Improve -explain rendering

compiler/src/dotty/tools/dotc/reporting/ConsoleReporter.scala

@@ -32,10 +32,6 @@ object ConsoleReporter {
     /** Prints the message with the given position indication. */
     def doReport(dia: Diagnostic)(using Context): Unit = {
       printMessage(messageAndPos(dia))
-      if Diagnostic.shouldExplain(dia) then
-        printMessage(explanation(dia.msg))
-      else if dia.msg.canExplain then
-        printMessage("\nlonger explanation available when compiling with `-explain`")
     }
   }
 }

compiler/src/dotty/tools/dotc/reporting/MessageRendering.scala

@@ -248,6 +248,19 @@ trait MessageRendering {
     else sb.append(msg.message)
     if (dia.isVerbose)
       appendFilterHelp(dia, sb)
+
+    if Diagnostic.shouldExplain(dia) then
+      sb.append(EOL).append(newBox())
+      sb.append(EOL).append(offsetBox).append(" Explanation (enabled by `-explain`)")
+      sb.append(EOL).append(newBox(soft = true))
+      dia.msg.explanation.split(EOL).foreach { line =>
+        sb.append(EOL).append(offsetBox).append(if line.isEmpty then "" else " ").append(line)
+      }
+      sb.append(EOL).append(endBox)
+    else if dia.msg.canExplain then
+      sb.append(EOL).append(offsetBox)
+      sb.append(EOL).append(offsetBox).append(" longer explanation available when compiling with `-explain`")
+
     sb.toString
   }
 

compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala

@@ -142,18 +142,17 @@ object ErrorReporting {
           |conforms to
           |  $expected
           |but the comparison trace ended with `false`:
-          """
+          |"""
       val c = ctx.typerState.constraint
       val constraintText =
         if c.domainLambdas.isEmpty then
           "the empty constraint"
         else
           i"""a constraint with:
              |$c"""
-      i"""
-        |${TypeComparer.explained(_.isSubType(found, expected), header)}
-        |
-        |The tests were made under $constraintText"""
+      i"""${TypeComparer.explained(_.isSubType(found, expected), header)}
+         |
+         |The tests were made under $constraintText"""
 
     /** Format `raw` implicitNotFound or implicitAmbiguous argument, replacing
      *  all occurrences of `${X}` where `X` is in `paramNames` with the

