Exclude Java module class in completion in imports

When completing imports, we don't want to show duplicates for instance
when the user does:

    import java.io.FileDesc<tab>

When completing imports, we filter out the Java module classes, to keep
only the classes. This avoids showing twice `java.io.FileDescriptor`.

Author: Duhemm

compiler/src/dotty/tools/dotc/interactive/Interactive.scala

@@ -205,8 +205,9 @@ object Interactive {
      *   3. are not a primary constructor,
      *   4. have an existing source symbol,
      *   5. are the module class in case of packages,
-     *   6. are mutable accessors, to exclude setters for `var`,
-     *   7. have same term/type kind as name prefix given so far
+     *   6. are not Java module classes when completing imports (to avoid duplicate results).
+     *   7. are mutable accessors, to exclude setters for `var`,
+     *   8. have same term/type kind as name prefix given so far
      *
      *  The reason for (2) is that we do not want to present compiler-synthesized identifiers
      *  as completion results. However, if a user explicitly writes all '$' characters in an
@@ -223,6 +224,7 @@ object Interactive {
       !sym.isPrimaryConstructor &&
       sym.sourceSymbol.exists &&
       (!sym.is(Package) || !sym.moduleClass.exists) &&
+      (!inImport || !sym.is(allOf(JavaDefined, Module), butNot = Package)) &&
       !sym.is(allOf(Mutable, Accessor)) &&
       (!termOnly || sym.isTerm) &&
       (!typeOnly || sym.isType)

language-server/test/dotty/tools/languageserver/CompletionTest.scala

@@ -116,4 +116,26 @@ class CompletionTest {
                          ("myClass", Class, "Object{...}"),
                          ("myTrait", Class, "Object{...}")))
   }
+
+  @Test def importJavaClass: Unit = {
+    code"""import java.io.FileDesc${m1}""".withSource
+      .completion(m1, Set(("FileDescriptor", Class, "Object{...}")))
+  }
+
+  @Test def importJavaStaticMethod: Unit = {
+    code"""import java.lang.System.lineSep${m1}""".withSource
+      .completion(m1, Set(("lineSeparator", Method, "(): String")))
+  }
+
+  @Test def importJavaStaticField: Unit = {
+    code"""import java.lang.System.ou${m1}""".withSource
+      .completion(m1, Set(("out", Field, "java.io.PrintStream")))
+  }
+
+  @Test def completeJavaModuleClass: Unit = {
+    code"""object O {
+             val out = java.io.FileDesc${m1}
+           }""".withSource
+      .completion(m1, Set(("FileDescriptor", Module, "java.io.FileDescriptor")))
+  }
 }