Merge pull request #14755 from dotty-staging/fix-14682

Fix 14682: fix overriding check in mergeSingleDenot

Author: olhotak

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

@@ -469,11 +469,12 @@ object Denotations {
                 else if sym1.is(Method) && !sym2.is(Method) then 1
                 else 0
 
+          val relaxedOverriding = ctx.explicitNulls && (sym1.is(JavaDefined) || sym2.is(JavaDefined))
           val matchLoosely = sym1.matchNullaryLoosely || sym2.matchNullaryLoosely
 
-          if symScore <= 0 && info2.overrides(info1, matchLoosely, checkClassInfo = false) then
+          if symScore <= 0 && info2.overrides(info1, relaxedOverriding, matchLoosely, checkClassInfo = false) then
             denot2
-          else if symScore >= 0 && info1.overrides(info2, matchLoosely, checkClassInfo = false) then
+          else if symScore >= 0 && info1.overrides(info2, relaxedOverriding, matchLoosely, checkClassInfo = false) then
             denot1
           else
             val jointInfo = infoMeet(info1, info2, safeIntersection)

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

@@ -1071,21 +1071,25 @@ object Types {
 
     /** Is this type a legal type for member `sym1` that overrides another
      *  member `sym2` of type `that`? This is the same as `<:<`, except that
+     *  @param relaxedCheck   if true type `Null` becomes a subtype of non-primitive value types in TypeComparer.
      *  @param matchLoosely   if true the types `=> T` and `()T` are seen as overriding each other.
      *  @param checkClassInfo if true we check that ClassInfos are within bounds of abstract types
      */
-    final def overrides(that: Type, matchLoosely: => Boolean, checkClassInfo: Boolean = true)(using Context): Boolean = {
+    final def overrides(that: Type, relaxedCheck: Boolean, matchLoosely: => Boolean, checkClassInfo: Boolean = true)(using Context): Boolean = {
       def widenNullary(tp: Type) = tp match {
         case tp @ MethodType(Nil) => tp.resultType
         case _ => tp
       }
-      !checkClassInfo && this.isInstanceOf[ClassInfo]
-      || (this.widenExpr frozen_<:< that.widenExpr)
-      || matchLoosely && {
-           val this1 = widenNullary(this)
-           val that1 = widenNullary(that)
-           ((this1 `ne` this) || (that1 `ne` that)) && this1.overrides(that1, false, checkClassInfo)
-         }
+      val overrideCtx = if relaxedCheck then ctx.relaxedOverrideContext else ctx
+      inContext(overrideCtx) {
+        !checkClassInfo && this.isInstanceOf[ClassInfo]
+        || (this.widenExpr frozen_<:< that.widenExpr)
+        || matchLoosely && {
+            val this1 = widenNullary(this)
+            val that1 = widenNullary(that)
+            ((this1 `ne` this) || (that1 `ne` that)) && this1.overrides(that1, relaxedCheck, false, checkClassInfo)
+          }
+      }
     }
 
     /** Is this type close enough to that type so that members

compiler/src/dotty/tools/dotc/transform/OverridingPairs.scala

@@ -217,11 +217,9 @@ object OverridingPairs:
     else
       // releaxed override check for explicit nulls if one of the symbols is Java defined,
       // force `Null` to be a subtype of non-primitive value types during override checking.
-      val overrideCtx = if ctx.explicitNulls && (member.is(JavaDefined) || other.is(JavaDefined))
-        then ctx.relaxedOverrideContext else ctx
+      val relaxedOverriding = ctx.explicitNulls && (member.is(JavaDefined) || other.is(JavaDefined))
       member.name.is(DefaultGetterName) // default getters are not checked for compatibility
-      || memberTp.overrides(otherTp,
-            member.matchNullaryLoosely || other.matchNullaryLoosely || fallBack
-          )(using overrideCtx)
+      || memberTp.overrides(otherTp, relaxedOverriding,
+            member.matchNullaryLoosely || other.matchNullaryLoosely || fallBack)
 
 end OverridingPairs

compiler/src/dotty/tools/dotc/transform/ResolveSuper.scala

@@ -113,9 +113,8 @@ object ResolveSuper {
         // Since the super class can be Java defined,
         // we use relaxed overriding check for explicit nulls if one of the symbols is Java defined.
         // This forces `Null` to be a subtype of non-primitive value types during override checking.
-        val overrideCtx = if ctx.explicitNulls && (sym.is(JavaDefined) || acc.is(JavaDefined))
-          then ctx.relaxedOverrideContext else ctx
-        if !otherTp.overrides(accTp, matchLoosely = true)(using overrideCtx) then
+        val relaxedOverriding = ctx.explicitNulls && (sym.is(JavaDefined) || acc.is(JavaDefined))
+        if !otherTp.overrides(accTp, relaxedOverriding, matchLoosely = true) then
           report.error(IllegalSuperAccessor(base, memberName, targetName, acc, accTp, other.symbol, otherTp), base.srcPos)
       bcs = bcs.tail
     }

