build: api-tape-replay-test

scripts/fixtures/build-api/plugin/plugin.zig

@@ -4,6 +4,9 @@ const std = @import("std");
 const builtin = @import("builtin");
 const sdk = @import("fizzy_sdk");
 const dvui = @import("dvui");
+const core = @import("core");
+const tape = @import("tape");
+const replay = @import("replay");
 const fixture_lib = @import("fixture_lib");
 
 pub const plugin_options = @import("fizzy_plugin_options");
@@ -19,6 +22,12 @@ comptime {
     }
 }
 
+// `tape` and `replay` are `core`'s own instances (design/build-api.md): the anchors a plugin
+// publishes through `core` are the very ones `replay` reads, so one file type serves both.
+comptime {
+    if (core.anchor != replay.anchor) @compileError("replay is not core's instance");
+}
+
 // The host writes plugin lifecycle state on the main UI thread.
 var plugin: sdk.Plugin = .{
     .state = undefined,
@@ -32,6 +41,7 @@ const vtable: sdk.Plugin.VTable = .{};
 pub fn register(host: *sdk.Host) !void {
     // Calls into the C source of the package's own dependency: it must have reached the link.
     if (fixture_lib.fixture_answer() != 42) return error.FixtureDependency;
+    try writeAndLoadTape(host.allocator);
     try host.registerPlugin(&plugin);
     try host.registerSurface(.{
         .id = plugin_id ++ ".surface",
@@ -47,3 +57,20 @@ fn draw(_: ?*anyopaque) !dvui.App.Result {
     dvui.label(@src(), "{s}", .{plugin_id}, .{});
     return .ok;
 }
+
+/// A plugin writes a demo with `tape.Script`, ships it as bytes and loads it back: the tape
+/// library a plugin imports is the one the host plays with.
+fn writeAndLoadTape(gpa: std.mem.Allocator) !void {
+    var owned = owned: {
+        var script: tape.Script = .init(gpa, plugin_id, plugin_options.name);
+        errdefer script.deinit();
+        try script.command(plugin_id ++ ".hello");
+        break :owned try script.finish();
+    };
+    defer owned.deinit();
+    const bytes = try tape.binary.encode(gpa, owned.tape, .{});
+    defer gpa.free(bytes);
+    var loaded = try tape.Tape.load(gpa, bytes, .{});
+    defer loaded.deinit();
+    if (!@hasDecl(replay.Player, "play")) return error.FixtureReplay;
+}