go: flag: it is not reasonable not to support "-flag x" for boolean flags.

The flag standard package says

 Command line flag syntax:

-flag
-flag=x
-flag x  // non-boolean flags only

One or two minus signs may be used; they are equivalent. 
The last form is not permitted for boolean flags because the meaning of the command

cmd -x *

will change if there is a file called 0, false, etc. 
You must use the -flag=false form to turn off a boolean flag.

It is not convinced that this exception is only made for boolean flags. Why isn’t it also made for number and string flags? It is the same situation for number and string flags.

IMO, it is totally unnecessary to make this exception. Shell expansions are common and normal. Go packages shouldn’t do anything to avoid some special shell expansions.

[update] What the package documentation should do is to just let users pay attention to shell expansions.