Support splitting spkg install into `spkg-build` and `spkg-install` (for SAGE_SUDO)

[mkoeppe]

Here's a new attempt toward #21537 that is perhaps more elegant.

Let's change build/bin/sage-spkg as follows:

• If spkg-build exists, call that, followed by $SAGE_SUDO spkg-install.
• Otherwise, just call spkg-install (withOUT $SAGE_SUDO). (Such packages cannot be installed into a SAGE_ROOT that is only root-writable, unless they use $SAGE_SUDO themselves.)

The patch changes two example packages, to demonstrate this: 4ti2 and lcalc.

Before the patch:

$ rm -Rf local/share/4ti2
$ mkdir local/share/4ti2
$ sudo chown root local/share/4ti2
$ ./sage -f 4ti2
[...]
[4ti2-1.6.7] mkdir: /Users/mkoeppe/s/sage/sage-rebasing/local/share/4ti2/doc: Permission denied
[4ti2-1.6.7] make[4]: *** [install-docDATA] Error 1
[...]
$ sudo chown root local/bin/ local/bin/lcalc
$ ./sage -f lcalc 
[...]
[lcalc-1.23.p14] cp -f lcalc /Users/mkoeppe/s/sage/sage-rebasing/local//bin/.
[lcalc-1.23.p14] cp: /Users/mkoeppe/s/sage/sage-rebasing/local//bin/./lcalc: Permission denied
[...] 

Then, after the patch:

$ export SAGE_SUDO="sudo -E"
$ ./sage -f 4ti2 lcalc  # succeeds

Other packages will be handled in follow-up tickets.

See also:

• #21844: Update developer manual regarding spkg-build, spkg-install, SAGE_SUDO
• Task ticket: #21537

[mkoeppe]

New commits:

​b5621b4	If spkg-build exists, run it, followed by $SAGE_SUDO spkg-install
​b595edd	4ti2: Call make install within $SUDO
​48053d0	lcalc: Split out spkg-build from spkg-install

[embray]

So, if I understand correctly, the point of calling spkg-install without $SAGE_SUDO if no spkg-build exists, is that for backwards-compatibility such packages should be assumed to be "special" in some way, and have to handle $SAGE_SUDO on their own. Is that correct?

[embray]

What is this about?

+    if [ ! -x spkg-build ]; then
+	echo >&2 "WARNING: spkg-build is not executable, making it executable"
+	chmod +x spkg-build
+    fi

Why not just require it to be executable in the first place?

[embray]

LGTM otherwise. This looks like what I had in mind in #21537.

[mkoeppe]

Replying to embray:

So, if I understand correctly, the point of calling spkg-install without $SAGE_SUDO if no spkg-build exists, is that for backwards-compatibility such packages should be assumed to be "special" in some way, and have to handle $SAGE_SUDO on their own. Is that correct?

That's right.

[mkoeppe]

Replying to embray:

What is this about?

+    if [ ! -x spkg-build ]; then
+	echo >&2 "WARNING: spkg-build is not executable, making it executable"
+	chmod +x spkg-build
+    fi

Why not just require it to be executable in the first place?

It's imitating existing code that does the same for spkg-install. I don't know why it does that. Hysterical raisins?

[embray]

I see that now. Might as well keep it for now then :(

[mkoeppe]

Thanks!

[embray]

Semi-related, see #22510.