Fix NotNullInfo for Case and Try; add more tests

Author: noti0na1

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

@@ -2136,7 +2136,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       }
       .asInstanceOf[List[CaseDef]]
     var nni = sel.notNullInfo
-    if(cases1.nonEmpty) nni = nni.seq(cases1.map(_.notNullInfo).reduce(_.alt(_)))
+    if cases1.nonEmpty then nni = nni.seq(cases1.map(_.notNullInfo).reduce(_.alt(_)))
     assignType(cpy.Match(tree)(sel, cases1), sel, cases1).cast(pt).withNotNullInfo(nni)
   }
 
@@ -2145,7 +2145,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     val cases1 = harmonic(harmonize, pt)(typedCases(cases, sel, wideSelType, pt.dropIfProto))
       .asInstanceOf[List[CaseDef]]
     var nni = sel.notNullInfo
-    if(cases1.nonEmpty) nni = nni.seq(cases1.map(_.notNullInfo).reduce(_.alt(_)))
+    if cases1.nonEmpty then nni = nni.seq(cases1.map(_.notNullInfo).reduce(_.alt(_)))
     assignType(cpy.Match(tree)(sel, cases1), sel, cases1).withNotNullInfo(nni)
   }
 
@@ -2218,13 +2218,11 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         // will end up taking too much memory. If it does, we should just limit
         // how much GADT constraints we infer - it's always sound to infer less.
         pat1.putAttachment(InferredGadtConstraints, ctx.gadt)
-      if (pt1.isValueType) // insert a cast if body does not conform to expected type if we disregard gadt bounds
+      if pt1.isValueType then // insert a cast if body does not conform to expected type if we disregard gadt bounds
         body1 = body1.ensureConforms(pt1)(using originalCtx)
-      val nni = pat1.notNullInfo.seq(
-        guard1.notNullInfoIf(false).alt(
-          guard1.notNullInfoIf(true).seq(body1.notNullInfo)
-        )
-      )
+      val nni = pat1.notNullInfo
+        .seq(guard1.notNullInfoIf(false).alt(guard1.notNullInfoIf(true)))
+        .seq(body1.notNullInfo)
       assignType(cpy.CaseDef(tree)(pat1, guard1, body1), pat1, body1).withNotNullInfo(nni)
     }
 
@@ -2329,16 +2327,25 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       untpd.Block(makeCanThrow(capabilityProof), expr)
 
   def typedTry(tree: untpd.Try, pt: Type)(using Context): Try = {
+    // We want to type check tree.expr first to comput NotNullInfo, but `addCanThrowCapabilities`
+    // uses the types of patterns in `tree.cases` to determine the capabilities.
+    // Hence, we create a copy of cases with empty body and type check that first, then type check
+    // the rest of the tree in order.
+    val casesEmptyBody1 = tree.cases.mapconserve(cpy.CaseDef(_)(body = EmptyTree))
+    val casesEmptyBody2 = typedCases(casesEmptyBody1, EmptyTree, defn.ThrowableType, WildcardType)
+
     val expr2 :: cases2x = harmonic(harmonize, pt) {
-      val cases1 = typedCases(tree.cases, EmptyTree, defn.ThrowableType, pt.dropIfProto)
-      val expr1 = typed(addCanThrowCapabilities(tree.expr, cases1), pt.dropIfProto)
+      val expr1 = typed(addCanThrowCapabilities(tree.expr, casesEmptyBody2), pt.dropIfProto)
+      val casesCtx = ctx.addNotNullInfo(expr1.notNullInfo.retractedInfo)
+      val cases1 = typedCases(tree.cases, EmptyTree, defn.ThrowableType, pt.dropIfProto)(using casesCtx)
       expr1 :: cases1
     }: @unchecked
-    val finalizer1 = typed(tree.finalizer, defn.UnitType)
     val cases2 = cases2x.asInstanceOf[List[CaseDef]]
-    val nni = expr2.notNullInfo.retractedInfo.seq(
-      cases2.map(_.notNullInfo.retractedInfo).fold(NotNullInfo.empty)(_.alt(_))
-    ).seq(finalizer1.notNullInfo)
+
+    var nni = expr2.notNullInfo.retractedInfo
+    if cases2.nonEmpty then nni = nni.seq(cases2.map(_.notNullInfo).reduce(_.alt(_)))
+    val finalizer1 = typed(tree.finalizer, defn.UnitType)(using ctx.addNotNullInfo(nni))
+    nni = nni.seq(finalizer1.notNullInfo)
     assignType(cpy.Try(tree)(expr2, cases2, finalizer1), expr2, cases2).withNotNullInfo(nni)
   }
 

tests/explicit-nulls/neg/i21380b.scala

@@ -1,8 +1,14 @@
-@main def test() = {
+def test1 =
   var x: String | Null = null
   x = ""
-  1 match {
+  1 match
     case 1 => x = null
-  }
+    case _ => x = x.trim() // ok
   x.replace("", "") // error
-}
+
+def test2(i: Int) =
+  var x: String | Null = null
+  i match
+    case 1 => x = "1"
+    case _ => x = " "
+  x.replace("", "") // ok

tests/explicit-nulls/neg/i21380c.scala

@@ -0,0 +1,34 @@
+def test1(i: Int): Int =
+  var x: String | Null = null
+  if i == 0 then x = ""
+  else x = ""
+  try
+    x = x.replace(" ", "") // ok
+    throw new Exception()
+  catch
+    case e: Exception =>
+      x = x.replaceAll(" ", "") // error
+      x = null
+  x.length // error
+
+def test2: Int =
+  var x: String | Null = null
+  try throw new Exception()
+  finally x = ""
+  x.length // ok
+
+def test3 =
+  var x: String | Null = ""
+  try throw new Exception()
+  catch case e: Exception =>
+    x = (??? : String | Null)
+  finally
+    val l = x.length // error
+
+def test4: Int =
+  var x: String | Null = null
+  try throw new Exception()
+  catch
+    case npe: NullPointerException => x = ""
+    case _ => x = ""
+  x.length // ok