Don't print response only if an empty dict/list/str

[jamesls]

The integer 0 should be printed as a result. This can happen
from a JMESPath expression, e.g length(something).

For example, currently:

$ aws ec2 describe-security-groups --query 'length(`[0,1]`)'
2
$ aws ec2 describe-security-groups --query 'length(`[0]`)'
1
$ aws ec2 describe-security-groups --query 'length(`[]`)'
<prints nothing>
$

Now you'll get:

$ aws ec2 describe-security-groups --query 'length(`[]`)'
0

cc @kyleknap @mtdowling @rayluo

[mtdowling]

Would it be possible to just do if response or response == 0:, or are we worried about other types that are falsey but should show up in the output?

[jamesls]

After looking at this again, I think we can just change this to explicitly check for '{}'.

The original intent of this (years ago) was that any AWS operation that did not have an associated output shape should not generate any CLI output. In older version of the CLI, some operations could generate either an empty dict or empty string.

However, with the switchover to the normalized model parser, anytime an operation does not have an output shape, botocore gives back a dictionary that only has the RequestMetadata key populated. Once the formatter's here strip that key out, we're left with an empty dictionary.

So it should be safe to update this to only check for an empty dictionary. This meets the constraint that anything without an output shape should not generate CLI output.

Does that work for you?

[mtdowling]

That makes sense. Works for me.

[rayluo]

Makes sense. By the way, will we also document this philosophy somewhere? Such as in the code as a comment paragraph?

[mtdowling]

This is no longer necessary

[jamesls]

@mtdowling Feedback incorporated.

[mtdowling]

🚢