Install an explicit version of wheel rather than latest (heroku#1007)

Before:
- if `wheel` was not already installed, then `get-pip.py` would
  automatically install the latest version on PyPI, which is `0.34.2`
  (or `0.33.6` for Python 3.4).
- if `wheel` was already installed, then it was left unchanged
  regardless of the version installed.

Now:
- if `wheel` is not already installed, then the same versions will be
  installed as before, except these versions are pinned and will now not
  change unexpectedly after future `wheel` releases.
- if `wheel` is already installed, then it's upgraded/downgraded to the
  target version as needed.

Partly addresses heroku#1000, though this change only helps builds where the
pip/setuptools/wheel install flow is triggered (currently only new apps
or ones where Python was purged or pip was not the correct version).

Since the wheel version is now known, it's output to the build log to
ease debugging and for parity with pip/setuptools.

The rest of heroku#1000 will be fixed in later commits.

CHANGELOG.md

@@ -2,7 +2,8 @@
 
 # Master
 
-- Output the installed version of pip and setuptools in the build log (#1007).
+- Install an explicit version of wheel rather than the latest release at the time (#1007).
+- Output the installed version of pip, setuptools and wheel in the build log (#1007).
 - Install setuptools from PyPI rather than a vendored copy (#1007).
 - Reduce the number of environment variables exposed to `bin/{pre,post}_compile` and other subprocesses (#1011)
 

bin/steps/python

@@ -138,10 +138,12 @@ fi
 
 PIP_VERSION='20.0.2'
 SETUPTOOLS_VERSION='39.0.1'
+WHEEL_VERSION='0.34.2'
 
 if [[ "${PYTHON_VERSION}" == ${PY34}* ]]; then
-  # Python 3.4 support was dropped in pip 19.2+.
+  # Python 3.4 support was dropped in pip 19.2+ and wheel 0.34.0+.
   PIP_VERSION='19.1.1'
+  WHEEL_VERSION='0.33.6'
 fi
 
 if [[ -f "$BUILD_DIR/Pipfile" ]]; then
@@ -163,13 +165,13 @@ fi
 # If a new Python has been installed or Pip isn't up to date:
 if [ "$FRESH_PYTHON" ] || [[ ! $(pip --version) == *${PIP_VERSION}* ]]; then
 
-  puts-step "Installing pip ${PIP_VERSION} and setuptools ${SETUPTOOLS_VERSION}"
+  puts-step "Installing pip ${PIP_VERSION}, setuptools ${SETUPTOOLS_VERSION} and wheel ${WHEEL_VERSION}"
 
   # Remove old installations.
   rm -fr /app/.heroku/python/lib/python*/site-packages/pip-*
   rm -fr /app/.heroku/python/lib/python*/site-packages/setuptools-*
 
-  /app/.heroku/python/bin/python "$GETPIP_PY" pip=="${PIP_VERSION}" "setuptools==${SETUPTOOLS_VERSION}" &> /dev/null
+  /app/.heroku/python/bin/python "$GETPIP_PY" pip=="${PIP_VERSION}" "setuptools==${SETUPTOOLS_VERSION}" "wheel==${WHEEL_VERSION}" &> /dev/null
 fi
 
 set -e

test/run-features

@@ -44,7 +44,7 @@ testStandardRequirements() {
 
 testPipenv() {
   compile "pipenv"
-  assertCaptured "Installing pip 9.0.2 and setuptools 39.0.1"
+  assertCaptured "Installing pip 9.0.2, setuptools 39.0.1 and wheel 0.34.2"
   assertCapturedSuccess
 }
 

test/run-versions

@@ -9,7 +9,7 @@ testPythonDefault() {
   compile "pythonDefault"
   assertCaptured $DEFAULT_PYTHON_VERSION
   assertNotCaptured "security update"
-  assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+  assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
   assertCaptured "Installing SQLite3"
   assertCapturedSuccess
 }
@@ -25,7 +25,7 @@ testPython2() {
       assertNotCaptured "python-2-7-eol-faq";
     fi
     assertNotCaptured "security update"
-    assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+    assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
     assertCaptured "Installing SQLite3"
     assertCapturedSuccess
 }
@@ -53,7 +53,7 @@ testPython3_4() {
   compile "python3_4"
   assertCaptured $LATEST_34
   assertNotCaptured "security update"
-  assertCaptured "Installing pip 19.1.1 and setuptools 39.0.1"
+  assertCaptured "Installing pip 19.1.1, setuptools 39.0.1 and wheel 0.33.6"
   # if cedar 14 and legacy binaries, fail. if cedar 14 and staging, succeed.
   if [[ ! -n $USE_STAGING_BINARIES ]] && [[ $STACK == "cedar-14" ]]; then
       assertCapturedError
@@ -89,7 +89,7 @@ testPython3_5() {
   compile "python3_5"
   assertCaptured $LATEST_35
   assertNotCaptured "security update"
-  assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+  assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
   assertCaptured "Installing SQLite3"
   assertCapturedSuccess
 }
@@ -112,7 +112,7 @@ testPython3_6() {
   compile "python3_6"
   assertCaptured $LATEST_36
   assertNotCaptured "security update"
-  assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+  assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
   assertCaptured "Installing SQLite3"
   assertCapturedSuccess
 }
@@ -139,7 +139,7 @@ testPython3_7() {
   else
     assertNotCaptured "security update"
     assertCaptured $LATEST_37
-    assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+    assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
     assertCaptured "Installing SQLite3"
     assertCapturedSuccess
   fi
@@ -183,7 +183,7 @@ testPython3_8() {
   else
     assertNotCaptured "security update"
     assertCaptured $LATEST_38
-    assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+    assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
     assertCaptured "Installing SQLite3"
     assertCapturedSuccess
   fi
@@ -202,7 +202,7 @@ testPypy3_6() {
   else
     assertCaptured "Installing pypy"
     assertCaptured "$PYPY_36"
-    assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+    assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
     assertCapturedSuccess
   fi
 }
@@ -214,7 +214,7 @@ testPypy2_7() {
   else
     assertCaptured "Installing pypy"
     assertCaptured "$PYPY_27"
-    assertCaptured "Installing pip 20.0.2 and setuptools 39.0.1"
+    assertCaptured "Installing pip 20.0.2, setuptools 39.0.1 and wheel 0.34.2"
     assertCapturedSuccess
   fi
 }