Date:   Wed, 5 Jan 2022 14:42:28 +0000
From:   James Clark <james.clark@....com>
To:     Nícolas F. R. A. Prado <n@...aprado.net>
Cc:     mchehab+huawei@...nel.org, nfraprado@...tonmail.com,
        corbet@....net, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] docs: automarkup.py: Fix invalid HTML link output and
 broken URI fragments



On 04/01/2022 21:58, Nícolas F. R. A. Prado wrote:
> Hello James,
> 
> On Tue, Jan 04, 2022 at 02:17:43PM +0000, James Clark wrote:
>>
>>
>> On 16/12/2021 19:27, James Clark wrote:
>>> Since commit d18b01789ae5 ("docs: Add automatic cross-reference for
>>> documentation pages"), references that were already explicitly defined
>>> with "ref:" and reffered to other pages with a path have been doubled.
>>> This is reported as the following error by Firefox:
>>>
>>>   Start tag "a" seen but an element of the same type was already open.
>>>   End tag "a" violates nesting rules.
>>>
>>> As well as the invalid HTML, this also obscures the URI fragment links
>>> to subsections because the second link overrides the first. For example
>>> on the page admin-guide/hw-vuln/mds.html the last link should be to the
>>> "Default Mitigations" subsection using a # URI fragment:
>>>
>>>   admin-guide/hw-vuln/l1tf.html#default-mitigations
>>>
>>> But it is obsured by a second link to the whole page:
>>>
>>>   admin-guide/hw-vuln/l1tf.html
>>>
>>
>> Bump. Is there a way this can be merged if there are no objections? It's
>> preventing me from adding links in the docs.
> 
> Sorry for the delay, I changed emails and wasn't monitoring that old one.
> 
> First of all, thank you for noticing and fixing this issue!
> 
> To be honest, it bothered me that you walked upwards on the node tree to figure
> out if the current node is a child of a reference node instead of figuring that
> out as the tree is traversed down, so I took a stab at implementing that. The
> aim was to only consider nodes that are:
> 
>   1. below a paragraph node, to avoid changing text outside the paragraphs like
>      titles and so on
>   2. not below a literal or reference, to avoid this issue you noticed
> 
> However I was not very happy with the end result either. The code got a bit
> messy, and while I thought it would be a lot faster than the upward walk, in the
> end it doesn't really make a difference: From my test-run this approach took
> 10m15s, while yours took 10m49s.
> 
> I'll include my patch at the end of this email for reference (to myself and
> others) if/when we revisit this in the future.
> 
> So this is to say that, while I think the best long-term solution would be to
> only walk the nodes we're interested in from the get go, your solution is way
> simpler and not noticibly slower, so let's go with it for now. I just have a
> little nit on the patch, see below.
> 

Thanks for reviewing, I've sent V2. Presumably the absolute simplest way is to remove
that function and do a search and replace to convert all bare page references to real
ones. Although I assumed that possibility was considered when the auto link function
was added in the first place.

