Add unit tests for issue 18238 - ensure we generate correct line positions for if conditions

[Cherry-picked af75f3b]

Author: WojciechMazur

compiler/test/dotty/tools/backend/jvm/SourcePositionsTest.scala

@@ -0,0 +1,116 @@
+package dotty.tools.backend.jvm
+
+import scala.language.unsafeNulls
+
+import org.junit.Assert._
+import org.junit.Test
+
+class SourcePositionsTest extends DottyBytecodeTest:
+  import ASMConverters._
+
+  @Test def issue18238_a(): Unit = {
+    val code =
+      """
+      |class Test {
+      |  def test(): Unit = {
+      |    var x = 3
+      |    var y = 2
+      |    while(true) {
+      |      if (x < y)
+      |        if (x >= y)
+      |          x += 1
+      |        else
+      |          y -= 1
+      |    }
+      |  }
+      |}""".stripMargin
+
+    checkBCode(code) { dir =>
+      val testClass = loadClassNode(dir.lookupName("Test.class", directory = false).input, skipDebugInfo = false)
+      val testMethod = getMethod(testClass, "test")
+      val lineNumbers = instructionsFromMethod(testMethod).collect{case ln: LineNumber => ln}
+      val expected = List(
+        LineNumber(4, Label(0)),   // var x
+        LineNumber(5, Label(4)),   // var y
+        LineNumber(6, Label(8)),   // while(true)
+        LineNumber(7, Label(13)),  // if (x < y)
+        LineNumber(8, Label(18)),  //   if (x >= y)
+        LineNumber(9, Label(23)),  //     x += 1
+        LineNumber(11, Label(27)), //     y -= 1
+        LineNumber(7, Label(32))   // <synthetic unit> point back to `if (x < y)
+      )
+      assertEquals(expected, lineNumbers)
+    }
+  }
+
+  @Test  def issue18238_b(): Unit = {
+    val code =
+      """
+      |class Test {
+      |  def test(): Unit = {
+      |    var x = 3
+      |    var y = 2
+      |    while(true) {
+      |      if (x < y)
+      |        if (x >= y)
+      |          x += 1
+      |        else
+      |          y -= 1
+      |      else ()
+      |    }
+      |  }
+      |}""".stripMargin
+
+    checkBCode(code) { dir =>
+      val testClass = loadClassNode(dir.lookupName("Test.class", directory = false).input, skipDebugInfo = false)
+      val testMethod = getMethod(testClass, "test")
+      val lineNumbers = instructionsFromMethod(testMethod).collect{case ln: LineNumber => ln}
+      val expected = List(
+        LineNumber(4, Label(0)),   // var x
+        LineNumber(5, Label(4)),   // var y
+        LineNumber(6, Label(8)),   // while(true)
+        LineNumber(7, Label(13)),  // if (x < y)
+        LineNumber(8, Label(18)),  //   if (x >= y)
+        LineNumber(9, Label(23)),  //     x += 1
+        LineNumber(11, Label(27)), //     y -= 1
+        LineNumber(12, Label(32))  // else ()
+      )
+      assertEquals(expected, lineNumbers)
+    }
+  }
+
+  @Test  def issue18238_c(): Unit = {
+    val code =
+      """
+      |class Test {
+      |  def test(): Unit = {
+      |    var x = 3
+      |    var y = 2
+      |    while(true) {
+      |      if (x < y)
+      |        if (x >= y)
+      |          x += 1
+      |        else
+      |          y -= 1
+      |      println()
+      |    }
+      |  }
+      |}""".stripMargin
+
+    checkBCode(code) { dir =>
+      val testClass = loadClassNode(dir.lookupName("Test.class", directory = false).input, skipDebugInfo = false)
+      val testMethod = getMethod(testClass, "test")
+      val lineNumbers = instructionsFromMethod(testMethod).collect{case ln: LineNumber => ln}
+      val expected = List(
+        LineNumber(4, Label(0)),   // var x
+        LineNumber(5, Label(4)),   // var y
+        LineNumber(6, Label(8)),   // while(true)
+        LineNumber(7, Label(13)),  // if (x < y)
+        LineNumber(8, Label(18)),  //   if (x >= y)
+        LineNumber(9, Label(23)),  //     x += 1
+        LineNumber(11, Label(27)), //     y -= 1
+        LineNumber(12, Label(31))  // println()
+      )
+      assertEquals(expected, lineNumbers)
+    }
+  }