Add a verifier to check if generated Dockerfiles are up-to-date.

src/main/scala/org/allenai/plugins/DockerBuildPlugin.scala

@@ -128,6 +128,20 @@ object DockerBuildPlugin extends AutoPlugin {
       "The value to use for WORKDIR when generating your Dockerfile. Defaults to \"/stage\"."
     )
 
+    ////////////////////////////////////////////////////////////////////////////////////////////////
+    // The following settings affect how the plugin behaves, but don't affect file or image output.
+    ////////////////////////////////////////////////////////////////////////////////////////////////
+
+    val verifyDockerfileIsStrict: SettingKey[Boolean] = Def.settingKey[Boolean](
+      "If true, the `verifyDockerfile` task will raise an error if the current Dockerfile does " +
+        "not match the generated one. Defaults to true."
+    )
+
+    val verifyDockerfileOnBuild: SettingKey[Boolean] = Def.settingKey[Boolean](
+      "If true, `dockerBuild` will depend on `verifyDockerfile`, and will not build if the " +
+        "Dockerfile is not up-to-date. Defaults to false."
+    )
+
     ////////////////////////////////////////////////////////////////////////////////////////////////
     // The following keys are for generating dockerfiles; and staging, building, running, and
     // pushing images. These should not be overridden from the defaults unless you know what you're
@@ -139,6 +153,12 @@ object DockerBuildPlugin extends AutoPlugin {
         "`dockerfileLocation`."
     )
 
+    val verifyDockerfile: TaskKey[Boolean] = Def.taskKey[Boolean](
+      "Checks if the Dockerfile that would be generated by `generateDockerfile` is the same as " +
+        "the Dockerfile at `dockerfileLocation`. This will raise an error if " +
+        "`verifyDockerfileIsStrict` is true, and print a warning otherwise."
+    )
+
     val dockerDependencyStage: TaskKey[File] = Def.taskKey[File](
       "Builds a staged directory under target/docker/dependencies containing project " +
         "dependencies. This will include a generated Dockerfile. This returns the staging " +
@@ -301,12 +321,27 @@ object DockerBuildPlugin extends AutoPlugin {
     }
   }
 
-  //////////////////////////////////////////////////////////////////////////////////////////////////
-  // Definitions for plugin tasks.
-  //////////////////////////////////////////////////////////////////////////////////////////////////
+  /** Task to read the current text of the main Dockerfile below the sigil line. This returns None
+    * if and only if the file exists, but the sigil line cannot be found, since this is considered
+    * a potential user error.
+    */
+  lazy val customDockerfileContents: Def.Initialize[Task[Option[String]]] = Def.task {
+    val dockerfile = dockerfileLocation.value
+    if (dockerfile.exists) {
+      val lines = IO.readLines(dockerfile)
+      val remainder = lines.dropWhile(_ != DOCKERFILE_SIGIL)
+      if (remainder.nonEmpty) {
+        Some(remainder.tail.mkString("\n") + "\n")
+      } else {
+        None
+      }
+    } else {
+      Some("")
+    }
+  }
 
-  /** Task to build a dockerfile using the current project's sbt settings to populate it. */
-  lazy val generateDockerfileDef: Def.Initialize[Task[Unit]] = Def.task {
+  /** Task to build dockerfile contents using the current project's sbt settings and return it. */
+  lazy val generatedDockerfileContents: Def.Initialize[Task[String]] = Def.task {
     val logger = Keys.streams.value.log
 
     // Create the copy commands.
@@ -352,7 +387,7 @@ object DockerBuildPlugin extends AutoPlugin {
     // Create the text for dockerMainArgs and CMD command.
     val dockerMainArgsText = dockerMainArgs.value.map('"' + _ + '"').mkString(", ")
 
-    val dockerfileContents = s"""# AUTOGENERATED
+    s"""# AUTOGENERATED
 # Most lines in this file are derived from sbt settings. These settings are printed above the lines
 # they affect.
 #
@@ -413,23 +448,52 @@ COPY lib lib
 # Do not remove this line unless you want your changes overwritten!
 $DOCKERFILE_SIGIL
 """
+  }
 
