Plug a hole in package object invalidation

scalac isn't sufficiently lazy in the way it deals with package
objects, which causes problems when:

  - a package object has an an ancestor defined under the same
    package
  - the source file defining that ancestor is recompiled but
    the package.scala file is not passed in for recompilation.

This can manifest as a compilation failure with the dreaded
"Symbol $ancestor is missing from the classpath" error
when the class file of the ancestor is _not_ on the classpath, or
undefined results when the stale classfile is included.

Zinc has logic to invalidate package.scala when any of its ancestors
are invalidated. But there is a hole in this logic: if instead an
inner class _within_ one of the ancestors is invalidated, the package
object is not invalidated, despite the fact that Zinc will delete
the class file of and recompile the ancestor.

This commit adds a test that failed with:

```
[info] About to run tests:
[info]  * source-dependencies/package-object-name-inner
...
[info] [debug] Initial set of included nodes: b.O
[info] [debug] Invalidated by transitive inheritance dependency: Set(b.O)
[info] [debug] The following modified names cause invalidation of b.A.Inner: Set(UsedName(o,[Default]))
[info] [debug] Change NamesChange(b.O,ModifiedNames(changes = UsedName(o,[Default]))) invalidates 2 classes due to The b.O has the following regular definitions changed:
[info] [debug] 	UsedName(o,[Default]).
[info] [debug]   > by transitive inheritance: Set(b.O)
[info] [debug]   >
[info] [debug]   > by member reference: Set(b.A.Inner)
[info] [debug]
[info] [debug] New invalidations:
[info] [debug] 	b.A.Inner
[info] [debug] Initial set of included nodes: b.A.Inner
[info] [debug] Previously invalidated, but (transitively) depend on new invalidations:
[info] [debug] Final step, transitive dependencies:
[info] [debug] 	Set(b.A.Inner)
[info] [debug] Invalidated classes: b.A.Inner
[info] [debug] Scala compilation took 0.256750554 s
[info] [debug] done compiling Scala sources
[info] [debug] merging /var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_af9f2f6e/target/early/output-5bdd0cb8-f4f2-4a4d-b629-ee22a2cbba25.jar into /var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_af9f2f6e/target/early/output.ja
[info] [debug] Initial set of included nodes: b.A.Inner
[info] [debug] compilation cycle 2
[info] [info] compiling 1 Scala source to /var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_af9f2f6e/target/classes ...
[info] [debug] Returning already retrieved and compiled bridge: /var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_1e020742/target-bridge-2.12.14.jar.
[info] [debug] [zinc] Running cached compiler 680859f9 for Scala compiler version 2.12.14
[info] [debug] [zinc] The Scala compiler is invoked with:
[info] [debug] 	-Ypickle-java
[info] [debug] 	-Ypickle-write
[info] [debug] 	/var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_af9f2f6e/target/early/output-5bdd0cb8-f4f2-4a4d-b629-ee22a2cbba25.jar
[info] [debug] 	-bootclasspath
[info] [debug] 	/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/resources.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/rt.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/sunrsasign.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/jsse.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/jce.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/charsets.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/lib/jfr.jar:/Users/jz/.jabba/jdk/[email protected]/Contents/Home/jre/classes:/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.14/scala-library-2.12.14.jar
[info] [debug] 	-classpath
[info] [debug] 	/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-compiler/2.12.14/scala-compiler-2.12.14.jar:/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-reflect/2.12.14/scala-reflect-2.12.14.jar:/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/modules/scala-xml_2.12/1.0.6/scala-xml_2.12-1.0.6.jar:/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/jline/jline/2.14.6/jline-2.14.6.jar:/Users/jz/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/fusesource/jansi/jansi/1.12/jansi-1.12.jar:/var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/sbt_af9f2f6e/target/classes
[info] [error] Symbol 'type b.A' is missing from the classpath.
[info] [error] This symbol is required by 'package b.package'.
[info] [error] Make sure that type A is in your classpath and check for conflicting dependencies with `-Ylog-classpath`.
[info] [error] A full rebuild may help if 'package.class' was compiled against an incompatible version of b.
[info] [error] one error found
[info] [debug] Compilation failed (CompilerInterface)
[info] [error] x source-dependencies/package-object-name-inner
[info] [error] sbt.internal.inc.BatchScriptRunner$PreciseScriptedError: {line 3} Command failed: 'compile'
[info] [error] Caused by: Compilation failed
[info] [error] 	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:335)
[info] [error] 	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
[info] [error] 	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[info] [error] 	at sbt.internal.inc.ProjectStructure.doCompile(IncHandler.scala:678)
[info] [error] 	at sbt.internal.inc.ProjectStructure.$anonfun$startCompilation$12(IncHandler.scala:575)
[info] [error] 	at scala.concurrent.impl.ExecutionContextImpl$DefaultThreadFactory$$anon$1$$anon$2.block(ExecutionContextImpl.scala:75)
[info] [error] 	at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3313)
[info] [error] 	at scala.concurrent.impl.ExecutionContextImpl$DefaultThreadFactory$$anon$1.blockOn(ExecutionContextImpl.scala:87)
[info] [error] 	at scala.concurrent.package$.blocking(package.scala:146)
[info] [error] 	at sbt.internal.inc.ProjectStructure.$anonfun$startCompilation$11(IncHandler.scala:573)
[info] [error] 	at scala.util.Success.$anonfun$map$1(Try.scala:255)
[info] [error] 	at scala.util.Success.map(Try.scala:213)
[info] [error] 	at scala.concurrent.Future.$anonfun$map$1(Future.scala:292)
[info] [error] 	at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:33)
[info] [error] 	at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:33)
[info] [error] 	at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:64)
[info] [error] 	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
[info] [error] 	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
[info] [error] 	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
[info] [error] 	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
[info] [error] 	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:175)
[info] [info] Log files of all scripted tests run: /var/folders/22/g1sv634d11j1d_lqlnhz9p2r0000gn/T/scripted-logs-b824d2a8
[error] Exception in thread "main" sbt.internal.inc.ScriptedRunnerImpl$ScriptedFailure$1$: 1 (out of 1) scripted tests failed:
[error] 	source-dependencies/package-object-name-inner
```

