From 18c9e30b192f69d8e9cb711c911eaa1d3baa8e09 Mon Sep 17 00:00:00 2001
From: Pooya Parsa <pooya@pi0.io>
Date: Tue, 11 Jun 2024 21:28:52 +0200
Subject: [PATCH] feat: custom merger to replace built-in defu (#160)

---
 README.md     | 64 +++++++++++++++++++++++++++++++++++----------------
 src/loader.ts | 20 ++++++++++------
 src/types.ts  |  2 ++
 3 files changed, 59 insertions(+), 27 deletions(-)

diff --git a/README.md b/README.md
index 140b134..3fc294b 100644
--- a/README.md
+++ b/README.md
@@ -163,6 +163,12 @@ Custom [unjs/jiti](https://github.com/unjs/jiti) options to import configuration
 
 Options passed to [unjs/giget](https://github.com/unjs/giget) when extending layer from git source.
 
+### `merger`
+
+Custom options merger function. Default is [defu](https://github.com/unjs/defu).
+
+**Note:** Custom merge function should deeply merge options with arguments high -> low priority.
+
 ### `envName`
 
 Environment name used for [environment specific configuration](#environment-specific-configuration).
@@ -216,10 +222,10 @@ export default {
 // base/config.ts
 export default {
   colors: {
-    primary: 'base_primary',
-    text: 'base_text'
-  }
-}
+    primary: "base_primary",
+    text: "base_text",
+  },
+};
 ```
 
 The loaded configuration would look like this:
@@ -228,21 +234,39 @@ The loaded configuration would look like this:
 const config = {
   dev: true,
   colors: {
-    primary: 'user_primary',
-    secondary: 'theme_secondary',
-    text: 'base_text'
-  }
-}
+    primary: "user_primary",
+    secondary: "theme_secondary",
+    text: "base_text",
+  },
+};
 ```
 
 Layers:
 
 ```js
 [
- { config: { /* theme config */ }, configFile:  "/path/to/theme/config.ts", cwd: "/path/to/theme " },
- { config: { /* base  config */ }, configFile: "/path/to/base/config.ts",   cwd: "/path/to/base" },
- { config: { /* dev   config */ }, configFile: "/path/to/config.dev.ts",    cwd: "/path/" },
-]
+  {
+    config: {
+      /* theme config */
+    },
+    configFile: "/path/to/theme/config.ts",
+    cwd: "/path/to/theme ",
+  },
+  {
+    config: {
+      /* base  config */
+    },
+    configFile: "/path/to/base/config.ts",
+    cwd: "/path/to/base",
+  },
+  {
+    config: {
+      /* dev   config */
+    },
+    configFile: "/path/to/config.dev.ts",
+    cwd: "/path/",
+  },
+];
 ```
 
 ## Extending config layer from remote sources
@@ -300,16 +324,16 @@ c12 tries to match [`envName`](#envname) and override environment config if spec
 ```js
 export default {
   // Default configuration
-  logLevel: 'info',
+  logLevel: "info",
 
   // Environment overrides
-  $test: { logLevel: 'silent' },
-  $development: { logLevel: 'warning' },
-  $production: { logLevel: 'error' },
+  $test: { logLevel: "silent" },
+  $development: { logLevel: "warning" },
+  $production: { logLevel: "error" },
   $env: {
-    staging: { logLevel: 'debug' }
-  }
-}
+    staging: { logLevel: "debug" },
+  },
+};
 ```
 
 ## Watching configuration
diff --git a/src/loader.ts b/src/loader.ts
index 5b33381..1e172a9 100644
--- a/src/loader.ts
+++ b/src/loader.ts
@@ -67,6 +67,9 @@ export async function loadConfig<
     };
   }
 
+  // Custom merger
+  const _merger = options.merger || defu;
+
   // Create jiti instance
   options.jiti =
     options.jiti ||
@@ -126,7 +129,7 @@ export async function loadConfig<
       // 3. user home
       rcSources.push(rc9.readUser({ name: options.rcFile, dir: options.cwd }));
     }
-    _configs.rc = defu({} as T, ...rcSources);
+    _configs.rc = _merger({} as T, ...rcSources);
   }
 
   // Load config from package.json
@@ -142,7 +145,7 @@ export async function loadConfig<
     ).filter((t) => t && typeof t === "string");
     const pkgJsonFile = await readPackageJSON(options.cwd).catch(() => {});
     const values = keys.map((key) => pkgJsonFile?.[key]);
-    _configs.packageJson = defu({} as T, ...values);
+    _configs.packageJson = _merger({} as T, ...values);
   }
 
   // Resolve config sources
@@ -155,7 +158,7 @@ export async function loadConfig<
   }
 
   // Combine sources
-  r.config = defu(
+  r.config = _merger(
     configs.overrides,
     configs.main,
     configs.rc,
@@ -168,7 +171,7 @@ export async function loadConfig<
     await extendConfig(r.config, options);
     r.layers = r.config._layers;
     delete r.config._layers;
-    r.config = defu(r.config, ...r.layers!.map((e) => e.config)) as T;
+    r.config = _merger(r.config, ...r.layers!.map((e) => e.config)) as T;
   }
 
   // Preserve unmerged sources as layers
@@ -190,7 +193,7 @@ export async function loadConfig<
 
   // Apply defaults
   if (options.defaults) {
-    r.config = defu(r.config, options.defaults) as T;
+    r.config = _merger(r.config, options.defaults) as T;
   }
 
   // Remove environment-specific and built-in keys start with $
@@ -296,6 +299,9 @@ async function resolveConfig<
     }
   }
 
+  // Custom merger
+  const _merger = options.merger || defu;
+
   // Download giget URIs and resolve to local path
   if (GIGET_PREFIXES.some((prefix) => source.startsWith(prefix))) {
     const { downloadTemplate } = await import("giget");
@@ -393,7 +399,7 @@ async function resolveConfig<
       ...res.config!.$env?.[options.envName],
     };
     if (Object.keys(envConfig).length > 0) {
-      res.config = defu(envConfig, res.config);
+      res.config = _merger(envConfig, res.config);
     }
   }
 
@@ -403,7 +409,7 @@ async function resolveConfig<
 
   // Overrides
   if (res.sourceOptions!.overrides) {
-    res.config = defu(res.sourceOptions!.overrides, res.config) as T;
+    res.config = _merger(res.sourceOptions!.overrides, res.config) as T;
   }
 
   // Always windows paths
diff --git a/src/types.ts b/src/types.ts
index 574a638..59444bf 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -133,6 +133,8 @@ export interface LoadConfigOptions<
 
   giget?: DownloadTemplateOptions;
 
+  merger?: (...sources: Array<T | null | undefined>) => T;
+
   extend?:
     | false
     | {