Handle an icon file that exists but isn't valid SVG

[pcbeingused333]

Three code paths read an icon file and call at_css("svg") without checking the result. When the file exists but isn't valid SVG — empty, truncated, or an HTML error page from a bad sync — at_css("svg") returns nil and the caller crashes with NoMethodError.

Sprite#symbol_from

svg_element = Nokogiri::XML(File.read(reference.file_path)).at_css("svg")
view_box = svg_element["viewBox"] || "0 0 24 24"
# => NoMethodError: undefined method `[]' for nil:NilClass

A missing icon is already handled (rescue Icons::IconNotFound → warn → skip). An unparseable one now is too — warn and skip.

Icon#svg

Nokogiri::HTML::DocumentFragment.parse(File.read(file_path)).at_css("svg")
  .tap { |svg| attach_attributes(to: svg) }   # attach_attributes(to: nil) => NoMethodError

Now raises Icons::IconNotFound (with a message noting the file isn't valid SVG), next to the existing Errno::ENOENT rescue.

SpriteIcon#sprite_svg parses a fixed template, so it's fine.

Tests

• sprite_test.rb — a temp library with one junk .svg and one real one: the sprite keeps the real symbol, omits the junk one, warns.
• icon_test.rb — an empty .svg raises IconNotFound.

Both fail on main (NoMethodError). bundle exec rake is green (91 runs, 0 failures).

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