-    // If there is already a Dockerfile, retain any contents past the sigil.
+  /** Task to check the current dockerfile contents against the generated contents, returning true
+    * if they are up-to-date.
+    */
+  lazy val checkDockerfile: Def.Initialize[Task[Boolean]] = Def.task {
+    val newContents = {
+      val generatedContents = generatedDockerfileContents.value
+      val customContents = customDockerfileContents.value.getOrElse("")
+      generatedContents + customContents
+    }
     val dockerfile = dockerfileLocation.value
-    val existingContents = if (dockerfile.exists) {
-      val lines = IO.readLines(dockerfile)
-      val remainder = lines.dropWhile(_ != DOCKERFILE_SIGIL)
-      if (remainder.nonEmpty) {
-        remainder.tail.mkString("\n")
-      } else {
-        logger.warn(s"Overwriting Dockerfile at $dockerfile...")
-        ""
-      }
-    } else {
+    val oldContents = if (dockerfile.exists) IO.read(dockerfileLocation.value) else ""
+
+    newContents == oldContents
+  }
+
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  // Definitions for plugin tasks.
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+
+  /** Task to build a dockerfile using the current project's sbt settings to populate it. */
+  lazy val generateDockerfileDef: Def.Initialize[Task[Unit]] = Def.task {
+    val generatedContents = generatedDockerfileContents.value
+    val customContents = customDockerfileContents.value.getOrElse {
+      Keys.streams.value.log(s"Overwriting Dockerfile at ${dockerfileLocation.value}...")
       ""
     }
+    IO.write(dockerfileLocation.value, generatedContents + customContents)
+  }
 
-    IO.write(dockerfile, dockerfileContents + existingContents + "\n")
+  /** Task verify that the current Dockerfile is up-to-date. Raises an error if
+    * verifyDockerfileIsStrict is true.
+    */
+  lazy val verifyDockerfileDef: Def.Initialize[Task[Boolean]] = Def.task {
+    val isUnchanged = checkDockerfile.value
+    if (!isUnchanged) {
+      val message = s"Dockerfile ${dockerfileLocation.value} is not up-to-date. Run " +
+        "the `generateDockerfile` task to fix."
+      if (verifyDockerfileIsStrict.value) {
+        sys.error(message)
+      } else {
+        Keys.streams.value.log.warn(message)
+      }
+    }
+    isUnchanged
   }
 
   /** Task to stage a docker image containing the dependencies of the current project. This is used
@@ -577,6 +641,27 @@ $DOCKERFILE_SIGIL
     dockerDependencyBuild.value
     dockerMainStage.value
 
+    // Verify the dockerfile.
+    if (verifyDockerfileOnBuild.value) {
+      val isUnchanged = checkDockerfile.value
+      // Note that due to sbt dependency semantics (the fact that all dependencies are always run),
+      // we duplicate the below logic in the verifyDockerfile task def. Otherwise, we couldn't
+      // control the error behavior via the verifyDockerfileOnBuild flag above.
+      if (!isUnchanged) {
+        if (verifyDockerfileIsStrict.value) {
+          sys.error(
+            s"Dockerfile ${dockerfileLocation.value} is not up-to-date, stopping build. Run " +
+              "`generateDockerfile` to update."
+          )
+        } else {
+          Keys.streams.value.log.warn(
+            s"Dockerfile ${dockerfileLocation.value} is not up-to-date. Run `generateDockerfile` " +
+              "to update."
+          )
+        }
+      }
+    }
+
     val logger = Keys.streams.value.log
     logger.info(s"Building main image ${mainImageNameSuffix.value}...")
 
@@ -690,7 +775,10 @@ $DOCKERFILE_SIGIL
     },
     dockerMainArgs := Seq.empty,
     dockerWorkdir := "/stage",
+    verifyDockerfileIsStrict := true,
+    verifyDockerfileOnBuild := false,
     generateDockerfile := generateDockerfileDef.value,
+    verifyDockerfile := verifyDockerfileDef.value,
     dockerDependencyStage := dependencyStageDef.value,
     dockerMainStage := mainImageStageDef.value,
     dockerDependencyBuild := dependencyBuildDef.value,

src/sbt-test/sbt-plugins/simple/docker/build.sbt

@@ -9,3 +9,5 @@ appendToDockerfile := {
   val dockerfile = dockerfileLocation.value
   IO.append(dockerfile, "# TESTING\n")
 }
+
+verifyDockerfileOnBuild := true

src/sbt-test/sbt-plugins/simple/test

@@ -93,3 +93,9 @@ $ exists docker/target/docker/main/lib/docker.docker-0.1-SNAPSHOT.jar
 
 # Test that we can re-run staging without error.
 > docker/dockerMainStage
+
+# Test that changes to the Dockerfile are detected.
+> docker/verifyDockerfile
+# Trigger a change in the file.
+> set dockerPorts.in(docker) += 1234
+-> docker/verifyDockerfile