Adds export and runtime_deps support to scala rule

This brings the scala rules a step closer to feature parity with java.

--
Change-Id: I21e6929a36f5084a29b230f1b91307dd5b012d4c
Reviewed-on: https://github.com/bazelbuild/bazel/pull/916
MOS_MIGRATED_REVID=114947019

7 files changed, 99 insertions, 31 deletions

diff --git a/tools/build_defs/scala/README.md b/tools/build_defs/scala/README.md
index 2589548217..20b40eadfe 100644
--- a/tools/build_defs/scala/README.md
+++ b/tools/build_defs/scala/README.md
@@ -28,8 +28,8 @@ scala_repositories()
 ## scala\_library / scala\_macro_library
 
 ```python
-scala_library(name, srcs, deps, data, main_class, resources, scalacopts, jvm_flags)
-scala_macro_library(name, srcs, deps, data, main_class, resources, scalacopts, jvm_flags)
+scala_library(name, srcs, deps, runtime_deps, exports, data, main_class, resources, scalacopts, jvm_flags)
+scala_macro_library(name, srcs, deps, runtime_deps, exports, data, main_class, resources, scalacopts, jvm_flags)
 ```
 
 `scala_library` generates a `.jar` file from `.scala` source files. This rule
@@ -76,6 +76,22 @@ In order to make a java rule use this jar file, use the `java_import` rule.
       </td>
     </tr>
     <tr>
+      <td><code>runtime_deps</code></td>
+      <td>
+        <p><code>List of labels, optional</code></p>
+        <p>List of other libraries to put on the classpath only at runtime. This is rarely needed in Scala.</p>
+      </td>
+    </tr>
+    <tr>
+      <td><code>exports</code></td>
+      <td>
+        <p><code>List of labels, optional</code></p>
+        <p>List of targets to add to the dependencies of those that depend on this target. Similar
+        to the `java_library` parameter of the same name. Use this sparingly as it weakens the
+        precision of the build graph.</p>
+      </td>
+    </tr>
+    <tr>
       <td><code>data</code></td>
       <td>
         <p><code>List of labels, optional</code></p>
@@ -135,7 +151,7 @@ In order to make a java rule use this jar file, use the `java_import` rule.
 ## scala_binary
 
 ```python
-scala_binary(name, srcs, deps, data, main_class, resources, scalacopts, jvm_flags)
+scala_binary(name, srcs, deps, runtime_deps, data, main_class, resources, scalacopts, jvm_flags)
 ```
 
 `scala_binary` generates a Scala executable. It may depend on `scala_library`, `scala_macro_library`
@@ -176,6 +192,13 @@ A `scala_binary` requires a `main_class` attribute.
       </td>
     </tr>
     <tr>
+      <td><code>runtime_deps</code></td>
+      <td>
+        <p><code>List of labels, optional</code></p>
+        <p>List of other libraries to put on the classpath only at runtime. This is rarely needed in Scala.</p>
+      </td>
+    </tr>
+    <tr>
       <td><code>data</code></td>
       <td>
         <p><code>List of labels, optional</code></p>
diff --git a/tools/build_defs/scala/scala.bzl b/tools/build_defs/scala/scala.bzl
index 6e2946b959..2bfc5782a4 100644
--- a/tools/build_defs/scala/scala.bzl
+++ b/tools/build_defs/scala/scala.bzl
@@ -117,14 +117,17 @@ cd $0.runfiles
       output=ctx.outputs.executable,
       content=content)
 
-def _collect_comp_run_jars(ctx):
-  compile_jars = set() # not transitive
-  runtime_jars = set() # this is transitive
-  for target in ctx.attr.deps:
+def _collect_jars(targets):
+  """Compute the runtime and compile-time dependencies from the given targets"""
+  compile_jars = set()  # not transitive
+  runtime_jars = set()  # this is transitive
+  for target in targets:
     found = False
     if hasattr(target, "scala"):
       compile_jars += [target.scala.outputs.ijar]
+      compile_jars += target.scala.transitive_compile_exports
       runtime_jars += target.scala.transitive_runtime_deps
+      runtime_jars += target.scala.transitive_runtime_exports
       found = True
     if hasattr(target, "java"):
       # see JavaSkylarkApiProvider.java, this is just the compile-time deps
@@ -137,32 +140,30 @@ def _collect_comp_run_jars(ctx):
       # support http_file pointed at a jar. http_jar uses ijar, which breaks scala macros
       runtime_jars += target.files
       compile_jars += target.files
-  return (compile_jars, runtime_jars)
+  return struct(compiletime = compile_jars, runtime = runtime_jars)
 
