Tests: Introduce lit substitutions for target triples corresponding to Swift releases.

For example, tests can now invoke the frontend passing `-target %target-swift-abi-5.3-triple` to compile with a deployment target coresponding to the Swift 5.3 release on the test `run_os`.

Author: tshortli

test/lit.cfg

@@ -426,15 +426,55 @@ swift_version = lit_config.params.get('swift-version',
 lit_config.note('Compiling with -swift-version ' + swift_version)
 config.swift_test_options = '-swift-version ' + swift_version
 
-# Load availability macros for known stdlib releases.
+# Loads availability macros for known stdlib releases.
 def load_availability_macros():
     path = os.path.join(os.path.dirname(__file__), "../utils/availability-macros.def")
     lines = open(path, 'r').read().splitlines()
     pattern = re.compile(r"\s*(#.*)?")
     return filter(lambda l: pattern.fullmatch(l) is None, lines)
+
+# Returns a tuple with the Swift ABI version (e.g. '5.0') and the corresponding
+# target triple (e.g. 'arm64-apple-ios12.2')
+def availability_macro_to_swift_abi_target_triple(macro):
+    # Use a regex and split to pull out the components of an availability macro
+    # that is formatted like this:
+    #    SwiftStdlib 5.0:macOS 10.14.4, iOS 12.2, watchOS 5.2, tvOS 12.2
+    matches = re.search(r'^[\s]*SwiftStdlib[\s]+([0-9\.]+)[\s]*:[\s]*(.+)', macro)
+    stdlib_vers = matches.group(1)
+    vers_by_platform = {}
+    for platform_vers in matches.group(2).split(', '):
+        components = platform_vers.split(' ')
+        vers_by_platform[components[0]] = components[1]
+
+    platform = {
+        'macosx': 'macOS',
+        'ios': 'iOS',
+        'maccatalyst': 'iOS',
+        'tvos': 'tvOS',
+        'watchos': 'watchOS'
+    }.get(run_os)
+
+    if platform is None:
+        return stdlib_vers, config.variant_triple
+
+    os_vers = vers_by_platform.get(platform)
+    if os_vers is None:
+        return stdlib_vers, config.variant_triple
+
+    if run_os == 'maccatalyst':
+        return stdlib_vers, '%s-%s-ios%s-macabi' % (run_cpu, run_vendor, os_vers)
+
+    return stdlib_vers, '%s-%s-%s%s%s' % (run_cpu, run_vendor, run_os,
+                                          os_vers, run_environment)
+
+# Add availability macros to the default frontend/driver flags and create target
+# triple substitutions for each stdlib version.
 for macro in load_availability_macros():
     config.swift_frontend_test_options += " -define-availability '{0}'".format(macro)
     config.swift_driver_test_options += " -Xfrontend -define-availability -Xfrontend '{0}'".format(macro)
+    (stdlib_vers, triple) = availability_macro_to_swift_abi_target_triple(macro)
+    config.substitutions.append(('%target-swift-abi-{}-triple'.format(stdlib_vers), triple))
+
 
 differentiable_programming = lit_config.params.get('differentiable_programming', None)
 if differentiable_programming is not None: