Do not fail if nothing to commit in shutdown hook - just warn

app/src/main/kotlin/org/virtuslab/bazelsteward/app/PullRequestManager.kt

@@ -75,7 +75,7 @@ data class PullRequestManager(
       if (hook.commands.isNotEmpty()) {
         hook.commands.forEach {
           Thread.sleep(1000)
-          CommandRunner.run(listOf("sh", "-c", it), workspaceRoot)
+          CommandRunner.runForOutput(listOf("sh", "-c", it), workspaceRoot)
         }
         git.commitSelectedFiles(hook.filesToCommit, hook.commitMessage)
         if (hook.runFor == HookRunFor.Commit) {

core/src/main/kotlin/org/virtuslab/bazelsteward/core/common/CommandRunner.kt

@@ -9,27 +9,35 @@ import java.nio.file.Path
 private val logger = KotlinLogging.logger {}
 
 class CommandRunner {
+  data class Result(val exitCode: Int, val stdout: String, val stderr: String) {
+    val isSuccess: Boolean
+      get() = exitCode == 0
+  }
 
   companion object {
-    suspend fun run(directory: Path, vararg command: String): String {
-      return run(command.toList(), directory)
+    suspend fun runForOutput(directory: Path, vararg command: String): String {
+      return runForOutput(command.toList(), directory)
+    }
+
+    suspend fun runForOutput(command: List<String>, directory: Path): String {
+      val result = run(command, directory)
+      if (result.isSuccess) {
+        return result.stdout
+      } else {
+        val message = "${command.joinToString(" ")}\n${result.stdout}\n${result.stderr}"
+        throw RuntimeException(message)
+      }
     }
 
-    suspend fun run(command: List<String>, directory: Path): String {
+    suspend fun run(command: List<String>, directory: Path): Result {
       logger.info { command.joinToString(" ") { if (it.contains(" ")) """"$it"""" else it } }
       return withContext(Dispatchers.IO) {
         val process = ProcessBuilder(command).directory(directory.toFile()).start()
           .onExit().await()
         val stdout = process.inputStream.bufferedReader().use { it.readText() }
         val stderr = process.errorStream.bufferedReader().use { it.readText() }
 
-        if (process.exitValue() == 0) {
-          stdout
-        } else {
-          throw RuntimeException(
-            "${command.joinToString(" ")}\n$stdout\n$stderr",
-          )
-        }
+        Result(process.exitValue(), stdout, stderr)
       }
     }
   }

core/src/main/kotlin/org/virtuslab/bazelsteward/core/common/GitClient.kt

@@ -5,7 +5,7 @@ import java.nio.file.Path
 
 class GitClient(private val repositoryRoot: Path) {
   private val quiet = "--quiet"
-  private val git = runBlocking { CommandRunner.run(listOf("sh", "-c", "which git"), repositoryRoot).trim() }
+  private val git = runBlocking { CommandRunner.runForOutput(listOf("sh", "-c", "which git"), repositoryRoot).trim() }
 
   suspend fun checkout(target: String, newBranch: Boolean = false) {
     val b = if (newBranch) "-b" else null
@@ -76,7 +76,11 @@ class GitClient(private val repositoryRoot: Path) {
   suspend fun run(vararg gitArgs: String?): String = run(gitArgs.toList())
 
   suspend fun run(gitArgs: List<String?>): String {
-    return CommandRunner.run(listOf(git) + gitArgs.filterNotNull(), repositoryRoot)
+    return CommandRunner.runForOutput(listOf(git) + gitArgs.filterNotNull(), repositoryRoot)
+  }
+
+  suspend fun runForResult(vararg args: String): CommandRunner.Result {
+    return CommandRunner.run(listOf(git) + args, repositoryRoot)
   }
 
   data class GitAuthor(val name: String, val email: String)

core/src/main/kotlin/org/virtuslab/bazelsteward/core/common/GitOperations.kt

@@ -77,7 +77,12 @@ class GitOperations(workspaceRoot: Path, private val baseBranch: String) {
 
   suspend fun commitSelectedFiles(filesToCommit: List<String>, commitMessage: String) {
     git.add(filesToCommit)
-    git.commit(commitMessage)
+    val noChanges = git.runForResult("git", "diff", "--quiet", "--exit-code", "--cached").isSuccess
+    if (noChanges) {
+      logger.warn { "No changes to commit" }
+    } else {
+      git.commit(commitMessage)
+    }
   }
 
   suspend fun squashLastTwoCommits() {

e2e/src/test/kotlin/org/virtuslab/bazelsteward/e2e/PostUpdateHookTest.kt

@@ -23,7 +23,7 @@ class PostUpdateHookTest : E2EBase() {
     val git = GitClient(localRoot)
     runBlocking {
       git.checkout("bazel-steward/io.arrow-kt/arrow-core/1.1.5")
-      val validationCommandOutput = CommandRunner.run(
+      val validationCommandOutput = CommandRunner.runForOutput(
         localRoot,
         "sh",
         "-c",
@@ -52,7 +52,7 @@ class PostUpdateHookTest : E2EBase() {
     val git = GitClient(localRoot)
     runBlocking {
       git.checkout("bazel-steward/io.arrow-kt/arrow-core/1.1.5")
-      val validationCommandOutput = CommandRunner.run(
+      val validationCommandOutput = CommandRunner.runForOutput(
         localRoot,
         "sh",
         "-c",

kinds/bazel/rules/src/main/kotlin/org/virtuslab/bazelsteward/bazel/rules/BazelRulesExtractor.kt

@@ -69,10 +69,10 @@ class BazelRulesExtractor {
       """.trimMargin(),
     )
     // solution from https://github.com/bazelbuild/bazel/issues/6377#issuecomment-1237791008
-    CommandRunner.run(workspaceRoot, "bazel", "build", "@all_external_repositories//:result.json")
+    CommandRunner.runForOutput(workspaceRoot, "bazel", "build", "@all_external_repositories//:result.json")
     workspaceFilePath.writeText(originalContent)
     deleteFile(tempFileForBzl)
-    val bazelPath = CommandRunner.run(workspaceRoot, "bazel", "info", "output_base").trim()
+    val bazelPath = CommandRunner.runForOutput(workspaceRoot, "bazel", "info", "output_base").trim()
     val resultFilePath = Path(bazelPath).resolve("external/all_external_repositories/result.json")
     if (!resultFilePath.exists()) {
       throw RuntimeException("Failed to find a file: $resultFilePath")

kinds/maven/src/main/kotlin/org/virtuslab/bazelsteward/maven/MavenDataExtractor.kt

@@ -18,7 +18,7 @@ class MavenDataExtractor(private val workspaceRoot: Path) {
   }
 
   private suspend fun extractFromFile(fileName: String): List<String> = withContext(Dispatchers.IO) {
-    val xml = CommandRunner.run(
+    val xml = CommandRunner.runForOutput(
       workspaceRoot,
       "bazel",
       "query",