Fix type compatibility on empty arrays (#4324)

broadinstitute · Oct 30, 2018 · fdc6fdf · fdc6fdf
1 parent de38c5e
commit fdc6fdf
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Showing 3 changed files with 18 additions and 4 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -6,6 +6,9 @@
 
 When the value `exit-code-timeout-seconds` is set, `check-alive` command is now only called once every timeout interval instead of each poll.
 
+### Bug fixes
+
+- Fixed a regression in Cromwell 36 that could cause operations on empty arrays to fail with a spurious type error (closes [#4318](https://github.com/broadinstitute/cromwell/issues/4318))
 
 ## 36 Release Notes
 

diff --git a/wom/src/main/scala/wom/types/WomType.scala b/wom/src/main/scala/wom/types/WomType.scala
@@ -199,9 +199,17 @@ object WomType {
       }
 
       if (asArrayTypes.forall(_.isDefined)) {
-          val arrs = asArrayTypes.map(_.get)
-          val memberType = lowestCommonSubtype(arrs.map(_.memberType))
-          Some(WomArrayType(memberType))
+        val arrs = asArrayTypes.map(_.get)
+
+        /*
+        WomNothingType is not coercible to any other type, yet a empty array of type WomArrayType(WomNothingType) is
+        compatible with every other array type. Detect this here so we don't attempt primitive coercion on a type
+        that cannot be coerced.
+
+        Equivalent to logic found in typeSpecificIsCoerceableFrom on WomArrayType.
+        */
+        val memberType = lowestCommonSubtype(arrs.map(_.memberType).filterNot(_.equals(WomNothingType)))
+        Some(WomArrayType(memberType))
       } else None
     }
   }

diff --git a/wom/src/test/scala/wom/types/WomTypeSpec.scala b/wom/src/test/scala/wom/types/WomTypeSpec.scala
@@ -179,7 +179,10 @@ class WomTypeSpec extends FlatSpec with Matchers {
       ))
     ), WomObjectType),
     (List(WomIntegerType, WomFloatType), WomFloatType),
-    (List(WomIntegerType, WomBooleanType), WomStringType)
+    (List(WomIntegerType, WomBooleanType), WomStringType),
+    (List(WomOptionalType(WomMaybeEmptyArrayType(WomSingleFileType)), WomMaybeEmptyArrayType(WomNothingType)), WomOptionalType(WomMaybeEmptyArrayType(WomSingleFileType))),
+    (List(WomMaybeEmptyArrayType(WomSingleFileType), WomMaybeEmptyArrayType(WomNothingType)), WomMaybeEmptyArrayType(WomSingleFileType)),
+    (List(WomMaybeEmptyArrayType(WomStringType), WomMaybeEmptyArrayType(WomIntegerType), WomMaybeEmptyArrayType(WomNothingType)), WomMaybeEmptyArrayType(WomStringType))
   )
 
   lcsTestCases foreach { case (types, expectedLcs) =>