#version 300 es
in vec4 vtx_pos;
out vec2 v_coord;
uniform mat3 t_mat;

void main(void)
{
vec3 tmp = t_mat * vec3(vtx_pos.xy, 1.0);
v_coord = tmp.xy;
gl_Position = vec4(vtx_pos.xy, 1.0, 1.0);
}

Running the parser on this code fails on the second like for the token "in"