[backport] SI-9616 False positive in unused import warning

This is a minimal backport of the fix for SI-9383.

3 files changed, 81 insertions, 12 deletions

diff --git a/test/files/neg/warn-unused-imports.check b/test/files/neg/warn-unused-imports.check
index 36c6dd03c3..0a53d7a9cd 100644
--- a/test/files/neg/warn-unused-imports.check
+++ b/test/files/neg/warn-unused-imports.check
@@ -1,33 +1,55 @@
-warn-unused-imports.scala:57: warning: Unused import
+warn-unused-imports_2.scala:133: error: type mismatch;
+ found   : Int(42)
+ required: Sample.X
+    f(42)                       // error
+      ^
+warn-unused-imports_2.scala:57: warning: Unused import
     import p1.A // warn
               ^
-warn-unused-imports.scala:62: warning: Unused import
+warn-unused-imports_2.scala:62: warning: Unused import
     import p1.{ A, B } // warn on A
                 ^
-warn-unused-imports.scala:67: warning: Unused import
+warn-unused-imports_2.scala:67: warning: Unused import
     import p1.{ A, B } // warn on both
                 ^
-warn-unused-imports.scala:67: warning: Unused import
+warn-unused-imports_2.scala:67: warning: Unused import
     import p1.{ A, B } // warn on both
                    ^
-warn-unused-imports.scala:73: warning: Unused import
+warn-unused-imports_2.scala:73: warning: Unused import
     import c._  // warn
              ^
-warn-unused-imports.scala:78: warning: Unused import
+warn-unused-imports_2.scala:78: warning: Unused import
     import p1._ // warn
               ^
-warn-unused-imports.scala:85: warning: Unused import
+warn-unused-imports_2.scala:85: warning: Unused import
     import c._  // warn
              ^
-warn-unused-imports.scala:91: warning: Unused import
+warn-unused-imports_2.scala:91: warning: Unused import
     import p1.c._  // warn
                 ^
-warn-unused-imports.scala:98: warning: Unused import
+warn-unused-imports_2.scala:98: warning: Unused import
     import p1._   // warn
               ^
-warn-unused-imports.scala:118: warning: Unused import
+warn-unused-imports_2.scala:118: warning: Unused import
     import p1.A   // warn
               ^
-error: No warnings can be incurred under -Xfatal-warnings.
-10 warnings found
+warn-unused-imports_2.scala:132: warning: Unused import
+    import Sample.Implicits._   // warn
+                            ^
+warn-unused-imports_2.scala:143: warning: Unused import
+    import Sample.Implicits.useless     // warn
+                            ^
+warn-unused-imports_2.scala:147: warning: Unused import
+    import java.io.File                 // warn
+                   ^
+warn-unused-imports_2.scala:148: warning: Unused import
+    import scala.concurrent.Future      // warn
+                            ^
+warn-unused-imports_2.scala:149: warning: Unused import
+    import scala.concurrent.ExecutionContext.Implicits.global // warn
+                                                       ^
+warn-unused-imports_2.scala:150: warning: Unused import
+    import p1.A                         // warn
+              ^
+16 warnings found
 one error found
diff --git a/test/files/neg/warn-unused-imports/sample_1.scala b/test/files/neg/warn-unused-imports/sample_1.scala
new file mode 100644
index 0000000000..d2f86239db
--- /dev/null
+++ b/test/files/neg/warn-unused-imports/sample_1.scala
@@ -0,0 +1,17 @@
+
+import language._
+
+object Sample {
+  trait X
+  trait Y
+
+  // import of the non-implicit should be unused
+  object Implicits {
+    def `int to X`(i: Int): X = null
+    implicit def `int to Y`(i: Int): Y = null
+    implicit def useless(i: Int): String = null
+  }
+
+  def f(x: X) = ???
+  def g(y: Y) = ???
+}
diff --git a/test/files/neg/warn-unused-imports.scala b/test/files/neg/warn-unused-imports/warn-unused-imports_2.scala
index b7a2f1c414..ded1186209 100644
--- a/test/files/neg/warn-unused-imports.scala
+++ b/test/files/neg/warn-unused-imports/warn-unused-imports_2.scala
@@ -123,3 +123,33 @@ trait Nested {
     println(new Warn { })
   }
 }
+
+// test unusage of imports from other compilation units after implicit search
+trait Outsiders {
+  {
+    //implicit search should not disable warning
+    import Sample._
+    import Sample.Implicits._   // warn
+    f(42)                       // error
+  }
+  {
+    import Sample._
+    import Sample.Implicits._   // nowarn
+    g(42)                       // ok
+  }
+  {
+    import Sample._
+    import Sample.Implicits.`int to Y`  // nowarn
+    import Sample.Implicits.useless     // warn
+    g(42)                       // ok
+  }
+  {
+    import java.io.File                 // warn
+    import scala.concurrent.Future      // warn
+    import scala.concurrent.ExecutionContext.Implicits.global // warn
+    import p1.A                         // warn
+    import p1.B                         // no warn
+    println("abc".bippy)
+    //Future("abc".bippy)
+  }
+}