Add configure check for python program

Add a configure check that looks for python3 and python in that order
since we had agreed in the past to prefer python3 over python in all
our code.  The patch also adjusts invocations through the various
Makefiles to use the set variable.

	* configure.ac: Check for python3 or python.
	* configure: Regenerated.
	* config.make.in (PYTHON): New variable.
	* benchtests/Makefile: Don't define PYTHON.
	(bench): Define target only if PYTHON was defined.
	* Rules: Don't define PYTHON.
	Define pretty printer targets only if PYTHON was defined.
	(tests-printers): Add to tests-unsupported if PYTHON is not
	found.
	(python-flags, python-invoke): Remove.
	(tests-printers-out): Use PYTHON instead of python-invoke.

6 files changed, 109 insertions, 18 deletions

diff --git a/ChangeLog b/ChangeLog
index 4f86f7a8cf..1fcd9eda10 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2016-12-22  Siddhesh Poyarekar  <siddhesh@sourceware.org>
+
+	* configure.ac: Check for python3 or python.
+	* configure: Regenerated.
+	* config.make.in (PYTHON): New variable.
+	* benchtests/Makefile: Don't define PYTHON.
+	(bench): Define target only if PYTHON was defined.
+	* Rules: Don't define PYTHON.
+	Define pretty printer targets only if PYTHON was defined.
+	(tests-printers): Add to tests-unsupported if PYTHON is not
+	found.
+	(python-flags, python-invoke): Remove.
+	(tests-printers-out): Use PYTHON instead of python-invoke.
+
 2016-12-21  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #20978]
diff --git a/Rules b/Rules
index fe18ce55de..558924d653 100644
--- a/Rules
+++ b/Rules
@@ -114,6 +114,11 @@ tests-printers-programs := $(addprefix $(objpfx),$(tests-printers))
 # .out files with the output of running the pretty printer tests.
 tests-printers-out := $(patsubst %,$(objpfx)%.out,$(tests-printers))
 
+ifndef PYTHON
+# Mark tests-printers tests as unsupported if we don't have PYTHON.
+tests-unsupported += $(tests-printers)
+endif
+
 ifeq ($(build-programs),yes)
 others: $(addprefix $(objpfx),$(others) $(sysdep-others) $(extra-objs))
 else
@@ -124,9 +129,9 @@ endif
 others: $(py-const)
 
 ifeq ($(run-built-tests),no)
-tests: $(addprefix $(objpfx),$(filter-out $(tests-unsupported),$(tests)) \
-			     $(test-srcs)) $(tests-special) \
-       $(tests-printers-programs)
+tests: $(addprefix $(objpfx),$(filter-out $(tests-unsupported),$(tests) \
+			       $(tests-printers-programs)) \
+			     $(test-srcs)) $(tests-special)
 xtests: tests $(xtests-special)
 else
 tests: $(tests:%=$(objpfx)%.out) $(tests-special) $(tests-printers-out)
@@ -255,16 +260,8 @@ endif
 
 endif	# tests
 
+ifdef PYTHON
 ifneq "$(strip $(tests-printers))" ""
-# We're defining this here for now; later it'll be defined at configure time
-# inside Makeconfig.
-PYTHON := python
-
-# Invoke Python using -B to avoid generating .pyc files on the source dir,
-# so that we can keep it read-only.
-python-flags := -B
-
-python-invoke := $(PYTHON) $(python-flags)
 
 # Static pattern rule for building the test programs for the pretty printers.
 $(tests-printers-programs): %: %.o $(tests-printers-libs) \
@@ -283,9 +280,10 @@ py-env := PYTHONPATH=$(py-const-dir):$(..)scripts:$${PYTHONPATH}
 $(tests-printers-out): $(objpfx)%.out: $(objpfx)% %.py %.c $(pretty-printers) \
 		       $(..)scripts/test_printers_common.py
 	$(test-wrapper-env) $(py-env) \
-	    $(python-invoke) $*.py $*.c $(objpfx)$* $(pretty-printers) > $@; \
+	    $(PYTHON) $*.py $*.c $(objpfx)$* $(pretty-printers) > $@; \
 	$(evaluate-test)
 endif
+endif
 
 
 .PHONY: distclean realclean subdir_distclean subdir_realclean \
diff --git a/benchtests/Makefile b/benchtests/Makefile
index f5d6dac6c7..9eef1e1243 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -18,8 +18,6 @@
 # Makefile for benchmark tests.  The only useful target here is `bench`.
 # Add benchmark functions in alphabetical order.
 
