Crate with a keyword containing space fails during publish, but not during dry run.

[patriksvensson]

Problem
I tried to specify a keyword within Cargo.toml that contained a space. Running cargo publish --dry-run showed that the package was valid, but submitting it to crates.io failed with an API error.

keywords = ["foo", "foo bar"]

I appreciate that you might not want to tie implementation details in crates.io to cargo publish in case this theoretically could be supported in other package repository implementations, but I thought I would report this anyway. If you decide that this is a bug, I'm more than happy to submit a pull request for it.

Steps

1. Create a new crate
2. Add a keyword with a space in it, such as keywords = ["foo", "foo bar"]
3. Run cargo publish --dry-run: Does not display any errors.
4. Publish crate using cargo publish: Returns an API error.

Possible Solution(s)
Display an error after a dry run if there is a space in a keyword.

Notes

The output from cargo publish:

> cargo publish
   Updating crates.io index
   Packaging foo v0.1.0 (D:\Source\github\patriksvensson\foo)
   Verifying foo v0.1.0 (D:\Source\github\patriksvensson\foo)
   Finished dev [unoptimized + debuginfo] target(s) in 1.06s
   Uploading foo v0.1.0 (D:\Source\github\patriksvensson\foo)
error: api errors (status 200 OK): invalid upload request: invalid value: string "foo bar", expected a valid keyword specifier at line 1 column 555

[ehuss]

Thanks for the report. This appears to be a duplicate of #4300, so closing in favor of that.