Make jar_library target export all its dependencies

src/python/pants/backend/jvm/targets/jar_library.py

@@ -76,6 +76,16 @@ def excludes(self):
     """
     return self.payload.excludes
 
+  @property
+  def exports(self):
+    """
+    :API: public
+    """
+
+    # It is currently aliased to dependencies. For future work see
+    # https://github.com/pantsbuild/pants/issues/4398
+    return self.dependencies
+
   @staticmethod
   def to_jar_dependencies(relative_to, jar_library_specs, build_graph):
     """Convenience method to resolve a list of specs to JarLibraries and return its jars attributes.

src/python/pants/backend/jvm/tasks/jvm_compile/compile_context.py

@@ -28,9 +28,14 @@ def _resolve_strict_dependencies(target):
 
 def _resolve_exports(target):
   for export in getattr(target, 'exports', []):
-    for exp in _resolve_exports(export):
-      yield exp
-    yield export
+    if type(export) in (AliasTarget, Target):
+      # If exported target is an alias, expand its dependencies.
+      for dep in _resolve_strict_dependencies(export):
+        yield dep
+    else:
+      for exp in _resolve_exports(export):
+        yield exp
+      yield export
 
 
 def strict_dependencies(target, dep_context):

testprojects/tests/scala/org/pantsbuild/testproject/exports/BUILD

@@ -25,3 +25,23 @@ scala_library(
   dependencies=[':C'],
   strict_deps=True,
 )
+
+target(
+  name='TB',
+  dependencies=[':B'],
+)
+
+scala_library(
+  name='TC',
+  sources = ['C.scala'],
+  dependencies=[':TB'],
+  exports=[':TB'],
+  strict_deps=True,
+)
+
+scala_library(
+  name='TD',
+  sources = ['D.scala'],
+  dependencies=[':TC'],
+  strict_deps=True,
+)