add option to not expand tabs in snippet

doc/UltiSnips.txt

@@ -250,6 +250,11 @@ snippet on. The options currently supported are >
        trigger (see above) even if it doesn't have any spaces. The resulting
        match is also passed to any python code blocks in your snippet
        definition as the local variable "match".
+   t   Don't expand tabs - By default, UltiSnips tries to expand leading tabs
+       in a snippet to match the results of automatic indentation. If this
+       option is set, UltiSnips will not try to do this expansion, and will
+       leave the tabs alone. This can be useful for snippets dealing with
+       tab delimited formats, etc..
 
 4.2 Plaintext Snippets                         *UltiSnips-plaintext-snippets*
 ----------------------

plugin/UltiSnips/__init__.py

@@ -354,11 +354,16 @@ class Snippet(object):
 
         v = []
         for line_num, line in enumerate(lines[0:]):
-            tabs = len(self._TABS.match(line).group(0))
+            if "t" in self._opts:
+                tabs = 0
+            else:
+                tabs = len(self._TABS.match(line).group(0))
+
             if line_num == 0:
                 line_ind = ""
             else:
                 line_ind = indent
+
             line_ind += tabs * self._util.sw * " "
             line_ind = self._util.indent_to_spaces(line_ind)
             line_ind = self._util.spaces_to_indent(line_ind)

test.py

@@ -1438,6 +1438,79 @@ class SnippetOptions_ExpandWordSnippets_ExpandSuffix3(
     keys = "[[test" + EX
     wanted = "[[Expand me!"
 
+####################
+# NO TAB EXPANSION #
+####################
+class _No_Tab_Expand(_VimTest):
+    snippets = ("test", "\t\tExpand\tme!\t", "", "t")
+
+class No_Tab_Expand_Simple(_No_Tab_Expand):
+    keys = "test" + EX
+    wanted = "\t\tExpand\tme!\t"
+
+class No_Tab_Expand_Leading_Spaces(_No_Tab_Expand):
+    keys = "  test" + EX
+    wanted = "  \t\tExpand\tme!\t"
+
+class No_Tab_Expand_Leading_Tabs(_No_Tab_Expand):
+    keys = "\ttest" + EX
+    wanted = "\t\t\tExpand\tme!\t"
+
+class No_Tab_Expand_No_TS(_No_Tab_Expand):
+    def _options_on(self):
+        self.send(":set sw=3\n")
+        self.send(":set sts=3\n")
+    def _options_off(self):
+        self.send(":set sw=8\n")
+        self.send(":set sts=0\n")
+    keys = "test" + EX
+    wanted = "\t\tExpand\tme!\t"
+
+class No_Tab_Expand_ET(_No_Tab_Expand):
+    def _options_on(self):
+        self.send(":set sw=3\n")
+        self.send(":set expandtab\n")
+    def _options_off(self):
+        self.send(":set sw=8\n")
+        self.send(":set noexpandtab\n")
+    keys = "test" + EX
+    wanted = "\t\tExpand\tme!\t"
+
+class No_Tab_Expand_ET_Leading_Spaces(_No_Tab_Expand):
+    def _options_on(self):
+        self.send(":set sw=3\n")
+        self.send(":set expandtab\n")
+    def _options_off(self):
+        self.send(":set sw=8\n")
+        self.send(":set noexpandtab\n")
+    keys = "  test" + EX
+    wanted = "  \t\tExpand\tme!\t"
+
+class No_Tab_Expand_ET_SW(_No_Tab_Expand):
+    def _options_on(self):
+        self.send(":set sw=8\n")
+        self.send(":set expandtab\n")
+    def _options_off(self):
+        self.send(":set sw=8\n")
+        self.send(":set noexpandtab\n")
+    keys = "test" + EX
+    wanted = "\t\tExpand\tme!\t"
+
+class No_Tab_Expand_ET_SW_TS(_No_Tab_Expand):
+    def _options_on(self):
+        self.send(":set sw=3\n")
+        self.send(":set sts=3\n")
+        self.send(":set ts=3\n")
+        self.send(":set expandtab\n")
+    def _options_off(self):
+        self.send(":set sw=8\n")
+        self.send(":set ts=8\n")
+        self.send(":set sts=0\n")
+        self.send(":set noexpandtab\n")
+    keys = "test" + EX
+    wanted = "\t\tExpand\tme!\t"
+
+
 #################
 # REGEX MATCHES #
 #################