Make $SAGE_LOCAL/bin/sage work again from any directory, in an environment without SAGE_* variables, following symlinks

[mkoeppe]

The feature introduced in #25486 (Discover SAGE_SCRIPTS_DIR to make $SAGE_LOCAL/bin/sage work from any directory, in an environment without SAGE_* variables) was killed by #30128 (enforce sourcing of sage-env-config before src/bin/sage-env).

We repair it, making sure that it works even if $0 is a symlink.

CC: @orlitzky @dimpase @jhpalmieri

Component: scripts

Keywords: sd111

Author: Michael Orlitzky

Branch/Commit: a63d256

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30888

[mkoeppe]

Dependencies: #29850

[mkoeppe]

Branch: u/mkoeppe/remove_unused_env_variable_sage_scripts_dir

[mkoeppe]

Commit: a318e9e

[mkoeppe]

Author: Matthias Koeppe

[mkoeppe]

Last 10 new commits:

c8e6910	Merge tag '9.3.beta1' into t/29951/src_bin_sage_env__make_sage_env_config_and_sage_local_optional
9ab593c	Install sage-env-config with sage_conf
a361580	build/pkgs/sage_conf/spkg-src: New
d02b597	build/pkgs/sagelib/src/setup.py: Do not install sage-env-config
1b4bc99	src/bin/sage: Only source sage-env-config if it exists
a1a6df5	src/bin/sage: Use python3 etc. from PATH instead of using SAGE_LOCAL
d30b410	build/pkgs/sage_conf/spkg-install: Build wheel manually
19f7eae	src/bin/sage-env: Make sage-env-config optional
ecde605	Merge branch 't/29850/install_sage_env_config_with_sage_conf' into t/30888/remove_unused_env_variable_sage_scripts_dir
a318e9e	src/bin/sage-env: Do not set SAGE_SCRIPTS_DIR

[mkoeppe]

comment:5

Turns out that SAGE_SCRIPTS_DIR is unused because the feature introduced in #25486 (Discover SAGE_SCRIPTS_DIR to make $SAGE_LOCAL/bin/sage work from any directory, in an environment without SAGE_* variables) was killed by #30128, as part of the quest to remove bashisms.

[mkoeppe]

comment:6

Unfortunately I did not notice it when I reviewed #30128.

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,2 +1,4 @@
-After #30128 (enforce sourcing of `sage-env-config` before `src/bin/sage-env`) and #29850, `SAGE_SCRIPTS_DIR`, set in `sage-env`, is not used for anything. We remove it.
+The feature introduced in #25486 (Discover `SAGE_SCRIPTS_DIR` to make `$SAGE_LOCAL/bin/sage` work from any directory, in an environment without SAGE_* variables) was killed by #30128 (enforce sourcing of `sage-env-config` before `src/bin/sage-env`).
 
+We repair it, making sure that it works even if $0 is a symlink.
+

[mkoeppe]

Changed commit from a318e9e to none

[mkoeppe]

Changed dependencies from #29850 to #29951

[mkoeppe]

Changed branch from u/mkoeppe/remove_unused_env_variable_sage_scripts_dir to none

[mkoeppe]

comment:7

Any takers for this one?

[mkoeppe]

Changed author from Matthias Koeppe to none

[orlitzky]

comment:8

What kind of solution is acceptable here? I've lost track of the big picture, but it looks like all of the important ./configure-time settings are in sage-env-config, but local/bin/sage can't find sage-env-config because the path to it (determined during ./configure) is contained in sage-env-config.

Are we allowed to stick autoconf values directly into local/bin/sage (after renaming with an .in suffix), like

: ${SAGE_ROOT:=@abs_top_srcdir@}

which would set a default value of SAGE_ROOT at ./configure-time, but still allow custom values of SAGE_ROOT to be set in the environment?

[mkoeppe]

comment:9

Replying to @orlitzky:

What kind of solution is acceptable here? I've lost track of the big picture, but it looks like all of the important ./configure-time settings are in sage-env-config, but local/bin/sage can't find sage-env-config because the path to it (determined during ./configure) is contained in sage-env-config.

The directory can be found from $0, with resolving symlinks.
Similar to what used to be in sage-env, but not bash-specific because it's for an executed script rather than a sourced script.

Are we allowed to stick autoconf values directly into local/bin/sage (after renaming with an .in suffix), like

: ${SAGE_ROOT:=@abs_top_srcdir@}

which would set a default value of SAGE_ROOT at ./configure-time, but still allow custom values of SAGE_ROOT to be set in the environment?

No, because the sage script is installed by setup.py and we plan to make this work even when configure has not been run.