bpo-31934: Abort when building out of a not clean source tree (GH-4255)

Makefile.pre.in

@@ -440,7 +440,17 @@ DTRACE_DEPS = \
 
 # Default target
 all:		@DEF_MAKE_ALL_RULE@
-build_all:	$(BUILDPYTHON) oldsharedmods sharedmods gdbhooks Programs/_testembed python-config
+build_all:	check-clean-src $(BUILDPYTHON) oldsharedmods sharedmods gdbhooks \
+		Programs/_testembed python-config
+
+# Check that the source is clean when building out of source.
+check-clean-src:
+	@if test -n "$(VPATH)" -a -f "$(srcdir)/Programs/python.o"; then \
+		echo "Error: The source directory ($(srcdir)) is not clean" ; \
+		echo "Building Python out of the source tree (in $(abs_builddir)) requires a clean source tree ($(abs_srcdir))" ; \
+		echo "Try to run: make -C \"$(srcdir)\" clean" ; \
+		exit 1; \
+	fi
 
 # Profile generation build must start from a clean tree.
 profile-clean-stamp:
@@ -542,7 +552,7 @@ coverage-report: regen-grammar regen-importlib
 # Run "Argument Clinic" over all source files
 # (depends on python having already been built)
 .PHONY=clinic
-clinic: $(BUILDPYTHON) $(srcdir)/Modules/_blake2/blake2s_impl.c
+clinic: check-clean-src $(BUILDPYTHON) $(srcdir)/Modules/_blake2/blake2s_impl.c
 	$(RUNSHARED) $(PYTHON_FOR_BUILD) $(srcdir)/Tools/clinic/clinic.py --make --srcdir $(srcdir)
 
 # Build the interpreter
@@ -1100,7 +1110,7 @@ altinstall: commoninstall
 			$$ensurepip --root=$(DESTDIR)/ ; \
 	fi
 
-commoninstall:  @FRAMEWORKALTINSTALLFIRST@ \
+commoninstall:  check-clean-src @FRAMEWORKALTINSTALLFIRST@ \
 		altbininstall libinstall inclinstall libainstall \
 		sharedinstall oldsharedinstall altmaninstall \
 		@FRAMEWORKALTINSTALLLAST@
@@ -1722,7 +1732,7 @@ patchcheck: @DEF_MAKE_RULE@
 Python/thread.o: @THREADHEADERS@
 
 # Declare targets that aren't real files
-.PHONY: all build_all sharedmods oldsharedmods test quicktest
+.PHONY: all build_all sharedmods check-clean-src oldsharedmods test quicktest
 .PHONY: install altinstall oldsharedinstall bininstall altbininstall
 .PHONY: maninstall libinstall inclinstall libainstall sharedinstall
 .PHONY: frameworkinstall frameworkinstallframework frameworkinstallstructure

Misc/NEWS.d/next/Build/2017-11-03-15-17-50.bpo-31934.8bUlpv.rst

+Abort the build when building out of a not clean source tree.