Remove readline support

Lix cannot be built with GNU readline, and we would "rather not" be GPL.

Change-Id: I0e86f0f10dab966ab1d1d467fb61fd2de50c00de

doc/manual/rl-next/readline-support-removed.md

@@ -0,0 +1,17 @@
+---
+synopsis: readline support removed
+cls: [1885]
+category: Packaging
+credits: [9999years]
+---
+
+Support for building Lix with [`readline`][readline] instead of
+[`editline`][editline] has been removed. `readline` support hasn't worked for a
+long time (attempting to use it would lead to build errors) and would make Lix
+subject to the GPL if it did work. In the future, we're hoping to replace
+`editline` with [`rustyline`][rustyline] for improved ergonomics in the `nix
+repl`.
+
+[readline]: https://en.wikipedia.org/wiki/GNU_Readline
+[editline]: https://github.com/troglobit/editline
+[rustyline]: https://github.com/kkawakam/rustyline

src/libcmd/repl-interacter.cc

@@ -8,10 +8,6 @@
 #include <string_view>
 #include <cerrno>
 
-#ifdef READLINE
-#include <readline/history.h>
-#include <readline/readline.h>
-#else
 // editline < 1.15.2 don't wrap their API for C++ usage
 // (added in https://github.com/troglobit/editline/commit/91398ceb3427b730995357e9d120539fb9bb7461).
 // This results in linker errors due to to name-mangling of editline C symbols.
@@ -20,7 +16,6 @@
 extern "C" {
 #include <editline.h>
 }
-#endif
 
 #include "finally.hh"
 #include "repl-interacter.hh"
@@ -115,17 +110,13 @@ ReadlineLikeInteracter::Guard ReadlineLikeInteracter::init(detail::ReplCompleter
     } catch (SysError & e) {
         logWarning(e.info());
     }
-#ifndef READLINE
     el_hist_size = 1000;
-#endif
     read_history(historyFile.c_str());
     auto oldRepl = curRepl;
     curRepl = repl;
     Guard restoreRepl([oldRepl] { curRepl = oldRepl; });
-#ifndef READLINE
     rl_set_complete_func(completionCallback);
     rl_set_list_possib_func(listPossibleCallback);
-#endif
     return restoreRepl;
 }
 

src/libutil/experimental-features.cc

@@ -247,7 +247,7 @@ constexpr std::array<ExperimentalFeatureDetails, numXpFeatures> xpFeatureDetails
         .tag = Xp::ReplAutomation,
         .name = "repl-automation",
         .description = R"(
-            Makes the repl not use readline/editline, print ENQ (U+0005) when ready for a command, and take commands followed by newline.
+            Makes the repl not use editline, print ENQ (U+0005) when ready for a command, and take commands followed by newline.
         )",
     },
 }};