fix bug that fails to display link in eldoc when url-hidding mode is enabled

[taquangtrung]

Hi,

Description

Currently, when the URL hiding feature is enabled, markdown eldoc always throws the error eldoc error: (wrong-type-argument stringp nil) when a cursor is put under the hidden URL.

I investigated the code and see that the problem is due to the fact that the regular expression matching state performed by (thing-at-point-looking-at markdown-regex-link-inline), which is used to get the URL, is cleared by the next call to (markdown--substitute-command-keys (if imagep "\\[markdown-insert-image]" "\\[markdown-insert-link]")).

So, this PR will fix this bug by getting the URL information early, before the call to markdown--substitute-command-keys.

Can anyone take a look and merge it if possible?

Thank you!

Related Issue

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the CONTRIBUTING.md document.
• I have updated the documentation in the README.md file if necessary.
• I have added an entry to CHANGES.md.
• I have added tests to cover my changes.
• All new and existing tests passed (using make test).

[syohex]

Could you show us the code which reproduces your issue or add unit tests ?

[taquangtrung]

The code that creates the issue is inside markdown-eldoc-function, in particular this part:

   ((and (or (thing-at-point-looking-at markdown-regex-link-inline)
             (thing-at-point-looking-at markdown-regex-link-reference))
         (or markdown-hide-urls markdown-hide-markup))
    (let* ((imagep (string-equal (match-string 1) "!"))
           (edit-keys (markdown--substitute-command-keys
                       (if imagep
                           "\\[markdown-insert-image]"
                         "\\[markdown-insert-link]")))
           (edit-str (propertize edit-keys 'face 'font-lock-constant-face))
           (referencep (string-equal (match-string 5) "["))
           (object (if referencep "reference" "URL")))
      (format "Hidden %s (%s to edit): %s" object edit-str
              (if referencep
                  (concat
                   (propertize "[" 'face 'markdown-markup-face)
                   (propertize (match-string-no-properties 6)
                               'face 'markdown-reference-face)
                   (propertize "]" 'face 'markdown-markup-face))
                (propertize (match-string-no-properties 6)
                            'face 'markdown-url-face)))))

The function call (thing-at-point-looking-at markdown-regex-link-inline) is supposed to be used to fetch URL information later by (match-string-no-properties 6).

But there is another call by markdown--substitute-command-keys at

 (edit-keys (markdown--substitute-command-keys
                       (if imagep
                           "\\[markdown-insert-image]"
                         "\\[markdown-insert-link]")))

which also performs regular expression matching. This call will clear the state produced by (thing-at-point-looking-at markdown-regex-link-inline).

Therefore the latter call to (match-string-no-properties 6) always produces nil.

In my patch, I put the call to (match-string-no-properties 6) to be earlier than markdown--substitute-command-keys

[syohex]

Sorry I would like you to show us sample markdown text and minimal configuration to reproduce this issue. And could you tell us how to reproduce in detail, cursor position, commands etc ?

[taquangtrung]

Ah I see. For example, I created and open a markdown file foo.md and put the following content into it: [This is a hidden link](http://hidden.link).

Then run M-x markdown-toggle-url-hiding, turn on eldoc-mode, and put the cursor under the link's text. There will be an error message like the below (the keyboard cursor is under the link text)

[taquangtrung]

Here is what obtained after applying my patch:

[syohex]

@taquangtrung Thanks for good explanation. I have merged your patch and added a unit test #675

[taquangtrung]

@syohex: thanks for the update!