fix: detect a negated option's positive pair by attribute, not flag string

lib/command.js

@@ -1128,14 +1128,18 @@ Expecting one of '${allowedValues.join("', '")}'`);
             this.getOptionValue(option.attributeName()) === undefined,
         )
         .forEach((option) => {
-          // check for lone negated option: --no-foo without a --foo option
-          const positiveLongFlag = option.long.replace(/^--no-/, '--');
-          if (!this._findOption(positiveLongFlag)) {
-            this.setOptionValueWithSource(
-              option.attributeName(),
-              true,
-              'default',
-            );
+          // Check for lone negated option: a --no-foo without any positive
+          // option sharing its attribute. Matching by attribute (like
+          // DualOptions) rather than by reconstructing the --foo flag string
+          // also recognises a differently-spelled positive such as -f or
+          // --fooBar as the pair, so it is not wrongly treated as lone.
+          const attributeName = option.attributeName();
+          const hasPositiveOption = this.options.some(
+            (candidate) =>
+              !candidate.negate && candidate.attributeName() === attributeName,
+          );
+          if (!hasPositiveOption) {
+            this.setOptionValueWithSource(attributeName, true, 'default');
           }
         });
 

tests/options.bool.test.js

@@ -120,6 +120,29 @@ describe('boolean option with non-boolean default', () => {
   });
 });
 
+describe('negated option paired with a differently-spelled positive', () => {
+  test('when short-only positive and negated then no implicit default', () => {
+    const program = new commander.Command();
+    program.option('-c', 'add cheese').option('--no-c', 'remove cheese');
+    program.parse([], { from: 'user' });
+    assert.equal(program.opts().c, undefined);
+  });
+
+  test('when camelCase positive and kebab-case negated then no implicit default', () => {
+    const program = new commander.Command();
+    program.option('--fooBar').option('--no-foo-bar');
+    program.parse([], { from: 'user' });
+    assert.equal(program.opts().fooBar, undefined);
+  });
+
+  test('when only negated (lone) then implicit default is still true', () => {
+    const program = new commander.Command();
+    program.option('--no-sauce');
+    program.parse([], { from: 'user' });
+    assert.equal(program.opts().sauce, true);
+  });
+});
+
 // Regression test for #1301 with `-no-` in middle of option
 describe('regression test for -no- in middle of option name', () => {
   test('when option not specified then value is undefined', () => {