Treat asserted set of terminated NotNullInfo as universal set; fix test

[Cherry-picked 00430c0]

Author: noti0na1

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -755,13 +755,13 @@ object Contexts {
 
   extension (c: Context)
     def addNotNullInfo(info: NotNullInfo) =
-      c.withNotNullInfos(c.notNullInfos.extendWith(info))
+      if c.explicitNulls then c.withNotNullInfos(c.notNullInfos.extendWith(info)) else c
 
     def addNotNullRefs(refs: Set[TermRef]) =
-      c.addNotNullInfo(NotNullInfo(refs, Set()))
+      if c.explicitNulls then c.addNotNullInfo(NotNullInfo(refs, Set())) else c
 
     def withNotNullInfos(infos: List[NotNullInfo]): Context =
-      if c.notNullInfos eq infos then c else c.fresh.setNotNullInfos(infos)
+      if !c.explicitNulls || (c.notNullInfos eq infos) then c else c.fresh.setNotNullInfos(infos)
 
     def relaxedOverrideContext: Context =
       c.withModeBits(c.mode &~ Mode.SafeNulls | Mode.RelaxedOverriding)

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

@@ -210,7 +210,7 @@ object Nullables:
     */
     @tailrec def impliesNotNull(ref: TermRef): Boolean = infos match
       case info :: infos1 =>
-        if info.asserted != null && info.asserted.contains(ref) then true
+        if info.asserted == null || info.asserted.contains(ref) then true
         else if info.retracted.contains(ref) then false
         else infos1.impliesNotNull(ref)
       case _ =>
@@ -290,8 +290,8 @@ object Nullables:
   extension (tree: Tree)
 
     /* The `tree` with added nullability attachment */
-    def withNotNullInfo(info: NotNullInfo): tree.type =
-      if !info.isEmpty then tree.putAttachment(NNInfo, info)
+    def withNotNullInfo(info: NotNullInfo)(using Context): tree.type =
+      if ctx.explicitNulls && !info.isEmpty then tree.putAttachment(NNInfo, info)
       tree
 
     /* Collect the nullability info from parts of `tree` */
@@ -310,13 +310,15 @@ object Nullables:
 
     /* The nullability info of `tree` */
     def notNullInfo(using Context): NotNullInfo =
-      val tree1 = stripInlined(tree)
-      tree1.getAttachment(NNInfo) match
-        case Some(info) if !ctx.erasedTypes => info
-        case _ =>
-          val nnInfo = tree1.collectNotNullInfo
-          tree1.withNotNullInfo(nnInfo)
-          nnInfo
+      if !ctx.explicitNulls then NotNullInfo.empty
+      else
+        val tree1 = stripInlined(tree)
+        tree1.getAttachment(NNInfo) match
+          case Some(info) if !ctx.erasedTypes => info
+          case _ =>
+            val nnInfo = tree1.collectNotNullInfo
+            tree1.withNotNullInfo(nnInfo)
+            nnInfo
 
     /* The nullability info of `tree`, assuming it is a condition that evaluates to `c` */
     def notNullInfoIf(c: Boolean)(using Context): NotNullInfo =

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

@@ -2514,6 +2514,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val vdef1 = assignType(cpy.ValDef(vdef)(name, tpt1, rhs1), sym)
     postProcessInfo(vdef1, sym)
     vdef1.setDefTree
+    val nnInfo = rhs1.notNullInfo
+    vdef1.withNotNullInfo(if sym.is(Lazy) then nnInfo.retractedInfo else nnInfo)
   }
 
   private def retractDefDef(sym: Symbol)(using Context): Tree =

tests/explicit-nulls/pos/after-termination.scala

@@ -0,0 +1,17 @@
+class C(val x: Int, val next: C | Null)
+
+def test1(x: String | Null, c: C | Null): Int =
+  return 0
+  // We know that the following code is unreachable,
+  // so we can treat `x`, `c`, and any variable/path non-nullable.
+  x.length + c.next.x
+
+def test2(x: String | Null, c: C | Null): Int =
+  throw new Exception()
+  x.length + c.next.x
+
+def fail(): Nothing = ???
+
+def test3(x: String | Null, c: C | Null): Int =
+  fail()
+  x.length + c.next.x

tests/explicit-nulls/unsafe-common/unsafe-overload.scala

@@ -16,8 +16,8 @@ class S {
   val o: O = ???
 
   locally {
-    def h1(hh: String => String) = ???
-    def h2(hh: Array[String] => Array[String]) = ???
+    def h1(hh: String => String): Unit = ???
+    def h2(hh: Array[String] => Array[String]): Unit = ???
     def f1(x: String | Null): String | Null = ???
     def f2(x: Array[String | Null]):  Array[String | Null] = ???
 
@@ -29,10 +29,10 @@ class S {
   }
 
   locally {
-    def h1(hh: String | Null => String | Null) = ???
-    def h2(hh: Array[String | Null] => Array[String | Null]) = ???
+    def h1(hh: String | Null => String | Null): Unit = ???
+    def h2(hh: Array[String | Null] => Array[String | Null]): Unit = ???
     def g1(x: String): String = ???
-    def g2(x: Array[String]):  Array[String] = ???
+    def g2(x: Array[String]): Array[String] = ???
 
     h1(g1) // error
     h1(o.g) // error
@@ -51,7 +51,7 @@ class S {
 
   locally {
     def g1(x: String): String = ???
-    def g2(x: Array[String]):  Array[String] = ???
+    def g2(x: Array[String]): Array[String] = ???
 
     o.i(g1) // error
     o.i(g2) // error