Allow missing "unversioned" python, as in CentOS 8 (#6883)

Summary:
RocksDB Makefile was assuming existence of 'python' command,
which is not present in CentOS 8. We avoid using 'python' if 'python3' is available.

Also added fancy logic to format-diff.sh to make clang-format-diff.py for Python2 work even with Python3 only (as some CentOS 8 FB machines come equipped)

Also, now use just 'python3' for PYTHON if not found so that an informative
"command not found" error will result rather than something weird.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6883

Test Plan: manually tried some variants, 'make check' on a fresh CentOS 8 machine without 'python' executable or Python2 but with clang-format-diff.py for Python2.

Reviewed By: gg814

Differential Revision: D21767029

Pulled By: pdillinger

fbshipit-source-id: 54761b376b140a3922407bdc462f3572f461d0e9

.gitignore

@@ -85,3 +85,5 @@ buckifier/*.pyc
 buckifier/__pycache__
 
 compile_commands.json
+clang-format-diff.py
+.py3/

Makefile

@@ -8,7 +8,9 @@
 
 BASH_EXISTS := $(shell which bash)
 SHELL := $(shell which bash)
-PYTHON?=$(shell which python)
+# Default to python3. Some distros like CentOS 8 do not have `python`.
+PYTHON?=$(shell which python3 || which python || echo python3)
+export PYTHON
 
 CLEAN_FILES = # deliberately empty, so we can append below.
 CFLAGS += ${EXTRA_CFLAGS}

TARGETS

@@ -1,4 +1,4 @@
-# This file @generated by `python buckifier/buckify_rocksdb.py`
+# This file @generated by `python3 buckifier/buckify_rocksdb.py`
 # --> DO NOT EDIT MANUALLY <--
 # This file is a Facebook-specific integration for buck builds, so can
 # only be validated by Facebook employees.

buckifier/buckify_rocksdb.py

@@ -20,10 +20,10 @@ from util import ColorString
 # User can pass extra dependencies as a JSON object via command line, and this
 # script can include these dependencies in the generate TARGETS file.
 # Usage:
-# $python buckifier/buckify_rocksdb.py
+# $python3 buckifier/buckify_rocksdb.py
 # (This generates a TARGET file without user-specified dependency for unit
 # tests.)
-# $python buckifier/buckify_rocksdb.py \
+# $python3 buckifier/buckify_rocksdb.py \
 #        '{"fake": { \
 #                      "extra_deps": [":test_dep", "//fakes/module:mock1"],  \
 #                      "extra_compiler_flags": ["-DROCKSDB_LITE", "-Os"], \

buckifier/check_buck_targets.sh

@@ -15,7 +15,7 @@ echo Backup original TARGETS file.
 
 cp TARGETS TARGETS.bkp
 
-python buckifier/buckify_rocksdb.py
+${PYTHON:-python3} buckifier/buckify_rocksdb.py
 
 TGT_DIFF=`git diff TARGETS | head -n 1`
 
@@ -24,9 +24,9 @@ then
   mv TARGETS.bkp TARGETS
   exit 0
 else
-  echo "Please run 'python buckifier/buckify_rocksdb.py' to update TARGETS file."
+  echo "Please run '${PYTHON:-python3} buckifier/buckify_rocksdb.py' to update TARGETS file."
   echo "Do not manually update TARGETS file."
-  python --version
+  ${PYTHON:-python3} --version
   mv TARGETS.bkp TARGETS
   exit 1
 fi

buckifier/targets_cfg.py

@@ -5,7 +5,7 @@ from __future__ import print_function
 from __future__ import unicode_literals
 
 rocksdb_target_header_template = \
-    """# This file \100generated by `python buckifier/buckify_rocksdb.py`
+    """# This file \100generated by `python3 buckifier/buckify_rocksdb.py`
 # --> DO NOT EDIT MANUALLY <--
 # This file is a Facebook-specific integration for buck builds, so can
 # only be validated by Facebook employees.

build_tools/format-diff.sh

@@ -26,16 +26,30 @@ while getopts ':ch' OPTION; do
   esac
 done
 
-if [ -z $CLANG_FORMAT_DIFF ]
-then
-CLANG_FORMAT_DIFF="clang-format-diff.py"
-fi
+REPO_ROOT="$(git rev-parse --show-toplevel)"
 
