test: add in a CodeActionTest suite

Author: ckipp01

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

@@ -0,0 +1,83 @@
+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.Assert._
+import org.junit.Test
+
+/** This is a test suite that is meant to test the actions attached 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,
+      "Rewrite to function value",
+      """|object Test:
+         |  def x: Int = 3
+         |  val test = (() => x)
+         |""".stripMargin
+      )
+
+  // Make sure we're not using the default reporter, which is the ConsoleReporter,
+  // meaning they will get reported in the test run and that's it.
+  private def newContext =
+    val rep = new StoreReporter(null) with UniqueMessagePositions with HideNonSensicalMessages
+    initialCtx.setReporter(rep).withoutColors
+
+  private def checkCodeAction(code: String, title: String, expected: String) =
+    ctx = newContext
+    val source = SourceFile.virtual("test", code).content
+    val runCtx = checkCompile("typer", code) { (_, _) => () }
+    val diagnostics = runCtx.reporter.removeBufferedMessages
+    assertEquals(diagnostics.size, 1)
+
+    val diagnostic = diagnostics.head
+    val actions = diagnostic.msg.actions.asScala.toList
+    assertEquals(actions.size, 1)
+
+    // TODO account for more than 1 action
+    val action = actions.head
+    assertEquals(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 $p2")
+        p2
+    else assertFailed("Expected a patch attatched to this action, but it was empty")
+
+    val delta = patches
+      .map: patch =>
+        patch.replacement.length - (patch.srcPos.end - patch.srcPos.start)
+      .sum
+
+    val result = new Array[Char](source.length + delta)
+
+    @tailrec def loop(ps: List[ActionPatch], inIdx: Int, outIdx: Int): Unit =
+      def copy(upTo: Int): Int =
+        val untouched = upTo - inIdx
+        System.arraycopy(source, inIdx, result, outIdx, untouched)
+        outIdx + untouched
+
+      ps match
+        case patch @ ActionPatch(srcPos, replacement) :: ps1 =>
+          val outNew = copy(srcPos.start)
+          replacement.copyToArray(result, outNew)
+          loop(ps1, srcPos.end, outNew + replacement.length)
+        case Nil =>
+          val outNew = copy(source.length)
+          assert(outNew == result.length, s"$outNew != ${result.length}")
+
+    loop(patches, 0, 0)
+    assertEquals(result.mkString, expected)