Fix #2808: Modify lifting of infix operations

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

@@ -725,6 +725,31 @@ object desugar {
       tree
   }
 
+  /** Translate infix operation expression
+    *
+    *     l op r     ==>    l.op(r)  if op is left-associative
+    *                ==>    r.op(l)  if op is right-associative
+    */
+  def binop(left: Tree, op: Ident, right: Tree)(implicit ctx: Context): Apply = {
+    def assignToNamedArg(arg: Tree) = arg match {
+      case Assign(Ident(name), rhs) => cpy.NamedArg(arg)(name, rhs)
+      case _ => arg
+    }
+    def makeOp(fn: Tree, arg: Tree, selectPos: Position) = {
+      val args: List[Tree] = arg match {
+        case Parens(arg) => assignToNamedArg(arg) :: Nil
+        case Tuple(args) => args.mapConserve(assignToNamedArg)
+        case _ => arg :: Nil
+      }
+      Apply(Select(fn, op.name).withPos(selectPos), args)
+    }
+
+    if (isLeftAssoc(op.name))
+      makeOp(left, right, Position(left.pos.start, op.pos.end, op.pos.start))
+    else
+      makeOp(right, left, Position(op.pos.start, right.pos.end))
+  }
+
   /** Make closure corresponding to function.
    *      params => body
    *  ==>
@@ -832,30 +857,6 @@ object desugar {
       Block(ldef, call)
     }
 
-    /** Translate infix operation expression  left op right
-     */
-    def makeBinop(left: Tree, op: Ident, right: Tree): Tree = {
-      def assignToNamedArg(arg: Tree) = arg match {
-        case Assign(Ident(name), rhs) => cpy.NamedArg(arg)(name, rhs)
-        case _ => arg
-      }
-      if (isLeftAssoc(op.name)) {
-        val args: List[Tree] = right match {
-          case Parens(arg) => assignToNamedArg(arg) :: Nil
-          case Tuple(args) => args mapConserve assignToNamedArg
-          case _ => right :: Nil
-        }
-        val selectPos = Position(left.pos.start, op.pos.end, op.pos.start)
-        Apply(Select(left, op.name).withPos(selectPos), args)
-      } else {
-        val x = UniqueName.fresh()
-        val selectPos = Position(op.pos.start, right.pos.end, op.pos.start)
-        new InfixOpBlock(
-          ValDef(x, TypeTree(), left).withMods(synthetic),
-          Apply(Select(right, op.name).withPos(selectPos), Ident(x).withPos(left.pos)))
-      }
-    }
-
     /** Create tree for for-comprehension `<for (enums) do body>` or
      *   `<for (enums) yield body>` where mapName and flatMapName are chosen
      *  corresponding to whether this is a for-do or a for-yield.
@@ -1066,10 +1067,10 @@ object desugar {
           if (!op.isBackquoted && op.name == tpnme.raw.AMP) AndTypeTree(l, r)     // l & r
           else if (!op.isBackquoted && op.name == tpnme.raw.BAR) OrTypeTree(l, r) // l | r
           else AppliedTypeTree(op, l :: r :: Nil) // op[l, r]
-        else if (ctx.mode is Mode.Pattern)
+        else {
+          assert(ctx.mode is Mode.Pattern) // expressions are handled separately by `binop`
           Apply(op, l :: r :: Nil) // op(l, r)
-        else // l.op(r), or val x = r; l.op(x), plus handle named args specially
-          makeBinop(l, op, r)
+        }
       case PostfixOp(t, op) =>
         if ((ctx.mode is Mode.Type) && !op.isBackquoted && op.name == tpnme.raw.STAR) {
           val seqType = if (ctx.compilationUnit.isJava) defn.ArrayType else defn.SeqType

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

@@ -96,16 +96,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
     override def isEmpty = true
   }
 
-  /** A block arising from a right-associative infix operation, where, e.g.
-   *
-   *     a +: b
-   *
-   *  is expanded to
-   *
-   *     { val x = a; b.+:(x) }
-   */
-  class InfixOpBlock(leftOperand: Tree, rightOp: Tree) extends Block(leftOperand :: Nil, rightOp)
-
   /** A block generated by the XML parser, only treated specially by
    *  `Positioned#checkPos` */
   class XMLBlock(stats: List[Tree], expr: Tree) extends Block(stats, expr)

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

@@ -665,6 +665,10 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
   def argCtx(app: untpd.Tree)(implicit ctx: Context): Context =
     if (untpd.isSelfConstrCall(app)) ctx.thisCallArgContext else ctx
 
