add incremental building for setuptools>=79

Makefile

@@ -115,12 +115,21 @@ clean:
 # "c_lib", ".cython_version", "build" in $(SAGE_SRC) are from old sage versions
 # Cleaning .so files (and .c and .cpp files associated with .pyx files) is for editable installs.
 # Also cython_debug is for editable installs.
+# 
+# NOTE: Editable installs with incremental compilation are now the default.
+# - First build: Full editable install with pip install -e
+# - Subsequent builds: Incremental compilation with setup.py build_ext --inplace
+# 
+# For manual incremental compilation, use the Sage Python environment:
+#   cd src && ../sage --python setup.py build_ext --inplace
+# This will only recompile changed Cython extensions in place.
+# Or use: make sagelib (which will rebuild all of sagelib)
 sagelib-clean:
 	@echo "Deleting Sage library build artifacts..."
 	if [ -d "$(SAGE_SRC)" ]; then \
 	    (cd "$(SAGE_SRC)" && \
 	     rm -rf c_lib .cython_version cython_debug; \
-	     rm -rf build; find . -name '*.pyc' -o -name "*.so" | xargs rm -f; \
+	     rm -rf build *.egg-info; find . -name '*.pyc' -o -name "*.so" | xargs rm -f; \
 	     rm -f $$(find . -name "*.pyx" | sed 's/\(.*\)[.]pyx$$/\1.c \1.cpp/'); \
 	     cd sage/ext/interpreters/ && rm -f *.so *.c *.h *.py* *.pxd) \
 	    && (cd "$(SAGE_ROOT)/build/pkgs/sagelib/src/" && rm -rf build); \
@@ -164,7 +173,7 @@ bdist-clean: clean
 distclean: build-clean
 	$(MAKE) misc-clean
 	@echo "Deleting all remaining output from build system ..."
-	rm -rf local
+	rm -rf local *.egg-info
 	rm -f src/bin/sage-env-config
 	rm -f prefix venv
 

build/pkgs/sagelib/spkg-install.in

@@ -46,9 +46,17 @@ SITEPACKAGESDIR=$(python3 -c 'import sysconfig; print(sysconfig.get_paths()["pur
 # does not shadow the namespace package sage during the build.
 (cd "$SITEPACKAGESDIR" && rm -f sage/__init__.py)
 if [ "$SAGE_EDITABLE" = yes ]; then
-    # Until https://github.com/sagemath/sage/issues/34209 switches us to PEP 660 editable wheels
-    export SETUPTOOLS_ENABLE_FEATURES=legacy-editable
-    sdh_pip_editable_install .
+    # Check if this is an incremental build by looking for existing editable install
+    if python3 -c "import importlib.metadata; importlib.metadata.distribution('sagemath-standard')" 2>/dev/null && \
+       python3 -c "import sage; import os; exit(0 if os.path.exists(os.path.join(os.path.dirname(sage.__file__), '..', 'setup.py')) else 1)" 2>/dev/null; then
+        echo "Detected existing editable install - performing incremental build"
+        # Use setup.py build_ext --inplace for incremental compilation
+        python3 setup.py build_ext --inplace || sdh_die "Error during incremental build"
+        # No need to reinstall - editable install is already in place
+    else
+        echo "Performing initial editable install"
+        sdh_pip_editable_install .
+    fi
 
     if [ "$SAGE_WHEELS" = yes ]; then
         # Additionally build a wheel (for use in other venvs)

m4/pyproject_toml_metadata.m4

@@ -14,10 +14,11 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
+    "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: Implementation :: CPython",
     "Topic :: Scientific/Engineering :: Mathematics",
 ]
-requires-python = ">=3.9, <3.13"
+requires-python = ">=3.9, <3.14"
 
 [project.urls]
 download = "https://doc.sagemath.org/html/en/installation/index.html"

m4/setup_cfg_metadata.m4

@@ -17,5 +17,6 @@ classifiers =
     Programming Language :: Python :: 3.10
     Programming Language :: Python :: 3.11
     Programming Language :: Python :: 3.12
+    Programming Language :: Python :: 3.13
     Programming Language :: Python :: Implementation :: CPython
     Topic :: Scientific/Engineering :: Mathematics