Build time significantly increases with overrides/.icons

[kcgthb]

I checked that...

• ... the documentation does not mention anything about my problem
• ... the problem doesn't occur with the default MkDocs template
• ... the problem is not in any of my customizations (CSS, JS, template)
• ... there are no open or closed issues that are related to my problem

Description

The site build time significantly increases (x8) when additional icons are enabled via overrides/.icons.

Expected behavior

Same, or at least comparable build times with or without additional icons.

Actual behavior

• without additional icons:

  $ grep -A3 pymdownx.emoji mkdocs.yml
    - pymdownx.emoji:
        emoji_index: !!python/name:materialx.emoji.twemoji
        emoji_generator: !!python/name:pymdownx.emoji.to_svg
        #    options:
        #  custom_icons:
        #    - overrides/.icons
  $ time mkdocs -q build
  
  real    0m8.947s
  user    0m8.744s
  sys     0m0.645s
  

• with additional icons:

  $ grep -A3 pymdownx.emoji mkdocs.yml
    - pymdownx.emoji:
        emoji_index: !!python/name:materialx.emoji.twemoji
        emoji_generator: !!python/name:pymdownx.emoji.to_svg
        options:
          custom_icons:
            - overrides/.icons
  $ time mkdocs -q build
  
  real    0m57.974s
  user    0m50.919s
  sys     0m7.643s
  

The actual icons don't seem to matter, nor the number of icons in overrides/.icons.

The issue doesn't seem to be specific to Material for MkDocs, but I couldn't find any reference to custom_icons in the PyMdown Extensions documentation so I'm not exactly sure where to report this.

What seems to be happening is that with custom_icons enabled, mkdocs spends more and more time to read each page, as it's progressing through them. In verbose mode you can see that each of the lines:

DEBUG   -  Reading: docs/page.md

takes longer to process than the previous one, and end up almost crawling to a halt.
Without custom_icons, the build process goes through all of then quickly, each page taking the same time to read.

Steps to reproduce the bug

1. enable custom icons in mkdocs.yml as per the documentation
2. build the pages with mdocs build or mkdocs serve

Package versions

• Python: Python 3.7.8
• MkDocs: mkdocs, version 1.1.2
• Material: Version: 5.5.12

Project configuration

markdown_extensions:
  - pymdownx.emoji:
      emoji_index: !!python/name:materialx.emoji.twemoji
      emoji_generator: !!python/name:pymdownx.emoji.to_svg
      options:
        custom_icons:
          - overrides/.icons

[squidfunk]

What happens when you set the emoji_generator to materialx?

markdown_extensions:
  - pymdownx.emoji:
      emoji_index: !!python/name:materialx.emoji.twemoji
      emoji_generator: !!python/name:materialx.emoji.to_svg # <-
      options:
        custom_icons:
          - overrides/.icons

[squidfunk]

Furthermore, have you tried reproducing the problem with a mint installation, only configuring icons for overrides?

[kcgthb]

What happens when you set the emoji_generator to materialx?

Same thing, apparently: reading .md pages is incrementally longer over the build process, and it ended up taking the same ~57s.

Interestingly, it's just the Reading phase that is longer, Building pages is still as quick as without custom_icons.

Furthermore, have you tried reproducing the problem with a mint installation, only configuring icons for overrides?

I just tried adding the Bootstrap icons to a straight git clone of Material for MkDocs (exactly like in the example at https://squidfunk.github.io/mkdocs-material/setup/changing-the-logo-and-icons/#additional-icons): I cloned the https://github.com/squidfunk/mkdocs-material.git repo, created the overrides/.icons directory and added the Boostrap icons in it, then enabling custom icons with:

markdown_extensions:
  - pymdownx.emoji:
      emoji_index: !!python/name:materialx.emoji.twemoji
      emoji_generator: !!python/name:materialx.emoji.to_svg
      options:
        custom_icons:
          - overrides/.icons

and the build time went from 5.7s to 32.3s

[squidfunk]

Thanks so far. Does it also happen with the default or readthedocs theme?

[kcgthb]

Yes, it seems to be happening with both the default mkdocs and readthedocs themes too.

I realize it may not be specific to Material for MkDocs, but I'm not sure any other theme uses custom_icons so I wasn't too sure where to report this. Thanks!

[squidfunk]

It's either specific to Material for MkDocs Extensions then, or MkDocs itself. @facelessuser, any idea?

[facelessuser]

What version of that is being used? Pretty sure I fixed that: facelessuser/mkdocs-material-extensions#10. But maybe not 🤷‍♂️ .

[facelessuser]

I think what I addressed was index getting bigger on every reload. I'm not aware of it getting bigger per page, but maybe...I'd have to take a look.

[squidfunk]

Thanks, @facelessuser! As this issue is not directly related to this project, I'm closing it. @kcgthb thanks for your thorough investigations!

[facelessuser]

If a solution is desired, please create a bug over at the repository and provide what version you are using. Assuming I can pin it down to something I'm doing, I can fix it.

[kcgthb]

Thank you both! I created facelessuser/mkdocs-material-extensions#14