Function check_expected_target_syntax 

pub fn check_expected_target_syntax(
    ctx: &Context<'_>,
    output: &mut TokenStream,
    target: DdOptVal<Target>,
)

Main entrypoint

Checks that output can be parsed as target.

If not, replaces output with something which will generate compiler error(s) which the user will find helpful:

• A compile_error! invocation with the original error span
• include_file!` for a generated temporary file containing the text of the output, so that the compiler will point to the actual error.