From 81ce14d58cfa8326f5e319fe7430ef4a3fe8dbd5 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <ethan.atkins@gmail.com>
Date: Thu, 25 Apr 2019 15:56:08 -0700
Subject: [PATCH] Allow calling TaskKey.previous in input tasks

I discovered that it wasn't possible to call .previous in an input task.
While I understand why you can't call .previous on an InputKey, I think
it makes sense to allow calling .previous on a TaskKey within an input
task.
---
 main-settings/src/main/scala/sbt/std/TaskMacro.scala   |  1 +
 .../sbt-test/actions/previous-in-input-task/build.sbt  | 10 ++++++++++
 sbt/src/sbt-test/actions/previous-in-input-task/test   |  5 +++++
 3 files changed, 16 insertions(+)
 create mode 100644 sbt/src/sbt-test/actions/previous-in-input-task/build.sbt
 create mode 100644 sbt/src/sbt-test/actions/previous-in-input-task/test

diff --git a/main-settings/src/main/scala/sbt/std/TaskMacro.scala b/main-settings/src/main/scala/sbt/std/TaskMacro.scala
index 650914c7a..198b4adb1 100644
--- a/main-settings/src/main/scala/sbt/std/TaskMacro.scala
+++ b/main-settings/src/main/scala/sbt/std/TaskMacro.scala
@@ -450,6 +450,7 @@ object TaskMacro {
 
     def expand(nme: String, tpe: Type, tree: Tree): Converted[c.type] = nme match {
       case WrapInitTaskName         => Converted.Success(wrapInitTask(tree)(c.WeakTypeTag(tpe)))
+      case WrapPreviousName         => Converted.Success(wrapInitTask(tree)(c.WeakTypeTag(tpe)))
       case ParserInput.WrapInitName => Converted.Success(wrapInitParser(tree)(c.WeakTypeTag(tpe)))
       case WrapInitInputName        => Converted.Success(wrapInitInput(tree)(c.WeakTypeTag(tpe)))
       case WrapInputName            => Converted.Success(wrapInput(tree)(c.WeakTypeTag(tpe)))
diff --git a/sbt/src/sbt-test/actions/previous-in-input-task/build.sbt b/sbt/src/sbt-test/actions/previous-in-input-task/build.sbt
new file mode 100644
index 000000000..a7e169d7e
--- /dev/null
+++ b/sbt/src/sbt-test/actions/previous-in-input-task/build.sbt
@@ -0,0 +1,10 @@
+import sjsonnew.BasicJsonProtocol._
+
+val cacheTask = taskKey[Int]("task")
+cacheTask := 1
+
+val checkTask = inputKey[Unit]("validate that the correct value is set by cacheTask")
+checkTask := {
+  val expected = Def.spaceDelimited("").parsed.head.toInt
+  assert(cacheTask.previous.getOrElse(0) == expected)
+}
\ No newline at end of file
diff --git a/sbt/src/sbt-test/actions/previous-in-input-task/test b/sbt/src/sbt-test/actions/previous-in-input-task/test
new file mode 100644
index 000000000..1b7969eea
--- /dev/null
+++ b/sbt/src/sbt-test/actions/previous-in-input-task/test
@@ -0,0 +1,5 @@
+> checkTask 0
+
+> cacheTask
+
+> checkTask 1
\ No newline at end of file