expand tilde prefix

main/src/main/scala/sbt/BuildPaths.scala

@@ -78,7 +78,29 @@ object BuildPaths {
 
   def getFileProperty(name: String): Option[File] = Option(System.getProperty(name)) flatMap {
     path =>
-      if (path.isEmpty) None else Some(new File(path))
+      if (path.isEmpty) None
+      else {
+        if (path.head == '~') {
+          val tildePath = expandTildePrefix(path)
+          Some(new File(tildePath))
+        } else {
+          Some(new File(path))
+        }
+      }
+  }
+
+  def expandTildePrefix(path: String): String = {
+    val tildePath = path.split("\\/").headOption match {
+      case Some("~")  => sys.env.getOrElse("HOME", "")
+      case Some("~+") => sys.env.getOrElse("PWD", "")
+      case Some("~-") => sys.env.getOrElse("OLDPWD", "")
+      case _          => ""
+    }
+
+    path.indexOf("/") match {
+      case -1 => tildePath
+      case _  => tildePath + path.substring(path.indexOf("/"))
+    }
   }
 
   def defaultVersionedGlobalBase(sbtVersion: String): File = defaultGlobalBase / sbtVersion

main/src/test/scala/BuildPathsTest.scala

@@ -0,0 +1,61 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt
+
+import org.specs2.mutable.Specification
+import sbt.BuildPaths
+
+object BuildPathsTest extends Specification {
+
+  private def assertExpandedPath(given: String, expected: String) = {
+    val actual = BuildPaths.expandTildePrefix(given)
+
+    actual must be equalTo (expected)
+  }
+
+  "expandTildePrefix" should {
+
+    "expand empty path to itself" in {
+      assertExpandedPath("", "")
+    }
+
+    "expand /home/user/path to itself" in {
+      assertExpandedPath("/home/user/path", "/home/user/path")
+    }
+
+    "expand /~/foo/ to itself" in {
+      assertExpandedPath("/~/foo/", "/~/foo/")
+    }
+
+    "expand ~ to $HOME" in {
+      assertExpandedPath("~", sys.env.getOrElse("HOME", ""))
+    }
+
+    "expand ~/foo/bar to $HOME/foo/bar" in {
+      assertExpandedPath("~/foo/bar", sys.env.getOrElse("HOME", "") + "/foo/bar")
+    }
+
+    "expand ~+ to $PWD" in {
+      assertExpandedPath("~+", sys.env.getOrElse("PWD", ""))
+    }
+
+    "expand ~+/foo/bar to $PWD/foo/bar" in {
+      assertExpandedPath("~+/foo/bar", sys.env.getOrElse("PWD", "") + "/foo/bar")
+    }
+
+    "expand ~- to $OLDPWD" in {
+      assertExpandedPath("~-", sys.env.getOrElse("OLDPWD", ""))
+    }
+
+    "expand ~-/foo/bar to $OLDPWD/foo/bar" in {
+      assertExpandedPath("~-/foo/bar", sys.env.getOrElse("OLDPWD", "") + "/foo/bar")
+    }
+
+  }
+
+}