\">
 			     (not (string-match "^[0-9]*$" search))
 			     (not (string-match "^\\*" search))
 			     (not (string-match "^/.*/$" search)))
-			(setq thefile (concat thefile "#"
-					      (org-solidify-link-text
-					       (org-link-unescape search)))))
+			(setq thefile
+			      (concat thefile
+				      (if (= (string-to-char search) ?#) "" "#")
+				      (org-solidify-link-text
+				       (org-link-unescape search)))))
 		    (when (string-match "^file:" desc)
 		      (setq desc (replace-match "" t t desc))
 		      (if (string-match "\\.org$" desc)