in fuse-ui-fabric/themes/seti/fileIcons.ts [16:24]
export function fileExtensionToIcon(path: string, theme: 'dark' | 'light'): IconDefinition {
const ext = (pathExt(path) || '').toLowerCase();
const cur = theme === 'dark' ? SetiTheme : SetiTheme.light;
const _default = theme === 'dark' ? '_default' : '_default_light';
const fileExtensionIcons = fileExtensionToIconIds(cur);
const iconId = cur.languageIds[ext] || cur.fileExtensions[ext] || fileExtensionIcons[ext] || _default;
return SetiTheme.iconDefinitions[iconId];
}