utils/check-package: add a check for 'default n' in Config.in files

Boolean Config.in symbols default to 'n', so we typically do not add such
redundant lines.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

utils/checkpackagelib/lib_config.py

@@ -242,6 +242,17 @@ class Indent(_CheckFunction):
                         text]
 
 
+class NoDefaultN(_CheckFunction):
+    DEFAULTN = re.compile(r"^\tdefault n$")
+
+    def check_line(self, lineno, text):
+        text_nocomments = text.split("#")[0].rstrip()
+        if self.DEFAULTN.match(text_nocomments):
+            return ["{}:{}: boolean symbols default to 'n', so 'default n' is redundant"
+                    .format(self.filename, lineno),
+                    text]
+
+
 class RedefinedConfig(_CheckFunction):
     CONFIG = re.compile(r"^\s*(menu|)config\s+(BR2_\w+)\b")
     IF = re.compile(r"^\s*if\s+([^#]*)\b")

utils/checkpackagelib/test_lib_config.py

@@ -387,6 +387,39 @@ def test_Indent(testname, filename, string, expected):
     assert warnings == expected
 
 
+NoDefaultN = [
+    ('good example',
+     'any',
+     'config BR2_PACKAGE_FOO\n'
+     '\tdefault y\n',
+     []),
+    ('default n',
+     'any',
+     'config BR2_PACKAGE_FOO\n'
+     '\tdefault n\n',
+     [['any:2: boolean symbols default to \'n\', so \'default n\' is redundant',
+       '\tdefault n\n']]),
+    ('default n with comment',
+     'any',
+     'config BR2_PACKAGE_FOO\n'
+     '\tdefault n # this is a comment\n',
+     [['any:2: boolean symbols default to \'n\', so \'default n\' is redundant',
+       '\tdefault n # this is a comment\n']]),
+    ('default n with trailing whitespace',
+     'any',
+     'config BR2_PACKAGE_FOO\n'
+     '\tdefault n  \t\n',
+     [['any:2: boolean symbols default to \'n\', so \'default n\' is redundant',
+       '\tdefault n  \t\n']])
+    ]
+
+
+@pytest.mark.parametrize('testname,filename,string,expected', NoDefaultN)
+def test_NoDefaultN(testname, filename, string, expected):
+    warnings = util.check_file(m.NoDefaultN, filename, string)
+    assert warnings == expected
+
+
 RedefinedConfig = [
     ('no redefinition',
      'any',