To reproduce:
1. Open attached project;
2. Select the Shader "TestSurfaceShader";
3. Notice the compilation error in the Inspector.

Expected result: shader is compiled successfully when input struct has a field with the same name as a field in the output.
Actual result: surface shader compile fails if input struct has a field with the same name as a field in the output, the error is thrown: "redefinition of 'surfInputAlpha'".

Reproduced on versions: 2018.1.0a1, 2018.1.0b10, 2018.2.0a3.
Not reproduced on version: 2017.3.1p3.

Fixed in: 2018.3.0a1, 2018.2.0b5, 2018.1.3f1