Add option to look for sources in alternate root paths

[epontan]

Add a new optional flag -r|--root ROOTPATHS, where ROOTPATHS is a colon separated list of paths, that will look for external sources in alternate roots.

This is particular useful when the run-time environment does not fully match the development environment. The #shellcheck source=file directive is useful, but has its limitations in certain scenarios. Also, in many cases the directive could be removed from scripts when the root flag is used.

Script example.bash:

#!/bin/bash
source /etc/foo/config

Example usage where etc/foo/config exists in skel/foo:

shellcheck -x -r skel/foo:skel/core example.bash

[austin987]

The help and your comment say semi colon, but the code is using a colon for delimiter.

[epontan]

The help and your comment say semi colon, but the code is using a colon for delimiter.

Thanks for noticing that! I don't know why I wrote semi-colon when I really was meaning colon :)
Anyway, it is fixed now.

[knirch]

This would resolve #510 #882 and potentially be useful for #539 #769

[koalaman]

Very nice, thanks!

I expanded this a bit into "source paths" (-P):

• For absolute paths, it behaves the same
• It also looks up relative paths based on these dirs (so -P "$PATH" will find . foo in any path entry)
• It accepts a special name SCRIPTDIR to allow you to search relative to the current script's directory
• It uses platform canonical search path parsing, so that c:\foo;d:\bar works as expected on Windows
• It allows you to specify multiple -P flags that accumulate, e.g. with export SHELLCHECK_OPTS='-P foo'; shellcheck -P bar ..
• It checks whether the files are allowed by the sandboxing to avoid errors exposing which files exist (only really matters for shellcheck.net)

[blueyed]

• It accepts a special name SCRIPTDIR to allow you to search relative to the current script's directory

I suggest using something more explicit here - since "SCRIPTDIR" might be a valid path.
It might make sense to have "./" be handled as "local to script file" instead.

I.e. instead of -P SCRIPTDIR/include you would use ./include, but include would still be relative to cwd.
Alternatively something like ::SCRIPTDIR:: could be used (i.e. something that contains characters not valid for filenames - would be ;;SCRIPTDIR;; on Windows then.
I can see that this might be ugly, but wanted to mention this since it is easy to adjust before having it release now still.