fix: StringIndexOutOfBoundsException in presentation compiler's hasColon method

presentation-compiler/src/main/dotty/tools/pc/completions/OverrideCompletions.scala

@@ -511,10 +511,10 @@ object OverrideCompletions:
       Context
   ): Option[Int] =
     defn match
-      case td: TypeDef if text.charAt(td.rhs.span.end) == ':' =>
+      case td: TypeDef if (td.rhs.span.end < text.length) && text.charAt(td.rhs.span.end) == ':' =>
         Some(td.rhs.span.end)
       case TypeDef(_, temp : Template) =>
-        temp.parentsOrDerived.lastOption.map(_.span.end).filter(text.charAt(_) == ':')
+        temp.parentsOrDerived.lastOption.map(_.span.end).filter(idx => text.length > idx && text.charAt(idx) == ':')
       case _ => None
 
   private def fallbackFromParent(parent: Tree, name: String)(using Context) =

presentation-compiler/test/dotty/tools/pc/tests/edit/AutoImplementAbstractMembersSuite.scala

@@ -75,39 +75,59 @@ class AutoImplementAbstractMembersSuite extends BaseCodeActionSuite:
          |""".stripMargin
     )
 
-  @Test def `empty-lines-between-members` =
+  @Test def `no-new-line` =
     checkEdit(
       """|package a
-         |
-         |object A {
-         |  trait Base {
-         |    def foo(x: Int): Int
-         |    def bar(x: String): String
-         |  }
-         |  class <<Concrete>> extends Base {
-         |
-         |    def bar(x: String): String = ???
-         |
-         |  }
-         |}
-         |""".stripMargin,
+          |
+          |trait X:
+          |  def foo: Unit
+          |
+          |class <<Y>> extends X""".stripMargin,
       """|package a
          |
-         |object A {
-         |  trait Base {
-         |    def foo(x: Int): Int
-         |    def bar(x: String): String
-         |  }
-         |  class Concrete extends Base {
-         |
+         |trait X:
+         |  def foo: Unit
          |
-         |    override def foo(x: Int): Int = ???
+         |class Y extends X {
          |
-         |    def bar(x: String): String = ???
+         |  override def foo: Unit = ???
          |
-         |  }
-         |}
-         |""".stripMargin
+         |}""".stripMargin,
+    )
+
+  @Test def `empty-lines-between-members` =
+    checkEdit(
+      """|package a
+        |
+        |object A {
+        |  trait Base {
+        |    def foo(x: Int): Int
+        |    def bar(x: String): String
+        |  }
+        |  class <<Concrete>> extends Base {
+        |
+        |    def bar(x: String): String = ???
+        |
+        |  }
+        |}
+        |""".stripMargin,
+      """|package a
+        |
+        |object A {
+        |  trait Base {
+        |    def foo(x: Int): Int
+        |    def bar(x: String): String
+        |  }
+        |  class Concrete extends Base {
+        |
+        |
+        |    override def foo(x: Int): Int = ???
+        |
+        |    def bar(x: String): String = ???
+        |
+        |  }
+        |}
+        |""".stripMargin
     )
 
   @Test def `objectdef` =