Add error parameter to PrintHelp exceptions

CHANGELOG.md

@@ -1,6 +1,11 @@
 # Changelog
 
 ## [Unreleased]
+### Added
+- Added `error` parameter to `PrintMessage` and `PrintHelpMessage`. When `true`, `CliktCommand.main` will exit with status code 1. ([#187](https://github.com/ajalt/clikt/issues/187))
+
+### Changed
+- When `printHelpOnEmptyArgs` is `true` and no arguments are present, or when `invokeWithoutSubcommand` is `false` and no subcommand is present, `CliktCommand.main` will now exit with status code 1 rather than 0. 
 
 ## [2.7.1] - 2020-05-19
 ### Fixed

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/core/CliktCommand.kt

@@ -275,14 +275,14 @@ abstract class CliktCommand(
             exitProcessMpp(e.statusCode)
         } catch (e: PrintHelpMessage) {
             echo(e.command.getFormattedHelp())
-            exitProcessMpp(0)
+            exitProcessMpp(if (e.error) 1 else 0)
         } catch (e: PrintCompletionMessage) {
             val s = if (e.forceUnixLineEndings) "\n" else currentContext.console.lineSeparator
             echo(e.message, lineSeparator = s)
             exitProcessMpp(0)
         } catch (e: PrintMessage) {
             echo(e.message)
-            exitProcessMpp(0)
+            exitProcessMpp(if (e.error) 1 else 0)
         } catch (e: UsageError) {
             echo(e.helpMessage(), err = true)
             exitProcessMpp(e.statusCode)

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/core/exceptions.kt

@@ -22,16 +22,20 @@ open class CliktError(message: String? = null, cause: Exception? = null) : Runti
 /**
  * An exception that indicates that the command's help should be printed.
  *
- * Execution should be immediately halted without an error.
+ * Execution should be immediately halted.
+ *
+ * @property error If true, execution should halt with an error. Otherwise, execution halt with no error code.
  */
-class PrintHelpMessage(val command: CliktCommand) : CliktError()
+class PrintHelpMessage(val command: CliktCommand, val error: Boolean = false) : CliktError()
 
 /**
  * An exception that indicates that a message should be printed.
  *
- * Execution should be immediately halted without an error.
+ * Execution should be immediately halted.
+ *
+ * @property error If true, execution should halt with an error. Otherwise, execution halt with no error code.
  */
-open class PrintMessage(message: String) : CliktError(message)
+open class PrintMessage(message: String, val error: Boolean = false) : CliktError(message)
 
 /**
  * Indicate that that the program finished in a controlled manner, and should complete with the given [statusCode]

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/parsers/Parser.kt

@@ -37,7 +37,7 @@ internal object Parser {
         prefixes.remove("")
 
         if (startingArgI > tokens.lastIndex && command.printHelpOnEmptyArgs) {
-            throw PrintHelpMessage(command)
+            throw PrintHelpMessage(command, error = true)
         }
 
         val positionalArgs = ArrayList<String>()
@@ -153,7 +153,7 @@ internal object Parser {
             command._arguments.forEach { it.postValidate(context) }
 
             if (subcommand == null && subcommands.isNotEmpty() && !command.invokeWithoutSubcommand) {
-                throw PrintHelpMessage(command)
+                throw PrintHelpMessage(command, error = true)
             }
 
             command.currentContext.invokedSubcommand = subcommand

clikt/src/commonTest/kotlin/com/github/ajalt/clikt/core/CliktCommandTest.kt

@@ -42,7 +42,7 @@ class CliktCommandTest {
     fun `invokeWithoutSubcommand=false`() {
         shouldThrow<PrintHelpMessage> {
             TestCommand(called = false).subcommands(TestCommand(called = false)).parse("")
-        }
+        }.error shouldBe true
 
         val child = TestCommand(called = true, name = "foo")
         TestCommand(called = true).subcommands(child).apply {
@@ -73,7 +73,9 @@ class CliktCommandTest {
     @JsName("printHelpOnEmptyArgs__true")
     fun `printHelpOnEmptyArgs = true`() {
         class C : TestCommand(called = false, printHelpOnEmptyArgs = true)
-        shouldThrow<PrintHelpMessage> { C().parse("") }
+        shouldThrow<PrintHelpMessage> {
+            C().parse("")
+        }.error shouldBe true
     }
 
     @Test