### Compilation failed:

error: 1: variables of type 'uint' may not be uniform
uniform uint a;
^^^^^^^^^^^^^^
error: 2: 'main' must return: 'vec4', 'float4', or 'half4'
void main() {
^^^^^^^^^^^
error: 3: unknown identifier 'sk_FragColor'
    sk_FragColor.xy = half2(unpackHalf2x16(a));
    ^^^^^^^^^^^^
error: 3: unknown identifier 'unpackHalf2x16'
    sk_FragColor.xy = half2(unpackHalf2x16(a));
                            ^^^^^^^^^^^^^^
error: 4: unknown identifier 'sk_FragColor'
    sk_FragColor.xy = half2(unpackUnorm2x16(a));
    ^^^^^^^^^^^^
error: 5: unknown identifier 'sk_FragColor'
    sk_FragColor.xy = half2(unpackSnorm2x16(a));
    ^^^^^^^^^^^^
error: 5: unknown identifier 'unpackSnorm2x16'
    sk_FragColor.xy = half2(unpackSnorm2x16(a));
                            ^^^^^^^^^^^^^^^
error: 6: unknown identifier 'sk_FragColor'
    sk_FragColor = half4(unpackUnorm4x8(a));
    ^^^^^^^^^^^^
error: 6: unknown identifier 'unpackUnorm4x8'
    sk_FragColor = half4(unpackUnorm4x8(a));
                         ^^^^^^^^^^^^^^
error: 7: unknown identifier 'sk_FragColor'
    sk_FragColor = half4(unpackSnorm4x8(a));
    ^^^^^^^^^^^^
error: 7: unknown identifier 'unpackSnorm4x8'
    sk_FragColor = half4(unpackSnorm4x8(a));
                         ^^^^^^^^^^^^^^
11 errors