nirvana api print fatal error invalid character '\x1b' looking for beginning of value

[narrowizard]

Is this a BUG REPORT or FEATURE REQUEST?:

Uncomment only one, leave it on its own line:

/kind bug

/kind feature

What happened: nirvana print a fatal error when running nirvana api.

$ nirvana api --output="./api"
INFO  0611-14:39:33.220+08 api.go:87 | No packages are specified, defaults to pkg/apis
FATAL 0611-14:40:03.467+08 api.go:61 | invalid character '\x1b' looking for beginning of value

What you expected to happen: the error is unexpected. How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:
after some searching, i find the error is reported by json.Unmarshal.
nirvana api generated a nirvana-generated*** file and run it to get a json formated api-definition string, then output the string to standard output(cmd). and read the string from standard output(cmd), decode it to &api.Definitions{}.
the error occur when my project output something to cmd.

https://github.com/caicloud/nirvana/blob/bf6c5fc90fa4e45dbed1e0675d1ef9687fc73a8c/utils/builder/builder.go#L172-L183

[lsytj0413]

/cc @iawia002

[iawia002]

So you are logging something in the init function of descriptors or modifiers file?

[narrowizard]

not exactly, init function in other package which is imported by descriptors. @iawia002

[iawia002]

Got it, I'll fix this when I'm free (may take days)