strings: reimplement to_snake_case with a correct semantic

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/string.nit b/lib/standard/string.nit
index 8db6a4e..cd2698c 100644 (file)
--- a/lib/standard/string.nit
+++ b/lib/standard/string.nit
@@ -976,30 +976,50 @@ abstract class String
        #
        #     assert "randomMethodId".to_snake_case == "random_method_id"
        #
-       # If `self` is upper, it is returned unchanged
+       # The rules are the following:
        #
-       #     assert "RANDOM_METHOD_ID".to_snake_case == "RANDOM_METHOD_ID"
+       # An uppercase is always converted to a lowercase
        #
-       # If the identifier is prefixed by an underscore, the underscore is ignored
+       #     assert "HELLO_WORLD".to_snake_case == "hello_world"
+       #
+       # An uppercase that follows a lowercase is prefixed with an underscore
+       #
+       #     assert "HelloTheWORLD".to_snake_case == "hello_the_world"
+       #
+       # An uppercase that follows an uppercase and is followed by a lowercase, is prefixed with an underscore
+       #
+       #     assert "HelloTHEWorld".to_snake_case == "hello_the_world"
+       #
+       # All other characters are kept as is; `self` does not need to be a proper CamelCased string.
        #
-       #     assert "_privateField".to_snake_case == "_private_field"
+       #     assert "=-_H3ll0Th3W0rld_-=".to_snake_case == "=-_h3ll0th3w0rld_-="
        fun to_snake_case: SELFTYPE
        do
-               if self.is_upper then return self
+               if self.is_lower then return self
 
                var new_str = new FlatBuffer.with_capacity(self.length)
-               var is_first_char = true
+               var prev_is_lower = false
+               var prev_is_upper = false
 
                for i in [0..length[ do
                        var char = chars[i]
-                       if is_first_char then 
-                               new_str.add(char.to_lower)
-                               is_first_char = false
+                       if char.is_lower then
+                               new_str.add(char)
+                               prev_is_lower = true
+                               prev_is_upper = false
                        else if char.is_upper then
-                               new_str.add('_')
+                               if prev_is_lower then
+                                       new_str.add('_')
+                               else if prev_is_upper and i+1 < length and chars[i+1].is_lower then
+                                       new_str.add('_')
+                               end
                                new_str.add(char.to_lower)
+                               prev_is_lower = false
+                               prev_is_upper = true
                        else
                                new_str.add(char)
+                               prev_is_lower = false
+                               prev_is_upper = false
                        end
                end