trac 30153: add, clarify some comments

build/make/Makefile.in

@@ -119,7 +119,7 @@ SCRIPT_PACKAGES = @SAGE_SCRIPT_PACKAGES@
 #
 # For example:
 #
-# inst_python2 = $(INST)/python2-$(vers_python2)
+# inst_python3 = $(INST)/python3-$(vers_python3)
 #
 # inst_git = $(INST)/.dummy
 
@@ -360,11 +360,11 @@ _clean-broken-gcc:
 # Define a function for generating the list of a package's dependencies
 # as $(inst_<pkgname>) variables.  For example, takes:
 #
-#     deps_cysignals = python2 cython pari | pip
+#     deps_cysignals = python3 cython pari | pip
 #
 # to:
 #
-#     $(inst_python2) $(inst_cython) $(inst_pari) | $(inst_pip)
+#     $(inst_python3) $(inst_cython) $(inst_pari) | $(inst_pip)
 #
 # If some value in the dependencies list is not a package name (e.g. it is
 # the name of some arbitrary file, or it is the '|' symbol) then it is just
@@ -382,25 +382,35 @@ pkg_deps = \
 
 # ============================= normal packages ==============================
 # Generate build rules for 'normal' packages; this template is used to generate
-# three rules in the form:
+# rules in the form:
 #
 # $(INST)/<pkgname>-<pkgvers>: <dependencies>
 #     +$(AM_V_at)sage-logger -p '$(SAGE_SPKG) <pkgname>-<pkgvers>' '$(SAGE_LOGS)/<pkgname>-<pkgvers>.log'
 #
 # <pkgname>: $(INST)/<pkgname>-<pkgvers>
 #
+# <pkgname>-build-deps: <dependencies>
+#
+# <pkgname>-no-deps:
+#     +$(AM_V_at)sage-logger -p '$(SAGE_SPKG) <pkgname>-<pkgvers>' '$(SAGE_LOGS)/<pkgname>-<pkgvers>.log'
+#
 # <pkgname>-clean:
 #     sage-spkg-uninstall <pkgname> '$(SAGE_LOCAL)'
 #
-# For example, for python2 this will expand to:
+# So <pkgname>-build-deps installs just the dependencies, while
+# <pkgname>-no-deps tries to install the package without its
+# dependencies. This is currently used in SAGE_SRC/bin/sage when
+# running 'sage -b' to build the Sage library.
+#
+# For example, for python3 this will expand to:
 #
-# $(INST)/python2-2.7.14: $(inst_zlib) $(inst_readline) $(inst_sqlite) $(inst_libpng) $(inst_bzip2)
-#     +$(AM_V_at)sage-logger -p '$(SAGE_SPKG) python2-2.7.14' '$(SAGE_LOGS)/python2-2.7.14.log'
+# $(INST)/python3-3.7.3: $(inst_zlib) $(inst_readline) $(inst_sqlite) $(inst_libpng) $(inst_bzip2) $(inst_xz) $(inst_libffi)
+#     +$(AM_V_at)sage-logger -p '$(SAGE_SPKG) python3-3.7.3' '$(SAGE_LOGS)/python3-3.7.3.log'
 #
-# python2: $(INST)/python2-2.7.14
+# python3: $(INST)/python3-3.7.3
 #
-# python2-clean:
-#     sage-spkg-uninstall python2 '$(SAGE_LOCAL)'
+# python3-clean:
+#     sage-spkg-uninstall python3 '$(SAGE_LOCAL)'
 #
 # Note: In these rules the $(INST)/<pkgname>-<pkgvers> target is used
 # explicitly, rather than expanding the $(inst_<pkgname>) variable, since
@@ -475,7 +485,7 @@ $(1)-no-deps:
 $(1)-clean:
 	-sage --pip uninstall -y -r '$$(SAGE_ROOT)/build/pkgs/$(1)/requirements.txt'
 
-.PHONY: $(1) $(1)-clean $(1)-build-deps $(1)-no-deps $(1)-clean
+.PHONY: $(1) $(1)-clean $(1)-build-deps $(1)-no-deps
 endef
 
 $(foreach pkgname,$(PIP_PACKAGES),\