Remove premature, brittle caching in lint

Author: som-snytt

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -215,15 +215,6 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       refInfos.register(tree)
     tree
 
-  override def prepareForTemplate(tree: Template)(using Context): Context =
-    ctx.fresh.setProperty(resolvedKey, Resolved())
-
-  override def prepareForPackageDef(tree: PackageDef)(using Context): Context =
-    ctx.fresh.setProperty(resolvedKey, Resolved())
-
-  override def prepareForStats(trees: List[Tree])(using Context): Context =
-    ctx.fresh.setProperty(resolvedKey, Resolved())
-
   override def transformOther(tree: Tree)(using Context): tree.type =
     tree match
     case imp: Import =>
@@ -289,7 +280,6 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
     case ByNameTypeTree(result) =>
       transformAllDeep(result)
     //case _: InferredTypeTree => // do nothing
-    //case _: Export => // nothing to do
     //case _ if tree.isType =>
     case _ =>
     tree
@@ -350,15 +340,6 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       && ctxsym.thisType.baseClasses.contains(sym.owner)
       && ctxsym.thisType.member(sym.name).hasAltWith(d => d.containsSym(sym) && !name.exists(_ != d.name))
 
-    // Attempt to cache a result at the given context. Not all contexts bear a cache, including NoContext.
-    // If there is already any result for the name and prefix, do nothing.
-    def addCached(where: Context, result: Precedence): Unit =
-      if where.moreProperties ne null then
-        where.property(resolvedKey) match
-        case Some(resolved) =>
-          resolved.record(sym, name, prefix, result)
-        case none =>
-
     // Avoid spurious NoSymbol and also primary ctors which are never warned about.
     // Selections C.this.toString should be already excluded, but backtopped here for eq, etc.
     if !sym.exists || sym.isPrimaryConstructor || sym.isEffectiveRoot || defn.topClasses(sym.owner) then return
@@ -367,12 +348,10 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
     // If the sym is an enclosing definition (the owner of a context), it does not count toward usages.
     val isLocal = sym.isLocalToBlock
     var candidate: Context = NoContext
-    var cachePoint: Context = NoContext // last context with Resolved cache
     var importer: ImportSelector | Null = null // non-null for import context
     var precedence = NoPrecedence // of current resolution
     var enclosed = false // true if sym is owner of an enclosing context
     var done = false
-    var cached = false
     val ctxs = ctx.outersIterator
     while !done && ctxs.hasNext do
       val cur = ctxs.next()
@@ -382,24 +361,7 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
         if cur.owner eq sym.owner then
           done = true // for local def, just checking that it is not enclosing
       else
-        val cachedPrecedence =
-          cur.property(resolvedKey) match
-          case Some(resolved) =>
-            // conservative, cache must be nested below the result context
-            if precedence.isNone then
-              cachePoint = cur // no result yet, and future result could be cached here
-            resolved.hasRecord(sym, name, prefix)
-          case none => NoPrecedence
-        cached = !cachedPrecedence.isNone
-        if cached then
-          // if prefer cached precedence, then discard previous result
-          if precedence.weakerThan(cachedPrecedence) then
-            candidate = NoContext
-            importer = null
-            cachePoint = cur // actual cache context
-            precedence = cachedPrecedence // actual cached precedence
-          done = true
-        else if cur.isImportContext then
+        if cur.isImportContext then
           val sel = matchingSelector(cur.importInfo.nn)
           if sel != null then
             if cur.importInfo.nn.isRootImport then
@@ -433,13 +395,6 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       refInfos.refs.addOne(sym)
     if candidate != NoContext && candidate.isImportContext && importer != null then
       refInfos.sels.put(importer, ())
-    // possibly record that we have performed this look-up
-    // if no result was found, take it as Definition (local or rooted head of fully qualified path)
-    val adjusted = if precedence.isNone then Definition else precedence
-    if !cached && (cachePoint ne NoContext) then
-      addCached(cachePoint, adjusted)
-    if cachePoint ne ctx then
-      addCached(ctx, adjusted) // at this ctx, since cachePoint may be far up the outer chain
   end resolveUsage
 end CheckUnused
 
@@ -451,15 +406,8 @@ object CheckUnused:
 
   val refInfosKey = Property.StickyKey[RefInfos]
 
-  val resolvedKey = Property.Key[Resolved]
-
   inline def refInfos(using Context): RefInfos = ctx.property(refInfosKey).get
 
-  inline def resolved(using Context): Resolved =
-    ctx.property(resolvedKey) match
-    case Some(res) => res
-    case _ => throw new MatchError("no Resolved for context")
-
   /** Attachment holding the name of an Ident as written by the user. */
   val OriginalName = Property.StickyKey[Name]
 
@@ -515,24 +463,6 @@ object CheckUnused:
     var inliners = 0 // depth of inline def (not inlined yet)
   end RefInfos
 
-  // Symbols already resolved in the given Context (with name and prefix of lookup).
-  class Resolved:
-    import PrecedenceLevels.*
-    private val seen = mutable.Map.empty[Symbol, List[(Name, Type, Precedence)]].withDefaultValue(Nil)
-    // if a result has been recorded, return it; otherwise, NoPrecedence.
-    def hasRecord(symbol: Symbol, name: Name, prefix: Type)(using Context): Precedence =
-      seen(symbol).find((n, p, _) => n == name && p =:= prefix) match
-      case Some((_, _, r)) => r
-      case none => NoPrecedence
-    // "record" the look-up result, if there is not already a result for the name and prefix.
-    def record(symbol: Symbol, name: Name, prefix: Type, result: Precedence)(using Context): Unit =
-      require(NoPrecedence.weakerThan(result))
-      seen.updateWith(symbol):
-        case svs @ Some(vs) =>
-          if vs.exists((n, p, _) => n == name && p =:= prefix) then svs
-          else Some((name, prefix, result) :: vs)
-        case none => Some((name, prefix, result) :: Nil)
-
   // Names are resolved by definitions and imports, which have four precedence levels:
   object PrecedenceLevels:
     opaque type Precedence = Int

tests/warn/i22971.scala

@@ -0,0 +1,34 @@
+//> using options -Wunused:imports
+
+package p:
+
+  trait Base
+  class Class extends Base
+
+  abstract class Entity[T: GetType]
+
+  class Thing extends Entity[Class]
+
+  trait GetType[T]
+
+  object GetType {
+    //implicit object GetTypeClass extends GetType[Class]
+    implicit val GetTypeClass: GetType[Class] = new GetType[Class] {}
+  }
+  object Main {
+    def main(args: Array[String]): Unit = {
+      import GetType.*
+      val e = GetTypeClass
+    }
+  }
+
+package q:
+
+  class C:
+    def f =
+      import p.*
+      GetType.GetTypeClass
+    def g =
+      import p.GetType.*
+      GetTypeClass
+  class D extends p.Entity[p.Class]