picker_utc of datetime widget is broken in #6980, resulting in a timezone mismatch

[hangvane]

Describe the bug

picker_utc is broken in #6980, that takes no effect on the behavior of processing timezone.

22370b1#diff-93df641b502cdffd0d6642a8c06ad7ba617a16ee4907262538db0820a966a886L161

As a result, the time displayed stored are mismatched.

If I pick the current time, I will get a time that is 8 hours early (in the filename slug: {{day}}-{{hour}}), and there's no way to change the behavior.

To Reproduce

1. Add a datetime widget

collections:
  - name: 'Post' # Used in routes, e.g., /admin/collections/blog
    label: 'post' # Used in the UI
    folder: 'source/_posts' # The path to the folder where the documents are stored
    create: true # Allow users to create new documents in this collection
    slug: '{{year}}{{month}}{{day}}-{{hour}}{{minute}}-{{filename}}' # Filename template, e.g., YYYY-MM-DD-title.md
    preview_path: '{{year}}-{{month}}/{{urlname}}.htm'
    fields: # The fields for each document, usually in front matter
      - {label: 'title', name: 'title', widget: 'string'}
      - {label: 'filename', name: 'filename', widget: 'string'}
      - {label: 'urlname', name: 'urlname', widget: 'string'}
      - {label: 'date', name: 'date', widget: 'datetime', picker_utc: true}

2. Edit the date in the UI
3. Check the front-matter and filename of the generated markdown file.

Expected behavior

The stored datetime string should be the same as picked.

Screenshots

Applicable Versions:

• Decap CMS version: 3.1.1
• Git provider: GitHub
• OS: Windows 11
• Browser version chrome 112

CMS configuration

collections:
  - name: 'Post' # Used in routes, e.g., /admin/collections/blog
    label: 'post' # Used in the UI
    folder: 'source/_posts' # The path to the folder where the documents are stored
    create: true # Allow users to create new documents in this collection
    slug: '{{year}}{{month}}{{day}}-{{hour}}{{minute}}-{{filename}}' # Filename template, e.g., YYYY-MM-DD-title.md
    preview_path: '{{year}}-{{month}}/{{urlname}}.htm'
    fields: # The fields for each document, usually in front matter
      - {label: 'title', name: 'title', widget: 'string'}
      - {label: 'filename', name: 'filename', widget: 'string'}
      - {label: 'urlname', name: 'urlname', widget: 'string'}
      - {label: 'date', name: 'date', widget: 'datetime', picker_utc: true}

Additional context

[martinjagodic]

A fix is released in v3.1.6 (#7091). @hangvane can you please test if it works now?

[msfjarvis]

This is still broken for me, when I try to use Decap to update a date I lose the TZ component and the invalid date causes Hugo to start ignoring that post. The change I made to my config.yml file is here, and this is what Decap did when I updated the date on a blog post: msfjarvis/msfjarvis.dev@feb7f75

[demshy]

@msfjarvis we also stumbled upon this issue on one of our projects, patch released just now in 3.1.8 seems so solve it for us. Do you mind checking it out?

[msfjarvis]

@msfjarvis we also stumbled upon this issue on one of our projects, patch released just now in 3.1.8 seems so solve it for us. Do you mind checking it out?

v3.1.8 fixed it, thank you!