All-dielectric metasurfaces have shown unprecedented abilities to control light polarization and phase, yet most previous relevant studies have been mainly limited to cross-polarized schemes. This paper presents dielectric metasurfaces that incorporate distinct half-waveplate-like hydrogenated amorphous silicon nanoposts and are shown to manipulate the wavefront of transmitted visible light exhibiting controllable linear polarization angles. An anomalous beam deflector is designed, and high performances including an absolute deflection efficiency of 82%, a polarization conversion efficiency of 96%, and an extinction ratio of 37 dB are first demonstrated in the cross-polarized scheme. Furthermore, the anomalously deflected light could hold a high degree of linear polarization (>0.96), which can be continuously rotated by varying the incident polarization angle. Based on this principle, we fabricate a metalens and experimentally observe the light focusing phenomenon at the location designed for the cross-polarized light. Moreover, the rotation of the linear polarization angle corresponding to the output focused beam spot is successfully validated by tailoring the incident polarization angle. The developed metalens can therefore be treated as equivalent to the combination of a half-waveplate and focusing lens. The proposed ultra-thin dielectric metasurfaces, which do not require the alignment of multiple elements, could be used to facilitate the development of ultra-compact photonics systems.