Make srcs mandatory

Author: coreywoodfield

rules/scala.bzl

@@ -87,6 +87,7 @@ _compile_attributes = {
             "-src.jar",
         ],
         flags = ["DIRECT_COMPILE_TIME_INPUT"],
+        mandatory = True,
     ),
     "data": attr.label_list(
         cfg = _scala_outgoing_transition,

src/main/scala/BUILD

@@ -51,6 +51,7 @@ register_zinc_toolchain(
 # IntelliJ libraries, so we can get a Scala SDK on sync.
 scala_library(
     name = "scala-sdk",
+    srcs = [],
     deps_used_whitelist = compiler_classpath_2_13,
     scala_toolchain_name = "annex_zinc_3",
     deps = compiler_classpath_2_13,
@@ -69,6 +70,7 @@ runtime_classpath_3 = [
 
 scala_library(
     name = "scala-sdk-3",
+    srcs = [],
     deps_used_whitelist = compiler_classpath_3,
     scala_toolchain_name = "annex_zinc_3",
     deps = compiler_classpath_3,