repl: Patch editline to recognize Meta-Left & Meta-Right

This applies https://github.com/troglobit/editline/pull/70 to our build
of editline, which translates `meta-left` and `meta-right` into
`fd_word` and `bk_word`. This makes `nix repl` soooo much nicer to use!

Note: My terminal renders `meta-left` as `\e\e[C` and `meta-right` as
`\e\e[D`.

Closes #501

Change-Id: I048b10cf17231bbf4e6bf38e1d1d8572cedaa194

doc/manual/rl-next/alt-left-and-alt-right-in-repl.md

@@ -0,0 +1,10 @@
+---
+synopsis: "`Alt+Left` and `Alt+Right` go back/forwards by words in `nix repl`"
+issues: [fj#501]
+cls: [1883]
+category: Fixes
+credits: 9999years
+---
+
+`nix repl` now recognizes `Alt+Left` and `Alt+Right` for navigating by words
+when entering input in `nix repl` on more terminals/platforms.

package.nix

@@ -22,6 +22,7 @@
   doxygen,
   editline-lix ? __forDefaults.editline-lix,
   editline,
+  fetchpatch,
   git,
   gtest,
   jq,
@@ -38,6 +39,7 @@
   mercurial,
   meson,
   ninja,
+  ncurses,
   openssl,
   pegtl,
   pkg-config,
@@ -81,7 +83,32 @@
     boehmgc-nix = boehmgc.override { enableLargeConfig = true; };
 
     editline-lix = editline.overrideAttrs (prev: {
-      configureFlags = prev.configureFlags or [ ] ++ [ (lib.enableFeature true "sigstop") ];
+      patches = (prev.patches or [ ]) ++ [
+        # Recognize `Alt-Left` and `Alt-Right` for navigating by words in more
+        # terminals/shells/platforms.
+        #
+        # See: https://github.com/troglobit/editline/pull/70/commits
+        (fetchpatch {
+          url = "https://github.com/troglobit/editline/pull/70/commits/d0f2a5bc2300b96b2434c7838184c1dfd6a639f5.diff";
+          hash = "sha256-0bbtYDUlk1wA0kpTtlaNI6KaCjLmAesZjcWBJZ+DpyQ=";
+        })
+
+        (fetchpatch {
+          url = "https://github.com/troglobit/editline/pull/70/commits/4c4455353a0a88bee09d5f27c28f81f747682fed.diff";
+          hash = "sha256-nVezspwVzeB/8zENeKgwPVum0W1MLv4dOW0967WbX5w=";
+        })
+      ];
+
+      configureFlags = (prev.configureFlags or [ ]) ++ [
+        # Enable SIGSTOP (Ctrl-Z) behavior.
+        (lib.enableFeature true "sigstop")
+        # Enable ANSI arrow keys.
+        (lib.enableFeature true "arrow-keys")
+        # Use termcap library to query terminal size.
+        (lib.enableFeature (ncurses != null) "termcap")
+      ];
+
+      nativeBuildInputs = (prev.nativeBuildInputs or [ ]) ++ [ ncurses ];
     });
 
     build-release-notes = callPackage ./maintainers/build-release-notes.nix { };