Add script to list transitive dependencies (apple#340)

See apple/swift-nio#2082

scripts/build_podspec.sh

@@ -88,7 +88,7 @@ for target in "${targets[@]}"; do
     else
       dependencies+=( "${newline}  s.dependency '$raw_dependency', '>= $nio_version', '< $next_major_version'" )
     fi
-  done < <("${here}/list_topsorted_dependencies.sh" -d "${target#Swift}" | sed 's/^NIO/SwiftNIO/')
+  done < <("${here}/list_transitive_dependencies.py" "${target#Swift}" | sed 's/^NIO/SwiftNIO/')
 
   cat > "${tmpdir}/${target}.podspec" <<- EOF
 Pod::Spec.new do |s|
@@ -114,8 +114,8 @@ Pod::Spec.new do |s|
 end
 EOF
 
-  pod repo update # last chance of getting the latest versions of previous pushed pods
   if $upload; then
+    pod repo update # last chance of getting the latest versions of previous pushed pods
     echo "Uploading ${tmpdir}/${target}.podspec"
     pod trunk push "${tmpdir}/${target}.podspec" --synchronous
   fi

scripts/list_transitive_dependencies.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftNIO open source project
+##
+## Copyright (c) 2022 Apple Inc. and the SwiftNIO project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of SwiftNIO project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+import json
+import sys
+import subprocess
+import tempfile
+
+
+def dump_package(path):
+    output = subprocess.check_output(["swift", "package", "dump-package"], cwd=path)
+    parsed = json.loads(output)
+    return parsed
+
+
+def clone_package(name, url, tag, directory):
+    path = directory + "/" + name
+    command = ["git", "clone", "--depth", "1", "--branch", tag, url, path]
+    subprocess.check_output(command, stderr=subprocess.DEVNULL)
+    return path
+
+
+class TransitiveDependencyResolver(object):
+    def __init__(self, temp_dir):
+        # Temporary directory to clone dependencies to.
+        self._temp_dir = temp_dir
+        # Cache of package dumps keyed by name.
+        self._packages = {}
+
+        package = dump_package(".")
+        self._root_package = package["name"]
+        self._packages[self._root_package] = package
+
+    def find_transitive_depenencies(self, module_name):
+        # All transitive dependencies. This doubles as the 'visited' modules so
+        # we need to remove the target module once we're done.
+        dependencies = set()
+
+        # Start from the root package.
+        self._find_transitive_dependencies(
+            module_name, self._packages[self._root_package], dependencies
+        )
+
+        dependencies.remove(module_name)
+        return dependencies
+
+    def _find_transitive_dependencies(self, module_name, package, dependencies):
+        if module_name in dependencies:
+            # Already visited
+            return
+
+        dependencies.add(module_name)
+        # Visit all dependencies of this module.
+        for target in package["targets"]:
+            if target["name"] != module_name:
+                # Not a target we care about.
+                continue
+
+            for dependency in target["dependencies"]:
+                if "byName" in dependency:
+                    # Target dependency from the package currently being
+                    # searched.
+                    self._find_transitive_dependencies(
+                        dependency["byName"][0], package, dependencies
+                    )
+                elif "product" in dependency:
+                    # Dependency is from another package.
+                    dependency_name = dependency["product"][0]
+                    package_name = dependency["product"][1]
+                    self._ensure_package_is_cached(package, package_name)
+                    self._find_transitive_dependencies(
+                        dependency_name, self._packages[package_name], dependencies
+                    )
+
+    def _ensure_package_is_cached(self, package, package_name):
+        if package_name in self._packages:
+            return
+
+        # Find the package dependency with the right name.
+        for package_dependency in package["dependencies"]:
+            dependency = package_dependency["sourceControl"][0]
+
+            is_right_package = (
+                dependency["identity"] == package_name
+                or dependency.get("nameForTargetDependencyResolutionOnly")
+                == package_name
+            )
+
+            if not is_right_package:
+                continue
+
+            url = dependency["location"]["remote"][0]
+            version = dependency["requirement"]["range"][0]["lowerBound"]
+            # Path to cloned package.
+            path = clone_package(package_name, url, version, self._temp_dir)
+            self._packages[package_name] = dump_package(path)
+            return
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        print("USAGE: {} MODULE".format(sys.argv[0]))
+        exit(1)
+
+    with tempfile.TemporaryDirectory() as temp_dir:
+        resolver = TransitiveDependencyResolver(temp_dir)
+        for dependency in resolver.find_transitive_depenencies(sys.argv[1]):
+            print(dependency)