Automatically use latest patch for each Swift release in CI (#739)

Author: kmahar

.evergreen/config.yml

@@ -330,6 +330,26 @@ functions:
           done
 
   "install swift":
+    - command: shell.exec
+      params:
+        working_dir: "src"
+        script: |
+          set -o xtrace
+          set -o errexit
+
+          if [ "${SWIFT_MINOR_VERSION}" = "main-snapshot" ]; then
+              export SWIFT_VERSION="${SWIFT_MINOR_VERSION}"
+          else
+              # otherwise, find the latest patch release for the specified version
+              ${PYTHON} -m virtualenv ./requests-env
+              ./requests-env/${VENV_BIN_DIR}/python3 -m pip install requests
+              export SWIFT_VERSION="$(./requests-env/${VENV_BIN_DIR}/python3 .evergreen/get_latest_swift_patch.py ${SWIFT_MINOR_VERSION})"
+          fi
+          echo "SWIFT_VERSION: $SWIFT_VERSION" > swift-version.yml
+          cat swift-version.yml
+    - command: expansions.update
+      params:
+        file: src/swift-version.yml
     - command: shell.exec
       params:
         working_dir: "src"
@@ -1094,27 +1114,27 @@ axes:
       - id: "5.1"
         display_name: "Swift 5.1"
         variables:
-           SWIFT_VERSION: "5.1.5"
+           SWIFT_MINOR_VERSION: "5.1"
       - id: "5.2"
         display_name: "Swift 5.2"
         variables:
-           SWIFT_VERSION: "5.2.5"
+           SWIFT_MINOR_VERSION: "5.2"
       - id: "5.3"
         display_name: "Swift 5.3"
         variables:
-          SWIFT_VERSION: "5.3.3"      
+          SWIFT_MINOR_VERSION: "5.3"      
       - id: "5.4"
         display_name: "Swift 5.4"
         variables:
-          SWIFT_VERSION: "5.4.2"
+          SWIFT_MINOR_VERSION: "5.4"
       - id: "5.5"
         display_name: "Swift 5.5"
         variables:
-          SWIFT_VERSION: "5.5.1"
+          SWIFT_MINOR_VERSION: "5.5"
       - id: "5.6-dev"
         display_name: "Swift 5.6-dev"
         variables:
-          SWIFT_VERSION: "main-snapshot"
+          SWIFT_MINOR_VERSION: "main-snapshot"
 
   - id: ssl-auth
     display_name: SSL and Auth

.evergreen/get_latest_swift_patch.py

@@ -0,0 +1,34 @@
+import re
+import requests
+import sys
+
+# This script accepts a version number in the form "x.y" as an argument. It will query the Swift Github
+# repo for releases and find the latest x.y.z patch release if available, and print out the matching tag.
+
+if len(sys.argv) != 2:
+    print("Expected 1 argument, but got: {}".format(sys.argv[1:]))
+    exit(1)
+
+version = sys.argv[1]
+components = version.split('.')
+if len(components) != 2:
+    print("Expected version number in form x.y, got {}".format(version))
+    exit(1)
+
+major = components[0]
+minor = components[1]
+
+version_regex = '^swift-({}\.{}(\.(\d+))?)-RELEASE$'.format(major, minor)
+
+release_data = requests.get('https://api.github.com/repos/apple/swift/releases').json()
+tag_names = map(lambda release: release['tag_name'], release_data)
+
+# find tags matching the specified regexes
+matches = filter(lambda match: match is not None, map(lambda tag: re.match(version_regex, tag), tag_names))
+
+# sort matches by their patch versions. patch versions of 0 are omitted so substitute 0 when the group is None.
+sorted_matches = sorted(matches, key=lambda match: int(match.group(2)[1:]) if match.group(2) is not None else 0, reverse=True)
+
+# map to the first match group which contains the full version number.
+sorted_version_numbers = map(lambda match: match.group(1), sorted_matches)
+print(next(sorted_version_numbers))