Add strict type checking via TypeScript

The code is still JavaScript, but now we get strict type checking in
Visual Studio Code and in continuous integration via `tsc` in `pnpm
typecheck`.

The docs generated by 'jsdoc' are a little funky, and we don't get as
much documentation in Visual Studio Code as I expected. I believe I can
fix these issues at some point with this foundation in place.

The actual changes include:

- Added @types/{chai,node}, jsdoc, and typescript as devDependencies.

- Added JSDoc-based @typedefs, including the standalone lib/types.js
  based on: "Stack Overflow: How to 'import' a typedef from one file to
  another in JSDoc using Node.js?"

  - https://stackoverflow.com/a/76872194

- Set .eslintrc to disable the no-undefined-types rule by extending
  "plugin:jsdoc/recommended-typescript-flavor-error". This is because
  the Handlebars types in lib/parser.js weren't trivial to replicate,
  and TypeScript finds those types just fine. This was based on advice
  from:

  > ...the config plugin:jsdoc/recommended-typescript-error should
  > disable the jsdoc/no-undefined-types rule because TypeScript itself
  > is responsible for reporting errors about invalid JSDoc types.
  >
  > - gajus/eslint-plugin-jsdoc#888 (comment)

  And:

  > If you are not using TypeScript syntax (your source files are still
  > .js files) but you are using the TypeScript flavor within JSDoc
  > (i.e., the default "typescript" mode in eslint-plugin-jsdoc) and you
  > are perhaps using allowJs and checkJs options of TypeScript's
  > tsconfig.json), you may use:
  >
  > ```json
  > {
  >   "extends": ["plugin:jsdoc/recommended-typescript-flavor"]
  > }
  > ```
  >
  > ...or to report with failing errors instead of mere warnings:
  >
  > ```json
  > {
  >   "extends": ["plugin:jsdoc/recommended-typescript-flavor-error"]
  > }
  > ```
  >
  > - https://github.com/gajus/eslint-plugin-jsdoc#eslintrc

  More background:

  - https://github.com/gajus/eslint-plugin-jsdoc/blob/main/docs/rules/no-undefined-types.md
  - gajus/eslint-plugin-jsdoc#99
  - gajus/eslint-plugin-jsdoc#1098
  - jsdoc/jsdoc#1537

- At the same time, extending "recommended-typescript-flavor-error"
  required adding the `// eslint-disable-next-line no-unused-vars`
  directive before each set of imports from lib/types.js.

- Added test/vitest.d.ts so TypeScript could find the custom toStartWith
  and toEndWith expect extension matchers.

- Added `pnpm typecheck && pnpm jsdoc` to `pnpm test:ci`.

.eslintrc

@@ -1,7 +1,7 @@
 {
-  "env" : {
+  "env": {
     "node": true,
-    "es2023" : true
+    "es2023": true
   },
   "parserOptions": {
     "ecmaVersion": "latest",
@@ -14,7 +14,7 @@
   ],
   "extends": [
     "eslint:recommended",
-    "plugin:jsdoc/recommended"
+    "plugin:jsdoc/recommended-typescript-flavor-error"
   ],
   "overrides": [
     {
@@ -25,7 +25,7 @@
       ]
     }
   ],
-  "rules" : {
+  "rules": {
     "@stylistic/js/comma-dangle": [
       "error", "never"
     ],

.gitignore

@@ -10,4 +10,6 @@ node_modules/
 out/
 pnpm-debug.log
 tmp/
+types/
 *.log
+*.tgz

README.md

@@ -5,7 +5,7 @@
 _**Status**: I've still got a bit of work to do before publishing v1.0.0. I need
 to add tests based on the mbland/tomcat-servlet-testing-example project from
 whence this came and add more documentation. I plan to finish this by
-2024-01-08._
+2024-01-11._
 
 Source: <https://github.com/mbland/rollup-plugin-handlebars-precompiler>
 

ci/vitest.config.js

@@ -1,5 +1,5 @@
 import { defineConfig, mergeConfig } from 'vitest/config'
-import baseConfig from '../vitest.config'
+import baseConfig from '../vitest.config.js'
 
 export default mergeConfig(baseConfig, defineConfig({
   test: {

index.js

@@ -37,24 +37,56 @@
  */
 
 import PluginImpl, { PLUGIN_NAME } from './lib/index.js'
+// eslint-disable-next-line no-unused-vars
+import { PluginOptions, Transform } from './lib/types.js'
 
