feat(libcmd): add zig based readline

src/libcmd/libcmd.zig

@@ -0,0 +1,5 @@
+pub const repl = @import("repl.zig");
+
+comptime {
+    _ = repl;
+}

src/libcmd/meson.build

@@ -1,4 +1,4 @@
-project('nix-cmd', 'cpp',
+project('nix-cmd', 'cpp', 'c',
   version : files('.zix-version'),
   default_options : [
     'cpp_std=c++2a',
@@ -10,6 +10,8 @@ project('nix-cmd', 'cpp',
   license : 'LGPL-2.1-or-later',
 )
 
+fs = import('fs')
+
 cxx = meson.get_compiler('cpp')
 
 subdir('nix-meson-build-support/deps-lists')
@@ -49,6 +51,12 @@ elif readline_flavor == 'readline'
     1,
     description: 'Use readline instead of editline',
   )
+elif readline_flavor == 'zig'
+  configdata.set(
+    'USE_ZIG_REPL',
+    1,
+    description: 'Use zig implementation for repl',
+  )
 else
   error('illegal editline flavor', readline_flavor)
 endif
@@ -113,10 +121,25 @@ headers = [config_h] + files(
   'repl.hh',
 )
 
+subdir('nix-meson-build-support/zig')
+
+sources += custom_target(
+  'zig build-obj',
+  command: [zig, 'build-lib', '-femit-h=@OUTDIR@/libcmd-zig.h', '-femit-bin=@OUTPUT@', '-ofmt=c', '-lc', zig_args, '@INPUT@'],
+  output: 'libcmd-zig.c',
+  input: 'libcmd.zig',
+  depend_files: [
+    'repl.zig',
+  ],
+)
+
+include_dirs += fs.parent(fs.parent(zig.full_path())) / 'lib' / 'zig'
+
 this_library = library(
   'nixcmd',
   sources,
   dependencies : deps_public + deps_private + deps_other,
+  include_directories : include_dirs,
   prelink : true, # For C++ static initializers
   install : true,
 )

src/libcmd/meson.options

@@ -9,7 +9,7 @@ option(
 option(
   'readline-flavor',
   type : 'combo',
-  choices : ['editline', 'readline'],
+  choices : ['editline', 'readline', 'zig'],
   value : 'editline',
   description : 'Which library to use for nice line editing with the Nix language REPL',
 )

src/libcmd/package.nix

@@ -28,7 +28,13 @@
   #
   # - editline (default)
   # - readline
-  readlineFlavor ? if stdenv.hostPlatform.isWindows then "readline" else "editline",
+  readlineFlavor ?
+    if stdenv.hostPlatform.isWindows then
+      "readline"
+    else if stdenv.hostPlatform.isLinux then
+      "zig"
+    else
+      "editline",
 }:
 
 let
@@ -51,10 +57,17 @@ mkMesonLibrary (finalAttrs: {
     ./meson.options
     (fileset.fileFilter (file: file.hasExt "cc") ./.)
     (fileset.fileFilter (file: file.hasExt "hh") ./.)
+    (fileset.fileFilter (file: file.hasExt "zig") ./.)
   ];
 
   buildInputs = [
-    ({ inherit editline readline; }.${readlineFlavor})
+    (
+      {
+        inherit editline readline;
+        zig = null;
+      }
+      .${readlineFlavor}
+    )
   ] ++ lib.optional enableMarkdown lowdown;
 
   propagatedBuildInputs = [

src/libcmd/repl-interacter.cc

@@ -4,6 +4,9 @@
 #include <readline/history.h>
 #include <readline/readline.h>
 #else
+#ifdef USE_ZIG_REPL
+extern "C" char* readline(const char* prompt);
+#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.
@@ -13,6 +16,7 @@ extern "C" {
 #include <editline.h>
 }
 #endif
+#endif
 
 #include "signals.hh"
 #include "finally.hh"
@@ -107,20 +111,24 @@ static int listPossibleCallback(char * s, char *** avp)
 ReadlineLikeInteracter::Guard ReadlineLikeInteracter::init(detail::ReplCompleterMixin * repl)
 {
     // Allow nix-repl specific settings in .inputrc
+#ifndef USE_ZIG_REPL
     rl_readline_name = "nix-repl";
+#endif
     try {
         createDirs(dirOf(historyFile));
     } catch (SystemError & e) {
         logWarning(e.info());
     }
-#ifndef USE_READLINE
+#if !defined(USE_READLINE) && !defined(USE_ZIG_REPL)
     el_hist_size = 1000;
 #endif
+#ifndef USE_ZIG_REPL
     read_history(historyFile.c_str());
+#endif
     auto oldRepl = curRepl;
     curRepl = repl;
     Guard restoreRepl([oldRepl] { curRepl = oldRepl; });
-#ifndef USE_READLINE
+#if !defined(USE_READLINE) && !defined(USE_ZIG_REPL)
     rl_set_complete_func(completionCallback);
     rl_set_list_possib_func(listPossibleCallback);
 #endif
@@ -200,7 +208,9 @@ bool ReadlineLikeInteracter::getLine(std::string & input, ReplPromptType promptT
 
 ReadlineLikeInteracter::~ReadlineLikeInteracter()
 {
+#ifndef USE_ZIG_REPL
     write_history(historyFile.c_str());
+#endif
 }
 
 };

src/libcmd/repl.zig

@@ -0,0 +1,31 @@
+const std = @import("std");
+
+var has_prompt = true;
+
+pub fn readline(prompt: [*:0]const u8) callconv(.C) ?[*:0]const u8 {
+    const stdout = std.io.getStdOut();
+    if (!has_prompt) {
+        stdout.writeAll(prompt[0..std.mem.len(prompt)]) catch @panic("Failed to write prompt");
+        has_prompt = true;
+    }
+
+    const stdin = std.io.getStdIn();
+
+    var line = std.ArrayList(u8).init(std.heap.c_allocator);
+    defer line.deinit();
+
+    stdin.reader().readUntilDelimiterArrayList(&line, '\n', std.math.maxInt(usize)) catch |err| switch (err) {
+        error.StreamTooLong => {
+            std.log.err("readline(\"{s}\") failed {}", .{ prompt[0..std.mem.len(prompt)], err });
+            return null;
+        },
+        else => return null,
+    };
+
+    has_prompt = line.items.len > 0;
+    return line.toOwnedSliceSentinel(0) catch null;
+}
+
+comptime {
+    @export(&readline, .{ .name = "readline" });
+}