-PYTHON := python
-
 subdir := benchtests
 
 include ../Makeconfig
@@ -146,7 +144,15 @@ bench-clean:
 	rm -f $(timing-type) $(addsuffix .o,$(timing-type))
 	rm -f $(addprefix $(objpfx),$(bench-extra-objs))
 
+# Define the bench target only if the target has a usable python installation.
+ifdef PYTHON
 bench: bench-build bench-set bench-func bench-malloc
+else
+bench:
+	@echo "The bench target needs python to run."
+	@exit 1
+endif
+
 # Target to only build the benchmark without running it.  We generate locales
 # only if we're building natively.
 ifeq (no,$(cross-compiling))
diff --git a/config.make.in b/config.make.in
index d2d9b8ab36..35e7e59663 100644
--- a/config.make.in
+++ b/config.make.in
@@ -126,6 +126,7 @@ MSGFMT = @MSGFMT@
 BASH = @BASH_SHELL@
 AWK = @AWK@
 PERL = @PERL@
+PYTHON = @PYTHON@
 
 # Additional libraries.
 LIBGD = @LIBGD@
diff --git a/configure b/configure
index 5cf3230b56..10b0fb7069 100755
--- a/configure
+++ b/configure
@@ -639,6 +639,8 @@ CXX_CMATH_HEADER
 CXX_CSTDLIB_HEADER
 CXX_SYSINCLUDES
 SYSINCLUDES
+PYTHON
+PYTHON_PROG
 AUTOCONF
 NM
 AWK
@@ -5086,17 +5088,73 @@ else
   AUTOCONF=no
 fi
 
+# Check for python3 if available, or else python.
+for ac_prog in python3 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_PROG+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$PYTHON_PROG"; then
+  ac_cv_prog_PYTHON_PROG="$PYTHON_PROG" # Let the user override the test.
+else
+as_save_IFS=$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_PROG="$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_PROG=$ac_cv_prog_PYTHON_PROG
+if test -n "$PYTHON_PROG"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $PYTHON_PROG" >&5
+$as_echo "$PYTHON_PROG" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+  test -n "$PYTHON_PROG" && break
+done
+test -n "$PYTHON_PROG" || PYTHON_PROG="no"
+
+case "x$PYTHON_PROG" in
+xno|x|x:) PYTHON_PROG=no ;;
+*) ;;
+esac
+
+if test "x$PYTHON_PROG" = xno; then
+  aux_missing="$aux_missing python"
+else
+  PYTHON="$PYTHON_PROG -B"
+
+fi
+
 test -n "$critic_missing" && as_fn_error $? "
 *** These critical programs are missing or too old:$critic_missing
 *** Check the INSTALL file for required versions." "$LINENO" 5
 
 test -n "$aux_missing" && { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING:
 *** These auxiliary programs are missing or incompatible versions:$aux_missing
-*** some features will be disabled.
+*** some features or tests will be disabled.
 *** Check the INSTALL file for required versions." >&5
 $as_echo "$as_me: WARNING:
 *** These auxiliary programs are missing or incompatible versions:$aux_missing
-*** some features will be disabled.
+*** some features or tests will be disabled.
 *** Check the INSTALL file for required versions." >&2;}
 
 # if using special system headers, find out the compiler's sekrit
diff --git a/configure.ac b/configure.ac
index d719fadeef..aa6e2d7e56 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1050,13 +1050,27 @@ else
   AUTOCONF=no
 fi
 
+# Check for python3 if available, or else python.
+AC_CHECK_PROGS(PYTHON_PROG, python3 python,no)
+case "x$PYTHON_PROG" in
+xno|x|x:) PYTHON_PROG=no ;;
+*) ;;
+esac
+
+if test "x$PYTHON_PROG" = xno; then
+  aux_missing="$aux_missing python"
+else
+  PYTHON="$PYTHON_PROG -B"
+  AC_SUBST(PYTHON)
+fi
+
 test -n "$critic_missing" && AC_MSG_ERROR([
 *** These critical programs are missing or too old:$critic_missing
 *** Check the INSTALL file for required versions.])
 
 test -n "$aux_missing" && AC_MSG_WARN([
 *** These auxiliary programs are missing or incompatible versions:$aux_missing
-*** some features will be disabled.
+*** some features or tests will be disabled.
 *** Check the INSTALL file for required versions.])
 
 # if using special system headers, find out the compiler's sekrit