add help

build.zig

@@ -150,7 +150,12 @@ pub fn build(b: *std.Build) !void {
     });
     const options = b.addOptions();
     options.addOption(bool, "long_tests", long_tests);
-    mod.addImport("build_options", options.createModule());
+
+    const git_describe = b.run(&.{ "git", "describe", "--always", "--dirty" });
+    options.addOption([]const u8, "version", git_describe);
+
+    const options_module = options.createModule();
+    mod.addImport("build_options", options_module);
     mod.linkLibrary(lib);
     mod.addIncludePath(upstream.path("include"));
 
@@ -192,6 +197,7 @@ pub fn build(b: *std.Build) !void {
                 // can be extremely useful in case of collisions (which can happen
                 // importing modules from different packages).
                 .{ .name = "pos", .module = mod },
+                .{ .name = "build_options", .module = options_module },
             },
         }),
     });

src/main.zig

@@ -1,6 +1,7 @@
 const builtin = @import("builtin");
 const std = @import("std");
 const pos = @import("pos");
+const build_options = @import("build_options");
 
 fn loadReplacements(allocator: std.mem.Allocator) !std.StringHashMap([]const u8) {
     var replacements = std.StringHashMap([]const u8).init(allocator);
@@ -305,7 +306,27 @@ pub fn main() !u8 {
             sentence_parse_only = .sentence
         else if (std.mem.eql(u8, arg, "--command-parse-only"))
             sentence_parse_only = .command
-        else if (sentence_arg == null)
+        else if (std.mem.eql(u8, arg, "--help") or std.mem.eql(u8, arg, "-h")) {
+            var stdout_writer = std.fs.File.stdout().writer(&.{});
+            const stdout = &stdout_writer.interface;
+            try stdout.print(
+                \\pos version {s}
+                \\
+                \\Usage: {s} [OPTIONS] <sentence>
+                \\
+                \\Options:
+                \\  --sentence-parse-only    Parse sentence and show parse tree
+                \\  --command-parse-only     Parse as command with replacements
+                \\  --help, -h               Show this help message
+                \\
+                \\Configuration:
+                \\  Replacements are loaded from:
+                \\    1. ./replacements.json (current directory)
+                \\    2. XDG_CONFIG_HOME/pos/replacements.json
+                \\
+            , .{ build_options.version, args[0] });
+            return 0;
+        } else if (sentence_arg == null)
             sentence_arg = arg;
     }