Rules: indentation: Fix check-multi-line-strings

For strings that continue on next line at a lower indentation level:

    Blaise Pascal: Je vous écris une longue lettre parce que
      je n'ai pas le temps d'en écrire une courte.

tests/rules/test_indentation.py

@@ -507,7 +507,7 @@ class ScalarIndentationTestCase(RuleTestCase):
         self.check('a key: multi\n'
                    '       line\n', conf)
         self.check('a key: multi\n'
-                   '  line\n', conf, problem=(2, 3))
+                   '  line\n', conf)
         self.check('a key: multi\n'
                    '        line\n', conf)
         self.check('a key:\n'
@@ -528,6 +528,8 @@ class ScalarIndentationTestCase(RuleTestCase):
                    ' line\n', conf, problem=(2, 2))
         self.check('- multi\n'
                    '   line\n', conf, problem=(2, 4))
+        self.check('a key: multi\n'
+                   '  line\n', conf, problem=(2, 3))
         self.check('a key: multi\n'
                    '        line\n', conf, problem=(2, 9))
         self.check('a key:\n'
@@ -546,24 +548,13 @@ class ScalarIndentationTestCase(RuleTestCase):
                 'document-start: disable\n')
         self.check('"multi\n'
                    ' line"\n', conf)
-        self.check('"multi\n'
-                   'line"\n', conf, problem=(2, 1))
         self.check('- "multi\n'
                    '   line"\n', conf)
-        self.check('- "multi\n'
-                   '  line"\n', conf, problem=(2, 3))
         self.check('a key: "multi\n'
                    '        line"\n', conf)
-        self.check('a key: "multi\n'
-                   '  line"\n', conf, problem=(2, 3))
-        self.check('a key: "multi\n'
-                   '       line"\n', conf, problem=(2, 8))
         self.check('a key:\n'
                    '  "multi\n'
                    '   line"\n', conf)
-        self.check('a key:\n'
-                   '  "multi\n'
-                   '  line"\n', conf, problem=(3, 3))
         self.check('- jinja2: "{% if ansible is defined %}\n'
                    '             {{ ansible }}\n'
                    '           {% else %}\n'
@@ -579,12 +570,23 @@ class ScalarIndentationTestCase(RuleTestCase):
     def test_check_multi_line_quoted(self):
         conf = ('indentation: {spaces: 2, check-multi-line-strings: yes}\n'
                 'document-start: disable\n')
+        self.check('"multi\n'
+                   'line"\n', conf, problem=(2, 1))
         self.check('"multi\n'
                    '  line"\n', conf, problem=(2, 3))
+        self.check('- "multi\n'
+                   '  line"\n', conf, problem=(2, 3))
         self.check('- "multi\n'
                    '    line"\n', conf, problem=(2, 5))
+        self.check('a key: "multi\n'
+                   '  line"\n', conf, problem=(2, 3))
+        self.check('a key: "multi\n'
+                   '       line"\n', conf, problem=(2, 8))
         self.check('a key: "multi\n'
                    '         line"\n', conf, problem=(2, 10))
+        self.check('a key:\n'
+                   '  "multi\n'
+                   '  line"\n', conf, problem=(3, 3))
         self.check('a key:\n'
                    '  "multi\n'
                    '    line"\n', conf, problem=(3, 5))

yamllint/rules/indentation.py

@@ -113,6 +113,18 @@ Use this rule to control the indentation.
         Je vous écris une longue lettre parce que
         je n'ai pas le temps d'en écrire une courte.
 
+   the following code snippet would **PASS**:
+   ::
+
+    Blaise Pascal: Je vous écris une longue lettre parce que
+                   je n'ai pas le temps d'en écrire une courte.
+
+   the following code snippet would **FAIL**:
+   ::
+
+    Blaise Pascal: Je vous écris une longue lettre parce que
+      je n'ai pas le temps d'en écrire une courte.
+
    the following code snippet would **FAIL**:
    ::
 
@@ -212,11 +224,7 @@ def check_scalar_indentation(conf, token, context):
         if token.start_mark.buffer[line_start + indent] == '\n':
             continue
 
-        if indent < expected_indent:
+        if indent != expected_indent:
-            yield LintProblem(line_no, indent + 1,
-                              ('wrong indentation: expected at least %d but '
-                               'found %d') % (expected_indent, indent))
-        elif conf['check-multi-line-strings'] and indent > expected_indent:
             yield LintProblem(line_no, indent + 1,
                               'wrong indentation: expected %d but found %d' %
                               (expected_indent, indent))
@@ -252,7 +260,8 @@ def check(conf, token, prev, next, context):
                               'wrong indentation: expected %d but found %d' %
                               (expected, found_indentation))
 
-    if isinstance(token, yaml.ScalarToken):
+    if (isinstance(token, yaml.ScalarToken) and
+            conf['check-multi-line-strings']):
         for problem in check_scalar_indentation(conf, token, context):
             yield problem