add char-diff highlighting within line diffs

Author: lihaoyi

utest/src/utest/Errors.scala

@@ -54,7 +54,39 @@ object AssertionError {
       case DiffElement.InBoth(x) => render0("  ", x, fansi.Attrs.Empty)
       case DiffElement.InFirst(x) => renderRed(x)
       case DiffElement.InSecond(x) => renderGreen(x)
-      case DiffElement.Diff(x, y) => renderRed(x) ++ renderGreen(y)
+      case DiffElement.Diff(x, y) =>
+        // Within any adjacent blocks of differing text, do a char-by-char
+        // diff between the two versions so we can underline the characters
+        // that differ between them
+        val subDiff = StringDiff.diff(x.map(_.plainText).mkString, y.map(_.plainText).mkString)
+        val sectionsX = subDiff.collect{
+          case DiffElement.InBoth(x) => (false, x.length)
+          case DiffElement.InFirst(x) => (true, x.length)
+          case DiffElement.Diff(x, y) => (true, x.length)
+        }
+
+        val sectionsY = subDiff.collect{
+          case DiffElement.InBoth(x) => (false, x.length)
+          case DiffElement.InSecond(x) => (true, x.length)
+          case DiffElement.Diff(x, y) => (true, y.length)
+        }
+
+        def sectionsToOverlays(sections: Seq[(Boolean, Int)]) = {
+          val buffer = collection.mutable.Buffer.empty[(fansi.Attrs, Int, Int)]
+          var index = 0
+          for ((underline, length) <- sections) {
+            val nextIndex = index + length
+            if (underline) buffer.append((fansi.Underlined.On, index, nextIndex))
+            index = nextIndex
+          }
+          buffer.toSeq
+        }
+
+        val overlaysX = sectionsToOverlays(sectionsX)
+        val overlaysY = sectionsToOverlays(sectionsY)
+
+        renderRed(splitLines(fansi.Str.join(x).overlayAll(overlaysX))) ++
+          renderGreen(splitLines(fansi.Str.join(y).overlayAll(overlaysY)))
     }
   }
   def render(msgPrefix: String, captured: Seq[TestValue]) = {

utest/test/src/test/utest/Main.scala

@@ -1,37 +1,12 @@
 package test.utest
 import utest._
-import scala.concurrent.{ExecutionContext, Future}
 
 object Main {
   def main(args: Array[String]): Unit = {
-    val tests = Tests{
-      test("test1"){
-        // throw new Exception("test1")
-      }
-      test("test2"){
-        test("inner"){
-          val a = 1
-          val b = 2
-          val c = 3
-          val d = 4
-          assertAll(
-            a == 1,
-            c == d,
-            ???
-          )
-        }
-      }
-      test("test3"){
-        val a = List[Byte](1, 2)
-        // a(10)
-      }
-    }
-
-
-    // Run, return results, and print streaming output with the default formatter
-    val results2 = TestRunner.runAndPrint(
-      tests,
-      "MyTestSuiteA"
+    try assert(
+      Seq("i am cow", "hear me moo", "i weigh twice as much as you", "and I look good on the barbecue", "!!!!!") ==
+      Seq("I AM COW", "hear me moo", "I weigh twice as much as you", "AND I look good on the barbecue", "???"),
     )
+    catch{case e: utest.AssertionError => println(e.coloredMessage)}
   }
 }