Pearl-bordered Fritillary Boloria euphrosyne
I've had great difficulty getting anywhere near this butterfly in the UK but here in the mountains of France this one conveniently posed for ten minutes in different positions.
The larval food plant is Viola riviniana (Common Dog-violet) but it has been observed that other violets are also used. My bet is that the frequency of observation of larval food plant is related to the scarcity of that plant and if Viola canina (Heath Dog-violet) was the commonest species then that would be used the most. As a botanist telling the difference between Common and Heath Dog-violets is not at all easy but perhaps they smell different to a butterfly.
According to UKbutterflies adults will feed on dark blue Ajuga reptans (Bugle), yellow Lotus corniculatus (Bird's-foot Trefoil), blue Hyacinthoides non-scripta (Bluebell), yellow Taraxacum sp (Dandelions) and Hieracium sp (Hawkweeds), pink Silene flos-cuculi (Ragged Robin), blue Prunella vulgaris (Self-heal), purple and blue Cirsium and Carduus species (Thistles) not to mention Potentilla erecta (Tormentil).
So anything really.