mllib: Add Common_utils.string_suffix function and extend test coverage.

mllib/common_utils.ml

@@ -98,6 +98,11 @@ let string_prefix str prefix =
   let n = String.length prefix in
   String.length str >= n && String.sub str 0 n = prefix
 
+let string_suffix str suffix =
+  let sufflen = String.length suffix
+  and len = String.length str in
+  len >= sufflen && String.sub str (len - sufflen) sufflen = suffix
+
 let rec string_find s sub =
   let len = String.length s in
   let sublen = String.length sub in

mllib/common_utils.mli

@@ -39,6 +39,7 @@ val output_spaces : out_channel -> int -> unit
 (** Write [n] spaces to [out_channel]. *)
 
 val string_prefix : string -> string -> bool
+val string_suffix : string -> string -> bool
 val string_find : string -> string -> int
 val replace_str : string -> string -> string -> string
 val string_nsplit : string -> string -> string list

mllib/common_utils_tests.ml

@@ -78,3 +78,24 @@ let () =
   assert (human_size (-1363149_L) = "-1.3M");
   assert (human_size 3650722201_L = "3.4G");
   assert (human_size (-3650722201_L) = "-3.4G")
+
+(* Test Common_utils.string_prefix, string_suffix, string_find. *)
+let () =
+  assert (string_prefix "" "");
+  assert (string_prefix "foo" "");
+  assert (string_prefix "foo" "foo");
+  assert (string_prefix "foo123" "foo");
+  assert (not (string_prefix "" "foo"));
+
+  assert (string_suffix "" "");
+  assert (string_suffix "foo" "");
+  assert (string_suffix "foo" "foo");
+  assert (string_suffix "123foo" "foo");
+  assert (not (string_suffix "" "foo"));
+
+  assert (string_find "" "" = 0);
+  assert (string_find "foo" "" = 0);
+  assert (string_find "foo" "o" = 1);
+  assert (string_find "foobar" "bar" = 3);
+  assert (string_find "" "baz" = -1);
+  assert (string_find "foobar" "baz" = -1)