[bug] conan download with optional user/channel does not work

Summary

Downloading Conan packages without user/channel (i.e. zlib/1.2.11 instead of zlib/1.2.11@conan/stable) does not work. Such packages are built on CCI and it will be good to be able to download them for debugging.

Environment Details (include every applicable attribute)

• Operating System+version: macOS 10.14.6
• Conan version: conan 1.19.3
• Python version: 3.7.4

Steps to reproduce (Include if Applicable)

1. Run conan download 'zlib/1.2.11:76f87539fc90ff313e0b3182641a9bb558a717d2' to download a package without explicit user/channel
2. Expected: package is downloaded
3. Actual: got the error ERROR: Provide a valid full reference without wildcards

Thoughts

The syntax for a short reference was given from Conan docs and from conan-center-index docs.

Anyway I tried following commands with the same error:

• conan download 'zlib/1.2.11@_/_#76f87539fc90ff313e0b3182641a9bb558a717d2'
• conan download 'zlib/1.2.11@/:76f87539fc90ff313e0b3182641a9bb558a717d2'

And this command with a different error “ERROR: Recipe not found: ‘zlib/1.2.11’”:

• conan download 'zlib/1.2.11@#76f87539fc90ff313e0b3182641a9bb558a717d2'

It is curious that if Conan is run with --package argument, it suggests to use the exactly failed command:

WARN: Usage of `--package` argument is deprecated. Use a full reference instead: `conan download [...] zlib/1.2.11:76f87539fc90ff313e0b3182641a9bb558a717d2`
ERROR: Provide a valid full reference without wildcards.

The same problem with upload command was fixed recently in https://github.com/conan-io/conan/issues/5822.

I suppose the check_valid_ref method should relax the requirements for short references…

[memsharded]

Submitted a possible fix, maybe for 1.20

[memsharded]

Reproduced.

Yes, the workaround is to use the deprecated way:

conan download zlib/1.2.11@ -p 76f87539fc90ff313e0b3182641a9bb558a717d2

I am going to check possible fixes