Fix #8842: Refine types of inlined inline vals

Author: nicolasstucki

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

@@ -1219,6 +1219,15 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(using Context) {
             super.typedIf(if1, pt)
       }
 
+    override def typedValDef(vdef: untpd.ValDef, sym: Symbol)(using Context): Tree =
+      val vdef1 =
+        if sym.is(Inline) then
+          val rhs = typed(vdef.rhs)
+          sym.info = rhs.tpe
+          untpd.cpy.ValDef(vdef)(vdef.name, untpd.TypedSplice(TypeTree(rhs.tpe)), untpd.TypedSplice(rhs))
+        else vdef
+      super.typedValDef(vdef1, sym)
+
     override def typedApply(tree: untpd.Apply, pt: Type)(using Context): Tree =
       constToLiteral(betaReduce(super.typedApply(tree, pt))) match {
         case res: Apply if res.symbol == defn.InternalQuoted_exprSplice

tests/pos/i8842a.scala

@@ -0,0 +1,5 @@
+inline def f(inline x: Int): Unit = {
+  inline val twice = x + x
+}
+
+def test: Unit = f(3)

tests/pos/i8842b.scala

@@ -0,0 +1,8 @@
+inline def f(inline x: Int): Unit = {
+  inline val twice = x + x
+  inline val thrice = twice + x
+  val res = thrice
+  res
+}
+
+def test: Unit = f(3)