Add regression test for issue 18726

[Cherry-picked cfe13a4]

Author: rochala

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionRelease11Suite.scala

@@ -0,0 +1,26 @@
+package dotty.tools.pc.tests.completion
+
+import dotty.tools.pc.base.BaseCompletionSuite
+
+import org.junit.Test
+import java.nio.file.Path
+
+class CompletionRelease11Suite extends BaseCompletionSuite:
+
+  override protected def scalacOptions(classpath: Seq[Path]): Seq[String] =
+    "-release:11" +: super.scalacOptions(classpath)
+
+  @Test def java11Symbols =
+    check(
+      """
+        |object A {
+        |  "".repea@@
+        |}""".stripMargin,
+      """repeat(x$0: Int): String
+        |replaceAll(x$0: String, x$1: String): String
+        |prependedAll[B >: A](prefix: IterableOnce[B]): IndexedSeq[B]
+        |prependedAll(prefix: String): String
+        |prependedAll[B >: Char](prefix: IterableOnce[B]): IndexedSeq[B]
+        |replaceAllLiterally(literal: String, replacement: String): String
+        |""".stripMargin
+    )

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionRelease8Suite.scala

@@ -0,0 +1,25 @@
+package dotty.tools.pc.tests.completion
+
+import dotty.tools.pc.base.BaseCompletionSuite
+
+import org.junit.Test
+import java.nio.file.Path
+
+class CompletionRelease8Suite extends BaseCompletionSuite:
+
+  override protected def scalacOptions(classpath: Seq[Path]): Seq[String] =
+    "-release:8" +: super.scalacOptions(classpath)
+
+  @Test def noJvm11Symbols =
+    check(
+      """
+        |object A {
+        |  "".repea@@
+        |}""".stripMargin,
+      """replaceAll(x$0: String, x$1: String): String
+        |prependedAll[B >: A](prefix: IterableOnce[B]): IndexedSeq[B]
+        |prependedAll(prefix: String): String
+        |prependedAll[B >: Char](prefix: IterableOnce[B]): IndexedSeq[B]
+        |replaceAllLiterally(literal: String, replacement: String): String
+        |""".stripMargin
+    )