Expose whether a human output is desired.

src/ui.toit

@@ -88,16 +88,23 @@ interface Printer:
   /** Emits the given $json-object of the given message-$kind. */
   emit-structured --kind/int json-object/any
 
+  /** Whether the printer wants a human representation for the given $kind. */
+  wants-human --kind/int -> bool
+
 /**
 A printer that prints human-readable output.
 */
 abstract class HumanPrinterBase implements Printer:
 
-  abstract needs-structured --kind/int -> bool
   abstract emit-structured --kind/int object/any
-
   abstract print_ str/string
 
+  needs-structured --kind/int -> bool:
+    return false
+
+  wants-human --kind/int -> bool:
+    return true
+
   emit --kind/int msg/string:
     prefix := ""
     if kind == Ui.ERROR:
@@ -190,11 +197,15 @@ Typically, this printer is used in shell scripts or other non-interactive
 */
 abstract class PlainPrinterBase implements Printer:
 
-  abstract needs-structured --kind/int -> bool
   abstract emit-structured --kind/int object/any
-
   abstract print_ str/string
 
+  needs-structured --kind/int -> bool:
+    return false
+
+  wants-human --kind/int -> bool:
+    return false
+
   emit --kind/int msg/string:
     print_ msg
 
@@ -673,6 +684,12 @@ class Ui:
   wants-structured --kind/int=RESULT -> bool:
     return printer_.needs-structured --kind=kind
 
+  /**
+  Whether the UI wants a human representation for the given $kind.
+  */
+  wants-human --kind/int=RESULT -> bool:
+    return printer_.wants-human --kind=kind
+
   /**
   Aborts the program with the given error message.
 
@@ -698,25 +715,22 @@ class Ui:
         --printer=printer or this.printer_
 
 class HumanPrinter extends HumanPrinterBase:
-  needs-structured --kind/int -> bool: return false
-
   print_ str/string:
     print str
 
   emit-structured --kind/int object/any:
     unreachable
 
 class PlainPrinter extends PlainPrinterBase:
-  needs-structured --kind/int -> bool: return false
-
   print_ str/string:
     print str
 
   emit-structured --kind/int object/any:
     unreachable
 
-class JsonPrinter extends PlainPrinterBase:
-  needs-structured --kind/int -> bool: return kind == Ui.RESULT
+class JsonPrinter extends HumanPrinterBase:
+  needs-structured --kind/int -> bool:
+    return kind == Ui.RESULT
 
   print_ str/string:
     print-on-stderr_ str

tests/ui-test.toit

@@ -347,7 +347,7 @@ test-json:
   ui := Ui --printer=printer
 
   // Anything that isn't a result is emitted on stderr as if it was
-  // a console Ui.
+  // a human Ui.
   ui.emit --info "hello"
   expect-equals "hello\n" printer.stderr
   printer.reset
@@ -364,9 +364,9 @@ test-json:
   expect-equals "{\"foo\":1,\"bar\":2}" printer.stdout
 
   ui.emit --warning "some warning"
-  expect-equals "some warning\n" printer.stderr
+  expect-equals "Warning: some warning\n" printer.stderr
   printer.reset
 
   ui.emit --error "some error"
-  expect-equals "some error\n" printer.stderr
+  expect-equals "Error: some error\n" printer.stderr
   printer.reset