pythongh-106259: Add minimal help target to Makefile (python#106260)

Co-authored-by: Erlend E. Aasland <erlend@python.org>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Doc/using/configure.rst

@@ -991,32 +991,99 @@ Main build steps
 Main Makefile targets
 ---------------------
 
-* ``make``: Build Python with the standard library.
-* ``make platform:``: build the ``python`` program, but don't build the
-  standard library extension modules.
-* ``make profile-opt``: build Python using Profile Guided Optimization (PGO).
-  You can use the configure :option:`--enable-optimizations` option to make
-  this the default target of the ``make`` command (``make all`` or just
-  ``make``).
-
-* ``make test``: Build Python and run the Python test suite with ``--fast-ci``
-  option. Variables:
-
-  * ``TESTOPTS``: additional regrtest command line options.
-  * ``TESTPYTHONOPTS``: additional Python command line options.
-  * ``TESTTIMEOUT``: timeout in seconds (default: 20 minutes).
-
-* ``make buildbottest``: Similar to ``make test``, but use ``--slow-ci``
-  option and default timeout of 20 minutes, instead of ``--fast-ci`` option
-  and a default timeout of 10 minutes.
-
-* ``make install``: Build and install Python.
-* ``make regen-all``: Regenerate (almost) all generated files;
-  ``make regen-stdlib-module-names`` and ``autoconf`` must be run separately
-  for the remaining generated files.
-* ``make clean``: Remove built files.
-* ``make distclean``: Same than ``make clean``, but remove also files created
-  by the configure script.
+make
+^^^^
+
+For the most part, when rebuilding after editing some code or
+refreshing your checkout from upstream, all you need to do is execute
+``make``, which (per Make's semantics) builds the default target, the
+first one defined in the Makefile.  By tradition (including in the
+CPython project) this is usually the ``all`` target. The
+``configure`` script expands an ``autoconf`` variable,
+``@DEF_MAKE_ALL_RULE@`` to describe precisely which targets ``make
+all`` will build. The three choices are:
+
+* ``profile-opt`` (configured with ``--enable-optimizations``)
+* ``build_wasm`` (configured with ``--with-emscripten-target``)
+* ``build_all`` (configured without explicitly using either of the others)
+
+Depending on the most recent source file changes, Make will rebuild
+any targets (object files and executables) deemed out-of-date,
+including running ``configure`` again if necessary. Source/target
+dependencies are many and maintained manually however, so Make
+sometimes doesn't have all the information necessary to correctly
+detect all targets which need to be rebuilt.  Depending on which
+targets aren't rebuilt, you might experience a number of problems. If
+you have build or test problems which you can't otherwise explain,
+``make clean && make`` should work around most dependency problems, at
+the expense of longer build times.
+
+
+make platform
+^^^^^^^^^^^^^
+
+Build the ``python`` program, but don't build the standard library
+extension modules. This generates a file named ``platform`` which
+contains a single line describing the details of the build platform,
+e.g., ``macosx-14.3-arm64-3.12`` or ``linux-x86_64-3.13``.
+
+
+make profile-opt
+^^^^^^^^^^^^^^^^
+
+Build Python using profile-guided optimization (PGO).  You can use the
+configure :option:`--enable-optimizations` option to make this the
+default target of the ``make`` command (``make all`` or just
+``make``).
+
+
+
+make clean
+^^^^^^^^^^
+
+Remove built files.
+
+
+make distclean
+^^^^^^^^^^^^^^
+
+In addition to the the work done by ``make clean``, remove files
+created by the configure script.  ``configure`` will have to be run
+before building again. [#]_
+
+
+make install
+^^^^^^^^^^^^
+
+Build the ``all`` target and install Python.
+
+
+make test
+^^^^^^^^^
+
+Build the ``all`` target and run the Python test suite with the
+``--fast-ci`` option. Variables:
+
+* ``TESTOPTS``: additional regrtest command-line options.
+* ``TESTPYTHONOPTS``: additional Python command-line options.
+* ``TESTTIMEOUT``: timeout in seconds (default: 10 minutes).
+
+
+make buildbottest
+^^^^^^^^^^^^^^^^^
+
+This is similar to ``make test``, but uses the ``--slow-ci``
+option and default timeout of 20 minutes, instead of ``--fast-ci`` option.
+
+
+make regen-all
+^^^^^^^^^^^^^^
+
+Regenerate (almost) all generated files. These include (but are not
+limited to) bytecode cases, and parser generator file.
+``make regen-stdlib-module-names`` and ``autoconf`` must be run
+separately for the remaining `generated files <#generated-files>`_.
+
 
 C extensions
 ------------
@@ -1311,3 +1378,14 @@ Linker flags
    Linker flags used for building the interpreter object files.
 
    .. versionadded:: 3.8
+
+
+.. rubric:: Footnotes
+
+.. [#] ``git clean -fdx`` is an even more extreme way to "clean" your
+   checkout. It removes all files not known to Git.
+   When bug hunting using ``git bisect``, this is
+   `recommended between probes <https://github.com/python/cpython/issues/114505#issuecomment-1907021718>`_
+   to guarantee a completely clean build. **Use with care**, as it
+   will delete all files not checked into Git, including your
+   new, uncommitted work.

Makefile.pre.in

@@ -653,6 +653,30 @@ all:		@DEF_MAKE_ALL_RULE@
 # all.
 .PHONY: all
 
+# Provide quick help for common Makefile targets.
+.PHONY: help
+help:
+	@echo "Run 'make' to build the Python executable and extension modules"
+	@echo ""
+	@echo "or 'make <target>' where <target> is one of:"
+	@echo "  test         run the test suite"
+	@echo "  install      install built files"
+	@echo "  regen-all    regenerate a number of generated source files"
+	@echo "  clinic       run Argument Clinic over source files"
+	@echo ""
+	@echo "  clean        to remove build files"
+	@echo "  distclean    'clean' + remove other generated files (patch, exe, etc)"
+	@echo ""
+	@echo "  recheck      rerun configure with last cmdline options"
+	@echo "  reindent     reindent .py files in Lib directory"
+	@echo "  tags         build a tags file (useful for Emacs and other editors)"
+	@echo "  list-targets list all targets in the Makefile"
+
+# Display a full list of Makefile targets
+.PHONY: list-targets
+list-targets:
+	@grep -E '^[A-Za-z][-A-Za-z0-9]+:' Makefile | awk -F : '{print $$1}'
+
 .PHONY: build_all
 build_all:	check-clean-src $(BUILDPYTHON) platform sharedmods \
 		gdbhooks Programs/_testembed scripts checksharedmods rundsymutil