build: generate a version number, show in log on startup

build.zig

@@ -26,6 +26,7 @@ const WasmTarget = @import("src/os/wasm/target.zig").Target;
 const LibtoolStep = @import("src/build/LibtoolStep.zig");
 const LipoStep = @import("src/build/LipoStep.zig");
 const XCFrameworkStep = @import("src/build/XCFrameworkStep.zig");
+const Version = @import("src/build/Version.zig");
 
 // Do a comptime Zig version requirement. The required Zig version is
 // somewhat arbitrary: it is meant to be a version that we feel works well,
@@ -43,7 +44,10 @@ comptime {
     }
 }
 
-// Build options, see the build options help for more info.
+/// The version of the next release.
+const app_version = std.builtin.Version{ .major = 0, .minor = 1, .patch = 0 };
+
+/// Build options, see the build options help for more info.
 var tracy: bool = false;
 var flatpak: bool = false;
 var app_runtime: apprt.Runtime = .none;
@@ -112,6 +116,28 @@ pub fn build(b: *std.build.Builder) !void {
         "Build and install the benchmark executables.",
     ) orelse false;
 
+    var version_string = b.option(
+        []const u8,
+        "version-string",
+        "A specific version string to use for the build. " ++
+            "If not specified, git will be used. This must be a semantic version.",
+    );
+
+    var version: std.SemanticVersion = if (version_string) |v|
+        try std.SemanticVersion.parse(v)
+    else version: {
+        const vsn = try Version.detect(b);
+        if (vsn.tag != null) @panic("tagged releases are not yet supported");
+
+        break :version .{
+            .major = app_version.major,
+            .minor = app_version.minor,
+            .patch = app_version.patch,
+            .pre = vsn.branch,
+            .build = vsn.short_hash,
+        };
+    };
+
     // We can use wasmtime to test wasm
     b.enable_wasmtime = true;
 
@@ -125,6 +151,8 @@ pub fn build(b: *std.build.Builder) !void {
         .optimize = optimize,
     });
     const exe_options = b.addOptions();
+    exe_options.addOption(std.SemanticVersion, "app_version", version);
+    exe_options.addOption([]const u8, "app_version_string", b.fmt("{}", .{version}));
     exe_options.addOption(bool, "tracy_enabled", tracy);
     exe_options.addOption(bool, "flatpak", flatpak);
     exe_options.addOption(apprt.Runtime, "app_runtime", app_runtime);

src/build/Version.zig

@@ -0,0 +1,53 @@
+const Version = @This();
+
+const std = @import("std");
+
+/// The short hash (7 characters) of the latest commit.
+short_hash: []const u8,
+
+/// True if there was a diff at build time.
+changes: bool,
+
+/// The tag -- if any -- that this commit is a part of.
+tag: ?[]const u8,
+
+/// The branch that was checked out at the time of the build.
+branch: []const u8,
+
+/// Initialize the version and detect it from the Git environment. This
+/// allocates using the build allocator and doesn't free.
+pub fn detect(b: *std.Build) !Version {
+    // Execute a bunch of git commands to determine the automatic version.
+    var code: u8 = 0;
+    const branch = try b.execAllowFail(&[_][]const u8{ "git", "-C", b.build_root.path orelse ".", "rev-parse", "--abbrev-ref", "HEAD" }, &code, .Ignore);
+
+    const short_hash = short_hash: {
+        const output = try b.execAllowFail(&[_][]const u8{ "git", "-C", b.build_root.path orelse ".", "log", "--pretty=format:%h", "-n", "1" }, &code, .Ignore);
+        break :short_hash std.mem.trimRight(u8, output, "\r\n ");
+    };
+
+    const tag = b.execAllowFail(&[_][]const u8{ "git", "-C", b.build_root.path orelse ".", "describe", "--exact-match", "--tags" }, &code, .Ignore) catch |err| switch (err) {
+        error.ExitCodeFailure => "", // expected
+        else => return err,
+    };
+
+    _ = b.execAllowFail(&[_][]const u8{
+        "git",
+        "-C",
+        b.build_root.path orelse ".",
+        "diff",
+        "--quiet",
+        "--exit-code",
+    }, &code, .Ignore) catch |err| switch (err) {
+        error.ExitCodeFailure => {}, // expected
+        else => return err,
+    };
+    const changes = code != 0;
+
+    return .{
+        .short_hash = short_hash,
+        .changes = changes,
+        .tag = if (tag.len > 0) std.mem.trimRight(u8, tag, "\r\n ") else null,
+        .branch = std.mem.trimRight(u8, branch, "\r\n "),
+    };
+}

src/build_config.zig

@@ -9,6 +9,10 @@ const assert = std.debug.assert;
 const apprt = @import("apprt.zig");
 const font = @import("font/main.zig");
 
+/// The semantic version of this build.
+pub const version = options.app_version;
+pub const version_string = options.app_version_string;
+
 /// The artifact we're producing. This can be used to determine if we're
 /// building a standalone exe, an embedded lib, etc.
 pub const artifact = Artifact.detect();

src/main.zig

@@ -128,6 +128,7 @@ pub const GlobalState = struct {
 
     pub fn init(self: *GlobalState) void {
         // Output some debug information right away
+        std.log.info("ghostty version={s}", .{build_config.version_string});
         std.log.info("runtime={}", .{build_config.app_runtime});
         std.log.info("font_backend={}", .{build_config.font_backend});
         std.log.info("dependency harfbuzz={s}", .{harfbuzz.versionString()});