the BOOK Ch. 1.1 Installation, "Working Offline": `cargo add` does not download crates, so `--offline` fails

Section

Introduction "Working Offline with This Book"

Problem

The section states that running

cargo new get-dependencies
cd get-dependencies
cargo add [email protected] [email protected]

"will cache the downloads for these packages so you will not need to download them later."

On current Cargo, cargo add only updates the registry index and writes Cargo.lock. It does not download the .crate files, so a later --offline build fails.

Steps to reproduce

# starting from an empty CARGO_HOME
cargo new get-dependencies
cd get-dependencies
cargo add [email protected] [email protected]

ls $CARGO_HOME/registry/
# -> only `index`; no `cache/`, no `src/`

cargo build --offline

Expected

The build succeeds using the cached packages.

Actual

error: failed to download `ahash v0.8.12`

Caused by:
  attempting to make an HTTP request, but --offline was specified

Running plain cargo build right after shows the packages had not been fetched yet:

Downloaded 156 crates (15.0MiB) in 11.55s

Only after that does --offline work.

Suggested fix

Add a fourth step (cargo build or cargo fetch) so the crate sources are actually downloaded before going offline.

Environment

• cargo 1.98.0 (797e8a9bc 2026-08-05)
• rustc 1.98.0 (88d9e12ae 2026-08-18)
• Windows 11