Update: add import as const feature

Author: sapphi-red

README.md

@@ -20,3 +20,23 @@ And then add this to `tsconfig.json`.
 ```
 
 If you're using VSCode, [switch to workspace version](https://code.visualstudio.com/docs/typescript/typescript-compiling#_using-the-workspace-version-of-typescript).
+
+## `.const.toml`
+
+If the file name ends with `.const.toml`, the typings will become as if you are using `as const`.
+
+For example it will be like below.
+
+`test.toml` and `test.const.toml`
+```toml
+key = 'val'
+```
+
+`index.ts`
+```ts
+import test from './test.toml'
+import testConst from './test.const.toml'
+
+type Test = typeof test // { key: string }
+type TestConst = typeof testConst // { readonly key: 'val' }
+```

src/createDts.ts

@@ -5,7 +5,8 @@ import { Logger } from './logger'
 export const createDtsSnapshot = (
   tsModule: typeof ts,
   scriptSnapshot: ts.IScriptSnapshot,
-  logger: Logger
+  logger: Logger,
+  useAsConst: boolean
 ): ts.IScriptSnapshot => {
   const text = scriptSnapshot.getText(0, scriptSnapshot.getLength())
 
@@ -20,7 +21,7 @@ export const createDtsSnapshot = (
     const data = toml.parse(text)
 
     dts = `
-declare const data = ${JSON.stringify(data)}
+declare const data = ${JSON.stringify(data)}${useAsConst ? ' as const' : ''}
 export default data
 `
   } catch (e) {

src/index.ts

@@ -1,7 +1,7 @@
 import type * as ts from 'typescript/lib/tsserverlibrary'
 import path from 'path'
 import { createDtsSnapshot } from './createDts'
-import { isToml } from './util'
+import { isToml, isConstToml } from './util'
 import { createLogger } from './logger'
 
 function init({
@@ -21,7 +21,12 @@ function init({
     ): ts.SourceFile => {
       if (isToml(fileName)) {
         logger.log(`create ${fileName}`)
-        scriptSnapshot = createDtsSnapshot(tsModule, scriptSnapshot, logger)
+        scriptSnapshot = createDtsSnapshot(
+          tsModule,
+          scriptSnapshot,
+          logger,
+          isConstToml(fileName)
+        )
       }
       const sourceFile = _createLanguageServiceSourceFile(
         fileName,
@@ -43,7 +48,12 @@ function init({
     ): ts.SourceFile => {
       if (isToml(sourceFile.fileName)) {
         logger.log(`update ${sourceFile.fileName}`)
-        scriptSnapshot = createDtsSnapshot(tsModule, scriptSnapshot, logger)
+        scriptSnapshot = createDtsSnapshot(
+          tsModule,
+          scriptSnapshot,
+          logger,
+          isConstToml(sourceFile.fileName)
+        )
       }
       sourceFile = _updateLanguageServiceSourceFile(
         sourceFile,

src/util.ts

@@ -1 +1,3 @@
 export const isToml = (filename: string): boolean => filename.endsWith('.toml')
+export const isConstToml = (filename: string): boolean =>
+  filename.endsWith('.const.toml')