Remove Python2 fallback and only advertise Python3 in the doc

[serge-sans-paille]

Summary

No change made at the .py level, only change the cmake and doc parts. Advertise Python3.6 in the doc, as it's the oldest Python3 version still maintained, as of https://www.python.org/downloads/

[serge-sans-paille]

Up? I'd like to land that one this week if possible.

[dblaikie]

Sounds OK - probably worth an email to llvm-dev to at least notify, if not seek buy-in/broader sign-off. And please watch the bots carefully once this is committed.

[serge-sans-paille]

Commited as of 5e31e226b5b2b682607a6578ff5adb33daf4fe39, I totally messed the differential revision :-)

clang/CMakeLists.txt

if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   include_directories("${LLVM_BINARY_DIR}/include" "${LLVM_MAIN_INCLUDE_DIR}")
   link_directories("${LLVM_LIBRARY_DIR}")
 
   set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin )
   set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
   set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
 
   if(LLVM_INCLUDE_TESTS)
-    find_package(Python3 COMPONENTS Interpreter)
-    if(NOT Python3_Interpreter_FOUND)
-      message(WARNING "Python3 not found, using python2 as a fallback")
-      find_package(Python2 COMPONENTS Interpreter REQUIRED)
-      if(Python2_VERSION VERSION_LESS 2.7)
-        message(SEND_ERROR "Python 2.7 or newer is required")
-      endif()
-
-      # Treat python2 as python3
-      add_executable(Python3::Interpreter IMPORTED)
-      set_target_properties(Python3::Interpreter PROPERTIES
-        IMPORTED_LOCATION ${Python2_EXECUTABLE})
-      set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
-    endif()
+    find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
     # Check prebuilt llvm/utils.
     if(EXISTS ${LLVM_TOOLS_BINARY_DIR}/FileCheck${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/count${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/not${CMAKE_EXECUTABLE_SUFFIX})
       set(LLVM_UTILS_PROVIDED ON)
     endif()
 

clang/tools/scan-build-py/README.md

 
 - It has been tested on FreeBSD, GNU/Linux and OS X.
 - Prepared to work on windows, but need help to make it.
 
 
 Prerequisites
 -------------
 
-1. **python** interpreter (version 2.7, 3.2, 3.3, 3.4, 3.5).
+1. **python** interpreter (version 3.6 or later).
 
 
 How to use
 ----------
 
 To run the Clang static analyzer against a project goes like this:
 
     $ scan-build <your build command>

clang/tools/scan-build/bin/set-xcode-analyzer

 #!/usr/bin/python
 
 # [PR 11661] Note that we hardwire to /usr/bin/python because we
 # want to the use the system version of Python on Mac OS X.
 # This one has the scripting bridge enabled.
 
 import sys
-if sys.version_info < (2, 7):
-    print "set-xcode-analyzer requires Python 2.7 or later"
+if sys.version_info < (3, 6):
+    print "set-xcode-analyzer requires Python 3.6 or later"
     sys.exit(1)
 
 import os
 import subprocess
 import re
 import tempfile
 import shutil
 import stat

lld/CMakeLists.txt

if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
 
   include(AddLLVM)
   include(TableGen)
   include(HandleLLVMOptions)
   include(CheckAtomic)
 
   if(LLVM_INCLUDE_TESTS)
-    find_package(Python3 COMPONENTS Interpreter)
-    if(NOT Python3_Interpreter_FOUND)
-      message(WARNING "Python3 not found, using python2 as a fallback")
-      find_package(Python2 COMPONENTS Interpreter REQUIRED)
-      if(Python2_VERSION VERSION_LESS 2.7)
-        message(SEND_ERROR "Python 2.7 or newer is required")
-      endif()
-
-      # Treat python2 as python3
-      add_executable(Python3::Interpreter IMPORTED)
-      set_target_properties(Python3::Interpreter PROPERTIES
-        IMPORTED_LOCATION ${Python2_EXECUTABLE})
-      set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
-    endif()
+    find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
     # Check prebuilt llvm/utils.
     if(EXISTS ${LLVM_TOOLS_BINARY_DIR}/FileCheck${CMAKE_EXECUTABLE_SUFFIX}
         AND EXISTS ${LLVM_TOOLS_BINARY_DIR}/not${CMAKE_EXECUTABLE_SUFFIX})
       set(LLVM_UTILS_PROVIDED ON)
     endif()
 
     if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py)

lldb/docs/resources/build.rst

 Depending on your platform and package manager, one might run any of the
 commands below.
 
 ::
 
   > yum install libedit-devel libxml2-devel ncurses-devel python-devel swig
   > sudo apt-get install build-essential subversion swig python3-dev libedit-dev libncurses5-dev
   > pkg install swig python
-  > pkgin install swig python27 cmake ninja-build
+  > pkgin install swig python36 cmake ninja-build
   > brew install swig cmake ninja
 
 Note that there's an `incompatibility
 <https://github.com/swig/swig/issues/1321>` between Python version 3.7 and later
 and swig versions older than 4.0.0 which makes builds of LLDB using debug
 versions of python unusable. This primarily affects Windows, as debug builds of
 LLDB must use debug python as well.
 

llvm/CMakeLists.txt

 endif()
 option(LLVM_ENABLE_PLUGINS "Enable plugin support" ${LLVM_ENABLE_PLUGINS_default})
 
 set(ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER FALSE CACHE BOOL
   "Enable the experimental new pass manager by default.")
 
 include(HandleLLVMOptions)
 
-find_package(Python3 COMPONENTS Interpreter)
-if(NOT Python3_Interpreter_FOUND)
-  message(WARNING "Python3 not found, using python2 as a fallback")
-  find_package(Python2 COMPONENTS Interpreter REQUIRED)
-  if(Python2_VERSION VERSION_LESS 2.7)
-    message(SEND_ERROR "Python 2.7 or newer is required")
-  endif()
-
-  # Treat python2 as python3
-  add_executable(Python3::Interpreter IMPORTED)
-  set_target_properties(Python3::Interpreter PROPERTIES
-    IMPORTED_LOCATION ${Python2_EXECUTABLE})
-  set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
-endif()
+find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
 ######
 
 # Configure all of the various header file fragments LLVM uses which depend on
 # configuration variables.
 set(LLVM_ENUM_TARGETS "")
 set(LLVM_ENUM_ASM_PRINTERS "")
 set(LLVM_ENUM_ASM_PARSERS "")

llvm/docs/GettingStarted.rst

 "known to work" versions of the package. The Notes column describes how LLVM
 uses the package and provides other details.
 
 =========================================================== ============ ==========================================
 Package                                                     Version      Notes
 =========================================================== ============ ==========================================
 `CMake <http://cmake.org/>`__                               >=3.13.4     Makefile/workspace generator
 `GCC <http://gcc.gnu.org/>`_                                >=5.1.0      C/C++ compiler\ :sup:`1`
-`python <http://www.python.org/>`_                          >=2.7        Automated test suite\ :sup:`2`
+`python <http://www.python.org/>`_                          >=3.6        Automated test suite\ :sup:`2`
 `zlib <http://zlib.net>`_                                   >=1.2.3.4    Compression library\ :sup:`3`
 `GNU Make <http://savannah.gnu.org/projects/make>`_         3.79, 3.79.1 Makefile/build processor\ :sup:`4`
 =========================================================== ============ ==========================================
 
 .. note::
 
    #. Only the C and C++ languages are needed so there's no need to build the
       other languages for LLVM's purposes. See `below` for specific version

llvm/docs/GettingStartedVS.rst

 Software
 --------
 You will need Visual Studio 2017 or higher, with the latest Update installed.
 
 You will also need the `CMake <http://www.cmake.org/>`_ build system since it
 generates the project files you will use to build with.
 
 If you would like to run the LLVM tests you will need `Python
-<http://www.python.org/>`_. Version 2.7 and newer are known to work. You will
+<http://www.python.org/>`_. Version 3.6 and newer are known to work. You will
 need `GnuWin32 <http://gnuwin32.sourceforge.net/>`_ tools, too.
 
 Do not install the LLVM directory tree into a path containing spaces (e.g.
 ``C:\Documents and Settings\...``) as the configure step will fail.
 
 
 Getting Started
 ===============

llvm/docs/HowToBuildOnARM.rst

cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release \
                          -DLLVM_TARGETS_TO_BUILD="ARM;X86;AArch64"
 
    Other options you can use are:
 
    .. code-block:: bash
 
      Use Ninja instead of Make: "-G Ninja"
      Build with assertions on: "-DLLVM_ENABLE_ASSERTIONS=True"
-     Force Python2: "-DPYTHON_EXECUTABLE=/usr/bin/python2"
      Local (non-sudo) install path: "-DCMAKE_INSTALL_PREFIX=$HOME/llvm/install"
      CPU flags: "DCMAKE_C_FLAGS=-mcpu=cortex-a15" (same for CXX_FLAGS)
 
    After that, just typing ``make -jN`` or ``ninja`` will build everything.
    ``make -jN check-all`` or ``ninja check-all`` will run all compiler tests. For
    running the test suite, please refer to :doc:`TestingGuide`.
 
 #. If you are building LLVM/Clang on an ARM board with 1G of memory or less,

llvm/docs/TestingGuide.rst

 infrastructure. It documents the structure of the LLVM testing
 infrastructure, the tools needed to use it, and how to add and run
 tests.
 
 Requirements
 ============
 
 In order to use the LLVM testing infrastructure, you will need all of the
-software required to build LLVM, as well as `Python <http://python.org>`_ 2.7 or
+software required to build LLVM, as well as `Python <http://python.org>`_ 3.6 or
 later.
 
 LLVM Testing Infrastructure Organization
 ========================================
 
 The LLVM testing infrastructure contains three major categories of tests:
 unit tests, regression tests and whole programs. The unit tests and regression
 tests are contained inside the LLVM repository itself under ``llvm/unittests``