feat: add layerinfo CLI command

- Add `layerinfo` command to show detailed layer information
- Shows provides, requires, and suggested composition order
- Add tip about using Layer.mergeAll to both overview and layerinfo
- Update README with layerinfo documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mattiamanzati

.changeset/add-layerinfo-command.md

@@ -0,0 +1,17 @@
+---
+"@effect/language-service": minor
+---
+
+Added `layerinfo` CLI command that provides detailed information about a specific exported layer.
+
+Features:
+- Shows layer type, location, and description
+- Lists services the layer provides and requires
+- Suggests optimal layer composition order using `Layer.provide`, `Layer.provideMerge`, and `Layer.merge`
+
+Example usage:
+```bash
+effect-language-service layerinfo --file ./src/layers/app.ts --name AppLive
+```
+
+Also added a tip to both `overview` and `layerinfo` commands about using `Layer.mergeAll(...)` to get suggested composition order.

README.md

@@ -255,6 +255,30 @@ Layers (2)
     Complete application layer
 ```
 
+### `effect-language-service layerinfo`
+This command provides detailed information about a specific exported layer, including what services it provides, what it requires, and a suggested composition order. Use `--file` to specify the file and `--name` to specify the layer name.
+
+Example output:
+```
+AppLive
+  ./src/layers/app.ts:39:14
+  Layer<Cache | UserRepository, never, never>
+
+Provides (2):
+  - Cache
+  - UserRepository
+
+Suggested Composition:
+  UserRepository.Default.pipe(
+    Layer.provide(DbConnection.Default),
+    Layer.provideMerge(Cache.Default),
+    Layer.provide(FileSystem.Default)
+  )
+
+Tip: Not sure you got your composition right? Just write all layers inside a Layer.mergeAll(...)
+command, and then run the layerinfo command to get the suggested composition order to use.
+```
+
 ## Configuring diagnostics
 
 You can either disable or change the severity of specific diagnostics by using comments in your code.

src/cli.ts

@@ -6,9 +6,11 @@ import * as NodeRuntime from "@effect/platform-node/NodeRuntime"
 import * as Console from "effect/Console"
 import * as Effect from "effect/Effect"
 import * as Layer from "effect/Layer"
+import packageJson from "../package.json"
 import { check } from "./cli/check"
 import { codegen } from "./cli/codegen"
 import { diagnostics } from "./cli/diagnostics"
+import { layerInfo } from "./cli/layerinfo"
 import { overview } from "./cli/overview"
 import { patch } from "./cli/patch"
 import { setup } from "./cli/setup"
@@ -19,11 +21,11 @@ const cliCommand = Command.make(
   "effect-language-service",
   {},
   () => Console.log("Please select a command or run --help.")
-).pipe(Command.withSubcommands([setup, patch, unpatch, check, diagnostics, codegen, overview]))
+).pipe(Command.withSubcommands([setup, patch, unpatch, check, diagnostics, codegen, overview, layerInfo]))
 
 const main = Command.run(cliCommand, {
   name: "effect-language-service",
-  version: "0.0.2"
+  version: packageJson.version
 })
 
 const cliLayers = Layer.merge(NodeContext.layer, TypeScriptContext.live(process.cwd()))