feat(composite-build): add gradle composite build (#4710)

.gitignore

@@ -64,4 +64,7 @@ codegen/*/bin
 benchmark/size/raw
 
 etc/
-temp/
+temp/
+
+# Gradle composite build properties
+codegen/local.properties

CONTRIBUTING.md

@@ -126,6 +126,22 @@ lerna run build --scope [package name] --include-dependencies
 
 You don't need to run this command if the dependency packages are not changed.
 
+## Gradle Composite Build
+
+The `aws-sdk-js-v3` repository uses Gradle as a build tool and has Gradle based dependencies such as `smithy` and `smithy-typescript`.
+To improve development experience when making changes to the dependencies locally, we can
+use the [Gradle composite build feature](https://docs.gradle.org/current/userguide/composite_builds.html),
+which allows picking up any local changes from dependencies automatically and rebuilding them when `aws-sdk-js-v3` is rebuilt.
+
+This also makes IDE integration more pleasant, as Intellij IDEA will open the included projects as modules when the Gradle build is imported.
+
+In order to utilise this feature, create a file `local.properties` in the `codegen` directory with the following content:
+
+```
+smithy=/Volumes/workplace/smithy
+smithy-typescript=/Volumes/workplace/smithy-typescript
+```
+
 ## Build caching
 
 Build caching is optionally available via Turborepo. See `turbo.json`.

codegen/settings.gradle.kts

@@ -13,8 +13,25 @@
  * permissions and limitations under the License.
  */
 
+import java.io.FileInputStream
+import java.nio.charset.StandardCharsets.UTF_8
+
 rootProject.name = "codegen"
 include(":smithy-aws-typescript-codegen")
 include(":sdk-codegen")
 include(":protocol-test-codegen")
 include(":generic-client-test-codegen")
+
+file(
+    java.nio.file.Paths.get(rootProject.projectDir.absolutePath, "local.properties"))
+    .takeIf { it.isFile }?.let { f ->
+        java.util.Properties().apply { load(java.io.InputStreamReader(FileInputStream(f), UTF_8)) }
+    }?.run {
+        listOf("smithy-typescript", "smithy")
+            .map { it to getProperty(it) }
+            .filterNot { it.second.isNullOrEmpty() }
+            .onEach { println("Found property `${it.first}`: ${it.second}") }
+            .map { file(it.second) }
+            .filter { it.isDirectory }
+            .forEach { includeBuild(it.absolutePath) }
+    }