Fixup interpreter constraints.

These were too narrow previously, we want to be able to use a 3.6 pex
on any 3.6 for example - with caveats that are out of scope for this PR.

build-support/bin/ci.sh

@@ -118,17 +118,11 @@ else
 fi
 export PY="${PY:-python${py_major_minor}}"
 
-# Also set PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS. We set this to the exact Python version
-# to resolve any potential ambiguity when multiple Python interpreters are discoverable, such as
-# Python 2.7.10 vs. 2.7.13. When running with Python 3, we must also set this constraint to ensure
-# all spawned subprocesses use Python 3 rather than the default of Python 2. This is in part
-# necessary to avoid the _Py_Dealloc error (#6985).
-py_major_minor_patch=$(${PY} -c 'import sys; print(".".join(map(str, sys.version_info[0:3])))')
-export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS:-['CPython==${py_major_minor_patch}']}"
+export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="['CPython==${py_major_minor}.*']"
 banner "Setting interpreter constraints to ${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS}"
 
 if [[ "${run_bootstrap:-false}" == "true" ]]; then
-  start_travis_section "Bootstrap" "Bootstrapping pants as a Python ${py_major_minor_patch} PEX"
+  start_travis_section "Bootstrap" "Bootstrapping pants as a Python ${py_major_minor} PEX"
   (
     if [[ "${run_bootstrap_clean:-false}" == "true" ]]; then
       ./build-support/python/clean.sh || die "Failed to clean before bootstrapping pants."

build-support/bin/release.sh

@@ -41,8 +41,7 @@ fi
 # to resolve any potential ambiguity when multiple Python interpreters are discoverable, such as
 # Python 2.7.13 vs. 2.7.15. We must also set this when running with Python 3 to ensure
 # that spawned subprocesses use Python 3.
-py_major_minor_patch=$(${PY} -c 'import sys; print(".".join(map(str, sys.version_info[0:3])))')
-export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS:-['CPython==${py_major_minor_patch}']}"
+export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="['CPython==${py_major_minor}.*']"
 
 function run_local_pants() {
   ${ROOT}/pants "$@"

pants

@@ -4,37 +4,37 @@
 
 REPO_ROOT=$(cd $(dirname "${BASH_SOURCE[0]}") && pwd -P)
 
-interpreter_constraints_sentinel_file_path='.python-interpreter-constraints'
+interpreter_id_sentinel_file_path='.python-interpreter-constraints'
 
-function clean_if_interpreter_constraints_changed() {
-  new_interpreter_constraints="$1"
+function clean_if_interpreter_changed() {
+  new_interpreter_id="$1"
 
   if [[ -n "${recursive_pants_shell_script_invocation:-}" ]]; then
     return 0
   fi
 
-  interpreter_constraints_file="${REPO_ROOT}/${interpreter_constraints_sentinel_file_path}"
+  interpreter_id_file="${REPO_ROOT}/${interpreter_id_sentinel_file_path}"
 
-  if [[ -f "${interpreter_constraints_file}" ]]; then
-    previous_interpreter_constraints="$(cat "${interpreter_constraints_file}")"
-    if [[ "${new_interpreter_constraints}" == "${previous_interpreter_constraints}" ]]; then
+  if [[ -f "${interpreter_id_file}" ]]; then
+    previous_interpreter_id="$(cat "${interpreter_id_file}")"
+    if [[ "${new_interpreter_id}" == "${previous_interpreter_id}" ]]; then
       return 0
     fi
   else
     cat >&2 <<EOF
-${interpreter_constraints_sentinel_file_path} not found in the buildroot.
+${interpreter_id_sentinel_file_path} not found in the buildroot.
 Forcing an initial clean-all.
 EOF
   fi
 
   export recursive_pants_shell_script_invocation='y'
   cat >&2 <<EOF
-Different interpreter constraints were set than were used in the previous Pants run.
-Clearing the cache and preparing a Python environment with these interpreter constraints:
-${new_interpreter_constraints}
+A different interpreter is being used than in the previous Pants run.
+Clearing the cache and preparing a Python environment with the new interpreter:
+${new_interpreter_id}
 EOF
   ./pants clean-all
-  echo "${new_interpreter_constraints}" > "${interpreter_constraints_file}"
+  echo "${new_interpreter_id}" > "${interpreter_id_file}"
   unset recursive_pants_shell_script_invocation
 }
 
@@ -94,18 +94,12 @@ source ${HERE}/build-support/bin/native/bootstrap_code.sh
 # Default to using Python 3 if not otherwise specified.
 export PY="${PY:-python3}"
 
-# Set interpreter constraints to exactly match the interpreter used for the venv, if not already set.
-# Note that $PY only impacts which virtualenv we use for the parent Pants process; we must also set
-# PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS to constrain spawned subprocesses such as tests. Without
-# any interpreter constraints, when PY is set to Python 3 we get the _Py_Dealloc exception (#6985) as
-# Pants will try to use Python 2 for subprocesses. Without setting minor version constraints, when using Python 3
-# we could end up using a different Python minor version for subprocesses than we do for Pants.
-py_major_minor_patch=$(${PY} -c 'import sys; print(".".join(map(str, sys.version_info[0:3])))')
-export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS:-['CPython==${py_major_minor_patch}']}"
-
 # We can currently assume the CI environment does not switch python versions within a shard.
 if [[ "${ONLY_USING_SINGLE_PYTHON_VERSION:-false}" != 'true' ]]; then
-  clean_if_interpreter_constraints_changed "${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS}"
+  interpreter_id="$(
+    ${PY} -c 'import os, sys; print("{}\n{}".format(sys.executable, sys.version))'
+  )"
+  clean_if_interpreter_changed "${interpreter_id}"
 fi
 
 PANTS_EXE="${HERE}/src/python/pants/bin/pants_loader.py"

pants2

@@ -8,9 +8,4 @@ REPO_ROOT=$(cd $(dirname "${BASH_SOURCE[0]}") && pwd -P)
 
 export PY="${PY:-python2.7}"
 
-# Allow spawned subprocesses, such as unit tests, to execute with either Python 2 and Python 3.
-# So long as the target does not have a compatibility constraint that requires only Python 3, the
-# interpreter selection will default to using Python 2 as this is the minimum acceptable interpreter.
-export PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS="${PANTS_PYTHON_SETUP_INTERPRETER_CONSTRAINTS:-['CPython>=2.7,<3','CPython>=3.6,<4']}"
-
 exec ${REPO_ROOT}/pants "$@"