Preserve type bounds for inlined definitions in posttyper (#17190)

Author: dwijnand

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

@@ -141,4 +141,7 @@ object Mode {
    *  Type `Null` becomes a subtype of non-primitive value types in TypeComparer.
    */
   val RelaxedOverriding: Mode = newMode(30, "RelaxedOverriding")
+
+  /** We are checking the original call of an Inlined node */
+  val InlinedCall: Mode = newMode(31, "InlinedCall")
 }

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

@@ -283,16 +283,14 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
           if tree.isType then
             checkNotPackage(tree)
           else
-            if tree.symbol.is(Inline) && !Inlines.inInlineMethod then
-              ctx.compilationUnit.needsInlining = true
             checkNoConstructorProxy(tree)
+            registerNeedsInlining(tree)
             tree.tpe match {
               case tpe: ThisType => This(tpe.cls).withSpan(tree.span)
               case _ => tree
             }
         case tree @ Select(qual, name) =>
-          if tree.symbol.is(Inline) then
-            ctx.compilationUnit.needsInlining = true
+          registerNeedsInlining(tree)
           if name.isTypeName then
             Checking.checkRealizable(qual.tpe, qual.srcPos)
             withMode(Mode.Type)(super.transform(checkNotPackage(tree)))
@@ -344,8 +342,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
         case tree: TypeApply =>
           if tree.symbol == defn.QuotedTypeModule_of then
             ctx.compilationUnit.needsStaging = true
-          if tree.symbol.is(Inline) then
-            ctx.compilationUnit.needsInlining = true
+          registerNeedsInlining(tree)
           val tree1 @ TypeApply(fn, args) = normalizeTypeArgs(tree)
           for arg <- args do
             checkInferredWellFormed(arg)
@@ -363,6 +360,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
         case Inlined(call, bindings, expansion) if !call.isEmpty =>
           val pos = call.sourcePos
           CrossVersionChecks.checkExperimentalRef(call.symbol, pos)
+          withMode(Mode.InlinedCall)(transform(call))
           val callTrace = Inlines.inlineCallTrace(call.symbol, pos)(using ctx.withSource(pos.source))
           cpy.Inlined(tree)(callTrace, transformSub(bindings), transform(expansion)(using inlineContext(call)))
         case templ: Template =>
@@ -507,6 +505,10 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
     private def normalizeErasedRhs(rhs: Tree, sym: Symbol)(using Context) =
       if (sym.isEffectivelyErased) dropInlines.transform(rhs) else rhs
 
+    private def registerNeedsInlining(tree: Tree)(using Context): Unit =
+      if tree.symbol.is(Inline) && !Inlines.inInlineMethod && !ctx.mode.is(Mode.InlinedCall) then
+        ctx.compilationUnit.needsInlining = true
+
     /** Check if the definition has macro annotation and sets `compilationUnit.hasMacroAnnotations` if needed. */
     private def registerIfHasMacroAnnotations(tree: DefTree)(using Context) =
       if !Inlines.inInlineMethod && MacroAnnotations.hasMacroAnnotation(tree.symbol) then

tests/neg/i17168.scala

@@ -0,0 +1,3 @@
+type F[X <: String] = X
+
+val a = summon[F[Int] =:= Int] // error

tests/pos/i13332super.scala

@@ -55,7 +55,7 @@ class Outer5 { self =>
     }
   }
 
-  lazy val o = new Outer5() // infinite init
+  final lazy val o = new Outer5() // infinite init
 
 }
 
@@ -142,7 +142,7 @@ def locally3 = {
   class Bar extends Foo {
 
     def hello =
-      val mQux = summon[Mirror.Of[Bar.super.foo.type]]
+      val mQux = summon[Mirror.Of[foo.type]]
       assert(mQux.fromProduct(EmptyTuple) == Qux)
   }
 
@@ -157,4 +157,4 @@ def locally3 = {
   testOuter6
   locally1
   locally2
-  locally3
+  locally3

tests/run/anon-mirror-gen-local.scala

@@ -150,7 +150,7 @@ class SubUniverse extends Universe {
 
 trait Whole {
   trait MixinA {
-    lazy val mixinB = new MixinB() {}
+    final lazy val mixinB = new MixinB() {}
   }
   trait MixinB {
     object A extends MixinB { // by inheriting `MixinB`, we should not check for inheritance from the right