Add support for Python 3.9.0 (#1090)

https://pythoninsider.blogspot.com/2020/10/python-390-is-now-available-and-you-can.html
https://www.python.org/downloads/release/python-390/
https://docs.python.org/release/3.9.0/whatsnew/3.9.html

Binaries generated using:

```
make deploy-runtimes RUNTIMES='python-3.9.0' STACKS='heroku-16 heroku-18' ENV_FILE=...
```

Closes @W-7791272@.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Python 3.9.0 is now available (CPython) (#1090).
 - Migrate from the `lang-python` S3 bucket to `heroku-buildpack-python` (#1089).
 - Remove `vendor/shunit2` (#1086).
 - Replace `BUILDPACK_VENDOR_URL` and `USE_STAGING_BINARIES` with `BUILDPACK_S3_BASE_URL` (#1085).

README.md

@@ -62,6 +62,7 @@ Specify a Python Runtime
 
 Supported runtime options include:
 
+- `python-3.9.0`
 - `python-3.8.6`
 - `python-3.7.9`
 - `python-3.6.12`

bin/compile

@@ -57,6 +57,7 @@ export S3_BASE_URL
 source "$BIN_DIR/default_pythons"
 
 # Supported Python Branches
+PY39="python-3.9"
 PY38="python-3.8"
 PY37="python-3.7"
 PY36="python-3.6"

bin/default_pythons

@@ -6,6 +6,7 @@
 # shellcheck disable=2034
 
 DEFAULT_PYTHON_VERSION="python-3.6.12"
+LATEST_39="python-3.9.0"
 LATEST_38="python-3.8.6"
 LATEST_37="python-3.7.9"
 LATEST_36="python-3.6.12"

bin/steps/pipenv-python-version

@@ -30,6 +30,9 @@ if [[ -f $BUILD_DIR/Pipfile ]]; then
                 if [ "$PYTHON" = 3.8 ]; then
                     echo "$LATEST_38" > "$BUILD_DIR/runtime.txt"
                 fi
+                if [ "$PYTHON" = 3.9 ]; then
+                    echo "$LATEST_39" > "$BUILD_DIR/runtime.txt"
+                fi
             fi
 
 

bin/steps/python

@@ -16,6 +16,12 @@ PYTHON_2_EOL_UPDATE="Python 2 has reached it's community EOL. Upgrade your Pytho
 
 # check if runtime exists
 if curl --output /dev/null --silent --head --fail "$VENDORED_PYTHON"; then
+  if [[ "$PYTHON_VERSION" == $PY39* ]]; then
+    if [ "$PYTHON_VERSION" != "$LATEST_39" ]; then
+      puts-warn "$SECURITY_UPDATE" "$LATEST_39"
+      echo "       Learn More: https://devcenter.heroku.com/articles/python-runtimes"
+    fi
+  fi
   if [[ "$PYTHON_VERSION" == $PY38* ]]; then
     # do things to alert the user of security release available
     if [ "$PYTHON_VERSION" != "$LATEST_38" ]; then

builds/runtimes/python-3.9.0

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Build Path: /app/.heroku/python/
+
+source $(dirname $0)/python3

test/fixtures/python3_9/runtime.txt

@@ -0,0 +1 @@
+python-3.9.0

test/fixtures/python3_9_warn/runtime.txt

@@ -0,0 +1 @@
+python-3.9.0

test/run-versions

@@ -140,6 +140,34 @@ testPython3_8_warn() {
   fi
 }
 
+testPython3_9() {
+  # Cedar-14 is EOL, so we're not building new major Python versions for it.
+  if [[ "${STACK}" = "cedar-14" ]]; then
+    return
+  fi
+  compile "python3_9"
+  assertNotCaptured "security update"
+  assertCaptured $LATEST_39
+  assertCaptured "Installing pip 20.1.1, setuptools 47.1.1 and wheel 0.34.2"
+  assertCaptured "Installing SQLite3"
+  assertCapturedSuccess
+}
+
+testPython3_9_warn() {
+  # Cedar-14 is EOL, so we're not building new major Python versions for it.
+  if [[ "${STACK}" = "cedar-14" ]]; then
+    return
+  fi
+  # Can't test the version warning until there is at least one old version of Python 3.9.
+  if [[ "${LATEST_39}" = "python-3.9.0" ]]; then
+    return
+  fi
+  compile "python3_9_warn"
+  assertCaptured "python-3.9.0"
+  assertCaptured "security update!"
+  assertCapturedSuccess
+}
+
 testPythonVersionInvalid() {
   compile "python_version_invalid"
   assertCaptured "Requested runtime (python-3.8.99) is not available for this stack"