Avoid using the current denotation in NamedType.disambiguate (#21414)

While recalculating denotation in NamedType (in `NamedType.memberDenot`,
which itself can be called from `NamedType.computeDenot` or
`NamedType.recomputeDenot`), it might call `NamedType.disambiguate`
which uses a denotation to decide about the correct overloaded method.
Using current denotation here might cause stale symbol errors, so
instead we use the `lastKnownDenotation`, which should be enough for the
use case here, as `targetName` should not change between phases/runs.

Later in the denotation recalculation a similar thing happens with
`SourceLanguage.apply`, where we also now avoid using currentDenotation,
as whether the symbol comes from java or Scala 2 should also not change
between phases/runs.

Author: jchyb

Diff for: compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -961,7 +961,7 @@ object Denotations {
     }
 
     def staleSymbolError(using Context): Nothing =
-      if symbol.isPackageObject && ctx.run != null && ctx.run.nn.isCompilingSuspended
+      if symbol.lastKnownDenotation.isPackageObject && ctx.run != null && ctx.run.nn.isCompilingSuspended
       then throw StaleSymbolTypeError(symbol)
       else throw StaleSymbolException(staleSymbolMsg)
 

Diff for: compiler/src/dotty/tools/dotc/core/TypeErasure.scala

@@ -24,11 +24,16 @@ enum SourceLanguage:
 object SourceLanguage:
   /** The language in which `sym` was defined. */
   def apply(sym: Symbol)(using Context): SourceLanguage =
-    if sym.is(JavaDefined) then
+    // We might be using this method while recalculating the denotation,
+    // so let's use `lastKnownDenotation`.
+    // This is ok as the source of the symbol and whether it is inline should
+    // not change between runs/phases.
+    val denot = sym.lastKnownDenotation
+    if denot.is(JavaDefined) then
       SourceLanguage.Java
     // Scala 2 methods don't have Inline set, except for the ones injected with `patchStdlibClass`
     // which are really Scala 3 methods.
-    else if sym.isClass && sym.is(Scala2x) || (sym.maybeOwner.is(Scala2x) && !sym.is(Inline)) then
+    else if denot.isClass && denot.is(Scala2x) || (denot.maybeOwner.lastKnownDenotation.is(Scala2x) && !denot.is(Inline)) then
       SourceLanguage.Scala2
     else
       SourceLanguage.Scala3

Diff for: compiler/src/dotty/tools/dotc/core/Types.scala

@@ -2494,7 +2494,10 @@ object Types extends TypeUtils {
     }
 
     private def disambiguate(d: Denotation)(using Context): Denotation =
-      disambiguate(d, currentSignature, currentSymbol.targetName)
+      // this method might be triggered while the denotation is already being recomputed
+      // in NamedType, so it's better to use lastKnownDenotation instead, as targetName
+      // should not change between phases/runs
+      disambiguate(d, currentSignature, currentSymbol.lastKnownDenotation.targetName)
 
     private def disambiguate(d: Denotation, sig: Signature | Null, target: Name)(using Context): Denotation =
       if (sig != null)

Diff for: tests/pos-macros/i20574/Exports.scala

@@ -0,0 +1,3 @@
+object Exports{
+  export OverloadedInline.*
+}

Diff for: tests/pos-macros/i20574/Macros.scala

@@ -0,0 +1,20 @@
+import scala.quoted.*
+
+object Macros{
+
+  inline def A() : String = {
+     ${ A_impl }
+  }
+
+  def A_impl(using Quotes): Expr[String] = {
+    Expr("Whatever")
+  }
+
+  inline def B[T]: Int = {
+    ${ B_Impl[T] }
+  }
+
+  def B_Impl[T](using Quotes): Expr[Int] = {
+    Expr(0)
+  }
+}

Diff for: tests/pos-macros/i20574/OverloadedInline.scala

@@ -0,0 +1,13 @@
+import Macros.*
+
+object OverloadedInline{
+
+    A()
+    inline def overloaded_inline[T]: Unit = {
+        overloaded_inline[T](0)
+    }
+
+    inline def overloaded_inline[T](dummy: Int): Unit = {
+        val crash = B[T]
+    }
+}

Diff for: tests/pos-macros/i20574/Test.scala

@@ -0,0 +1,5 @@
+import Exports.*
+
+object Test {
+   overloaded_inline[Unit]
+}