feat(dart): let a project choose its vodozemac release

nix/dart/vodozemac/default.nix

@@ -1,22 +1,73 @@
 { lib, flake-parts-lib, ... }:
 importingFlake: {
   options.perSystem = flake-parts-lib.mkPerSystemOption (
-    { pkgs, ... }:
+    { config, pkgs, ... }:
     let
       # The very package `packages.famedly-vodozemac` is built from, called
       # again rather than read off `self'`: reaching into the flake's own
       # packages from inside an option declaration would make the projects
       # depend on config that is derived from the projects.
-      vodozemac = pkgs.callPackage ./native.nix { };
+      vodozemac = pkgs.callPackage ./native.nix {
+        source = pkgs.callPackage ./source.nix {
+          inherit (config.famedly.standards.dart.vodozemac) version hash cargoHash;
+        };
+      };
     in
     {
+      options.famedly.standards.dart.vodozemac = {
+        version = lib.mkOption {
+          description = ''
+            Which dart-vodozemac release to build the bindings from.
+
+            Keep it equal to the `vodozemac` — or `flutter_vodozemac` —
+            constraint in the project's `pubspec.yaml`. The Dart package that
+            calls these bindings is generated from this very release, and a
+            project talking to bindings it was not generated against fails when
+            a call is made rather than when it is built, so a pre-commit hook
+            compares the two.
+
+            The default is the release we would like everyone on. A project that
+            cannot follow yet sets its own, together with both hashes below,
+            which is why they are options at all: nothing forces two projects
+            onto one version of a dependency.
+          '';
+
+          type = lib.types.str;
+          default = "0.5.0";
+        };
+
+        hash = lib.mkOption {
+          description = ''
+            Hash of the release's source tree, which changes with `version`.
+            Nix names the value it expected when this one disagrees.
+          '';
+
+          type = lib.types.str;
+          default = "sha256-H3g0is/+Cf3xBqqxw6qCjZSv5ZjftNSQP4hdwwEsOrs=";
+        };
+
+        cargoHash = lib.mkOption {
+          description = ''
+            Hash of the crate's vendored dependencies, which changes with the
+            release's `Cargo.lock`. One lockfile, so one vendor: which
+            dependencies a target links is decided when it is built, not when
+            they are resolved, and both targets share this.
+          '';
+
+          type = lib.types.str;
+          default = "sha256-eKKrcroV2yl/FV2WmgZWFPO5MPAGz0xCvpr0fgIuGZ4=";
+        };
+      };
+
       options.famedly.standards.dart.projects = lib.mkOption {
         type = lib.types.attrsOf (
           lib.types.submodule (
             { config, ... }:
             {
               options.vodozemac.enable = lib.mkEnableOption ''
-                the vodozemac bindings for this project.
+                the vodozemac bindings for this project. Which release they are
+                built from is `famedly.standards.dart.vodozemac.version`, since
+                the bindings are built once for the repository.
 
                 Points `flutter_rust_bridge`'s library lookup at the nix-built
                 library, so `vod.init` finds it without the project having to
@@ -54,11 +105,15 @@ importingFlake: {
       needed = lib.any (project: project.vodozemac.enable) (
         lib.attrValues config.famedly.standards.dart.projects
       );
+
+      source = pkgs.callPackage ./source.nix {
+        inherit (config.famedly.standards.dart.vodozemac) version hash cargoHash;
+      };
     in
     lib.mkMerge [
       (lib.mkIf (config.famedly.standards.dart.projects != { }) {
-        packages.famedly-vodozemac = pkgs.callPackage ./native.nix { };
-        packages.famedly-vodozemac-web = pkgs.callPackage ./web.nix { };
+        packages.famedly-vodozemac = pkgs.callPackage ./native.nix { inherit source; };
+        packages.famedly-vodozemac-web = pkgs.callPackage ./web.nix { inherit source; };
       })
 
       # The lookup itself goes through `runtime.env`; this only makes entering

nix/dart/vodozemac/native.nix

@@ -1,14 +1,11 @@
 {
-  callPackage,
   fixDarwinDylibNames,
   lib,
   rustPlatform,
+  source,
   stdenv,
 }:
 
-let
-  source = callPackage ./source.nix { };
-in
 rustPlatform.buildRustPackage {
   pname = "famedly-vodozemac";
 

nix/dart/vodozemac/source.nix

@@ -2,29 +2,31 @@
 # native library and the WebAssembly module are the same crate compiled twice,
 # and a version that drifted between them fails at the first call and not
 # before.
-{ fetchFromGitHub }:
+{
+  fetchFromGitHub,
+  version,
+  hash,
+  cargoHash,
+}:
 
 let
-  # Keep in sync with the `vodozemac` constraint in consumers' `pubspec.yaml`,
-  # which a pre-commit hook checks. The tags follow the Flutter plugin.
-  version = "0.5.0";
-
   src = fetchFromGitHub {
     owner = "famedly";
     repo = "dart-vodozemac";
+
+    # The repository is a Flutter plugin; its tags follow that plugin's version,
+    # which for the releases we build is the Dart package's as well.
     tag = version;
-    hash = "sha256-H3g0is/+Cf3xBqqxw6qCjZSv5ZjftNSQP4hdwwEsOrs=";
+
+    inherit hash;
   };
 in
 {
-  inherit version src;
+  inherit version src cargoHash;
 
   # The repository is a Flutter plugin; only the crate is interesting to us.
   sourceRoot = "${src.name}/rust";
 
-  # One lockfile, so one vendor for both targets.
-  cargoHash = "sha256-eKKrcroV2yl/FV2WmgZWFPO5MPAGz0xCvpr0fgIuGZ4=";
-
   meta = {
     description = "Dart bindings for the vodozemac Matrix cryptography library";
     homepage = "https://github.com/famedly/dart-vodozemac";

nix/dart/vodozemac/web.nix

@@ -7,12 +7,12 @@
 {
   binaryen,
   buildPackages,
-  callPackage,
   cargo,
   lib,
   removeReferencesTo,
   rustPlatform,
   rustc,
+  source,
   stdenv,
   symlinkJoin,
   wasm-bindgen-cli_0_2_100,
@@ -21,8 +21,6 @@
 }:
 
 let
-  source = callPackage ./source.nix { };
-
   # The stem `wasm-bindgen` writes, and the name the Dart package looks up.
   crate = "vodozemac_bindings_dart";