repl: Handle user-defined res definitions

compiler/src/dotty/tools/repl/ReplCompiler.scala

@@ -88,6 +88,16 @@ class ReplCompiler extends Compiler {
     var valIdx = state.valIndex
     val defs = new mutable.ListBuffer[Tree]
 
+    /** If the user inputs a definition that's name is of the form REPL_RES_PREFIX and a number,
+     *  such as `val res9 = 1`, we bump `valIdx` to avoid name clashes.  lampepfl/dotty#3536 */
+    def maybeBumpValIdx(tree: Tree): Unit = tree match
+      case tuple: Tuple   => for t <- tuple.trees do maybeBumpValIdx(t)
+      case patDef: PatDef => for p <- patDef.pats do maybeBumpValIdx(p)
+      case tree: NameTree => name.show.stripPrefix(str.REPL_RES_PREFIX).toIntOption match
+        case Some(n) if n >= valIdx => valIdx = n + 1
+        case _                      =>
+      case _              =>
+
     flattened.foreach {
       case expr @ Assign(id: Ident, _) =>
         // special case simple reassignment (e.g. x = 3)
@@ -101,6 +111,7 @@ class ReplCompiler extends Compiler {
         val vd = ValDef(resName, TypeTree(), expr).withSpan(expr.span)
         defs += vd
       case other =>
+        maybeBumpValIdx(other)
         defs += other
     }
 

compiler/test-resources/repl/i3536

@@ -0,0 +1,19 @@
+scala> val res0 = 1
+val res0: Int = 1
+
+scala> res0
+val res1: Int = 1
+
+
+scala> val res99 = 9
+val res99: Int = 9
+
+scala> res99
+val res100: Int = 9
+
+
+scala> val res50 = 5
+val res50: Int = 5
+
+scala> res50
+val res101: Int = 5

compiler/test-resources/repl/i3536_bind

@@ -0,0 +1,4 @@
+scala> val res10 @ Some(_) = Option(1)
+val res10: Some[Int] = Some(1)
+scala> res10
+val res11: Some[Int] = Some(1)

compiler/test-resources/repl/i3536_defdef

@@ -0,0 +1,4 @@
+scala> def res20 = 1
+def res20: Int
+scala> res20
+val res21: Int = 1

compiler/test-resources/repl/i3536_object

@@ -0,0 +1,4 @@
+scala> object res30 { override def toString = "res30" }
+// defined object res30
+scala> res30
+val res31: res30.type = res30

compiler/test-resources/repl/i3536_patterndef

@@ -0,0 +1,5 @@
+scala> val (res40, res41) = (1, 0)
+val res40: Int = 1
+val res41: Int = 0
+scala> res40
+val res42: Int = 1

compiler/test-resources/repl/i3536_typedef

@@ -0,0 +1,4 @@
+scala> type res50 = Int
+// defined alias type res50 = Int
+scala> 1
+val res51: Int = 1

compiler/test-resources/repl/i3536_var

@@ -0,0 +1,4 @@
+scala> var res60 = 1
+var res60: Int = 1
+scala> res60
+val res61: Int = 1