From 69ae4f3073f762df53793228492474d43f56cee3 Mon Sep 17 00:00:00 2001
From: Roman Iakovlev <iakovlev@live.de>
Date: Thu, 26 Oct 2017 19:05:04 +0200
Subject: [PATCH] Add a check for a change in SBT version before reload

Fixes #1055
---
 main/src/main/scala/sbt/Main.scala            | 22 ++++++++++++++++++-
 .../project/sbt-version-change/build.sbt      |  8 +++++++
 .../changes/build.properties                  |  1 +
 .../sbt-test/project/sbt-version-change/test  |  4 ++++
 4 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 sbt/src/sbt-test/project/sbt-version-change/build.sbt
 create mode 100644 sbt/src/sbt-test/project/sbt-version-change/changes/build.properties
 create mode 100644 sbt/src/sbt-test/project/sbt-version-change/test

diff --git a/main/src/main/scala/sbt/Main.scala b/main/src/main/scala/sbt/Main.scala
index f8faddff8..61fe64cd0 100644
--- a/main/src/main/scala/sbt/Main.scala
+++ b/main/src/main/scala/sbt/Main.scala
@@ -56,7 +56,8 @@ import StandardMain._
 
 import java.io.{ File, IOException }
 import java.net.URI
-import java.util.Locale
+import java.util.{ Locale, Properties }
+
 import scala.util.control.NonFatal
 import BasicCommandStrings.{ Shell, TemplateCommand }
 import CommandStrings.BootCommand
@@ -672,7 +673,26 @@ object BuiltinCommands {
   def loadProjectImpl: Command =
     Command(LoadProjectImpl)(_ => Project.loadActionParser)(doLoadProject)
 
+  def checkSBTVersionChanged(state: State): Unit = {
+    import sbt.io.syntax._
+    val app = state.configuration.provider
+    val buildProps = state.baseDir / "project" / "build.properties"
+    // First try reading the sbt version from build.properties file.
+    val sbtVersionOpt = if (buildProps.exists) {
+      val buildProperties = new Properties()
+      IO.load(buildProperties, buildProps)
+      Option(buildProperties.getProperty("sbt.version"))
+    } else None
+
+    sbtVersionOpt.foreach(version =>
+      if (version != app.id.version()) {
+        state.log.warn(s"""sbt version mismatch, current: ${app.id
+          .version()}, in build.properties: "$version", use 'reboot' to use the new value.""")
+    })
+  }
+
   def doLoadProject(s0: State, action: LoadAction.Value): State = {
+    checkSBTVersionChanged(s0)
     val (s1, base) = Project.loadAction(SessionVar.clear(s0), action)
     IO.createDirectory(base)
     val s = if (s1 has Keys.stateCompilerCache) s1 else registerCompilerCache(s1)
diff --git a/sbt/src/sbt-test/project/sbt-version-change/build.sbt b/sbt/src/sbt-test/project/sbt-version-change/build.sbt
new file mode 100644
index 000000000..8bc0b3ddf
--- /dev/null
+++ b/sbt/src/sbt-test/project/sbt-version-change/build.sbt
@@ -0,0 +1,8 @@
+TaskKey[Unit]("checkSbtVersionWarning") := {
+	val state = Keys.state.value
+	val logging = state.globalLogging
+	val currVersion = state.configuration.provider.id.version()
+	val contents = IO.read(logging.backing.file)
+	assert(contents.contains(s"""sbt version mismatch, current: $currVersion, in build.properties: "1.1.1", use 'reboot' to use the new value."""))
+	()
+}
\ No newline at end of file
diff --git a/sbt/src/sbt-test/project/sbt-version-change/changes/build.properties b/sbt/src/sbt-test/project/sbt-version-change/changes/build.properties
new file mode 100644
index 000000000..9f782f704
--- /dev/null
+++ b/sbt/src/sbt-test/project/sbt-version-change/changes/build.properties
@@ -0,0 +1 @@
+sbt.version=1.1.1
\ No newline at end of file
diff --git a/sbt/src/sbt-test/project/sbt-version-change/test b/sbt/src/sbt-test/project/sbt-version-change/test
new file mode 100644
index 000000000..b46c8dd3c
--- /dev/null
+++ b/sbt/src/sbt-test/project/sbt-version-change/test
@@ -0,0 +1,4 @@
+> help
+$ copy-file changes/build.properties project/build.properties
+> reload
+> checkSbtVersionWarning