Experiment 1

ts/project.ts

@@ -5,7 +5,7 @@ import { Environment } from "./environment.ts";
 import { Executable, mkShellExecutable } from "./executable.ts";
 import { hasTag } from "./internal/utils.ts";
 import { NixStrLitInterpolatable } from "./nix.ts";
-import { Package, mkShellPackage } from "./package.ts";
+import { mkShellPackage, Package } from "./package.ts";
 import { markAsMayNotExport } from "./internal/may_not_export.ts";
 
 /**
@@ -15,16 +15,16 @@ import { markAsMayNotExport } from "./internal/may_not_export.ts";
  */
 export type Project = ProjectHelpers & ProjectData;
 
-type ProjectData = {
+export type ProjectData = {
   tag: "project";
   description: string;
   defaultEnvironment?: Environment;
   defaultExecutable?: Executable;
 };
 
-export type Plugin<Dependencies, Additions> = <T extends ProjectData>(
-  project: T & Dependencies,
-) => Omit<T, keyof Additions> & Additions;
+export type Plugin<Additions> = (
+  project: Project
+) => Additions;
 
 type ProjectHelpers = {
   /**
@@ -82,10 +82,10 @@ type ProjectHelpers = {
    *   .add(self => self.addExecutable("codegen")`${self.mainPackage}/bin/codegen`)
    * ```
    */
-  add<T extends ProjectData, U extends ProjectData>(
+  add<T extends Project, Additions>(
     this: T,
-    fn: (p: T) => U,
-  ): U;
+    fn: Plugin<Additions>,
+  ): Omit<T, keyof Additions> & Additions;
 
   /**
    * Adds an `Executable` with the given name to the Project
@@ -219,11 +219,14 @@ const proxyEnvironmentHelpers = (): ProjectHelpers => ({
     return mkShellPackage(defaultEnvironment, s, ...args);
   },
 
-  add<T extends ProjectData, U extends ProjectData>(
+  add<T extends Project, Additions>(
     this: T,
-    fn: (p: T) => U,
-  ): U {
-    return fn(this);
+    fn: Plugin<Additions>
+  ): Omit<T, keyof Additions> & Additions {
+    return {
+      ...this,
+      ...fn(this),
+    };
   },
 
   addExecutable<T extends ProjectData, Name extends string>(
@@ -256,8 +259,7 @@ const proxyEnvironmentHelpers = (): ProjectHelpers => ({
       [
         `${exportName} exports the return type of "addExecutable", but this is not the proper usage of addExecutable.`,
         'Did you forget the template literal? Example usage: project.addExecutable("executable-name")`shell script to run`',
-      ].join(" "),
-    );
+      ].join(" "));
     return templateLiteralFn;
   },
 
@@ -291,8 +293,7 @@ const proxyEnvironmentHelpers = (): ProjectHelpers => ({
       [
         `${exportName} exports the return type of "addCheck", but this is not the proper usage of addCheck.`,
         'Did you forget the template literal? Example usage: project.addCheck("check-name")`shell script to run`',
-      ].join(" "),
-    );
+      ].join(" "));
     return templateLiteralFn;
   },