Make os.home a def (#239)

In some environments the home directory is not configured, thus
`user.home` can be set to e.g. "?" (like in the issue the Scala CLI team
has bumped into). See [OpenJDK
sources](https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/libjava/java_props_md.c#L508)

In those cases using e.g. `os.pwd` throws, since the `os.home` is also
initialized.
This fix allows `os.pwd` to still be used when `user.home` is set to
something weird.

One example of such environment with `user.home` set to "?" is running
Jenking on CloudBees, the results of trying to run Scala CLI there
looked like this, since we heavily use os.pwd in our code base:

Pull request: #239

---------

Co-authored-by: Lorenzo Gabriele <lorenzolespaul@gmail.com>
Co-authored-by: Tobias Roeser <le.petit.fou@web.de>

Author: 3 people

build.sc

@@ -126,6 +126,7 @@ object os extends Module {
   object jvm extends Cross[OsJvmModule](scalaVersions)
   trait OsJvmModule extends OsModule with MiMaChecks {
     object test extends ScalaTests with OsLibTestModule
+    object nohometest extends ScalaTests with OsLibTestModule
   }
 
   object native extends Cross[OsNativeModule](scalaVersions)
@@ -134,6 +135,7 @@ object os extends Module {
     object test extends ScalaNativeTests with OsLibTestModule {
       def nativeLinkStubs = true
     }
+    object nohometest extends ScalaNativeTests with OsLibTestModule
   }
 
   object watch extends Module {

os/nohometest/src/NoHomeTests.scala

@@ -0,0 +1,25 @@
+package test.os
+
+import utest._
+
+object NoHomeTests extends TestSuite {
+  private lazy val isWindows = sys.props("os.name").toLowerCase().contains("windows")
+
+  val tests = Tests {
+    test("pwd when home is not available") {
+      System.setProperty("user.home", "?")
+      val homeException = intercept[IllegalArgumentException] { os.home }
+        .getMessage()
+
+      val expectedException =
+        if (isWindows)
+          "Illegal char <?> at index 0: ?"
+        else
+          "requirement failed: ? is not an absolute path"
+
+      assert(homeException == expectedException)
+      os.pwd
+      ()
+    }
+  }
+}

os/src-jvm/package.scala

@@ -23,10 +23,17 @@ package object os {
     os.ResourcePath.resource(resRoot)
   }
 
+  // See https://github.com/com-lihaoyi/os-lib/pull/239
+  // and https://github.com/lightbend/mima/issues/794
+  // why the need the inner object to preserve binary compatibility
+  private object _home {
+    lazy val value = Path(System.getProperty("user.home"))
+  }
+
   /**
    * The user's home directory
    */
-  val home: Path = Path(System.getProperty("user.home"))
+  def home: Path = _home.value
 
   /**
    * The current working directory for this process.

os/src-native/package.scala

@@ -16,10 +16,17 @@ package object os {
     path
   }
 
+  // See https://github.com/com-lihaoyi/os-lib/pull/239
+  // and https://github.com/lightbend/mima/issues/794
+  // why the need the inner object to preserve binary compatibility
+  private object _home {
+    lazy val value = Path(System.getProperty("user.home"))
+  }
+
   /**
    * The user's home directory
    */
-  val home: Path = Path(System.getProperty("user.home"))
+  def home: Path = _home.value
 
   /**
    * The current working directory for this process.