SC2034 can be incorrectly masked by source

[smoser]

$ cat foo
#!/bin/bash
dosomething() {
   local f="hello"
   echo "hello"
}

source bar

$ cat bar
#!/bin/bash
hello() {
    local f="abc"
    echo "hi $f"
}

Now run shellcheck on foo', it complains correctly that variable f' is not used.

$ shellcheck foo
In foo line 3:
   local f="hello"
         ^-- SC2034 (warning): f appears unused. Verify use (or export if used externally).


In foo line 7:
source bar
       ^-^ SC1091 (info): Not following: bar was not specified as input (see shellcheck -x).

For more information:
  https://www.shellcheck.net/wiki/SC2034 -- f appears unused. Verify use (or ...
  https://www.shellcheck.net/wiki/SC1091 -- Not following: bar was not specif...

shell returned 1

But if you add bar to the command line, then it will not fail.

$ shellcheck foo bar && echo GOOD
GOOD

In the above, variable f is unused, but shellcheck assumes that because file bar used a variable named f, that it must have been intentional, even though bar declared f.