Better error report when crate name is empty

[orowith2os]

Problem

When adding a crate via cargo add, if one adds a space before the version (such that it's cargo add chumsky @1.0.0-alpha.6 instead of cargo add [email protected] ), Cargo will panic with the following failed assertion:

    Updating crates.io index
thread 'main' panicked at src/cargo/core/dependency.rs:164:9:
assertion failed: !name.is_empty()
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Proposed Solution

When the crate name to add is empty, print a nicer error instead.

Notes

Here's another potentially interesting output to look at:

oro@CrystalBox /r/m/o/V/vala-thingy (master)> cargo add chumsky@ 1.0.0-alpha.6
error: invalid version requirement ``

Caused by:
  unexpected end of input while parsing major version number

[epage]

The panic has since been fixed (either #13164 or #13152). Using nightly, I get

error: package name cannot be empty

It could be interesting to explore what are common cases that we can detect and provide better suggestions. For example, as the person who merged cargo add into cargo (ie I should know better), I recently did something like cargo add winnow 0.5.13 (this started as a friendly jab about chumsky but I think it honestly was with winnow).

[orowith2os]

Maybe it would be feasible to detect a version tag, on its own, and suggest merging it with a crate without a version tag?