Strip Nulls from Java members when unsafeNulls is enabled

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3746,6 +3746,15 @@ class Typer extends Namer
         if target <:< pt then
           return readapt(tree.cast(target))
 
+      // if unsafeNulls is enabled, try to strip nulls from Java function calls
+      if Nullables.unsafeNullsEnabled then
+        tree match
+          case _: Apply | _: Select if tree.symbol.is(JavaDefined) =>
+            wtp match
+              case OrNull(wtp1) => return readapt(tree.cast(wtp1))
+              case _ =>
+          case _ =>
+
       def recover(failure: SearchFailureType) =
         if canDefineFurther(wtp) || canDefineFurther(pt) then readapt(tree)
         else err.typeMismatch(tree, pt, failure)

tests/explicit-nulls/unsafe-common/unsafe-java-call/J.java

@@ -0,0 +1,17 @@
+public class J {
+  public String f1() {
+    return "";
+  }
+
+  public int f2() {
+    return 0;
+  }
+
+  public <T> T g1() {
+    return null;
+  }
+}
+
+class J2<T> {
+  public T x = null;
+}

tests/explicit-nulls/unsafe-common/unsafe-java-call/S.scala

@@ -0,0 +1,37 @@
+// Check Java calls have been cast to non-nullable.
+
+val j: J = new J
+
+val s1: String = j.f1() // error
+
+val s1n: String | Null = j.f1()
+
+val i1: Int = j.f2()
+
+val s2: String = j.g1[String]()  // error
+
+val s2n: String | Null = j.g1[String]()
+
+val s3: String = j.g1[String | Null]()  // error
+
+val s3n: String | Null = j.g1[String | Null]()
+
+val i2: Int = j.g1[Int]()  // error
+
+val a1: Any = j.g1[Any]()
+
+val ar1: AnyRef = j.g1[AnyRef]()  // error
+
+val n1: Null = j.g1[Null]()
+
+val ar2: AnyRef = j.g1[Null]()  // error
+
+def clo1[T]: T = j.g1[T]()  // error
+
+def clo2[T <: AnyRef]: T = j.g1[T | Null]()  // error
+
+def clo3[T >: Null <: AnyRef | Null]: T = j.g1[T]()
+
+def testJ2[T]: T =
+  val j2: J2[T] = new J2
+  j2.x // error