Refactor AMP modes

[westonruter]

This PR intends to refactor the AMP modes in the plugin in order to resolve three issues:

• Fixes Always allow switching from Transitional to Native #2312: Always allow switching from Transitional to Native on sites that are defined with add_theme_support('amp', ['paired' => true]).
• Fixes Restore suppression of validation error warnings appearing in Reader mode #2311: Restore suppression of validation error warnings appearing in Reader mode
• Fixes Add functionality for users to chose AMP + Stories, AMP-only, Stories-only #2470: Add functionality for users to chose AMP + Stories, AMP-only, Stories-only
  • Ensure availability of Latest Stories block and Story post embed.
  • Include enabled experiences in generator tag, as well as website mode.
• Fixes Phase out “Native” terminology in favor of “AMP-first” #2507: Phase out “Native” terminology in favor of “AMP-first”
  • Rename historical references of native to standard, and paired to transitional.

Always allow switching themes with built-in Transitional support to Native

When a theme had add_theme_support( 'amp', array( 'paired' => true ) ) they would see:

Now, they see this instead:

This allows a theme which declares support for both AMP and non-AMP, to just opt to only serve AMP pages instead of being paired mode. This allows a theme like Neve to be used in either mode, even though it is defined as being paired => true.

Additionally, if they had add_theme_support( 'amp' ) then before they would see:

Now they see a slightly tweaked message:

Notice the link to the ecosystem page is moved to the bottom.

Generator Tag

Given a site in transitional mode with both website and stories experiences enabled, the generator tag is now:

<meta name="generator" content="AMP Plugin v1.2-beta2; mode=transitional; experiences=website,stories">

Note the new experiences param. If switching to standard (formerly native) mode, this is also reflected:

<meta name="generator" content="AMP Plugin v1.2-beta2; mode=standard; experiences=website,stories">

If stories is disabled, then this is shown as:

<meta name="generator" content="AMP Plugin v1.2-beta2; mode=standard; experiences=website">

If website is disabled but stories is enabled, then:

<meta name="generator" content="AMP Plugin v1.2-beta2; mode=none; experiences=stories">

[amedina]

Excellent. These changes increase both user friendliness and flexibility. Kudos on removing the option for Reader mode when Transitional mode is added via theme support.

[amedina]

This allows a theme which declares support for both AMP and non-AMP, to just opt to only serve AMP pages instead of being paired mode.

This means users can go from Transitional to Native also in all cases. It would be good to allow users in Transitional mode to chose Native AMP for some pages. This would enable sites to track progress of the "AMPlification" of their content ~ Your site is 86% Native AMP, 14% Transitional or Your site is 86% Native AMP, 10% Transitional, 4% no-AMP.

[amedina]

And when Bento AMP is a thing, the scores can be detailed at an even higher granular level.

[westonruter]

Chosing AMP-first for some URLs but paired for others is somewhat described under the “Mixed-Some-Only-AMP” mode in #934

IMO that adds a lot of complexity that I highly doubt users would be likely to leverage. Possibly some complicated changes to validation logic as well. Unsure how scores would be calculated.

Decisions not options.

I think we should help users get to AMP-first on URLs that support it. For other templates/URLs, non-AMP would be served unless the theme is using Bento AMP components.

[amedina]

I don't think the complexity will be much higher; and the benefit will be significant especially if weighed by the benefit of being able to measure the progression of a site towards AMP first.

And it also captures the essence of a Transitional mode: the site is converted progressively to AMP first.

The current Transitional approach is to wait until full parity (visual, functional) is achieved for all templates, before the "AMP-first" switch is turned. In this case, 95% of the site can be ready to switch, but it needs to wait for the rest to achieve full parity.

[amedina]

This means users can go from Transitional to Native also in all cases. It would be good to allow users in Transitional mode to chose Native AMP for some pages. This would enable sites to track progress of the "AMPlification" of their content ~ Your site is 86% Native AMP, 14% Transitional or Your site is 86% Native AMP, 10% Transitional, 4% no-AMP.

Closing the loop on this. We agree that a more fluid model for the Transitional mode would facilitate the transition of sites towards AMP-first experiences by avoiding the current all-or-nothing approach. However, we will be able to achieve this in a much easier way once Bento AMP is available. With Bento AMP a fully fluid transitional mode can be achieved without a lot of the complexity.

[amedina]

A few minor comments. Ready to ship.

[westonruter]

@amedina FYI, in 9737cd7 I've made it so that stories always have auto-accepting sanitization, and along with that I've shortened the warning to remove wording that is not relevant in non-website experience: