Icon( Feather.gitlab, size: 16, color: Colors.grey)

flutter_icons/fonts/MaterialCommunityIcons.ttf
flutter_icons/fonts/FontAwesome.ttf
flutter_icons/fonts/FontAwesome5_Solid.ttf
flutter_icons/fonts/FontAwesome5_Brands.ttf
flutter_icons/fonts/Ionicons.ttf
flutter_icons/fonts/MaterialIcons.ttf
flutter_icons/fonts/weathericons.ttf
flutter_icons/fonts/Entypo.ttf
flutter_icons/fonts/AntDesign.ttf
flutter_icons/fonts/SimpleLineIcons.ttf
flutter_icons/fonts/Foundation.ttf
flutter_icons/fonts/Feather.ttf
flutter_icons/fonts/Zocial.ttf
flutter_icons/fonts/FontAwesome5_Regular.ttf
flutter_icons/fonts/Octicons.ttf
flutter_icons/fonts/EvilIcons.ttf

version:1.1.0
cannot find Ionicons.school_outline.
some other outlined icons are also missing, ios-school-outline、md-school-outline etc.

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.0.2, on Linux, locale en_GB.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[✗] Chrome - develop for the web (Cannot find Chrome executable at google-chrome)
   ! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.
[!] Android Studio (not installed)
[✓] VS Code (version 1.53.2)
[✓] Connected device (1 available)

! Doctor found issues in 2 categories.

Can't Find Some icons, especially Ionicons. Some Icons I noticed to be missing are
* Ionicons.ellipsis-horizontal-circle
* Ionicons.ellipsis-horizontal-circle-outline
* Ionicons.paper-plane-outline
* Ionicons.ios-paper-plane-outline
* MaterialIcons.all-inbox

///searches all libs and returns the first finding
IconData data = IconCache('altimeter')
///searches only Material Icons 
IconData data = IconCache('altimeter', IconLib.mdi)
///searches only Material Icons 
IconData data = IconCache('mdi.altimeter')
 

import 'package:flutter/material.dart';
import 'package:flutter_icons/flutter_icons.dart';
import 'package:logging/logging.dart';

final _log = new Logger('ui.icon_cache.dart');

enum IconLib {
  ///All Icons
  all,

  ///Ant Design Icons
  ant,

  ///Entypo Icons
  ent,

  ///Evil Icons
  evi,

  ///Feather Icons
  fea,

  ///Font Awesome Icons
  faw,

  ///Foundation Icons
  fou,

  ///Ionicons Icons
  ion,

  ///Material Community Icons
  mco,

  ///Material Icons
  mdi,

  ///Octicons Icons
  oct,

  ///Simple Line Icons
  sli,

  ///Zocial Icons
  zoc,

  ///Weather Icons
  wea
}

class IconCache {
  static final IconCache _singleton = new IconCache._internal();

  factory IconCache() {
    return _singleton;
  }

  IconCache._internal();

  IconData operator [](String name) {
    return _singleton.icon(name);
  }

  IconLib _fromString(String iconLibEnumPrefix) => IconLib.values.firstWhere(
      (e) => e.toString().split('.').last == iconLibEnumPrefix,
      orElse: null);

  // The format is like 'mdi.car' which loads the car
  // icon from the Material Design Icons
  //if the name contains the prefix separated with a dot and the prefix
  // is the default than the prefix is taken from the name. e.g. mdi.car
  IconData icon(String name, {IconLib prefix = IconLib.all}) {
    String iconName;
    IconLib namePrefix;

    //if the name contains the prefix separated with a dot and the prefix
    // is the default than the prefix is taken from the name. e.g. mdi.car
    if (name.contains('.') && prefix == IconLib.all) {
      namePrefix = _fromString(name.split('.').first);
      iconName = name.split('.').last;
      //defaults to all lib
      if (namePrefix == null || iconName == null) throw ArgumentError();
      return _iconInternal(namePrefix, iconName);
    } else {
      return _iconInternal(prefix, name);
    }
  }

  IconData _iconInternal(IconLib prefix, String name) {
    IconData data;
    if (prefix != IconLib.all) {
      data = _extractIconFromSpecificLib(prefix, name);
      if (data == null || data.codePoint == null) {
        _log.finest('Could not load Icon $name ');
        return MaterialIcons.getIconData('error');
      } else {
        return data;
      }
    }
    return _searchIconsInAllLibs(data, name, prefix);
  }

  _searchIconsInAllLibs(IconData data, String name, IconLib prefix) {
    try {
      //return MdiIcons()[name];
      data = _searchMaterialIcons(name);

      if (data == null) {
        data = _searchMaterialCommunityIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchMaterialCommunityIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchAntDesignIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchEntypoIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchEvilIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchFeatherIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchFontAwesomeIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchFoundationIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchIonIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchOcticonsIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchSimpleLineIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchZocialIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        data = _searchWeatherIcons(name);
      } else {
        return data;
      }
      if (data == null) {
        _log.finest('Could not load Icon $name from lib: $prefix');
        return MaterialIcons.getIconData('error');
      } else {
        _log.finest('Could not load Icon $name, from lib: $prefix}');
        return MaterialIcons.getIconData('error');
      }
    } catch (e) {
      _log.finest(
          'Could not load Icon $name, from lib: $prefix, Error: ${e.toString()}');
      return MaterialIcons.getIconData('error');
    }
  }

  IconData _extractIconFromSpecificLib(IconLib prefix, String name) {
    switch (prefix) {
      case IconLib.ant:
        return _searchAntDesignIcons(name);
        break;
      case IconLib.all:
        _log.finest('Could not load Icon $name');
        return MaterialIcons.getIconData('error');

        break;
      case IconLib.ent:
        return _searchEntypoIcons(name);
        break;
      case IconLib.evi:
        return _searchEvilIcons(name);
        break;
      case IconLib.fea:
        return _searchFeatherIcons(name);
        break;
      case IconLib.faw:
        return _searchFontAwesomeIcons(name);
        break;
      case IconLib.fou:
        return _searchFoundationIcons(name);
        break;
      case IconLib.ion:
        return _searchIonIcons(name);
        break;
      case IconLib.mco:
        return _searchMaterialCommunityIcons(name);
        break;
      case IconLib.mdi:
        return _searchMaterialIcons(name);
        break;
      case IconLib.oct:
        return _searchOcticonsIcons(name);
        break;
      case IconLib.sli:
        return _searchSimpleLineIcons(name);
        break;
      case IconLib.zoc:
        return _searchZocialIcons(name);
        break;
      case IconLib.wea:
        return _searchWeatherIcons(name);
        break;
      default:
        {
          _log.finest('Could not load Icon $name');
          return MaterialIcons.getIconData('error');
        }
    }
  }

  IconData _searchWeatherIcons(String name) {
    IconData data = WeatherIcons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchZocialIcons(String name) {
    IconData data = Zocial.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchSimpleLineIcons(String name) {
    IconData data = SimpleLineIcons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchOcticonsIcons(String name) {
    IconData data = Octicons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchIonIcons(String name) {
    IconData data = Ionicons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchFoundationIcons(String name) {
    IconData data = Foundation.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchFontAwesomeIcons(String name) {
    IconData data = FontAwesome.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchFeatherIcons(String name) {
    IconData data = Feather.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchEvilIcons(String name) {
    IconData data = EvilIcons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchEntypoIcons(String name) {
    IconData data = Entypo.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchAntDesignIcons(String name) {
    IconData data = AntDesign.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchMaterialIcons(String name) {
    IconData data = MaterialIcons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }

  IconData _searchMaterialCommunityIcons(String name) {
    IconData data = MaterialCommunityIcons.getIconData(name);
    if (data == null || data.codePoint == null) {
      return null;
    } else {
      return data;
    }
  }
}