line_length: Allow mapping values with long unbreakable lines

tests/rules/test_line_length.py

@@ -84,6 +84,8 @@ class LineLengthTestCase(RuleTestCase):
                    'another:\n'
                    '  - https://localhost/very/very/long/url\n'
                    '...\n', conf)
+        self.check('---\n'
+                   'long_line: http://localhost/very/very/long/url\n', conf)
 
         conf = 'line-length: {max: 20, allow-non-breakable-words: no}'
         self.check('---\n' + 30 * 'A' + '\n', conf, problem=(2, 21))
@@ -106,3 +108,6 @@ class LineLengthTestCase(RuleTestCase):
                    'another:\n'
                    '  - https://localhost/very/very/long/url\n'
                    '...\n', conf, problem=(5, 21))
+        self.check('---\n'
+                   'long_line: http://localhost/very/very/long/url\n'
+                   '...\n', conf, problem=(2, 21))

yamllint/rules/line_length.py

@@ -72,6 +72,7 @@ Use this rule to set a limit to lines length.
             http://localhost/very/very/very/very/very/very/very/very/long/url
 """
 
+import yaml
 
 from yamllint.linter import LintProblem
 
@@ -96,6 +97,11 @@ def check(conf, line):
                 if line.buffer.find(' ', start, line.end) == -1:
                     return
 
+                line_yaml = yaml.safe_load(line.content)
+                if (isinstance(line_yaml, dict) and
+                        ' ' not in line_yaml.popitem()[1]):
+                    return
+
         yield LintProblem(line.line_no, conf['max'] + 1,
                           'line too long (%d > %d characters)' %
                           (line.end - line.start, conf['max']))