[cbh] Do not show empty error highlighting messages when compiler hig…

…hlighting is on #SCL-22848 fixed

- We still show messages not associated with any source file at position 1:1 in all source files (when opened). This will be addressed separately.

scala/compiler-integration/src/org/jetbrains/plugins/scala/compiler/highlighting/CompilerMessages.scala

@@ -14,7 +14,8 @@ private object CompilerMessages {
       case bspMessageTemplate(_, position) => position
       case line => line
     }
-    trimmedMessage.stripSuffix(suffix).trim
+    val noSuffix = trimmedMessage.stripSuffix(suffix).trim
+    if (noSuffix.isBlank) trimmedMessage else noSuffix
   }
 
   def isUnusedImport(description: String): Boolean =

scala/compiler-integration/test/org/jetbrains/plugins/scala/compiler/highlighting/CompilerMessagesTest.scala

@@ -20,4 +20,27 @@ class CompilerMessagesTest {
     val actual = CompilerMessages.description(originalMessage)
     assertEquals(expected, actual)
   }
+
+  @Test
+  def deprecationWarningsMessage(): Unit = {
+    val originalMessage = "there were 4 deprecation warnings; re-run with -deprecation for details\n\n"
+    val expected = "there were 4 deprecation warnings; re-run with -deprecation for details"
+    val actual = CompilerMessages.description(originalMessage)
+    assertEquals(expected, actual)
+  }
+
+  @Test
+  def oneLineMessage(): Unit = {
+    val originalMessage = "This is a one line error message"
+    val actual = CompilerMessages.description(originalMessage)
+    assertEquals(originalMessage, actual)
+  }
+
+  @Test
+  def blankAfterProcessing(): Unit = {
+    val originalMessage = "\n\nSome message  \n  "
+    val expected = "Some message"
+    val actual = CompilerMessages.description(originalMessage)
+    assertEquals(expected, actual)
+  }
 }