test: add in a CodeActionTest suite

Author: ckipp01

compiler/test/dotty/tools/dotc/reporting/CodeActionTest.scala

@@ -0,0 +1,73 @@
+package dotty.tools.dotc.reporting
+
+import dotty.tools.DottyTest
+import dotty.tools.dotc.rewrites.Rewrites
+import dotty.tools.dotc.rewrites.Rewrites.ActionPatch
+import dotty.tools.dotc.util.SourceFile
+
+import scala.annotation.tailrec
+import scala.jdk.CollectionConverters.*
+import scala.runtime.Scala3RunTime.assertFailed
+
+import org.junit.Test
+
+/** This is a test suite that is meant to test the actions acttatched to the
+  * diagnostic for a given code snippet.
+  */
+class CodeActionTest extends DottyTest {
+
+  @Test def convertToFunctionValue =
+    checkCodeAction(
+      """|object Test:
+         |  def x: Int = 3
+         |  val test = x _
+         |""".stripMargin,
+      "Make function value",
+      """|object Test:
+         |  def x: Int = 3
+         |  val test = (() => x)
+         |""".stripMargin
+      )
+
+  private def checkCodeAction(code: String, title: String, expected: String) =
+    val source = SourceFile.virtual("test", code).content
+    val result = checkCompile("typer", code):
+      case (_, ctx) =>
+        val diagnostics = ctx.reporter.pendingMessages
+        assert(diagnostics.size == 1, s"Only expecting a single diagnostic here, but got ${diagnostics.size}")
+
+        val diagnostic = diagnostics.head
+        val actions = diagnostic.msg.actions.asScala.toList
+        assert(actions.size == 1, "Right now only a signle action is being tested for. This needs to be updated this fails.")
+
+        // TODO account for more than 1 action
+        val action = actions.head
+        assert(action.title == title)
+        val patches = action.patches.asScala.toList
+        if patches.nonEmpty then
+          patches.reduceLeft {(p1, p2) =>
+            assert(p1.srcPos.span.end <= p2.srcPos.span.start, s"overlapping patches $p1 and $p2")
+            p2
+          }
+        else assertFailed("Expected a patch attatched to this action, but it was empty")
+
+        val result = new Array[Char](source.length)
+
+        @tailrec def loop(ps: List[ActionPatch], inIdx: Int, outIdx: Int): Unit =
+          def copy(upTo: Int): Int =
+            val untouched = upTo - inIdx
+            System.arraycopy(source, inIdx, result, outIdx, untouched)
+            outIdx + untouched
+
+          ps match
+            case patch @ ActionPatch(srcPos, replacement) :: ps1 =>
+              val outNew = copy(srcPos.start)
+              replacement.copyToArray(result, outNew)
+              loop(ps1, srcPos.end, outNew + replacement.length)
+            case Nil =>
+              val outNew = copy(source.length)
+              assert(outNew == result.length, s"$outNew != ${result.length}")
+
+        loop(patches, 0, 0)
+        assert(result.mkString == expected)
+}