Tcl Library Source Code

As mentioned on the Core list, the default path is also wrong on macOS.
However, on macOS the script uses ::tcl_pkgPath, but that has the same
value as auto_path on macOS and does not exist on Windows.

The script would work correctly on macOS if it used the first path on the
auto_path list, instead of the last.  On Windows the correct path is the
last one on the auto_path list, but the script does not use auto_path at
all.

The actual code is:

        if {[string match [info nameofexecutable]* [info library]]} {
            # Starkit
            set libdir [file join [file dirname [file dirname [info nameofexecutable]]] lib]
        } else {
            # Unwrapped.
            if {[catch {set libdir [lindex $::tcl_pkgPath end]}]} {
                set libdir [file dirname [info library]]
            }
        }

The catch statement succeeds on macOS, giving the wrong answer, and fails
on Windows causing the result of [info library] to be used.  On Windows
[info library] returns //zipfs:/lib/tcl/tcl_library.

The default values of auto_path on linux, windows and macOS (with a
framewor build) are as follows (where $PREFIX is the prefix on unix
and the value of INSTALLDIR on Windows)

linux: //zipfs:/lib/tcl/tcl_library //zipfs:/lib/tcl $PREFIX/lib

Windows: //zipfs:/lib/tcl/tcl_library //zipfs:/lib/tcl $PREFIX/lib

macOS: /Library/Frameworks/Tcl.framework/Versions/9.1/Resources/Scripts
 /Library/Frameworks/Tcl.framework/Versions/9.1/Resources /usr/local/lib
 $HOME/Library/Tcl /Library/Tcl $HOME/Library/Frameworks
 /Library/Frameworks /Library/Frameworks/Tk.framework/Versions

For macOS many of those paths would never contain a package, and are
unlikely to even exist.  But that is more of a Tcl issue than a
Tcllib issue.

I think that one solution (given the current state of things) would
be to use the first item in the auto_path which does not begin with
"//zipfs:" as the default installation path.  That is guaranteed to
be a place where Tcl will look, and it is likely to also be a writable
directory, at least in the case where one is running the installer as
root on a unix system.