Escape _ in term names to make it not interfere with mangling. Fixes #…

…374 (#389)

* Escape _ in term names to make it not interfere with mangling. Fixes #374
* Fix type in generated file's name

build.sbt

@@ -277,7 +277,7 @@ lazy val tests =
             .split("/")
             .mkString(".")
         }.filter(_ != "tests.Suite").mkString("Seq(", ", ", ")")
-        val file = (sourceManaged in Compile).value / "tests" / "Disover.scala"
+        val file = (sourceManaged in Compile).value / "tests" / "Discover.scala"
         IO.write(file,
                  s"""
           package tests

nscplugin/src/main/scala/scala/scalanative/nscplugin/NirNameEncoding.scala

@@ -59,7 +59,8 @@ trait NirNameEncoding { self: NirCodeGen =>
       owner member ("init" +: mangledParams).mkString("_")
     } else {
       val mangledRetty = mangledType(tpe.resultType, retty = true)
-      owner member (id +: (mangledParams :+ mangledRetty)).mkString("_")
+      owner member (id.replace("_", "__") +: (mangledParams :+ mangledRetty))
+        .mkString("_")
     }
   }
 

unit-tests/src/main/scala/scala/scalanative/issues/_374Suite.scala

@@ -0,0 +1,11 @@
+package scala.scalanative.issues
+
+object _374Suite extends tests.Suite {
+  test("#374") {
+    assert("42" == bar(42))
+    assert("bar" == bar_i32())
+  }
+
+  def bar(i: Int): String = i.toString
+  def bar_i32(): String   = "bar"
+}