This is fixed by searching for descendant package objects of any class
defined in the set of invalidated files, rather than just descendants
of invalidated classes.

internal/zinc-core/src/main/scala/sbt/internal/inc/IncrementalNameHashing.scala

@@ -44,9 +44,16 @@ private[inc] class IncrementalNameHashingCommon(
       apis: APIs
   ): Set[String] = {
     val findSubclasses = relations.inheritance.internal.reverse _
+    val invalidatedClassesAndCodefinedClasses = for {
+      cls <- invalidatedClasses.iterator
+      file <- relations.definesClass(cls).iterator
+      cls1 <- relations.classNames(file)
+    } yield cls1
+
     debug("Invalidate package objects by inheritance only...")
     val invalidatedPackageObjects =
-      transitiveDeps(invalidatedClasses, log)(findSubclasses).filter(_.endsWith(".package"))
+      transitiveDeps(invalidatedClassesAndCodefinedClasses.toSet, log)(findSubclasses)
+        .filter(_.endsWith(".package"))
     debug(s"Package object invalidations: ${invalidatedPackageObjects.mkString(", ")}")
     invalidatedPackageObjects
   }

zinc/src/sbt-test/source-dependencies/package-object-name-inner/A.scala

@@ -0,0 +1,7 @@
+package b
+
+class A {
+  class Inner {
+    O.o
+  }
+}

zinc/src/sbt-test/source-dependencies/package-object-name-inner/O.scala

@@ -0,0 +1,5 @@
+package b
+
+object O {
+  def o = ""
+}

zinc/src/sbt-test/source-dependencies/package-object-name-inner/b.scala

@@ -0,0 +1 @@
+package object b extends A

zinc/src/sbt-test/source-dependencies/package-object-name-inner/changes/O1.scala

@@ -0,0 +1,5 @@
+package b
+
+object O {
+  def o = 42
+}

zinc/src/sbt-test/source-dependencies/package-object-name-inner/test

@@ -0,0 +1,4 @@
+> compile
+$ copy-file changes/O1.scala O.scala
+> compile
+> checkIterations 3