From fe3f7feae446bc4345c2842d5e4629d98b7e1e33 Mon Sep 17 00:00:00 2001
From: Marco Pennekamp <marco.pennekamp@jetbrains.com>
Date: Thu, 4 May 2023 21:32:35 +0200
Subject: [PATCH] [AA] KT-58257 Introduce `KotlinModuleDependentsProvider`

- Event-based session invalidation requires knowledge about the
  dependents of a `KtModule`. This is because, when the session for a
  module is invalidated, all sessions for modules which depend on that
  module, directly or indirectly, must also be invalidated.
- Note that the approach with modification trackers relied on module
  dependencies. Events have an opposite flow of information compared to
  modification trackers: Modification trackers request whether a change
  occurred, while events publish that a change occurred. Thus, the
  modules which need to be incorporated into the invalidation dynamic
  are also flipped: dependents instead of dependencies.
- `KotlinModuleDependentsProvider` is designed to work generally. It can
  be used for purposes beyond session invalidation.
---
 .../KotlinModuleDependentsProvider.kt         | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KotlinModuleDependentsProvider.kt

diff --git a/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KotlinModuleDependentsProvider.kt b/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KotlinModuleDependentsProvider.kt
new file mode 100644
index 00000000000..828658ad42e
--- /dev/null
+++ b/analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KotlinModuleDependentsProvider.kt
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.analysis.project.structure
+
+import com.intellij.openapi.project.Project
+
+/**
+ * [KotlinModuleDependentsProvider] provides dependents for a [KtModule], which are modules that depend on the [KtModule].
+ *
+ * Implementations of this provider should ensure that results are provided in reasonable time, for example by caching results, as its
+ * functions may be called frequently.
+ */
+public abstract class KotlinModuleDependentsProvider {
+    /**
+     * Returns all direct dependents of [module], excluding [module] if it depends on itself.
+     */
+    public abstract fun getDirectDependents(module: KtModule): Set<KtModule>
+
+    /**
+     * Returns all direct and indirect dependents of [module], excluding [module] if it depends on itself.
+     */
+    public abstract fun getTransitiveDependents(module: KtModule): Set<KtModule>
+
+    public companion object {
+        public fun getInstance(project: Project): KotlinModuleDependentsProvider =
+            project.getService(KotlinModuleDependentsProvider::class.java)
+    }
+}