error: could not find `Cargo.toml` in `...` or any parent directory

error: could not find Cargo.toml in <dir> or any parent directory means Cargo looked for a package manifest in the current folder and in every folder above it, and found none. Cargo commands such as build, run and test need to run inside a package. cd into the project, pass --manifest-path, or create a package with cargo new or cargo init.

Reproduce it

cargo build
echo "exit status: $?"

error: could not find `Cargo.toml` in `/tmp/work` or any parent directory
exit status: 101

Cargo searches upwards, so running it in a subfolder of a package (such as src/) works; only folders outside every package fail.

Fixes

cargo new -q --vcs none hello
cargo run -q --manifest-path hello/Cargo.toml
cd hello/src && cargo run -q

Hello, world!
Hello, world!