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

@@ -767,7 +767,7 @@ object RefChecks {
           for (mbrd <- self.member(name).alternatives) {
             val mbr = mbrd.symbol
             val mbrType = mbr.info.asSeenFrom(self, mbr.owner)
-            if (!mbrType.overrides(mbrd.info, matchLoosely = true))
+            if (!mbrType.overrides(mbrd.info, relaxedCheck = false, matchLoosely = true))
               report.errorOrMigrationWarning(
                 em"""${mbr.showLocated} is not a legal implementation of `$name` in $clazz
                     |  its type             $mbrType

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -52,7 +52,6 @@ class CompilationTests {
       ),
       compileFile("tests/pos-special/typeclass-scaling.scala", defaultOptions.and("-Xmax-inlines", "40")),
       compileFile("tests/pos-special/i7296.scala", defaultOptions.and("-source", "future", "-deprecation", "-Xfatal-warnings")),
-      compileFile("tests/pos-special/notNull.scala", defaultOptions.and("-Yexplicit-nulls")),
       compileDir("tests/pos-special/adhoc-extension", defaultOptions.and("-source", "future", "-feature", "-Xfatal-warnings")),
       compileFile("tests/pos-special/i7575.scala", defaultOptions.andLanguageFeature("dynamics")),
       compileFile("tests/pos-special/kind-projector.scala", defaultOptions.and("-Ykind-projector")),
@@ -137,7 +136,6 @@ class CompilationTests {
       compileFilesInDir("tests/neg-custom-args/erased", defaultOptions.and("-language:experimental.erasedDefinitions")),
       compileFilesInDir("tests/neg-custom-args/allow-double-bindings", allowDoubleBindings),
       compileFilesInDir("tests/neg-custom-args/allow-deep-subtypes", allowDeepSubtypes),
-      compileFilesInDir("tests/neg-custom-args/explicit-nulls", defaultOptions.and("-Yexplicit-nulls")),
       compileFilesInDir("tests/neg-custom-args/no-experimental", defaultOptions.and("-Yno-experimental")),
       compileDir("tests/neg-custom-args/impl-conv", defaultOptions.and("-Xfatal-warnings", "-feature")),
       compileDir("tests/neg-custom-args/i13946", defaultOptions.and("-Xfatal-warnings", "-feature")),
@@ -249,6 +247,7 @@ class CompilationTests {
       compileFilesInDir("tests/explicit-nulls/pos-separate", explicitNullsOptions),
       compileFilesInDir("tests/explicit-nulls/pos-patmat", explicitNullsOptions and "-Xfatal-warnings"),
       compileFilesInDir("tests/explicit-nulls/unsafe-common", explicitNullsOptions and "-language:unsafeNulls"),
+      compileFile("tests/explicit-nulls/pos-special/i14682.scala", explicitNullsOptions and "-Ysafe-init"),
     )
   }.checkCompile()
 

tests/neg-custom-args/explicit-nulls/byname-nullables.check renamed to tests/explicit-nulls/neg/byname-nullables.check

