Print shell completion with an exeption rather than calling echo directly

Author: ajalt

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Changelog
 
 ## [Unreleased]
+### Changed
+- Shell completion code is now printed by throwing a `PrintCompletionMessage` (a subclass of `PrintMessage`) rather than calling `echo` directly.
 
 ## [2.2.0] - 2019-09-25
 ### Added

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

@@ -93,8 +93,7 @@ abstract class CliktCommand(
         }
         val envval = System.getenv(envvar) ?: return
         val completion = CompletionGenerator.generateCompletion(command = this, zsh = "zsh" in envval)
-        echo(completion, lineSeparator = "\n")
-        exitProcess(1)
+        throw PrintCompletionMessage(completion, forceUnixLineEndings = true)
     }
 
     /**
@@ -232,6 +231,10 @@ abstract class CliktCommand(
         } catch (e: PrintHelpMessage) {
             echo(e.command.getFormattedHelp())
             exitProcess(0)
+        } catch (e: PrintCompletionMessage) {
+            val s = if (e.forceUnixLineEndings) "\n" else context.console.lineSeparator
+            echo(e.message, lineSeparator = s)
+            exitProcess(0)
         } catch (e: PrintMessage) {
             echo(e.message)
             exitProcess(0)

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

@@ -30,7 +30,17 @@ class PrintHelpMessage(val command: CliktCommand) : CliktError()
  *
  * Execution should be immediately halted without an error.
  */
-class PrintMessage(message: String) : CliktError(message)
+open class PrintMessage(message: String) : CliktError(message)
+
+/**
+ * An exception that indicates that shell completion code should be printed.
+ *
+ * Execution should be immediately halted without an error.
+ *
+ * @param forceUnixLineEndings if true, all line endings in the message should be `\n`, regardless
+ *   of the current operating system.
+ */
+class PrintCompletionMessage(message: String, val forceUnixLineEndings: Boolean): PrintMessage(message)
 
 /**
  * An internal exception that signals a usage error.