Merge pull request #2933 from Kabie/Regex.replace

Fix and enhance &Regex.replace/4

Signed-off-by: José Valim <[email protected]>

Author: josevalim

lib/elixir/lib/regex.ex

@@ -419,8 +419,8 @@ defmodule Regex do
 
   The replacement can be either a string or a function. The string
   is used as a replacement for every match and it allows specific
-  captures to be accessed via `\N`, where `N` is the capture. In
-  case `\0` is used, the whole match is inserted.
+  captures to be accessed via `\N` or `\g{N}`, where `N` is the
+  capture. In case `\0` is used, the whole match is inserted.
 
   When the replacement is a function, the function may have arity
   N where each argument maps to a capture, with the first argument
@@ -479,6 +479,11 @@ defmodule Regex do
   defp precompile_replacement(""),
     do: []
 
+  defp precompile_replacement(<<?\\, ?g, ?{, rest :: binary>>) when byte_size(rest) > 0 do
+    {ns, <<?}, rest :: binary>>} = pick_int(rest)
+    [List.to_integer(ns) | precompile_replacement(rest)]
+  end
+
   defp precompile_replacement(<<?\\, x, rest :: binary>>) when x < ?0 or x > ?9 do
     case precompile_replacement(rest) do
       [head | t] when is_binary(head) ->
@@ -550,7 +555,7 @@ defmodule Regex do
       cond do
         is_binary(part) ->
           part
-        part > tuple_size(indexes) ->
+        part >= tuple_size(indexes) ->
           ""
         true ->
           get_index(string, elem(indexes, part))

lib/elixir/lib/string.ex

@@ -650,13 +650,14 @@ defmodule String do
       iex> String.replace("a,b,c", ",", "-", global: false)
       "a-b,c"
 
-  The pattern can also be a regex. In those cases, one can give `\N`
-  in the `replacement` string to access a specific capture in the regex:
+  The pattern can also be a regex. In those cases, one can give `\N` or
+  `\g{N}` in the `replacement` string to access a specific capture in the
+  regex:
 
       iex> String.replace("a,b,c", ~r/,(.)/, ",\\1\\1")
       "a,bb,cc"
 
-  Notice we had to escape the escape character `\`. By giving `&`,
+  Notice we had to escape the escape character `\`. By giving `\0`,
   one can inject the whole matched pattern in the replacement string.
 
   When strings are used as a pattern, a developer can also use the

lib/elixir/test/elixir/regex_test.exs

@@ -189,6 +189,10 @@ defmodule RegexTest do
     assert Regex.replace(~r(b), "abc", "d") == "adc"
     assert Regex.replace(~r(b), "abc", "[\\0]") == "a[b]c"
     assert Regex.replace(~r[(b)], "abc", "[\\1]") == "a[b]c"
+    assert Regex.replace(~r[(b)], "abc", "[\\2]") == "a[]c"
+    assert Regex.replace(~r[(b)], "abc", "[\\3]") == "a[]c"
+    assert Regex.replace(~r(b), "abc", "[\\g{0}]") == "a[b]c"
+    assert Regex.replace(~r[(b)], "abc", "[\\g{1}]") == "a[b]c"
 
     assert Regex.replace(~r(b), "abcbe", "d") == "adcde"
     assert Regex.replace(~r(b), "abcbe", "d", global: false) == "adcbe"