[google_fonts] Add WOFF and WOFF2 font format support for web

[Frank3K]

Description

Web applications benefit significantly from using WOFF2 font files instead of TTF/OTF. WOFF2 is a compressed format
specifically designed for web delivery, resulting in smaller file sizes and faster load times. This is especially
important for Flutter web apps where every byte counts for initial page load performance.

Size comparison (Roboto Regular):

• TTF: 146,004 bytes
• WOFF2: 63,424 bytes (~56% smaller)

Currently, google_fonts only supports TTF and OTF formats, even on web platforms where WOFF2 would be more efficient.
This PR adds support for WOFF2 and WOFF formats on web, allowing developers to bundle more efficient font files for their
web applications.

What

This PR adds support for .woff2 and .woff font file extensions when running on web platforms, while maintaining
backward compatibility with .ttf and .otf files.

Changes:

• Add kIsWeb check to support web-optimized font formats (.woff2, .woff) in addition to .ttf and .otf
• Make findFamilyWithVariantAssetPath testable by adding an optional isWeb parameter (defaults to kIsWeb)
• Add @visibleForTesting annotation to enable comprehensive testing without exposing internal API
• Add 20 tests covering web-specific, non-web-specific, and common behavior

Platform behavior:

• Web: Supports .woff2, .woff, .ttf, .otf
• Non-web: Supports .ttf, .otf (unchanged)

Implementation Notes

The implementation maintains the existing behavior where the order of assets in the manifest determines which file type
is chosen when multiple formats are available for the same font. While this feels a bit odd (ideally, there would be a
preference order), this is how the function already works for TTF/OTF. In practice, this is not an issue when only one
file type per font is bundled, which is the common case.

Getting WOFF2 Files

Developers can convert TTF/OTF fonts to WOFF2 using Google's woff2_compress tool:
https://github.com/google/woff2

Example:

woff2_compress Roboto-Regular.ttf

Testing

All existing tests pass, plus 20 new tests that verify:

• ✅ WOFF2 and WOFF formats work on web
• ✅ WOFF2 and WOFF formats are ignored on non-web platforms
• ✅ TTF and OTF continue to work on all platforms
• ✅ Common behavior (null handling, family/variant matching) works consistently

Breaking Changes

None. This is a backward-compatible addition that only expands the supported file formats on web platforms.
EOF

Pre-Review Checklist

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• I signed the CLA.
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• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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Footnotes

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[gemini-code-assist]

Code Review

This pull request adds support for WOFF and WOFF2 font formats on the web, which is a great performance improvement due to smaller file sizes. The changes are well-implemented, introducing a check for kIsWeb to conditionally allow the new formats. The findFamilyWithVariantAssetPath function has been thoughtfully refactored to be testable, and the new tests are comprehensive, covering web, non-web, and common scenarios. The decision to maintain the existing asset selection logic based on manifest order to ensure backward compatibility is sensible. Overall, this is a high-quality contribution.

[guidezpl]

please pull updates and correct version

[Frank3K]

Done in 1bac768.

[guidezpl]

please clarify that this only concerns loading fonts locally during development, or bundled with the app (or in this case hosted in the site's assets).

When relevant files aren't found in the asset manifest, the package fetches font files from the Google Fonts API, and I'm not sure what the current behavior is (does it detect web requests and return woff2?). In any case, please also create an issue to associate with this PR and any future work regarding HTTP fetching of woff2 files.

[Frank3K]

please clarify that this only concerns loading fonts locally during development, or bundled with the app (or in this case hosted in the site's assets).

Done in 1bac768.

When relevant files aren't found in the asset manifest, the package fetches font files from the Google Fonts API, and I'm not sure what the current behavior is (does it detect web requests and return woff2?).

I've tested this and it downloads a ttf, not a woff2. When checking the source I learned that it's hard-coded to ttf:

packages/packages/google_fonts/lib/src/google_fonts_descriptor.dart

Lines 36 to 51 in 2e46240

	class GoogleFontsFile {
	/// Creates a font file descriptor with expected hash and length validation.
	///
	/// The [expectedFileHash] is used to verify the integrity of the downloaded
	/// file, and [expectedLength] is checked to ensure the file size is correct.
	GoogleFontsFile(this.expectedFileHash, this.expectedLength);
	/// The expected hash of the font file for validation.
	final String expectedFileHash;
	/// The expected length in bytes of the font file.
	final int expectedLength;
	/// The URL from which the font file can be downloaded.
	String get url => 'https://fonts.gstatic.com/s/a/$expectedFileHash.ttf';
	}

In any case, please also create an issue to associate with this PR and any future work regarding HTTP fetching of woff2 files.

I'll do that and add a link to this PR.

[Frank3K]

I'll do that and add a link to this PR.

Done: flutter/flutter#180998.

[guidezpl]

Thanks for the PR! just a couple of notes, since I updated this package recently

[Frank3K]

Thanks for the PR! just a couple of notes, since I updated this package recently

Thanks for reviewing! I've made the requested changes and created the issue for HTTP WOFF2 fetching (flutter/flutter#180998).

Let me know if there's anything else needed to get this merged. Also, feel free to push any changes directly to this branch if that's easier for you.

[guidezpl]

Looks great, thanks!