Fix #9538: type of empty expression

Author: december32

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -376,10 +376,14 @@ class ReplDriver(settings: Array[String],
       }
 
     case TypeOf(expr) =>
-      compiler.typeOf(expr)(newRun(state)).fold(
-        displayErrors,
-        res => out.println(SyntaxHighlighting.highlight(res)(using state.context))
-      )
+      expr match {
+        case "" => out.println(s":type <expression>.")
+        case _  =>
+          compiler.typeOf(expr)(newRun(state)).fold(
+            displayErrors,
+            res => out.println(SyntaxHighlighting.highlight(res)(using state.context))
+          )
+      }
       state
 
     case DocOf(expr) =>

compiler/test-resources/repl/i9538

@@ -0,0 +1,2 @@
+scala>:type
+:type <expression>.

compiler/test/dotty/tools/repl/TypeTests.scala

@@ -21,4 +21,9 @@ class TypeTests extends ReplTest {
       run(":type x")
       assertEquals("Int", storedOutput().trim)
     }
+
+  @Test def typeOfEmpty = fromInitialState { implicit s =>
+    run(":type")
+    assertEquals(":type <expression>.", storedOutput().trim)
+  }
 }