Detect and flag deep findMember recursions

Deep findMember recursions can happen as a recult of illegal cyclic structures.
I don't think there's a complete way to avoid these structures before the cyclic search
can happen. So we now detect it by imposing a recursion limit (configurable, by default 100).

Author: odersky

compiler/src/dotty/tools/dotc/config/Config.scala

@@ -184,11 +184,6 @@ object Config {
    */
   final val LogPendingFindMemberThreshold = 9
 
-  /** Maximal number of outstanding recursive calls to findMember before backing out
-   *  when findMemberLimit is set.
-   */
-  final val PendingFindMemberLimit = LogPendingFindMemberThreshold * 4
-
   /** When in IDE, turn StaleSymbol errors into warnings instead of crashing */
   final val ignoreStaleInIDE = true
 }

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -63,7 +63,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val Xhelp = BooleanSetting("-X", "Print a synopsis of advanced options.")
   val XnoForwarders = BooleanSetting("-Xno-forwarders", "Do not generate static forwarders in mirror classes.")
   val XminImplicitSearchDepth = IntSetting("-Xmin-implicit-search-depth", "Set number of levels of implicit searches undertaken before checking for divergence.", 5)
-  val xmaxInlines = IntSetting("-Xmax-inlines", "Maximal number of successive inlines", 32)
+  val XmaxInlines = IntSetting("-Xmax-inlines", "Maximal number of successive inlines", 32)
   val XmaxClassfileName = IntSetting("-Xmax-classfile-name", "Maximum filename length for generated classes", 255, 72 to 255)
   val Xmigration = VersionSetting("-Xmigration", "Warn about constructs whose behavior may have changed since version.")
   val Xprint = PhasesSetting("-Xprint", "Print out program after")
@@ -74,6 +74,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val XmainClass = StringSetting("-Xmain-class", "path", "Class for manifest's Main-Class entry (only useful with -d <jar>)", "")
   val XnoValueClasses = BooleanSetting("-Xno-value-classes", "Do not use value classes. Helps debugging.")
   val XreplLineWidth = IntSetting("-Xrepl-line-width", "Maximal number of columns per line for REPL output", 390)
+  val XmaxMemberRecursions = IntSetting("-Xmax-member-recursions", "Maximal number of recursive calls to find-member", 100)
   val XfatalWarnings = BooleanSetting("-Xfatal-warnings", "Fail the compilation if there are any warnings.")
   val XverifySignatures = BooleanSetting("-Xverify-signatures", "Verify generic signatures in generated bytecode.")
 

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

@@ -326,10 +326,4 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
 
 object TypeOps {
   @sharable var track = false // !!!DEBUG
-
-  /** When a property with this key is set in a context, it limits the number
-   *  of recursive member searches. If the limit is reached, findMember returns
-   *  NoDenotation.
-   */
-  val findMemberLimit = new Property.Key[Unit]
 }

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

@@ -648,17 +648,15 @@ object Types {
 
       val recCount = ctx.findMemberCount
       if (recCount >= Config.LogPendingFindMemberThreshold) {
-        if (ctx.property(TypeOps.findMemberLimit).isDefined &&
-            ctx.findMemberCount > Config.PendingFindMemberLimit)
-          return NoDenotation
+        if (ctx.findMemberCount > ctx.settings.XmaxMemberRecursions.value)
+          throw new CyclicFindMember(pre, name)
         ctx.pendingMemberSearches = name :: ctx.pendingMemberSearches
       }
       ctx.findMemberCount = recCount + 1
-      //assert(ctx.findMemberCount < 20)
       try go(this)
       catch {
         case ex: Throwable =>
-          core.println(i"findMember exception for $this member $name, pre = $pre")
+          core.println(s"findMember exception for $this member $name, pre = $pre, recCount = $recCount")
           throw ex // DEBUG
       }
       finally {
@@ -4562,6 +4560,10 @@ object Types {
     if (ctx.debug) printStackTrace()
   }
 
+  class CyclicFindMember(pre: Type, name: Name)(implicit ctx: Context) extends TypeError(
+    i"""member search with prefix $pre too deep.
+       |searches, from inner to outer: .${ctx.pendingMemberSearches}% .%""")
+
   private def otherReason(pre: Type)(implicit ctx: Context): String = pre match {
     case pre: ThisType if pre.cls.givenSelfType.exists =>
       i"\nor the self type of $pre might not contain all transitive dependencies"

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

@@ -257,13 +257,13 @@ object Inliner {
    *            and body that replace it.
    */
   def inlineCall(tree: Tree, pt: Type)(implicit ctx: Context): Tree =
-    if (enclosingInlineds.length < ctx.settings.xmaxInlines.value) {
+    if (enclosingInlineds.length < ctx.settings.XmaxInlines.value) {
       val body = bodyToInline(tree.symbol) // can typecheck the tree and thereby produce errors
       if (ctx.reporter.hasErrors) tree else new Inliner(tree, body).inlined(pt)
     }
     else errorTree(
       tree,
-      i"""|Maximal number of successive inlines (${ctx.settings.xmaxInlines.value}) exceeded,
+      i"""|Maximal number of successive inlines (${ctx.settings.XmaxInlines.value}) exceeded,
           |Maybe this is caused by a recursive inline method?
           |You can use -Xmax:inlines to change the limit."""
     )