generate version string during build (#34)

* generate version string during build

* format

* extract base version number from build.zig.zon

* code cleanup

.gitignore

@@ -22,3 +22,4 @@ zig-out/
 /evmone/
 /lib/evmone/
 .vscode
+src/version.zig

build.zig

@@ -1,10 +1,59 @@
 const std = @import("std");
 const LazyPath = std.Build.LazyPath;
 
+// extract version string from build.zig.zon. The zon parser hasn't been merged
+// into the std yet as of zig 0.13.0.
+fn extractVersionFromZon(allocator: std.mem.Allocator) ![]const u8 {
+    const version_field_decl = ".version = \"";
+    var build_zon_file = try std.fs.cwd().openFile("build.zig.zon", .{});
+    const build_zon_stat = try build_zon_file.stat();
+    const build_zon = try build_zon_file.readToEndAlloc(allocator, build_zon_stat.size);
+    const version_start = std.mem.indexOf(u8, build_zon, version_field_decl);
+    if (version_start == null) {
+        return error.CantFindVersionFieldStart;
+    }
+    const version_offset = version_start.? + version_field_decl.len;
+    const version_end = std.mem.indexOf(u8, build_zon[version_offset..], "\"");
+    if (version_end == null) {
+        return error.CantFindVersionFieldEnd;
+    }
+    return build_zon[version_offset .. version_offset + version_end.?];
+}
+
+fn gitRevision(b: *std.Build) []const u8 {
+    var returncode: u8 = undefined;
+    const git_run = b.runAllowFail(&[_][]const u8{
+        "git",
+        "rev-parse",
+        "--short",
+        "HEAD",
+    }, &returncode, .Ignore) catch v: {
+        break :v "unstable";
+    };
+    return std.mem.trim(u8, git_run, " \t\n\r");
+}
+
 // Although this function looks imperative, note that its job is to
 // declaratively construct a build graph that will be executed by an external
 // runner.
-pub fn build(b: *std.Build) void {
+pub fn build(b: *std.Build) !void {
+    const version_file_path = "src/version.zig";
+
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    const version = try extractVersionFromZon(allocator);
+
+    var version_file = try std.fs.cwd().createFile(version_file_path, .{});
+    defer version_file.close();
+
+    const git_rev = gitRevision(b);
+
+    try version_file.writeAll(b.fmt(
+        \\pub const version = "{s}+{s}";
+    , .{ version, git_rev }));
+
     // Standard target options allows the person running `zig build` to choose
     // what target to build for. Here we do not override the defaults, which
     // means any target is allowed, and the default is native. Other options

src/main.zig

@@ -15,6 +15,7 @@ const httpz = @import("httpz");
 const engine_api = @import("engine_api/engine_api.zig");
 const json = std.json;
 const simargs = @import("simargs");
+const version = @import("version.zig").version;
 
 fn engineAPIHandler(req: *httpz.Request, res: *httpz.Response) !void {
     if (try req.json(engine_api.EngineAPIRequest)) |payload| {
@@ -53,7 +54,7 @@ pub fn main() !void {
 
     // TODO print usage upon failure (requires upstream changes)
     // TODO generate version from build and add it here
-    const opts = try simargs.parse(gpa.allocator(), PhantArgs, "", null);
+    const opts = try simargs.parse(gpa.allocator(), PhantArgs, "", version);
     defer opts.deinit();
 
     const port: u16 = if (opts.args.engine_api_port == null) 8551 else opts.args.engine_api_port.?;
@@ -70,6 +71,7 @@ pub fn main() !void {
     }
 
     std.log.info("Welcome to phant! 🐘", .{});
+    std.log.info("version: {s}", .{version});
     try config.dump(allocator);
 
     var engine_api_server = try httpz.Server().init(allocator, .{