When pkgname is an array, makepkg calls the function package_"$name" for each name in the array.
When pkgname is an scalar, makepkg calls the function package.

bash does not differentiate arrays from scalars.

Hence if I got a PKGBUILD file that has an array of pkgname's and I only want one package so I remove all but one element from the array, makepkg will attempt to call the function package which will not exist. A fix/workaround to this issue would be to add this line somewhere before the PKGBUILD file is sourced:

package () { [ -n "${pkgname[0]}" ] && package_"${pkgname[0]}"; }
or
package () { [ -n "$pkgname" ] && package_"$pkgname"; }

This way, if the PKGBUILD defines a function package, it overwrites the above definition and the above has no affect. If the PKGBUILD does not define a function package(), then you don't expect it to be called. If it is called and package_"$pkgname" exists, that is probably what you want to call.

This would fix the issue mentioned in the paragraph beginning "Hence".