Force the type of an annotation's typeSymbol beofre checking isStatic

Before 2.13, `isStatic` is implemented by
`isNonBottomSubClass(StaticAnnotationClass)`
which forces the annotation symbol's type.

In 2.13, Java annotations are identified by flags. This check doesn't
force the info, and the flags are missing if the info is still a
`ClassfileLoader`.

This leads to spurious API changes (annotation goes missing) if the
depending if the info is already forced or not.

A fix for this will be in 2.13.7, but we should still work around it
in Zinc to make sure zinc works correctly on 2.13.0-6.

internal/compiler-bridge/src/main/scala/xsbt/ExtractAPI.scala

@@ -838,9 +838,14 @@ class ExtractAPI[GlobalType <: Global](
       }
       implicit def compat(ann: AnnotationInfo): IsStatic = new IsStatic(ann)
 
-      // scala/bug#11679 annotations of inherited members may be absent from the compile time classpath
-      // so avoid calling `isNonBottomSubClass` on these stub symbols which would trigger a fatal error.
-      annotations.filter(ann => !isStub(ann.atp.typeSymbol) && ann.isStatic)
+      // `isStub` for scala/bug#11679: annotations of inherited members may be absent from the compile time
+      // classpath so avoid calling `isNonBottomSubClass` on these stub symbols which would trigger an error.
+      //
+      // `initialize` for sbt/zinc#998: 2.13 identifies Java annotations by flags. Up to 2.13.6, this is done
+      // without forcing the info of `ann.atp.typeSymbol`, flags are missing it's still a `ClassfileLoader`.
+      annotations.filter(
+        ann => !isStub(ann.atp.typeSymbol) && { ann.atp.typeSymbol.initialize; ann.isStatic }
+      )
     }
 
   private def isStub(sym: Symbol): Boolean = sym match {

zinc/src/sbt-test/source-dependencies/trait-local-change/build.json

@@ -0,0 +1,8 @@
+{
+  "projects": [
+    {
+      "name": "pro",
+      "scalaVersion": "2.13.6"
+    }
+  ]
+}

zinc/src/sbt-test/source-dependencies/trait-local-change/changes/A2.scala

@@ -0,0 +1,3 @@
+trait A {
+  def f: String = "b"
+}

zinc/src/sbt-test/source-dependencies/trait-local-change/pro/A.scala

@@ -0,0 +1,3 @@
+trait A {
+  def f: String = "a"
+}

zinc/src/sbt-test/source-dependencies/trait-local-change/pro/B.scala

@@ -0,0 +1 @@
+class B extends A

zinc/src/sbt-test/source-dependencies/trait-local-change/test

@@ -0,0 +1,7 @@
+> pro/clean
+> pro/compile
+$ copy-file changes/A2.scala pro/A.scala
+# Second compilation round, there should be no third round (we don't need to recompile B.scala)
+> pro/compile
+# Check that there were only two rounds of compilation
+> pro/checkIterations 2