James

>>
>> Thanks
>> James
>>
>>> The full HTML with the double <a> tags looks like this:
>>>
>>>   <a class="reference internal" href="l1tf.html#default-mitigations">
>>>     <span class="std std-ref">
>>>       <a class="reference internal" href="l1tf.html">
>>>         <span class="doc">L1TF - L1 Terminal Fault</span>
>>>       </a>
>>>     </span>
>>>   </a>
>>>
>>> After this commit, there is only a single link:
>>>
>>>   <a class="reference internal" href="l1tf.html#default-mitigations">
>>>     <span class="std std-ref">Documentation/admin-guide/hw-vuln//l1tf.rst</span>
>>>   </a>
>>>
>>> Now that the second link is removed, the browser correctly jumps to the
>>> default-mitigations subsection when clicking the link.
>>>
>>> The fix is to check that nodes in the document to be modified are not
>>> already references. A reference is counted as any text that is a
>>> descendant of a reference type node. Only plain text should be converted
>>> to new references, otherwise the doubling occurs.
>>>
>>> Testing
>>> =======
>>>
>>>  * Test that the build stdout is the same (ignoring ordering), and that
>>>    no new warnings are printed.
>>>
>>>  * Diff all .html files and check that the only modifications occur
>>>    to the bad double links.
>>>
>>>  * The auto linking of bare references to pages without "ref:" is still
>>>    working.
>>>
>>> Fixes: d18b01789ae5 ("docs: Add automatic cross-reference for
>>>        documentation pages")
>>> Signed-off-by: James Clark <james.clark@....com>
>>> ---
>>>  Documentation/sphinx/automarkup.py | 18 +++++++++++++++---
>>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/sphinx/automarkup.py b/Documentation/sphinx/automarkup.py
>>> index acf5473002f3..3fee247b55b3 100644
>>> --- a/Documentation/sphinx/automarkup.py
>>> +++ b/Documentation/sphinx/automarkup.py
>>> @@ -280,10 +280,22 @@ def auto_markup(app, doctree, name):
>>>      # avoid adding cross-references to functions that have been explicitly
>>>      # marked with cc:func:.
>>>      #
> 
> Could you add your function above this comment so it doesn't get separated from
> the code it's commenting on?
> 
> Actually, the comment about the literal could be moved inside your function...
> 
>>> +    def text_but_not_a_reference(node):
> 
> ...here:
>     #
>     # The nodes.literal test catches ``literal text``, its purpose is to
>     # avoid adding cross-references to functions that have been explicitly
>     # marked with cc:func:.
>     #
> 
>>> +        if not isinstance(node, nodes.Text) or isinstance(node.parent, nodes.literal):
>>> +            return False
>>> +
>>> +        child_of_reference = False
>>> +        parent = node.parent
>>> +        while parent:
>>> +            if isinstance(parent, nodes.Referential):
>>> +                child_of_reference = True
>>> +                break
>>> +            parent = parent.parent
>>> +        return not child_of_reference
>>> +
> 
> and the comment about refactoring the loop should be left here:
> 
>     #
>     # This loop could eventually be improved on.  Someday maybe we
>     # want a proper tree traversal with a lot of awareness of which
>     # kinds of nodes to prune.  But this works well for now.
>     #
> 
> With this,
> 
> Reviewed-by: N�colas F. R. A. Prado <n@...aprado.net>
> 
> Thanks,
> N�colas
> 
>>>      for para in doctree.traverse(nodes.paragraph):
>>> -        for node in para.traverse(nodes.Text):
>>> -            if not isinstance(node.parent, nodes.literal):
>>> -                node.parent.replace(node, markup_refs(name, app, node))
>>> +        for node in para.traverse(condition=text_but_not_a_reference):
>>> +            node.parent.replace(node, markup_refs(name, app, node))
>>>  
>>>  def setup(app):
>>>      app.connect('doctree-resolved', auto_markup)
>>>
>>
> 
> Uncleaned/unoptimized patch for walking down the tree:
> 
> diff --git a/Documentation/sphinx/automarkup.py b/Documentation/sphinx/automarkup.py
> index acf5473002f3..4738c99bbbfb 100644
> --- a/Documentation/sphinx/automarkup.py
> +++ b/Documentation/sphinx/automarkup.py
> @@ -271,19 +271,48 @@ def get_c_namespace(app, docname):
>  def auto_markup(app, doctree, name):
>      global c_namespace
>      c_namespace = get_c_namespace(app, name)
> -    #
> -    # This loop could eventually be improved on.  Someday maybe we
> -    # want a proper tree traversal with a lot of awareness of which
> -    # kinds of nodes to prune.  But this works well for now.
> -    #
> -    # The nodes.literal test catches ``literal text``, its purpose is to
> -    # avoid adding cross-references to functions that have been explicitly
> -    # marked with cc:func:.
> -    #
> -    for para in doctree.traverse(nodes.paragraph):
> -        for node in para.traverse(nodes.Text):
> -            if not isinstance(node.parent, nodes.literal):
> -                node.parent.replace(node, markup_refs(name, app, node))
> +
> +    def find_suitable_nodes(root):
> +        pending_nodes = [root]
> +        top_nodes = []
> +        final_nodes = []
> +        index = 0
> +
> +        def is_top_node(node):
> +            return isinstance(node, nodes.paragraph)
> +
> +        def is_bottom_node(node):
> +            return isinstance(node, nodes.Referential) or isinstance(node, nodes.literal)
> +
> +        while index < len(pending_nodes):
> +            current_node = pending_nodes[index]
> +            if is_top_node(current_node):
> +                top_nodes.append(current_node)
> +            else:
> +                pending_nodes.extend(current_node.children)
> +            index += 1
> +
> +        index = 0
> +        while index < len(top_nodes):
> +            current_node = top_nodes[index]
> +            for child in current_node.children:
> +                if not is_bottom_node(child):
> +                    final_nodes.append(child)
> +            index += 1
> +
> +        index = 0
> +        while index < len(final_nodes):
> +            current_node = final_nodes[index]
> +            for child in current_node.children:
> +                if not is_bottom_node(child):
> +                    final_nodes.append(child)
> +            index += 1
> +
> +        return final_nodes
> +
> +    for node in find_suitable_nodes(doctree):
> +        if isinstance(node, nodes.Text):
> +            node.parent.replace(node, markup_refs(name, app, node))
> 
>  def setup(app):
>      app.connect('doctree-resolved', auto_markup)
> --
> 

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