Survive erroneous infix operations

Also, more tests

Author: odersky

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

@@ -1693,7 +1693,8 @@ class Typer extends Namer
       val defs = new mutable.ListBuffer[Tree]
       def lift(app: Tree): Tree = (app: @unchecked) match {
         case Apply(fn, args) =>
-          tpd.cpy.Apply(app)(fn, LiftImpure.liftArgs(defs, fn.tpe, 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) =>

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.scala

@@ -1,14 +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 foo() = { println("foo") ; 5 }
+  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 = {
-    val c = new C
-    foo() m1_: c
-    foo() m2_: c
+    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
   }
 }