+  /** Typecheck application. Result could be an `Apply` node,
+   *  or, if application is an operator assignment, also an `Assign` or
+   *  Block node.
+   */
   def typedApply(tree: untpd.Apply, pt: Type)(implicit ctx: Context): Tree = {
 
     def realApply(implicit ctx: Context): Tree = track("realApply") {

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

@@ -664,12 +664,7 @@ class Typer extends Namer
 
   def typedBlock(tree: untpd.Block, pt: Type)(implicit ctx: Context) = track("typedBlock") {
     val (exprCtx, stats1) = typedBlockStats(tree.stats)
-    val ept =
-      if (tree.isInstanceOf[untpd.InfixOpBlock])
-        // Right-binding infix operations are expanded to InfixBlocks, which may be followed by arguments.
-        // Example: `(a /: bs)(op)` expands to `{ val x = a; bs./:(x) } (op)` where `{...}` is an InfixBlock.
-        pt
-      else pt.notApplied
+    val ept = pt.notApplied
     val expr1 = typedExpr(tree.expr, ept)(exprCtx)
     ensureNoLocalRefs(
       cpy.Block(tree)(stats1, expr1).withType(expr1.tpe), pt, localSyms(stats1))
@@ -1679,6 +1674,31 @@ class Typer extends Namer
     res
   }
 
+  /** Translate infix operation expression `l op r` to
+   *
+   *    l.op(r)   			    if `op` is left-associative
+   *    { val x = l; r.op(l) }  if `op` is right-associative call-by-value and `l` is impure
+   *    r.op(l)                 if `op` is right-associative call-by-name or `l` is pure
+   */
+  def typedInfixOp(tree: untpd.InfixOp, pt: Type)(implicit ctx: Context): Tree = {
+    val untpd.InfixOp(l, op, r) = tree
+    val app = typedApply(desugar.binop(l, op, r), pt)
+    if (untpd.isLeftAssoc(op.name)) app
+    else {
+      val defs = new mutable.ListBuffer[Tree]
+      def lift(app: Tree): Tree = (app: @unchecked) match {
+        case Apply(fn, args) =>
+          if (app.tpe.isError) app
+          else tpd.cpy.Apply(app)(fn, LiftImpure.liftArgs(defs, fn.tpe, args))
+        case Assign(lhs, rhs) =>
+          tpd.cpy.Assign(app)(lhs, lift(rhs))
+        case Block(stats, expr) =>
+          tpd.cpy.Block(app)(stats, lift(expr))
+      }
+      Applications.wrapDefs(defs, lift(app))
+    }
+  }
+
   /** Retrieve symbol attached to given tree */
   protected def retrieveSym(tree: untpd.Tree)(implicit ctx: Context) = tree.removeAttachment(SymOfTree) match {
     case Some(sym) =>
@@ -1765,6 +1785,7 @@ class Typer extends Namer
           case tree: untpd.TypedSplice => typedTypedSplice(tree)
           case tree: untpd.UnApply => typedUnApply(tree, pt)
           case tree: untpd.DependentTypeTree => typed(untpd.TypeTree().withPos(tree.pos), pt)
+          case tree: untpd.InfixOp if ctx.mode.isExpr => typedInfixOp(tree, pt)
           case tree @ untpd.PostfixOp(qual, Ident(nme.WILDCARD)) => typedAsFunction(tree, pt)
           case untpd.EmptyTree => tpd.EmptyTree
           case _ => typedUnadapted(desugar(tree), pt)

compiler/test-resources/repl/errmsgs

@@ -57,7 +57,7 @@ scala> class Foo() { def bar: Int = 1 }; val foo = new Foo(); foo.barr
 scala> val x: List[Int] = "foo" :: List(1)
 1 | val x: List[Int] = "foo" :: List(1)
   |                    ^^^^^
-  |                    found:    String($1$)
+  |                    found:    String("foo")
   |                    required: Int
   |
 scala> { def f: Int = g; val x: Int = 1; def g: Int = 5; }

tests/neg/i2808.scala

@@ -0,0 +1,7 @@
+class C {}
+
+object Test {
+  def foo1() = { println("foo1") ; 5 }
+  val c = new C
+  foo1() m1_: c // error
+}

tests/run/i2808.check

@@ -0,0 +1,8 @@
+foo1
+foo3
+foo1
+bar
+bar
+foo3
+bar
+bar

tests/run/i2808.scala

@@ -0,0 +1,30 @@
+class C {
+  def m1_:(f: Int) = ()
+  def m2_:(f: => Int) = ()
+  def m3_:(f: Int)(implicit c: C) = ()
+  def m4_:(f: => Int)(implicit c: C) = ()
+
+}
+
+object Test {
+  def foo1() = { println("foo1") ; 5 }
+  def foo2() = { println("foo2") ; 5 }
+  def foo3() = { println("foo3") ; 5 }
+  def foo4() = { println("foo4") ; 5 }
+
+  def main(args: Array[String]): Unit = {
+    implicit val c = new C
+    foo1() m1_: c // foo1
+    foo2() m2_: c
+    foo3() m3_: c // foo3
+    foo4() m4_: c
+
+    def bar() = { println("bar"); c }
+    foo1() m1_: bar() // foo1
+                      // bar
+    foo2() m2_: bar() // bar
+    foo3() m3_: bar() // foo3
+                      // bar
+    foo4() m4_: bar() // bar
+  }
+}