\[ \left (1-f'(x)\right ) \cos (y(x))-f'(x)+f(x) \sin (y(x))+y'(x)-1=0 \] ✗ Mathematica : cpu = 24.0666 (sec), leaf count = 0 , could not solve
DSolve[-1 + f[x]*Sin[y[x]] + Cos[y[x]]*(1 - Derivative[1][f][x]) - Derivative[1][f][x] + Derivative[1][y][x] == 0, y[x], x]
✓ Maple : cpu = 1.331 (sec), leaf count = 41
\[ \left \{ y \left ( x \right ) =2\,\arctan \left ( {\frac {-{{\rm e}^{\int \!f \left ( x \right ) \,{\rm d}x}}+\int \!{{\rm e}^{\int \!f \left ( x \right ) \,{\rm d}x}}\,{\rm d}xf \left ( x \right ) +f \left ( x \right ) {\it \_C1}}{{\it \_C1}+\int \!{{\rm e}^{\int \!f \left ( x \right ) \,{\rm d}x}}\,{\rm d}x}} \right ) \right \} \]