src/doc/en/developer: Update on spkg-install scripts of script packages

src/doc/en/developer/packaging.rst

@@ -117,8 +117,8 @@ the following source types:
 
    - the file ``package-version.txt`` is optional;
 
-   - installing the package runs the installation script ``spkg-install``
-     (see :ref:`section-spkg-install`);
+   - installing the package runs the installation script ``spkg-install`` or
+     ``spkg-install.in`` (see :ref:`section-spkg-install`);
 
    - Sage records the version number of the package installed using a file in
      ``$SAGE_LOCAL/var/lib/sage/installed/`` and will rerun the installation
@@ -134,8 +134,8 @@ the following source types:
 To summarize: the package source type is determined as follows: if
 there is a file ``requirements.txt``, it is a ``pip`` package. If not,
 then if there is a ``checksums.ini`` file, it is ``normal`` or ``wheel``.
-Otherwise, if it has an ``spkg-install`` script, it is a ``script`` package,
-and if it does not, then it is a ``dummy`` package.
+Otherwise, if it has an ``spkg-install`` or ``spkg-install.in`` script,
+it is a ``script`` package, and if it does not, then it is a ``dummy`` package.
 
 
 .. _section-directory-structure:
@@ -358,13 +358,10 @@ at build time,  which should to the appropriate system-specific
 Install scripts of script packages
 ----------------------------------
 
-A script package has a single install script named ``spkg-install``.
+For script packages, it is also possible to use an install script named ``spkg-install``.
 It needs to be an executable shell script; it is not subject to the templating
-described in the previous section.
-
-Sage runs ``spkg-install`` from the directory ``$SAGE_ROOT/build/pkgs/<package>``
-in the environment obtained by sourcing the files ``src/bin/sage-env``,
-``build/bin/sage-build-env-config``, and ``build/bin/sage-build-env``.
+described in the previous section and will be executed directly from
+the build directory.
 
 .. _section-sdh-helpers:
 

src/doc/en/installation/source.rst

@@ -1016,7 +1016,7 @@ Environment variables dealing with specific Sage packages:
 - :envvar:`PARI_CONFIGURE` - use this to pass extra parameters to
   PARI's ``Configure`` script, for example to specify graphics
   support (which is disabled by default). See the file
-  :file:`build/pkgs/pari/spkg-install` for more information.
+  :file:`build/pkgs/pari/spkg-install.in` for more information.
 
 - :envvar:`SAGE_TUNE_PARI` - if yes, enable PARI self-tuning. Note that
   this can be time-consuming. If you set this variable to "yes", you