Fix #12267: Constraints should not cross phases

bench/profiles/stdlib.yml

@@ -0,0 +1,15 @@
+charts:
+
+    - name: "scala stdlib-2.13"
+      url: https://github.com/dotty-staging/scala/commits/stdLib213-dotty-community-build
+      lines:
+        - key: stdlib213
+          label: bootstrapped
+
+scripts:
+
+    stdlib213:
+        - source $PROG_HOME/dotty/bench/scripts/stdlib213
+
+config:
+    pr_base_url: "https://github.com/lampepfl/dotty/pull/"

compiler/src/dotty/tools/dotc/Run.scala

@@ -202,7 +202,10 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
           Stats.trackTime(s"$phase ms ") {
             val start = System.currentTimeMillis
             val profileBefore = profiler.beforePhase(phase)
-            units = phase.runOn(units)
+
+            // invariant: constraint should not cross phase boundary
+            ctx.typerState.ensureSegregated { units = phase.runOn(units) }
+
             profiler.afterPhase(phase, profileBefore)
             if (ctx.settings.Xprint.value.containsPhase(phase))
               for (unit <- units)

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

@@ -159,5 +159,18 @@ class TyperState() {
     s"TS[${ids(this).mkString(", ")}]"
   }
 
+  /** Execute the operation with an empty constraint and make sure no leak
+   *  of constraints.
+   *
+   *  Side effect: the method will reset the constraint associated with the context.
+   */
+  def ensureSegregated[T](op: => T)(using Context): T =
+    this.constraint = OrderingConstraint.empty
+    val res = op
+    // force instantiate tvars
+    // see tests/pos/t2619b.scala
+    ctx.typerState.gc()
+    res
+
   def stateChainStr: String = s"$this${if (previous == null) "" else previous.stateChainStr}"
 }

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

@@ -4019,7 +4019,14 @@ object Types {
       case tycon: TypeRef if tycon.symbol.isOpaqueAlias =>
         tycon.translucentSuperType.applyIfParameterized(args)
       case _ =>
-        tryNormalize.orElse(superType)
+        val x = tryNormalize
+        if x.exists then
+          record("try norm OK")
+          record(i"try norm OK $x")
+          x
+        else
+          record("try norm KO")
+          superType
     }
 
     inline def map(inline op: Type => Type)(using Context) =
@@ -4038,6 +4045,9 @@ object Types {
       case tycon: TypeRef =>
         def tryMatchAlias = tycon.info match {
           case MatchAlias(alias) =>
+            record(i"try match alias")
+            record(i"try match alias $this in ${ctx.owner.ownersIterator.toList}%, %")
+            //new Error().printStackTrace()
             trace(i"normalize $this", typr, show = true) {
               MatchTypeTrace.recurseWith(this) {
                 alias.applyIfParameterized(args).tryNormalize

tests/pos/t2619b.scala

@@ -0,0 +1,8 @@
+abstract class AbstractModule
+
+object ModuleBE extends AbstractModule
+object ModuleBF extends AbstractModule
+
+object ModuleBM extends AbstractModule {
+    def ms: List[AbstractModule] = List(ModuleBE) ::: List(ModuleBF)
+}