Fix hot reload when users update many files "simultaneously"

[karreiro]

WHY are these changes introduced?

Some users rely on tools over their theme (like Webpack) to update multiple files in a very short period of time.

The message.date.modified list may contain multiple files in that kind of scenario. However, if the first file of the list doesn't require refreshing the entire page, while the second file does, the changes from the second file are not covered by the hot reload mechanism.

WHAT is this pull request doing?

This pull request introduces changes in the hot-reload.js module to analyze all modified files instead of considering only the first one (inspired by #1458).

How to test your changes?

Download the reproducer_remove_me.rb here.

# Initialize a new theme
$ shopify-dev theme init my_theme

# `theme serve` it
$ cd my_theme
$ pwd
/Users/karreiro/theme # ← Keep this path in mind
$ shopify-dev theme serve

# Open a a different terminal window
# Use the path above as a parameter for the `reproducer_remove_me.rb` reproducer
$ ruby reproducer_remove_me.rb /Users/karreiro/theme/my_theme

Before this PR:

After this PR:

Post-release steps

None.

Update checklist

• I've added a CHANGELOG entry for this PR (if the change is public-facing)
• I've considered possible cross-platform impacts (Mac, Linux, Windows).
• I've left the version number as is (we'll handle incrementing this when releasing).
• I've included any post-release steps in the section above.

[macournoyer]

🤩