output.txt

$ cargo new test-project
$ cd test-project 
$ mkdir subdir
$ touch subdir/Cargo.toml
$ cargo build
failed to parse manifest at `/home/daboross/test-project/subdir/Cargo.toml`

Caused by:
  No `package` or `project` section found.
$ rm -r subdir
$ mkdir -p subdir/Cargo.toml
$ cargo build
An unknown error occurred

To learn more, run the command again with --verbose.
$ cargo build --verbose
Is a directory (os error 21)
$