Partial support for mixed tabs and spaces.

Also account for 1 tab == 1 indent.

autoload/indent_guides.vim

@@ -41,8 +41,8 @@ function! indent_guides#enable()
   " will automagically figure out whether to use tabs or spaces
   for l:level in range(s:start_level, s:indent_levels)
     let l:group      = 'IndentGuides' . ((l:level % 2 == 0) ? 'Even' : 'Odd')
-    let l:pattern    = '^\s\{' . (l:level * s:indent_size - s:indent_size) . '\}\zs'
-    let l:pattern   .= '\s\{' . s:guide_size . '\}'
+    let l:pattern    = '^\s*\%' . ((l:level - 1) * s:indent_size + 1) . 'v\zs'
+    let l:pattern   .= '\s*\%' . (((l:level - 1) * s:indent_size + 1) + s:guide_size) . 'v'
     let l:pattern   .= '\ze'
 
     " define the higlight pattern and add to list
@@ -207,12 +207,17 @@ endfunction
 "
 function! indent_guides#calculate_guide_size()
   let l:guide_size  = g:indent_guides_guide_size
-  let l:indent_size = indent_guides#get_indent_size()
 
-  if l:indent_size > 1 && l:guide_size >= 1
-    let l:guide_size = (l:guide_size > s:indent_size) ? s:indent_size : l:guide_size
-  else
+  if &expandtab == 0 && &tabstop == s:indent_size
     let l:guide_size = s:indent_size
+  else
+    if s:indent_size > 1 && l:guide_size >= 1
+      if l:guide_size > s:indent_size
+        let l:guide_size = s:indent_size
+      end
+    else
+      let l:guide_size = s:indent_size
+    endif
   endif
 
   return l:guide_size
@@ -223,7 +228,7 @@ endfunction
 " being used.
 "
 function! indent_guides#get_indent_size()
-  return (&l:expandtab == 1) ? &l:shiftwidth : 1
+  return &l:shiftwidth
 endfunction
 
 "

test-files/test-ts2sw2et.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=2:sw=2:et
+vim:tw=78:ts=2:sw=2:et:nolist
 
 test
   test

test-files/test-ts2sw2noet.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=2:sw=2:noet
+vim:tw=78:ts=2:sw=2:noet:nolist
 
 test
 	test

test-files/test-ts4sw4et.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=4:sw=4:et
+vim:tw=78:ts=4:sw=4:et:nolist
 
 test
     test

test-files/test-ts4sw4noet.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=4:sw=4:noet
+vim:tw=78:ts=4:sw=4:noet:nolist
 
 test
 	test

test-files/test-ts8sw2noet.txt

@@ -0,0 +1,24 @@
+vim:tw=78:ts=8:sw=2:noet:nolist
+
+test
+  test
+    test
+      test
+	test
+	  test
+	    test
+	      test
+		test
+		  test
+		    test
+		      test
+			test
+			  test
+			    test
+			      test
+				test
+				  test
+				    test
+				      test
+					test
+					  test

test-files/test-ts8sw8et.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=8:sw=8:et
+vim:tw=78:ts=8:sw=8:et:nolist
 
 test
         test

test-files/test-ts8sw8noet.txt

@@ -1,4 +1,4 @@
-vim:tw=78:ts=8:sw=8:noet
+vim:tw=78:ts=8:sw=8:noet:nolist
 
 test
 	test