compiler/test-resources/repl/errmsgs

@@ -6,45 +6,51 @@ scala> val x: List[String] = List(1)
   |                            ^
   |                            Found:    (1 : Int)
   |                            Required: String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> val y: List[List[String]] = List(List(1))
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | val y: List[List[String]] = List(List(1))
   |                                       ^
   |                                       Found:    (1 : Int)
   |                                       Required: String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> val z: (List[String], List[Int]) = (List(1), List("a"))
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | val z: (List[String], List[Int]) = (List(1), List("a"))
   |                                          ^
   |                                          Found:    (1 : Int)
   |                                          Required: String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | val z: (List[String], List[Int]) = (List(1), List("a"))
   |                                                   ^^^
   |                                                  Found:    ("a" : String)
   |                                                  Required: Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 2 errors found
 scala> val a: Inv[String] = new Inv(new Inv(1))
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | val a: Inv[String] = new Inv(new Inv(1))
   |                              ^^^^^^^^^^
   |                              Found:    Inv[Int]
   |                              Required: String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> val b: Inv[String] = new Inv(1)
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | val b: Inv[String] = new Inv(1)
   |                              ^
   |                              Found:    (1 : Int)
   |                              Required: String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> abstract class C { type T; val x: T; val s: Unit = { type T = String; var y: T = x; locally { def f() = { type T = Int; val z: T = y }; f() } }; }
 -- [E007] Type Mismatch Error: -------------------------------------------------
@@ -55,7 +61,8 @@ scala> abstract class C { type T; val x: T; val s: Unit = { type T = String; var
   |
   |where:    T  is a type in class C
   |          T² is a type in the initializer of value s which is an alias of String
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 -- [E007] Type Mismatch Error: -------------------------------------------------
 1 | abstract class C { type T; val x: T; val s: Unit = { type T = String; var y: T = x; locally { def f() = { type T = Int; val z: T = y }; f() } }; }
   |                                                                                                                                    ^
@@ -64,7 +71,8 @@ longer explanation available when compiling with `-explain`
   |
   |where:    T  is a type in the initializer of value s which is an alias of String
   |          T² is a type in method f which is an alias of Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 2 errors found
 scala> class Foo() { def bar: Int = 1 }; val foo = new Foo(); foo.barr
 -- [E008] Not Found Error: -----------------------------------------------------
@@ -78,33 +86,38 @@ scala> val x: List[Int] = "foo" :: List(1)
   |                    ^^^^^
   |                    Found:    ("foo" : String)
   |                    Required: Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> while (((  foo ))) {}
 -- [E006] Not Found Error: -----------------------------------------------------
 1 | while (((  foo ))) {}
   |            ^^^
   |            Not found: foo
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> val a: iDontExist = 1
 -- [E006] Not Found Error: -----------------------------------------------------
 1 | val a: iDontExist = 1
   |        ^^^^^^^^^^
   |        Not found: type iDontExist
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> def foo1(x: => Int) = x _
 -- [E099] Syntax Error: --------------------------------------------------------
 1 | def foo1(x: => Int) = x _
   |                       ^^^
   |Only function types can be followed by _ but the current expression has type Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> def foo2(x: => Int): () => Int = x _
 -- [E099] Syntax Error: --------------------------------------------------------
 1 | def foo2(x: => Int): () => Int = x _
   |                                  ^^^
   |Only function types can be followed by _ but the current expression has type Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

compiler/test-resources/repl/i13208.default.scala

@@ -5,5 +5,6 @@ scala> try 1
   | ^^^^^
   | A try without catch or finally is equivalent to putting
   | its body in a block; no exceptions are handled.
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 val res0: Int = 1

compiler/test-resources/repl/i2063

@@ -3,19 +3,22 @@ scala> 	class Foo extends Bar // with one tab
 1 | 	class Foo extends Bar // with one tab
   | 	                  ^^^
   | 	                  Not found: type Bar
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala>                                                                               class Foo extends Bar // with spaces
 -- [E006] Not Found Error: -----------------------------------------------------
 1 |                                                                               class Foo extends Bar // with spaces
   |                                                                                                 ^^^
   |                                                       Not found: type Bar
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala>                                                                                  class Foo extends Bar // with tabs
 -- [E006] Not Found Error: -----------------------------------------------------
 1 |                                                                                  class Foo extends Bar // with tabs
   |                                                                                                    ^^^
   |                                                       Not found: type Bar
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

compiler/test-resources/repl/i2213

@@ -3,7 +3,8 @@ scala> def x
 1 | def x
   |      ^
   |      Missing return type
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 scala> def x: Int
 -- [E067] Syntax Error: --------------------------------------------------------
 1 | def x: Int

compiler/test-resources/repl/i4217

@@ -6,5 +6,6 @@ scala> def foo(x: Option[Int]) = x match { case None => }
   |                           match may not be exhaustive.
   |
   |                           It would fail on pattern case: Some(_)
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 def foo(x: Option[Int]): Unit

compiler/test-resources/repl/i4566

@@ -4,5 +4,6 @@ scala> object test { type ::[A, B]; def a: Int :: Int = ???; def b: Int = a }
   |                                                                    ^
   |                                                      Found:    Int :: Int
   |                                                      Required: Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

compiler/test-resources/repl/i7644

@@ -3,7 +3,8 @@ scala> class T extends CanEqual
 1 | class T extends CanEqual
   |       ^
   |       Cannot extend sealed trait CanEqual in a different source file
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 -- [E056] Syntax Error: --------------------------------------------------------
 1 | class T extends CanEqual
   |                 ^^^^^^^^
@@ -14,7 +15,8 @@ scala> class T extends CanEqual
 1 | class T extends CanEqual
   |       ^
   |       Cannot extend sealed trait CanEqual in a different source file
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 -- [E056] Syntax Error: --------------------------------------------------------
 1 | class T extends CanEqual
   |                 ^^^^^^^^