@@ -1,27 +1,27 @@
--- [E007] Type Mismatch Error: tests/neg-custom-args/explicit-nulls/byname-nullables.scala:19:24 -----------------------
+-- [E007] Type Mismatch Error: tests/explicit-nulls/neg/byname-nullables.scala:19:24 -----------------------------------
 19 |    if x != null then f(x)   // error: f is call-by-name
    |                        ^
    |                        Found:    (x : String | Null)
    |                        Required: String
    |
    | longer explanation available when compiling with `-explain`
--- Error: tests/neg-custom-args/explicit-nulls/byname-nullables.scala:43:32 --------------------------------------------
+-- Error: tests/explicit-nulls/neg/byname-nullables.scala:43:32 --------------------------------------------------------
 43 |    if x != null then f(identity(x), 1)   // error: dropping not null check fails typing
    |                        ^^^^^^^^^^^
    |                     This argument was typed using flow assumptions about mutable variables
    |                     but it is passed to a by-name parameter where such flow assumptions are unsound.
    |                     Wrapping the argument in `byName(...)` fixes the problem by disabling the flow assumptions.
    |
    |                     `byName` needs to be imported from the `scala.compiletime` package.
--- Error: tests/neg-custom-args/explicit-nulls/byname-nullables.scala:68:24 --------------------------------------------
+-- Error: tests/explicit-nulls/neg/byname-nullables.scala:68:24 --------------------------------------------------------
 68 |    if x != null then f(x, 1)   // error: dropping not null check typechecks OK, but gives incompatible result type
    |                        ^
    |                     This argument was typed using flow assumptions about mutable variables
    |                     but it is passed to a by-name parameter where such flow assumptions are unsound.
    |                     Wrapping the argument in `byName(...)` fixes the problem by disabling the flow assumptions.
    |
    |                     `byName` needs to be imported from the `scala.compiletime` package.
--- [E134] Type Error: tests/neg-custom-args/explicit-nulls/byname-nullables.scala:81:22 --------------------------------
+-- [E134] Type Error: tests/explicit-nulls/neg/byname-nullables.scala:81:22 --------------------------------------------
 81 |    if x != null then f(byName(x), 1)   // error: none of the overloaded methods match argument types
    |                      ^
    |                      None of the overloaded alternatives of method f in object Test7 with types

tests/neg-custom-args/explicit-nulls/byname-nullables.scala renamed to tests/explicit-nulls/neg/byname-nullables.scala

@@ -1,4 +1,4 @@
--- Error: tests/neg-custom-args/explicit-nulls/byname-nullables1.scala:10:6 --------------------------------------------
+-- Error: tests/explicit-nulls/neg/byname-nullables1.scala:10:6 --------------------------------------------------------
 10 |    f(x.fld != null) // error
    |      ^^^^^^^^^^^^^
    |      This argument was typed using flow assumptions about mutable variables

tests/neg-custom-args/explicit-nulls/byname-nullables1.check renamed to tests/explicit-nulls/neg/byname-nullables1.check

@@ -1,18 +1,18 @@
--- [E134] Type Error: tests/neg-custom-args/explicit-nulls/i7883.scala:6:11 --------------------------------------------
+-- [E134] Type Error: tests/explicit-nulls/neg/i7883.scala:6:11 --------------------------------------------------------
 6 |      case r(hd, tl) => Some((hd, tl))  // error // error // error
   |           ^
   |           None of the overloaded alternatives of method unapplySeq in class Regex with types
   |            (m: scala.util.matching.Regex.Match): Option[List[String]]
   |            (c: Char): Option[List[Char]]
   |            (s: CharSequence): Option[List[String]]
   |           match arguments (String | Null)
--- [E006] Not Found Error: tests/neg-custom-args/explicit-nulls/i7883.scala:6:30 ---------------------------------------
+-- [E006] Not Found Error: tests/explicit-nulls/neg/i7883.scala:6:30 ---------------------------------------------------
 6 |      case r(hd, tl) => Some((hd, tl))  // error // error // error
   |                              ^^
   |                              Not found: hd
   |
   | longer explanation available when compiling with `-explain`
--- [E006] Not Found Error: tests/neg-custom-args/explicit-nulls/i7883.scala:6:34 ---------------------------------------
+-- [E006] Not Found Error: tests/explicit-nulls/neg/i7883.scala:6:34 ---------------------------------------------------
 6 |      case r(hd, tl) => Some((hd, tl))  // error // error // error
   |                                  ^^
   |                                  Not found: tl

tests/neg-custom-args/explicit-nulls/byname-nullables1.scala renamed to tests/explicit-nulls/neg/byname-nullables1.scala

@@ -0,0 +1,27 @@
+class C1:
+  sealed abstract class Name {
+    type ThisName <: Name
+    def compareTo(that: ThisName): Int = ???
+  }
+
+  class LocalName extends Name with Comparable[LocalName] {
+    type ThisName = LocalName
+  }
+
+  val localName = LocalName()
+  println(localName)
+  var count = 0
+
+class C2:
+  sealed abstract class Name {
+    type ThisName <: Name
+    def compareTo(that: ThisName | Null): Int = ???
+  }
+
+  class LocalName extends Name with Comparable[LocalName] {
+    type ThisName = LocalName
+  }
+
+  val localName = LocalName()
+  println(localName)
+  var count = 0