Merge pull request #15403 from albertpchen/fix-given-within-for-comprehension

Preserve modifiers when desugaring for-comps

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1577,10 +1577,10 @@ object desugar {
        *  also replaced by Binds with fresh names.
        */
       def makeIdPat(pat: Tree): (Tree, Ident) = pat match {
-        case Bind(name, pat1) =>
+        case bind @ Bind(name, pat1) =>
           if name == nme.WILDCARD then
             val name = UniqueName.fresh()
-            (cpy.Bind(pat)(name, pat1), Ident(name))
+            (cpy.Bind(pat)(name, pat1).withMods(bind.mods), Ident(name))
           else (pat, Ident(name))
         case id: Ident if isVarPattern(id) && id.name != nme.WILDCARD => (id, id)
         case Typed(id: Ident, _) if isVarPattern(id) && id.name != nme.WILDCARD => (pat, id)
@@ -1679,7 +1679,12 @@ object desugar {
           val rhss = valeqs map { case GenAlias(_, rhs) => rhs }
           val (defpat0, id0) = makeIdPat(gen.pat)
           val (defpats, ids) = (pats map makeIdPat).unzip
-          val pdefs = valeqs.lazyZip(defpats).lazyZip(rhss).map(makePatDef(_, Modifiers(), _, _))
+          val pdefs = valeqs.lazyZip(defpats).lazyZip(rhss).map { (valeq, defpat, rhs) =>
+            val mods = defpat match
+              case defTree: DefTree => defTree.mods
+              case _ => Modifiers()
+            makePatDef(valeq, mods, defpat, rhs)
+          }
           val rhs1 = makeFor(nme.map, nme.flatMap, GenFrom(defpat0, gen.expr, gen.checkMode) :: Nil, Block(pdefs, makeTuple(id0 :: ids)))
           val allpats = gen.pat :: pats
           val vfrom1 = GenFrom(makeTuple(allpats), rhs1, GenCheckMode.Ignore)

tests/run/fors.check

@@ -44,3 +44,8 @@ hello  world
 hello  world 
 hello/1~2 hello/3~4 /1~2 /3~4 world/1~2 world/3~4 
 (2,1) (4,3) 
+
+testGivens
+123
+456
+0

tests/run/fors.scala

@@ -74,7 +74,6 @@ object Test extends App {
 
     // arrays
     for (x <- ar) print(x + " "); println()
-
   }
 
   /////////////////// filtering with case ///////////////////
@@ -109,9 +108,38 @@ object Test extends App {
     for case (x, y) <- xs do print(s"${(y, x)} "); println()
   }
 
+  def testGivens(): Unit = {
+    println("\ntestGivens")
+
+    // bound given that is summoned in subsequent bind
+    for
+      a <- List(123)
+      given Int = a
+      b = summon[Int]
+    do
+      println(b)
+
+    // generated given that is summoned in subsequent bind
+    for
+      given Int <- List(456)
+      x = summon[Int]
+    do
+      println(x)
+
+    // pick the correct given
+    for
+      a <- List(789)
+      given Int = a
+      given Int <- List(0)
+      x = summon[Int]
+    do
+      println(x)
+  }
+
   ////////////////////////////////////////////////////
 
   testOld()
   testNew()
   testFiltering()
+  testGivens()
 }