refactor: simplify manifest_path option checks
refactor: simplify manifest_path option checks

graydon/rust,graydon/rust,rust-lang/rustfmt,rust-lang/rustfmt,graydon/rust,graydon/rust,graydon/rust,SingingTree/rustfmt,graydon/rust,SingingTree/rustfmt,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust