installation: improve compatibility with legacy systems

- downgrade requirements on pyqt, scipy, pyqtgraph, setuptools,
  setuptools_scm and gdal
- add a fallback to setup.py so that it is possible to install when
  setuptools lacks support for pep621
- update installation docs

docs/source/installation.rst

@@ -3,35 +3,43 @@ Installation
 
 Kite is written for `Python 3 <https://python.org>`_, the installation has been tested on Debian based distributions (e.g. Ubuntu and Mint), MacOSX, and `Anaconda <https://anaconda.org/pyrocko/kite>`_.
 
-Debian / Ubuntu
----------------
+System-wide installation on Debian / Ubuntu
+-------------------------------------------
 
 As a mandatory prerequisite you have to install Pyrocko, visit `Pyrocko installation instructions <https://pyrocko.org/docs/current/install/index.html>`_ for details.
 
 .. code-block :: sh
     :caption: Installation from source and ``apt-get``
 
-    sudo apt-get install python3-dev python3-pyqt5 python3-pyqt5 python3-pyqt5.qtopengl python3-scipy python3-numpy python3-pyqtgraph
+    # satisfy Kite's requirements with system packages
+    sudo apt-get install python3-dev python3-pyqt5 python3-pyqt5 python3-pyqt5.qtopengl python3-scipy python3-numpy python3-pyqtgraph python3-geojson python3-setuptools python3-setuptools-scm
 
-    git clone https://github.com/Turbo87/utm
-    cd utm
-    sudo python3 setup.py install
+    # install the utm package with pip (no system package available)
+    sudo pip3 install utm
 
+   # get Kite's source code with git
     git clone https://github.com/pyrocko/kite
     cd kite
-    sudo python3 setup.py install
 
+    # compile and install with pip, but disable automatic dependency resolution (--no-deps)
+    sudo pip3 install . --no-build-isolation --no-deps
 
-PIP
----
 
-An installation through ``pip`` requires the same prerequisites as above:
+Installation with ``pip`` into virtual environment ``venv``
+-----------------------------------------------------------
 
 .. code-block :: sh
-    :caption: Installation through pip
+    :caption: Installation into venv
 
-    sudo pip3 install utm
-    sudo pip3 install git+https://github.com/pyrocko/kite
+   # create and activate venv
+   python3 -m venv venv
+   source venv/bin/activate
+
+   # get Kite's source code with git
+   git clone https://github.com/pyrocko/kite
+   cd kite
+   # install prerequisites with pip, compile and install Kite
+   pip install .
 
 
 MacOS (Sierra, MacPorts)

pyproject.toml

@@ -1,9 +1,9 @@
 [build-system]
 requires = [
   "wheel",
-  "setuptools >= 61.0.0",
+  "setuptools >= 52.0.0",
   "oldest-supported-numpy",
-  "setuptools_scm[toml]>=6.2",
+  "setuptools_scm[toml]>=5.0",
 ]
 build-backend = "setuptools.build_meta"
 
@@ -34,9 +34,9 @@ classifiers = [
 ]
 dependencies = [
   "numpy>=1.17.3",
-  "scipy>=1.8.0",
-  "PyQt5>=5.15.7",
-  "pyqtgraph==0.12.4",
+  "scipy>=1.6.0",
+  "PyQt5>=5.15.0",
+  "pyqtgraph==0.11.0",
   "pyrocko>=2022.06.10",
   "utm>=0.7.0",
   "geojson>=2.5.0",
@@ -48,7 +48,7 @@ GitHub = "https://github.com/pyrocko/kite"
 Issues = "https://github.com/pyrocko/kite/issues"
 
 [project.optional-dependencies]
-gdal = ["gdal>=3.5.0"]
+gdal = ["gdal>=3.2.0"]
 development = ["flake8", "black", "pre-commit"]
 tests = ["pytest"]
 

setup.py

@@ -1,11 +1,16 @@
 #!/usr/bin/env python3
 import os
 import platform
+import sys
 import tempfile
 from distutils.sysconfig import get_python_inc
 from os.path import join as pjoin
 
+from pkg_resources import parse_version
 from setuptools import Extension, setup
+from setuptools import __version__ as setuptools_version
+
+have_pep621_support = parse_version(setuptools_version) >= parse_version("61.0.0")
 
 try:
     import numpy
@@ -117,6 +122,59 @@ def _have_openmp():
     omp_lib = []
 
 
+if not have_pep621_support:
+    try:
+        import toml
+    except ImportError:
+        sys.exit(
+            """Your setuptools version is too old to support PEP621-compliant
+            installs. You may either update setuptools or, if this is not
+            possible, install the "toml" package (python3-toml package on
+            deb-based systems) to enable a fallback mechanism."""
+        )
+
+    tomldata = toml.load(
+        open(os.path.join(os.path.dirname(__file__), "pyproject.toml"))
+    )
+    metadata = dict(
+        use_scm_version=True,
+        package_data={"kite": ["spool/res/*", "talpa/res/*"]},
+        ext_package="kite",
+    )
+    metadata["setup_requires"] = tomldata["build-system"]["requires"]
+    metadata["packages"] = tomldata["tool"]["setuptools"]["packages"]
+
+    for k in ["classifiers", "description", "name", "keywords"]:
+        metadata[k] = tomldata["project"][k]
+
+    metadata["license"] = tomldata["project"]["license"]["text"]
+
+    metadata["python_requires"] = tomldata["project"]["requires-python"]
+    first_author = list(tomldata["project"]["authors"])[0]
+    metadata["author"] = ", ".join(
+        author["name"] for author in tomldata["project"]["authors"]
+    )
+    metadata["author_email"] = first_author["email"]
+
+    metadata["extras_require"] = {}
+    for k_opt in tomldata["project"]["optional-dependencies"]:
+        metadata["extras_require"][k_opt] = tomldata["project"][
+            "optional-dependencies"
+        ][k_opt]
+
+    metadata["install_requires"] = tomldata["project"]["dependencies"]
+    metadata["entry_points"] = {
+        "console_scripts": [
+            "%s = %s" % (k, v) for (k, v) in tomldata["project"]["scripts"].items()
+        ],
+        "gui_scripts": [
+            "%s = %s" % (k, v) for (k, v) in tomldata["project"]["gui-scripts"].items()
+        ],
+    }
+else:
+    metadata = {}
+
+
 setup(
     ext_modules=[
         Extension(
@@ -135,5 +193,6 @@ def _have_openmp():
             extra_link_args=omp_lib,
             language="c",
         ),
-    ]
+    ],
+    **metadata,
 )