- Issue #16262: fix out-of-src-tree builds, if mercurial is not installed.

Makefile.pre.in

@@ -308,7 +308,7 @@ 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=	@DISABLE_ASDLGEN@ $(srcdir)/Parser/asdl_c.py
+ASDLGEN=	@ASDLGEN@ $(srcdir)/Parser/asdl_c.py
 
 ##########################################################################
 # Python

Misc/NEWS

@@ -191,6 +191,8 @@ Tests
 Build
 -----
 
+- Issue #16262: fix out-of-src-tree builds, if mercurial is not installed.
+
 - Issue #15298: ensure _sysconfigdata is generated in build directory, not
   source directory.
 

Parser/asdl_c.py

@@ -5,7 +5,6 @@
 # handle fields that have a type but no name
 
 import os, sys
-import subprocess
 
 import asdl
 

configure.ac

@@ -1000,12 +1000,12 @@ if test "$cross_compiling" = yes; then
 fi
 AC_SUBST(READELF)
 
-AC_SUBST(DISABLE_ASDLGEN)
-DISABLE_ASDLGEN=""
-AC_CHECK_PROG(HAS_PYTHON, python, found, not-found)
-if test $HAS_HG != found -o $HAS_PYTHON != found
-then
-    DISABLE_ASDLGEN="@echo hg: $HAS_HG, python: $HAS_PYTHON! cannot run \$(srcdir)/Parser/asdl_c.py #"
+AC_SUBST(ASDLGEN)
+AC_CHECK_PROGS(PYTHON, python$PACKAGE_VERSION python3 python, not-found)
+if $PYTHON = not-found; then
+    ASDLGEN="@echo python: $PYTHON! cannot run \$(srcdir)/Parser/asdl_c.py #"
+else
+    ASDLGEN="$PYTHON"
 fi