Enforce that only one task in a group can use `T.ctx().dest` https://github.com/lihaoyi/mill/issues/62

1 files changed, 17 insertions, 2 deletions

diff --git a/core/test/src/mill/eval/FailureTests.scala b/core/test/src/mill/eval/FailureTests.scala
index 86eccb3f..d4758a12 100644
--- a/core/test/src/mill/eval/FailureTests.scala
+++ b/core/test/src/mill/eval/FailureTests.scala
@@ -1,6 +1,6 @@
 package mill.eval
-
-import mill.util.TestEvaluator
+import mill.T
+import mill.util.{TestEvaluator, TestUtil}
 import ammonite.ops.pwd
 import utest._
 import utest.framework.TestPath
@@ -85,6 +85,21 @@ object FailureTests extends TestSuite{
         expectedRawValues = Seq(Result.Skipped)
       )
     }
+    'multipleUsesOfDest - {
+      object build extends TestUtil.BaseModule {
+        // Using `T.ctx(  ).dest` twice in a single task is ok
+        def left = T{ + T.ctx().dest.toString.length + T.ctx().dest.toString.length }
+
+        // Using `T.ctx(  ).dest` once in two different tasks is not ok
+        val task = T.task{ T.ctx().dest.toString.length  }
+        def right = T{ task() + left() + T.ctx().dest.toString().length }
+      }
+
+      val check = new TestEvaluator(build, workspace, pwd)
+      val Right(_) = check(build.left)
+      val Left(Result.Exception(e, _)) = check(build.right)
+      assert(e.getMessage.contains("`dest` can only be used in one place"))
+    }
   }
 }