-def _scala_library_impl(ctx):
-  (cjars, rjars) = _collect_comp_run_jars(ctx)
+def _lib(ctx, use_ijar):
+  jars = _collect_jars(ctx.attr.deps)
+  (cjars, rjars) = (jars.compiletime, jars.runtime)
   _write_manifest(ctx)
-  _compile(ctx, cjars, True)
+  _compile(ctx, cjars, use_ijar)
 
   rjars += [ctx.outputs.jar]
-  scalaattr = struct(outputs = struct(ijar=ctx.outputs.ijar, class_jar=ctx.outputs.jar),
-                     transitive_runtime_deps = rjars)
-  runfiles = ctx.runfiles(
-      files = list(rjars),
-      collect_data = True)
-  return struct(
-      scala = scalaattr,
-      runfiles=runfiles)
+  rjars += _collect_jars(ctx.attr.runtime_deps).runtime
 
-def _scala_macro_library_impl(ctx):
-  (cjars, rjars) = _collect_comp_run_jars(ctx)
-  _write_manifest(ctx)
-  _compile(ctx, cjars, False)
+  ijar = None
+  if use_ijar:
+    ijar = ctx.outputs.ijar
+  else:
+    # macro code needs to be available at compile-time, so set ijar == jar
+    ijar = ctx.outputs.jar
 
-  rjars += [ctx.outputs.jar]
-  # macro code needs to be available at compiletime, so set ijar == jar
-  scalaattr = struct(outputs = struct(ijar=ctx.outputs.jar, class_jar=ctx.outputs.jar),
-                     transitive_runtime_deps = rjars)
+  texp = _collect_jars(ctx.attr.exports)
+  scalaattr = struct(outputs = struct(ijar=ijar, class_jar=ctx.outputs.jar),
+                     transitive_runtime_deps = rjars,
+                     transitive_compile_exports = texp.compiletime,
+                     transitive_runtime_exports = texp.runtime
+                     )
   runfiles = ctx.runfiles(
       files = list(rjars),
       collect_data = True)
@@ -170,10 +171,16 @@ def _scala_macro_library_impl(ctx):
       scala = scalaattr,
       runfiles=runfiles)
 
+def _scala_library_impl(ctx):
+  return _lib(ctx, True)
+
+def _scala_macro_library_impl(ctx):
+  return _lib(ctx, False)  # don't build the ijar for macros
+
 # Common code shared by all scala binary implementations.
 def _scala_binary_common(ctx, cjars, rjars):
   _write_manifest(ctx)
-  _compile(ctx, cjars, False)
+  _compile(ctx, cjars, False)  # no need to build an ijar for an executable
 
   runfiles = ctx.runfiles(
       files = list(rjars) + [ctx.outputs.executable] + [ctx.file._java] + ctx.files._jdk,
@@ -183,16 +190,20 @@ def _scala_binary_common(ctx, cjars, rjars):
       runfiles=runfiles)
 
 def _scala_binary_impl(ctx):
-  (cjars, rjars) = _collect_comp_run_jars(ctx)
+  jars = _collect_jars(ctx.attr.deps)
+  (cjars, rjars) = (jars.compiletime, jars.runtime)
   cjars += [ctx.file._scalareflect]
   rjars += [ctx.outputs.jar, ctx.file._scalalib, ctx.file._scalareflect]
+  rjars += _collect_jars(ctx.attr.runtime_deps).runtime
   _write_launcher(ctx, rjars)
   return _scala_binary_common(ctx, cjars, rjars)
 
 def _scala_test_impl(ctx):
-  (cjars, rjars) = _collect_comp_run_jars(ctx)
+  jars = _collect_jars(ctx.attr.deps)
+  (cjars, rjars) = (jars.compiletime, jars.runtime)
   cjars += [ctx.file._scalareflect, ctx.file._scalatest, ctx.file._scalaxml]
   rjars += [ctx.outputs.jar, ctx.file._scalalib, ctx.file._scalareflect, ctx.file._scalatest, ctx.file._scalaxml]
+  rjars += _collect_jars(ctx.attr.runtime_deps).runtime
   _write_test_launcher(ctx, rjars)
   return _scala_binary_common(ctx, cjars, rjars)
 
