Do not update Symbol defTrees when retyping after Inlining

The scaladoc for the defTree method in Symbol states: "The tree defining
the symbol at pickler time ...", but that was never really true.
Previously, since the setDefTree method was used in Typer, in any
retyping procedure those methods would be called again, with the main
example being erasure, where we would lose parts of type information from
those trees. Usually this was not an issue, since they weren't used after
Erasure.
However, the suspend mechanism used when compiling
macros with calls to them can cause the macro tree to go through
erasure, have their defTrees updated there, and then used for earlier
phases, with the problematic phase here being the init-checker, which
uses defTree calls extensively.
In the issue minimisation, init-checker was expecting a MethodType (due to the
missing TypeApply there), and instead got a PolyType, causing a crash.

Coincidentally in the past we would sometimes also get issues about
.tree method in Quotes returning unexpected stuff due to the same issue,
so this should also help there.

Author: jchyb

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

@@ -367,6 +367,7 @@ object Contexts {
 
     /** Is current phase after TyperPhase? */
     final def isAfterTyper = base.isAfterTyper(phase)
+    final def isAfterInlining = base.isAfterInlining(phase)
     final def isTyper = base.isTyper(phase)
 
     /** Is this a context for the members of a class definition? */

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

@@ -305,6 +305,8 @@ object Phases {
     }
 
     final def isAfterTyper(phase: Phase): Boolean = phase.id > typerPhase.id
+    final def isAfterInlining(phase: Phase): Boolean =
+      inliningPhase != NoPhase && phase.id > inliningPhase.id
     final def isTyper(phase: Phase): Boolean = phase.id == typerPhase.id
   }
 

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

@@ -2974,7 +2974,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           typedExpr(_, tpt1.tpe.widenExpr)
     val vdef1 = assignType(cpy.ValDef(vdef)(name, tpt1, rhs1), sym)
     postProcessInfo(vdef1, sym)
-    vdef1.setDefTree
+    if (!ctx.isAfterInlining) vdef1.setDefTree
 
     migrate(ImplicitToGiven.valDef(vdef1))
 
@@ -3097,7 +3097,8 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
     if (!sym.isOneOf(Synthetic | InlineProxy | Param) && sym.info.finalResultType.isRepeatedParam)
       report.error(em"Cannot return repeated parameter type ${sym.info.finalResultType}", sym.srcPos)
     mdef.ensureHasSym(sym)
-    mdef.setDefTree
+    if (!ctx.isAfterInlining) mdef.setDefTree
+    else mdef
 
   def typedTypeDef(tdef: untpd.TypeDef, sym: Symbol)(using Context): Tree = ctx.profiler.onTypedDef(sym) {
     val TypeDef(name, rhs) = tdef

tests/pos-macros/i22584/Macro.scala

@@ -22,7 +22,7 @@ object Macros {
         }
       }
 
-    val expected = "List(DefDef(boolean,List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Boolean)],Select(This(Ident(MyClass1)),boolean)), DefDef(finalVal,List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class lang)),class String)],Select(This(Ident(MyClass1)),finalVal)), DefDef(int,List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Int)],Select(This(Ident(MyClass1)),int)), DefDef(string,List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,module class lang)),class String)],Select(This(Ident(MyClass1)),string)))"
+    val expected = "List(ValDef(boolean,TypeTree[TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),object scala),class Boolean)],EmptyTree), ValDef(finalVal,Ident(String),Literal(Constant(result))), ValDef(int,TypeTree[TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),object scala),class Int)],EmptyTree), ValDef(string,TypeTree[TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class scala)),object Predef),type String)],EmptyTree))"
     assert(caseFieldValOrDefDefs.toString == expected)
 
     '{ () }

tests/pos/i21176-a/Macro.scala

@@ -0,0 +1,12 @@
+//> using options -Wsafe-init
+import scala.quoted.*
+
+class Macro:
+  def tuple[T](name: String): (String, List[T]) = (name, List[T]())
+  inline def nameTuple[T]: (String, List[T]) = tuple(Macro.named)
+
+object Macro:
+  def namedMacro(using q: Quotes): Expr[String] =
+    Expr("test")
+
+  inline def named: String = ${Macro.namedMacro}

tests/pos/i21176-a/Main.scala

@@ -0,0 +1,7 @@
+//> using options -Wsafe-init
+class Test extends Macro:
+  val abc = nameTuple[Int]
+
+@main
+def run(): Unit =
+  println(new Test().abc)