feat(printer): mk printers more easily configurable

munit/shared/src/main/scala/munit/Assertions.scala

@@ -303,10 +303,12 @@ trait Assertions extends MacroCompat.CompileErrorMacro {
   }
   def clues(clue: Clue[_]*): Clues = new Clues(clue.toList)
 
+  def printer: Printer = EmptyPrinter
+
   def munitPrint(clue: => Any): String = {
     clue match {
       case message: String => message
-      case value           => Printers.print(value)
+      case value           => Printers.print(value, printer)
     }
   }
 

munit/shared/src/main/scala/munit/Printer.scala

@@ -14,6 +14,84 @@ trait Printer {
   def height: Int = 100
   def isMultiline(string: String): Boolean =
     string.contains('\n')
+
+  /**
+   * Combine two printers into a single printer.
+   *
+   * Order is important : this printer will be tried first, then the other printer.
+   * The new Printer's height will be the max of the two printers' heights.
+   *
+   * Comibining two printers can be useful if you want to customize Printer for
+   * some types somewhere, but want to add more specialized printers for some tests
+   *
+   * {{{
+   * trait MySuites extends FunSuite {
+   *   override val printer = Printer.apply {
+   *     case long => s"${l}L"
+   *   }
+   * }
+   *
+   * trait SomeOtherSuites extends MySuites {
+   *   override val printer = Printer.apply {
+   *     case m: SomeCaseClass => m.someCustomToString
+   *   } orElse super.printer
+   * }
+   *
+   * }}}
+   */
+  def orElse(other: Printer): Printer = {
+    val h = this.height
+    val p: (Any, StringBuilder, Int) => Boolean = this.print
+    new Printer {
+      def print(value: Any, out: StringBuilder, indent: Int): Boolean =
+        p.apply(value, out, indent) || other.print(
+          value,
+          out,
+          indent
+        )
+      override def height: Int = h.max(other.height)
+    }
+  }
+
+}
+
+object Printer {
+
+  def apply(
+      height: Int
+  )(partialPrint: PartialFunction[Any, String]): Printer = {
+    val h = height
+    new Printer {
+      def print(value: Any, out: StringBuilder, indent: Int): Boolean =
+        value match {
+          case simpleValue =>
+            partialPrint.lift.apply(simpleValue).fold(false) { string =>
+              out.append(string)
+              true
+            }
+        }
+
+      override def height: Int = h
+    }
+  }
+
+  /**
+   * Utiliy constructor defining a printer for some types.
+   *
+   * This might be useful for some types which default pretty-printers
+   * do not output helpful diffs.
+   *
+   * {{{
+   * type ByteArray = Array[Byte]
+   * val listPrinter = Printer.apply {
+   *   case ll: ByteArray => ll.map(String.format("%02x", b)).mkString(" ")
+   * }
+   * val bytes = Array[Byte](1, 5, 8, 24)
+   * Printers.print(bytes, listPrinter) // "01 05 08 18"
+   * }}}
+   */
+  def apply(partialPrint: PartialFunction[Any, String]): Printer =
+    apply(100)(partialPrint)
 }
 
 /** Default printer that does not customize the pretty-printer */

tests/shared/src/test/scala/munit/CustomPrinterSuite.scala

@@ -0,0 +1,141 @@
+package munit
+
+import org.scalacheck.Prop.forAll
+import munit.internal.console.Printers
+import org.scalacheck.Arbitrary.arbitrary
+import org.scalacheck.Prop
+
+class CustomPrinterSuite extends FunSuite with ScalaCheckSuite {
+
+  private case class Foo(i: Int)
+
+  private case class Bar(l: List[Int])
+
+  private case class FooBar(foo: Foo, bar: Bar)
+
+  private val genFoo = arbitrary[Int].map(Foo(_))
+
+  // limit size to 10 to have a reasonable number of values
+  private val genBar = arbitrary[List[Int]].map(l => Bar(l.take(10)))
+
+  private val genFooBar = for {
+    foo <- genFoo
+    bar <- genBar
+  } yield FooBar(foo, bar)
+
+  private val longPrinter: Printer = Printer.apply { case l: Long =>
+    s"MoreThanInt($l)"
+  }
+
+  private val fooPrinter: Printer = Printer.apply { case Foo(i) =>
+    s"Foo(INT($i))"
+  }
+
+  private val listPrinter: Printer = Printer.apply { case l: List[_] =>
+    l.mkString("[", ",", "]")
+  }
+
+  private val intPrinter: Printer = Printer.apply { case i: Int =>
+    s"NotNaN($i)"
+  }
+
+  private val isScala213: Boolean = BuildInfo.scalaVersion.startsWith("2.13")
+
+  private def checkProp(
+      options: TestOptions,
+      isEnabled: Boolean = true
+  )(p: => Prop): Unit = {
+    test(options) {
+      assume(isEnabled, "disabled test")
+      p
+    }
+  }
+
+  checkProp("long") {
+    forAll(arbitrary[Long]) { (l: Long) =>
+      val obtained = Printers.print(l, longPrinter)
+      val expected = s"MoreThanInt($l)"
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("list") {
+    forAll(arbitrary[List[Int]]) { l =>
+      val obtained = Printers.print(l, listPrinter)
+      val expected = l.mkString("[", ",", "]")
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("product") {
+    forAll(genFoo) { foo =>
+      val obtained = Printers.print(foo, fooPrinter)
+      val expected = s"Foo(INT(${foo.i}))"
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("int in product", isEnabled = isScala213) {
+    forAll(genFoo) { foo =>
+      val obtained = Printers.print(foo, intPrinter)
+      val expected = s"Foo(\n  i = NotNaN(${foo.i})\n)"
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("list in product", isEnabled = isScala213) {
+    forAll(genBar) { bar =>
+      val obtained = Printers.print(bar, listPrinter)
+      val expected = s"Bar(\n  l = ${bar.l.mkString("[", ",", "]")}\n)"
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("list and int in product", isEnabled = isScala213) {
+    forAll(genFooBar) { foobar =>
+      val obtained = Printers
+        .print(foobar, listPrinter.orElse(intPrinter))
+        .stripMargin
+        .stripLeading()
+        .stripTrailing()
+      val expected =
+        s"""|FooBar(
+            |  foo = Foo(
+            |    i = NotNaN(${foobar.foo.i})
+            |  ),
+            |  bar = Bar(
+            |    l = ${foobar.bar.l.mkString("[", ",", "]")}
+            |  )
+            |)
+            |""".stripMargin.stripLeading().stripTrailing()
+      assertEquals(obtained, expected)
+    }
+  }
+
+  checkProp("all ints in product", isEnabled = isScala213) {
+    forAll(genFooBar) { foobar =>
+      val obtained = Printers
+        .print(foobar, intPrinter)
+        .filterNot(_.isWhitespace)
+
+      val expectedbBarList = foobar.bar.l match {
+        case Nil => "Nil"
+        case l =>
+          l.map(i => s"NotNaN($i)").mkString("List(", ",", ")")
+      }
+
+      val expected =
+        s"""|FooBar(
+            |  foo = Foo(
+            |    i = NotNaN(${foobar.foo.i})
+            |  ),
+            |  bar = Bar(
+            |    l = $expectedbBarList
+            |  )
+            |)
+            |""".stripMargin.filterNot(_.isWhitespace)
+      assertEquals(obtained, expected)
+    }
+  }
+
+}