compiler/test-resources/repl/importFromObj

@@ -10,7 +10,8 @@ scala> buf += xs
   |        ^^
   |        Found:    (o.xs : List[Int])
   |        Required: Int
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> buf ++= xs
 val res0: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 2, 3)

compiler/test-resources/repl/notFound

@@ -3,12 +3,14 @@ scala>  Foo
 1 |  Foo
   |  ^^^
   |  Not found: Foo
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala>  Bar
 -- [E006] Not Found Error: -----------------------------------------------------
 1 |  Bar
   |  ^^^
   |  Not found: Bar
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

compiler/test-resources/repl/nowarn.scala

@@ -5,7 +5,8 @@ scala> @annotation.nowarn def f = try 1 // @nowarn doesn't work on first line, c
   |                            ^^^^^
   |                   A try without catch or finally is equivalent to putting
   |                   its body in a block; no exceptions are handled.
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 def f: Int
 scala> @annotation.nowarn def f = try 1
 def f: Int
@@ -16,7 +17,8 @@ scala> def f = try 1
   |         ^^^^^
   |         A try without catch or finally is equivalent to putting
   |         its body in a block; no exceptions are handled.
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 def f: Int
 scala> @annotation.nowarn def f = { 1; 2 }
 def f: Int
@@ -26,5 +28,6 @@ scala> def f = { 1; 2 }
 1 | def f = { 1; 2 }
   |           ^
   |A pure expression does nothing in statement position; you may be omitting necessary parentheses
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 def f: Int

compiler/test-resources/repl/overrides

@@ -3,7 +3,8 @@ scala> class B { override def foo(i: Int): Unit = {}; }
 1 | class B { override def foo(i: Int): Unit = {}; }
   |                        ^
   |                        method foo overrides nothing
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 scala> class A { def foo: Unit = {}; }
 // defined class A
@@ -12,5 +13,6 @@ scala> class B extends A { override def foo(i: Int): Unit = {}; }
 1 | class B extends A { override def foo(i: Int): Unit = {}; }
   |                                  ^
   |      method foo has a different signature than the overridden declaration
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

compiler/test-resources/repl/reset-command

@@ -22,7 +22,8 @@ scala> resetNoArgsStillWorks
 1 | resetNoArgsStillWorks
   | ^^^^^^^^^^^^^^^^^^^^^
   | Not found: resetNoArgsStillWorks
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found
 
 scala>:settings "-Dfoo=bar baz"

compiler/test-resources/type-printer/type-mismatch

@@ -8,5 +8,6 @@ scala> val x: Foo[String] = res0
   |                      ^^^^
   |                      Found:    (res0 : Foo[Int])
   |                      Required: Foo[String]
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 1 error found

tests/neg-custom-args/explicit-nulls/byname-nullables.check

@@ -3,8 +3,8 @@
    |                        ^
    |                        Found:    (x : String | Null)
    |                        Required: String
-
-longer explanation available when compiling with `-explain`
+   |
+   | longer explanation available when compiling with `-explain`
 -- Error: tests/neg-custom-args/explicit-nulls/byname-nullables.scala:43:32 --------------------------------------------
 43 |    if x != null then f(identity(x), 1)   // error: dropping not null check fails typing
    |                        ^^^^^^^^^^^

tests/neg-custom-args/explicit-nulls/i7883.check

@@ -10,11 +10,11 @@
 6 |      case r(hd, tl) => Some((hd, tl))  // error // error // error
   |                              ^^
   |                              Not found: hd
-
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`
 -- [E006] Not Found Error: tests/neg-custom-args/explicit-nulls/i7883.scala:6:34 ---------------------------------------
 6 |      case r(hd, tl) => Some((hd, tl))  // error // error // error
   |                                  ^^
   |                                  Not found: tl
-
-longer explanation available when compiling with `-explain`
+  |
+  | longer explanation available when compiling with `-explain`