#147 Toggle boolean flags instead of setting to true

Closes #147

RELEASE-NOTES.adoc

@@ -1,5 +1,9 @@
 = picocli Release Notes
 
+== 0.9.8 - Bugfix and enhancements release for public review. API may change.
+
+* #147 Toggle boolean flags instead of setting to `true`
+
 == 0.9.7 - Bugfix and enhancements release for public review. API may change.
 
 * #127 Added support for nested sub-subcommands

docs/index.adoc

@@ -74,7 +74,7 @@ The below example shows options with one or more names, options that take an opt
 ----
 class Tar {
     @Option(names = "-c", description = "create a new archive")
-    boolean extract;
+    boolean create;
 
     @Option(names = { "-f", "--file" }, paramLabel = "ARCHIVE", description = "the archive file")
     File archive;
@@ -1110,6 +1110,8 @@ Note that the `CommandLine.run` convenience method cannot be used with subcomman
 
 
 === Boolean Parameters
+By default the value of a boolean field is toggled to its logical negative when the field's option is specified on the command line.
+
 It is possible to let end users explicitly specify "true" or "false" as a parameter for a boolean option by defining an explicit <<Arity>> attribute. A boolean option with `arity = "0..1"` accepts zero to one parameters, `arity = "1"` means the option _must_ have one parameter. For example:
 
 [source, java]

src/main/java/picocli/CommandLine.java

@@ -1483,7 +1483,8 @@ private int applyValueToSingleValuedField(Field field,
                     if (value != null) {
                         args.push(value); // we don't consume the value
                     }
-                    value = "true";      // just specifying the option name sets the boolean to true
+                    Boolean currentValue = (Boolean) field.get(command);
+                    value = String.valueOf(currentValue == null ? true : !currentValue); // #147 toggle existing boolean value
                 }
             }
             if (noMoreValues && value == null) {

src/test/java/picocli/CommandLineTest.java

@@ -2705,7 +2705,7 @@ class App {
         assertEquals("2", ((App) commandLine.getCommand()).string);
 
         commandLine = new CommandLine(new App()).setOverwrittenOptionsAllowed(true);
-        commandLine.parse("-v", "--verbose");
+        commandLine.parse("-v", "--verbose", "-v"); // F -> T -> F -> T
         assertEquals(true, ((App) commandLine.getCommand()).bool);
     }
 
@@ -2728,4 +2728,21 @@ class A {
         }
         commandLine.parse("-u", "foo", "-p", "abc");
     }
+
+    @Test
+    public void testToggleBooleanValue() {
+        class App {
+            @Option(names = "-a") boolean primitiveFalse = false;
+            @Option(names = "-b") boolean primitiveTrue = true;
+            @Option(names = "-c") Boolean objectFalse = false;
+            @Option(names = "-d") Boolean objectTrue = true;
+            @Option(names = "-e") Boolean objectNull = null;
+        }
+        App app = CommandLine.populateCommand(new App(), "-a -b -c -d -e".split(" "));
+        assertTrue(app.primitiveFalse);
+        assertFalse(app.primitiveTrue);
+        assertTrue(app.objectFalse);
+        assertFalse(app.objectTrue);
+        assertTrue(app.objectNull);
+    }
 }