# HG changeset patch
# Parent  a2bfec367cefdee19ec8a47311baa3eac1b410b1
Issue #28143: Find a python2 command or use PYTHON_FOR_GEN to run scripts

Configure now searches for commands called python2.7, python2, and python,
and sets PYTHON_FOR_GEN to the result. PYTHON_FOR_GEN can be overridden by
the user if desired. If no Python command is found, the build fails with an
error message.

diff -r a2bfec367cef Makefile.pre.in
--- a/Makefile.pre.in	Sat Sep 17 07:54:55 2016 +0000
+++ b/Makefile.pre.in	Sun Sep 18 00:49:43 2016 +0000
@@ -200,6 +200,7 @@
 PYTHON=		python$(EXE)
 BUILDPYTHON=	python$(BUILDEXE)
 
+PYTHON_FOR_GEN=@PYTHON_FOR_GEN@
 PYTHON_FOR_BUILD=@PYTHON_FOR_BUILD@
 _PYTHON_HOST_PLATFORM=@_PYTHON_HOST_PLATFORM@
 HOST_GNU_TYPE=  @host@
@@ -306,8 +307,9 @@
 AST_ASDL=	$(srcdir)/Parser/Python.asdl
 
 ASDLGEN_FILES=	$(srcdir)/Parser/asdl.py $(srcdir)/Parser/asdl_c.py
-# XXX Note that a build now requires Python exist before the build starts
-ASDLGEN=	$(srcdir)/Parser/asdl_c.py
+# Note that a build now requires Python to exist before the build starts.
+# Use "make touch" to fix up screwed up file mtimes in a checkout.
+ASDLGEN=	$(PYTHON_FOR_GEN) $(srcdir)/Parser/asdl_c.py
 
 ##########################################################################
 # Python
@@ -741,7 +743,7 @@
 				$(STRINGLIB_HEADERS)
 
 $(OPCODETARGETS_H): $(OPCODETARGETGEN_FILES)
-	$(OPCODETARGETGEN) $(OPCODETARGETS_H)
+	$(PYTHON_FOR_GEN) $(OPCODETARGETGEN) $(OPCODETARGETS_H)
 
 Python/ceval.o: $(OPCODETARGETS_H)
 
diff -r a2bfec367cef Misc/NEWS
--- a/Misc/NEWS	Sat Sep 17 07:54:55 2016 +0000
+++ b/Misc/NEWS	Sun Sep 18 00:49:43 2016 +0000
@@ -186,6 +186,9 @@
 Build
 -----
 
+- Issue #28143: Try to find a python2 command or use PYTHON_FOR_GEN to run
+  scripts like Parser/asdl_c.py that regenerate files to bootstrap the build.
+
 - Issue #15819: The Include directory in the build tree is already searched;
   drop unused code trying to add it again.
 
diff -r a2bfec367cef configure
--- a/configure	Sat Sep 17 07:54:55 2016 +0000
+++ b/configure	Sun Sep 18 00:49:43 2016 +0000
@@ -743,6 +743,7 @@
 VERSION
 GENERATED_COMMENT
 PYTHON_FOR_BUILD
+PYTHON_FOR_GEN
 host_os
 host_vendor
 host_cpu
@@ -2915,6 +2916,56 @@
 # pybuilddir.txt will be created by --generate-posix-vars in the Makefile
 rm -f pybuilddir.txt
 
+for ac_prog in python$PACKAGE_VERSION python2 python
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_prog_PYTHON_FOR_GEN+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$PYTHON_FOR_GEN"; then
+  ac_cv_prog_PYTHON_FOR_GEN="$PYTHON_FOR_GEN" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_prog_PYTHON_FOR_GEN="$ac_prog"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+PYTHON_FOR_GEN=$ac_cv_prog_PYTHON_FOR_GEN
+if test -n "$PYTHON_FOR_GEN"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PYTHON_FOR_GEN" >&5
+$as_echo "$PYTHON_FOR_GEN" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+  test -n "$PYTHON_FOR_GEN" && break
+done
+test -n "$PYTHON_FOR_GEN" || PYTHON_FOR_GEN="not-found"
+
+if test "$PYTHON_FOR_GEN" = not-found; then
+    PYTHON_FOR_GEN='@echo "Cannot generate $@, python not found !" && \
+    echo "To skip re-generation of $@ run <make touch> or <make -t $@>." && \
+    echo "Otherwise, set python in PATH and run configure or run <make PYTHON_FOR_GEN=python>." && false &&'
+fi
+
+
 if test "$cross_compiling" = yes; then
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for python interpreter for cross build" >&5
 $as_echo_n "checking for python interpreter for cross build... " >&6; }
diff -r a2bfec367cef configure.ac
--- a/configure.ac	Sat Sep 17 07:54:55 2016 +0000
+++ b/configure.ac	Sun Sep 18 00:49:43 2016 +0000
@@ -19,6 +19,14 @@
 # pybuilddir.txt will be created by --generate-posix-vars in the Makefile
 rm -f pybuilddir.txt
 
+AC_CHECK_PROGS(PYTHON_FOR_GEN, python$PACKAGE_VERSION python2 python, not-found)
+if test "$PYTHON_FOR_GEN" = not-found; then
+    PYTHON_FOR_GEN='@echo "Cannot generate $@, python not found !" && \
+    echo "To skip re-generation of $@ run <make touch> or <make -t $@>." && \
+    echo "Otherwise, set python in PATH and run configure or run <make PYTHON_FOR_GEN=python>." && false &&'
+fi
+AC_SUBST(PYTHON_FOR_GEN)
+
 if test "$cross_compiling" = yes; then
     AC_MSG_CHECKING([for python interpreter for cross build])
     if test -z "$PYTHON_FOR_BUILD"; then