-# Check clang-format-diff.py
-if ! which $CLANG_FORMAT_DIFF &> /dev/null
-then
-  if [ ! -f ./clang-format-diff.py ]
-  then
+if [ "$CLANG_FORMAT_DIFF" ]; then
+  echo "Note: CLANG_FORMAT_DIFF='$CLANG_FORMAT_DIFF'"
+  # Dry run to confirm dependencies like argparse
+  if $CLANG_FORMAT_DIFF --help >/dev/null < /dev/null; then
+    true #Good
+  else
+    exit 128
+  fi
+else
+  # First try directly executing the possibilities
+  if clang-format-diff.py --help &> /dev/null < /dev/null; then
+    CLANG_FORMAT_DIFF=clang-format-diff.py
+  elif $REPO_ROOT/clang-format-diff.py --help &> /dev/null < /dev/null; then
+    CLANG_FORMAT_DIFF=$REPO_ROOT/clang-format-diff.py
+  else
+    # This probably means we need to directly invoke the interpreter.
+    # But first find clang-format-diff.py
+    if [ -f "$REPO_ROOT/clang-format-diff.py" ]; then
+      CFD_PATH="$REPO_ROOT/clang-format-diff.py"
+    elif which clang-format-diff.py &> /dev/null; then
+      CFD_PATH="$(which clang-format-diff.py)"
+    else
       echo "You didn't have clang-format-diff.py and/or clang-format available in your computer!"
       echo "You can download clang-format-diff.py by running: "
       echo "    curl --location http://goo.gl/iUW1u2 -o ${CLANG_FORMAT_DIFF}"
@@ -48,23 +62,11 @@ then
       echo "Then, move both files (i.e. ${CLANG_FORMAT_DIFF} and clang-format) to some directory within PATH=${PATH}"
       echo "and make sure ${CLANG_FORMAT_DIFF} is executable."
       exit 128
-  else
-    if [ -x ./clang-format-diff.py ]
-    then
-      PATH=$PATH:.
-    else
-      CLANG_FORMAT_DIFF="python ./clang-format-diff.py"
     fi
-  fi
-fi
-
-# Check argparse, a library that clang-format-diff.py requires.
-python 2>/dev/null << EOF
-import argparse
-EOF
-
-if [ "$?" != 0 ]
-then
+    # Check argparse pre-req on interpreter, or it will fail
+    if echo import argparse | ${PYTHON:-python3}; then
+      true # Good
+    else
       echo "To run clang-format-diff.py, we'll need the library "argparse" to be"
       echo "installed. You can try either of the follow ways to install it:"
       echo "  1. Manually download argparse: https://pypi.python.org/pypi/argparse"
@@ -72,6 +74,28 @@ then
       echo "  3. pip install argparse (if you have pip)"
       exit 129
     fi
+    # Unfortunately, some machines have a Python2 clang-format-diff.py
+    # installed but only a Python3 interpreter installed. Rather than trying
+    # different Python versions that might be installed, we can try migrating
+    # the code to Python3 if it looks like Python2
+    if grep -q "print '" "$CFD_PATH" && \
+       ${PYTHON:-python3} --version | grep -q 'ython 3'; then
+      if [ ! -f "$REPO_ROOT/.py3/clang-format-diff.py" ]; then
+        echo "Migrating $CFD_PATH to Python3 in a hidden file"
+        mkdir -p "$REPO_ROOT/.py3"
+        ${PYTHON:-python3} -m lib2to3 -w -n -o "$REPO_ROOT/.py3" "$CFD_PATH" > /dev/null || exit 128
+      fi
+      CFD_PATH="$REPO_ROOT/.py3/clang-format-diff.py"
+    fi
+    CLANG_FORMAT_DIFF="${PYTHON:-python3} $CFD_PATH"
+    # This had better work after all those checks
+    if $CLANG_FORMAT_DIFF --help >/dev/null < /dev/null; then
+      true #Good
+    else
+      exit 128
+    fi
+  fi
+fi
 
 # TODO(kailiu) following work is not complete since we still need to figure
 # out how to add the modified files done pre-commit hook to git's commit index.

tools/check_all_python.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 import glob
 

tools/db_crashtest.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 from __future__ import absolute_import, division, print_function, unicode_literals
 

tools/ldb_test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 from __future__ import absolute_import, division, print_function, unicode_literals
 

tools/write_stress_runner.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
 from __future__ import absolute_import, division, print_function, unicode_literals