feat: add On-Demand Resources (ODR) tag support

[kramnadroj]

Problem

There was no programmatic way to assign On-Demand Resource tags to files in an Xcode project using mod-pbxproj. Users were forced to either mutate .pbxproj files directly via shell scripts, or use PBXGenericObject parsing as an undocumented workaround. This was raised in issue #298.

ODR requires two distinct mutations to the project file:

1. Setting ASSET_TAGS in the settings of a PBXBuildFile entry to associate a file with specific tags
2. Registering those same tags in KnownAssetTags under attributes in the PBXProject section

Neither was supported.

Solution

PBXBuildFile — new methods following the same pattern as ATTRIBUTES:

• get_asset_tags() — returns the current ASSET_TAGS list for a build file
• add_asset_tags(tags) — adds one or more tags (string or list)
• remove_asset_tags(tags) — removes tags and cleans up empty settings
• create() now accepts asset_tags=None

PBXProject — new methods for managing the project-level tag registry:

• add_known_asset_tags(tags) — adds tags to attributes.KnownAssetTags (no duplicates)
• remove_known_asset_tags(tags) — removes tags and cleans up empty attributes

FileOptions — new asset_tags=None parameter for the high-level API. When add_file() is called with asset tags, the library automatically updates both the build file's ASSET_TAGS and the project's KnownAssetTags in one step.

Usage

project.add_file("resources/level1.dataset",
                 file_options=FileOptions(asset_tags=['level1', 'bonus-content']))

This produces the correct structure in the .pbxproj:

// PBXBuildFile section
AB1234 /* level1.dataset in Resources */ = {
    isa = PBXBuildFile;
    fileRef = AB5678 /* level1.dataset */;
    settings = {ASSET_TAGS = (level1, "bonus-content", ); };
};

// PBXProject section
attributes = {
    KnownAssetTags = (level1, "bonus-content", );
};

Tests

• TestPBXBuildFile — 10 new tests covering get_asset_tags, add_asset_tags, remove_asset_tags, creation with tags, and cleanup of empty settings
• TestPBXProject — 7 new tests covering add_known_asset_tags, remove_known_asset_tags, duplicate prevention, and cleanup of empty attributes
• TestProjectFiles — 3 new integration tests verifying that FileOptions(asset_tags=...) correctly sets ASSET_TAGS on build files and registers tags in KnownAssetTags, and that files added without tags are unaffected

Closes #298

[kramnadroj]

Committer here. Not a dev. A QA that found your tool super useful for this use case. Tasked claude with adding it for others. Unsure if you have any AI rules in the repo