@@ -213,6 +224,7 @@ _common_attrs = {
       allow_files=_scala_filetype,
       non_empty=True),
   "deps": attr.label_list(),
+  "runtime_deps": attr.label_list(),
   "data": attr.label_list(allow_files=True, cfg=DATA_CFG),
   "resources": attr.label_list(allow_files=True),
   "scalacopts":attr.string_list(),
@@ -223,6 +235,7 @@ scala_library = rule(
   implementation=_scala_library_impl,
   attrs={
       "main_class": attr.string(),
+      "exports": attr.label_list(allow_files=False),
       } + _implicit_deps + _common_attrs,
   outputs={
       "jar": "%{name}_deploy.jar",
@@ -235,6 +248,7 @@ scala_macro_library = rule(
   implementation=_scala_macro_library_impl,
   attrs={
       "main_class": attr.string(),
+      "exports": attr.label_list(allow_files=False),
       "_scala-reflect": attr.label(default=Label("@scala//:lib/scala-reflect.jar"), single_file=True, allow_files=True),
       } + _implicit_deps + _common_attrs,
   outputs={
diff --git a/tools/build_defs/scala/test/BUILD b/tools/build_defs/scala/test/BUILD
index cd9ad27bc3..4ef5e95ba7 100644
--- a/tools/build_defs/scala/test/BUILD
+++ b/tools/build_defs/scala/test/BUILD
@@ -49,6 +49,18 @@ scala_test(
 scala_library(
     name = "OtherLib",
     srcs = ["OtherLib.scala"],
+    exports = ["Exported"],  # test of exported target
+)
+
+scala_library(
+    name = "Exported",
+    srcs = ["Exported.scala"],
+    runtime_deps = ["Runtime"],
+)
+
+scala_library(
+    name = "Runtime",
+    srcs = ["Runtime.scala"],
 )
 
 java_library(
diff --git a/tools/build_defs/scala/test/Exported.scala b/tools/build_defs/scala/test/Exported.scala
new file mode 100644
index 0000000000..82264ec5de
--- /dev/null
+++ b/tools/build_defs/scala/test/Exported.scala
@@ -0,0 +1,11 @@
+package scala.test
+
+object Exported {
+  def message: String = {
+    // terrible, don't do this in real code:
+    val msg = Class.forName("scala.test.Runtime")
+      .newInstance
+      .toString
+    "you all, everybody. " + msg
+  }
+}
diff --git a/tools/build_defs/scala/test/HelloLib.scala b/tools/build_defs/scala/test/HelloLib.scala
index a1fef111da..974c8b7298 100644
--- a/tools/build_defs/scala/test/HelloLib.scala
+++ b/tools/build_defs/scala/test/HelloLib.scala
@@ -4,6 +4,7 @@ object HelloLib {
   def printMessage(arg: String) {
     println(getOtherLibMessage(arg))
     println(getOtherJavaLibMessage(arg))
+    println(Exported.message)
   }
 
   def getOtherLibMessage(arg: String) : String = {
diff --git a/tools/build_defs/scala/test/OtherLib.scala b/tools/build_defs/scala/test/OtherLib.scala
index f696242d40..2f69f68a7b 100644
--- a/tools/build_defs/scala/test/OtherLib.scala
+++ b/tools/build_defs/scala/test/OtherLib.scala
@@ -3,6 +3,8 @@ package scala.test
 // It is just to show how a Scala library can depend on another Scala library.
 object OtherLib {
   def getMessage(): String = {
-    return "scala!"
+    // This won't compile because Exported is exported, not a dep:
+    // Exported.message
+    "scala!"
   }
 }
diff --git a/tools/build_defs/scala/test/Runtime.scala b/tools/build_defs/scala/test/Runtime.scala
new file mode 100644
index 0000000000..e64c06d82b
--- /dev/null
+++ b/tools/build_defs/scala/test/Runtime.scala
@@ -0,0 +1,5 @@
+package scala.test
+
+class Runtime {
+  override def toString = "I am Runtime"
+}