Misleading message when using invalid (?) include field

[Thomasdezeeuw]

Problem

When using an invalid (?) include field in Cargo.toml cargo package will fail with "failed to verify package tarball".

Steps

1. Create a new repo, cargo init tmp && cd tmp
2. Add include = [ "./src/main.rs" ] to Cargo.toml.
3. Add and commit everything: git add . && git commit -m "init".
4. Package (or publish) the create: cargo package

   Packaging tmp v0.1.0 (/private/var/folders/lq/rzq0zxld0bb5mcy4jl1txrf00000gn/T/tmp.1svg10Al/tmp)
   Verifying tmp v0.1.0 (/private/var/folders/lq/rzq0zxld0bb5mcy4jl1txrf00000gn/T/tmp.1svg10Al/tmp)
error: failed to verify package tarball

Caused by:
  failed to read `/private/var/folders/lq/rzq0zxld0bb5mcy4jl1txrf00000gn/T/tmp.1svg10Al/tmp/target/package/tmp-0.1.0/Cargo.toml`

Caused by:
  No such file or directory (os error 2)

Possible Solution(s)

In the actual code I dropped ./ from the include field and it worked, it doesn't seem to be the case with a new crate.

Notes

Output of cargo version: cargo 1.35.0-nightly (0e35bd8 2019-03-13) (currently can't get a newer version due to clippy being broken on nightly).

[ehuss]

I think this is the same as #4660.

@alexcrichton Do you know if there's a reason why include does not automatically add Cargo.toml? I can sympathize with implicit magic making it hard to understand how something works, but in this case making everyone add it seems a little unnecessary.

[alexcrichton]

@ehuss seems like a reasonable bug in Cargo, agreed we should just include it by default