Json config file must be overriden by env variable and by command-line argument

[VonC]

Fix #25

I have added a "value copy" in item, in order to be able to restore that copied value after the JSON unmarshalling (

opts/node_parse.go

Lines 145 to 155 in 8ed9e9c

	//second round, unmarshal directly into the struct, overwrites envs and flags
	if c := n.internalOpts.ConfigPath; c != "" {
	b, err := ioutil.ReadFile(c)
	if err == nil {
	v := n.val.Addr().Interface() //*struct
	err = json.Unmarshal(b, v)
	if err != nil {
	return fmt.Errorf("Invalid config file: %s", err)
	}
	}
	}

)

Before, the JSON unmarshalled directly in item.val meant that any parameter/environment variable (previously set in item.val) was overridden.

Now, a "--myparam myvalue" correctly takes precedence over a static default "myparam" value stored in a JSON file.
Same for a MYPARAM environment variable.

All tests are OK.

[jpillora]

Thanks for the PR! Took a quick look, I think the true solution to this is a multistage flags parse.

• parse flags into plain strings
• has config flag? Unmarshal json onto struct
• Unmarshal remaining plain string flags onto struct (existing logic)

This removes the need to store copies on item, and keeps the code simpler (1 pass instead of 2)

This would require a pkg/flag replacement but also enables multi shorts (ps -aux) and flags after args.

I’ll consider this if the above turns out to be too complex. Need to evaluate it.

[VonC]

@jpillora OK. I don't fully get the multistage approach, so I look forward to see your patch.

In the meantime, I'll keep my fork: that item copy solution was simpler for me to implement.

I didn't test multi short options though. Are they currently supported by opts?

[hans-d]

any news on this ?

[jpillora]

Unfortunately no. I'd like to write my own flag parser, so I can peek at the flags without storing the result on the struct.