Fix missing before in PR events

gradle-plugin/plugin/src/functionalTest/kotlin/com/emergetools/android/gradle/NoVcsEmergePluginTest.kt

@@ -4,6 +4,7 @@ import com.emergetools.android.gradle.base.EmergeGradleRunner
 import com.emergetools.android.gradle.mocks.assertSuccessfulUploadRequests
 import com.emergetools.android.gradle.tasks.internal.SaveExtensionConfigTask.Companion.EmergePluginExtensionData
 import com.emergetools.android.gradle.utils.EnvUtils.withGitHubPREvent
+import com.emergetools.android.gradle.utils.EnvUtils.withGitHubPREventNoBefore
 import com.emergetools.android.gradle.utils.EnvUtils.withGitHubPushEvent
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.decodeFromStream
@@ -130,4 +131,27 @@ class NoVcsEmergePluginTest : EmergePluginTest() {
     // BaseSha not set by default
     assertNull(configuration.vcsOptions!!.baseSha)
   }
+
+  @Test
+  fun `Assert previousSha and baseSha are the same on first commit to PR`() {
+    val runner = EmergeGradleRunner.create("no-vcs-params")
+    val configurationJson = File(runner.tempProjectDir, "emerge_config.json")
+
+    runner
+      .withArguments("saveExtensionConfig", "--outputPath", configurationJson.path)
+      .withDebugTasks()
+      .withGitHubPREventNoBefore()
+      .assert { result, _ ->
+        result.assertSuccessfulTask(":saveExtensionConfig")
+      }
+      .build()
+
+    val configuration = Json.decodeFromStream<EmergePluginExtensionData>(
+      configurationJson.inputStream()
+    )
+
+    assertEquals("github_head_sha", configuration.vcsOptions!!.sha)
+    assertEquals("github_base_sha", configuration.vcsOptions!!.baseSha)
+    assertEquals("github_base_sha", configuration.vcsOptions!!.previousSha)
+  }
 }

gradle-plugin/plugin/src/functionalTest/kotlin/com/emergetools/android/gradle/SimpleEmergePluginTest.kt

@@ -4,6 +4,7 @@ import com.emergetools.android.gradle.base.EmergeGradleRunner
 import com.emergetools.android.gradle.mocks.assertSuccessfulUploadRequests
 import com.emergetools.android.gradle.tasks.internal.SaveExtensionConfigTask.Companion.EmergePluginExtensionData
 import com.emergetools.android.gradle.utils.EnvUtils.withGitHubPREvent
+import com.emergetools.android.gradle.utils.EnvUtils.withGitHubPREventNoBefore
 import junit.framework.TestCase.assertEquals
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.decodeFromStream

gradle-plugin/plugin/src/functionalTest/kotlin/com/emergetools/android/gradle/utils/EnvUtils.kt

@@ -16,6 +16,17 @@ object EnvUtils {
     )
   }
 
+  fun EmergeGradleRunner.withGitHubPREventNoBefore(): EmergeGradleRunner {
+
+    val resource = this.javaClass.getResource("/github-event-mocks/mock_pr_event_no_before.json")
+    val jsonFile = File(resource.toURI())
+
+    return withEnvironment(
+      "GITHUB_EVENT_NAME" to "pull_request",
+      "GITHUB_EVENT_PATH" to jsonFile.path,
+    )
+  }
+
   fun EmergeGradleRunner.withGitHubPushEvent(): EmergeGradleRunner {
 
     val resource = this.javaClass.getResource("/github-event-mocks/mock_push_event.json")

gradle-plugin/plugin/src/functionalTest/resources/github-event-mocks/mock_pr_event_no_before.json

@@ -0,0 +1,13 @@
+{
+  "number": 123,
+  "pull_request": {
+    "head": {
+      "ref": "feature",
+      "sha": "github_head_sha"
+    },
+    "base": {
+      "ref": "main",
+      "sha": "github_base_sha"
+    }
+  }
+}

gradle-plugin/plugin/src/main/kotlin/com/emergetools/android/gradle/util/GitHub.kt

@@ -70,7 +70,9 @@ internal class GitHub(private val execOperations: ExecOperations) {
   fun previousSha(): String? {
     return when {
       isPush() -> getPushEventData().before
-      isPullRequest() -> getPullRequestEventData().before
+      // In the case of the first commit on a PR, the before sha is not available.
+      // We want previousSha to be the last commit on main, so we'll fallback to baseSha
+      isPullRequest() -> getPullRequestEventData().before ?: baseSha()
       else -> null
     }
   }
@@ -109,8 +111,8 @@ internal class GitHub(private val execOperations: ExecOperations) {
   data class GitHubPullRequestEvent(
     @SerialName("pull_request")
     val pr: GitHubPullRequest,
-    val before: String,
     val number: Int,
+    val before: String? = null,
   )
 
   @Serializable