Add changelog requirement action for major/minor bumps (#174)

"Warn Version Bump" will fail if a PR contains a major/minor bump
without a changelog. There most recent test commits show what this
failure looks like.

.github/workflows/warn-version-bump.yml

@@ -0,0 +1,48 @@
+name: Warn Version Bump
+
+on: pull_request
+
+jobs:
+  warn-version-bump:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout target branch
+        uses: actions/[email protected]
+        with:
+          ref: ${{ github.base_ref }}
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v3
+        with:
+          java-version: 17
+          distribution: temurin
+          cache: gradle
+
+      - name: Generate the api file
+        run: |
+          ./gradlew exportApi --no-daemon
+
+      - name: Save public.api from target branch
+        run: |
+          mkdir ~/common/ && \
+          mkdir ~/generativeai/ && \
+          mv generativeai/public.api ~/generativeai/public.api && \
+          mv common/public.api ~/common/public.api
+
+      - name: Checkout branch
+        uses: actions/[email protected]
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v3
+        with:
+          java-version: 17
+          distribution: temurin
+          cache: gradle
+
+      - name: Copy saved api to branch
+        run: |
+          mv ~/generativeai/public.api generativeai/public.api && \
+          mv ~/common/public.api common/public.api
+      - name: Run API versioning check
+        run: |
+          if ! test -d .changes || git diff --quiet ${{ github.event.pull_request.base.sha }}..HEAD .changes ; then ./gradlew warnVersionBump ; else exit 0 ; fi

plugins/src/main/java/com/google/gradle/plugins/ChangelogPlugin.kt

@@ -20,6 +20,7 @@ import com.google.gradle.tasks.FindChangesTask
 import com.google.gradle.tasks.MakeChangeTask
 import com.google.gradle.tasks.MakeReleaseNotesTask
 import com.google.gradle.tasks.WarnAboutApiChangesTask
+import com.google.gradle.tasks.WarnVersionBumpTask
 import com.google.gradle.types.Changelog
 import com.google.gradle.types.RandomWordsGenerator
 import com.google.gradle.util.apply
@@ -34,6 +35,7 @@ import com.google.gradle.util.regularOutputFile
 import com.google.gradle.util.tempFile
 import org.gradle.api.Plugin
 import org.gradle.api.Project
+import org.gradle.api.file.RegularFile
 import org.gradle.api.file.RegularFileProperty
 import org.gradle.api.tasks.Delete
 import org.gradle.api.tasks.Optional
@@ -85,14 +87,22 @@ abstract class ChangelogPlugin : Plugin<Project> {
 
       tasks.register<MakeChangeTask>("makeChange") {
         val changeMessage = provideProperty<String>("changeMessage")
-        val changeName = RandomWordsGenerator.generateString()
-        val changeOutput = extension.outputDirectory.childFile("$changeName.json")
+        val changeName = provideProperty<String>("changeName")
+          .orElse(RandomWordsGenerator.generateString())
+        val changeOutput = extension.outputDirectory.childFile("${changeName.get()}.json")
 
         changesFile.set(fileChanges)
         message.set(changeMessage)
         outputFile.set(changeOutput)
       }
 
+      tasks.register<WarnVersionBumpTask>("warnVersionBump") {
+        if (export.isPresent) {
+          export.set(apiPlugin.exportFile)
+        }
+        changesFile.set(fileChanges)
+      }
+
       tasks.register<WarnAboutApiChangesTask>("warnAboutApiChanges") {
         changesFile.set(fileChanges)
         outputFile.set(extension.apiChangesFile)

plugins/src/main/java/com/google/gradle/tasks/WarnVersionBumpTask.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gradle.tasks
+
+import com.google.gradle.types.LinesChanged
+import com.google.gradle.types.VersionType.*
+import org.gradle.api.DefaultTask
+import org.gradle.api.file.RegularFileProperty
+import org.gradle.api.tasks.InputFile
+import org.gradle.api.tasks.Optional
+import org.gradle.api.tasks.TaskAction
+import org.gradle.api.tasks.TaskExecutionException
+
+/**
+ * A Gradle task to warn about API version bumps beyond what is expected
+ *
+ * The task uses the provided [changesFile] to infer if merging the changes currently present in the
+ * repo will have an impact on the public api.
+ *
+ * @property changesFile a file containing a [LinesChanged]; representing the changes made in this
+ *   repo
+ * @throws TaskExecutionException if changes cause an minor or major API bump
+ */
+abstract class WarnVersionBumpTask : DefaultTask() {
+  @get:[Optional InputFile] abstract val export: RegularFileProperty
+
+  @get:InputFile abstract val changesFile: RegularFileProperty
+
+  @TaskAction
+  fun add() {
+    val diff = LinesChanged.fromFile(changesFile.asFile.get())
+
+    if (diff.bump == MAJOR || diff.bump == MINOR) {
+      if (export.isPresent) {
+        throw TaskExecutionException(this, Exception("Based on exported API, changes are ${diff.bump}, higher than PATCH. If this is intended, add a changelog entry. Otherwise, revert the changes."))
+      } else {
+        throw TaskExecutionException(this, Exception("Based on last release API, changes are ${diff.bump}, higher than PATCH. If this is intended, add a changelog entry. Otherwise, revert the changes. To compare local changes, run exportApi on a commit first."))
+      }
+    }
+  }
+}