 /**
  * A Rollup plugin object for precompiling Handlebars templates.
  * @module rollup-plugin-handlebars-precompiler
  */
 
+/**
+ * @typedef {object} RollupPlugin
+ * @property {string} name - plugin name
+ * @property {Function} resolveId - resolves the plugin's own import ID
+ * @property {Function} load - emits the plugin's helper module code
+ * @property {Function} transform - emits JavaScript code compiled from
+ *   Handlebars templates
+ * @see https://rollupjs.org/plugin-development/
+ */
+
 /**
  * Returns a Rollup plugin object for precompiling Handlebars templates.
  * @function default
- * @param {object} options object containing Handlebars compiler API options
- * @returns {object} a Rollup plugin that precompiles Handlebars templates
+ * @param {PluginOptions} options - plugin configuration options
+ * @returns {RollupPlugin} - the configured plugin object
  */
 export default function HandlebarsPrecompiler(options) {
   const p = new PluginImpl(options)
   return {
     name: PLUGIN_NAME,
-    resolveId(id) { if (p.shouldEmitHelpersModule(id)) return id },
-    load(id) { if (p.shouldEmitHelpersModule(id)) return p.helpersModule() },
-    transform(code, id) { if (p.isTemplate(id)) return p.compile(code, id) }
+
+    /**
+     * @param {string} id - import identifier to resolve
+     * @returns {(string | undefined)} - the plugin ID if id matches it
+     * @see https://rollupjs.org/plugin-development/#resolveid
+     */
+    resolveId: function (id) {
+      return p.shouldEmitHelpersModule(id) ? id : undefined
+    },
+
+    /**
+     * @param {string} id - import identifier to load
+     * @returns {(string | undefined)} - the plugin helper module if id matches
+     * @see https://rollupjs.org/plugin-development/#load
+     */
+    load: function (id) {
+      return p.shouldEmitHelpersModule(id) ? p.helpersModule() : undefined
+    },
+
+    /** @type {Transform} */
+    transform: function (code, id) {
+      return p.isTemplate(id) ? p.compile(code, id) : undefined
+    }
   }
 }

jsconfig.json

@@ -0,0 +1,16 @@
+{
+  "compilerOptions": {
+    "checkJs": true,
+    "lib": [
+      "ES2022"
+    ],
+    "module": "node16",
+    "target": "es2020",
+    "strict": true
+  },
+  "exclude": [
+    "node_modules/**",
+    "coverage*/**",
+    "jsdoc/**"
+  ]
+}

lib/index.js

@@ -37,19 +37,27 @@
  */
 
 import collectPartials from './partials.js'
+import {
+  // eslint-disable-next-line no-unused-vars
+  Compiled, PartialName, PartialPath, PluginOptions, SourceMap, Transform
+} from './types.js'
 import { createFilter } from '@rollup/pluginutils'
 import Handlebars from 'handlebars'
 
 export const PLUGIN_NAME = 'handlebars-precompiler'
 const DEFAULT_INCLUDE = ['**/*.hbs', '**/*.handlebars', '**/*.mustache']
 const DEFAULT_EXCLUDE = 'node_modules/**'
 const DEFAULT_PARTIALS = '**/_*'
-const DEFAULT_PARTIAL_NAME = id => {
+
+/** @type {PartialName} */
+const DEFAULT_PARTIAL_NAME = function (id) {
   return id.replace(/.*\//, '')    // extract the basename
     .replace(/\.[^.]*$/, '')       // remove the file extension, if present
     .replace(/^[^[:alnum:]]*/, '') // strip leading non-alphanumeric characters
 }
-const DEFAULT_PARTIAL_PATH = (partialName, importerPath) => {
+
+/** @type {PartialPath} */
+const DEFAULT_PARTIAL_PATH = function (partialName, importerPath) {
   return `./_${partialName}.${importerPath.replace(/.*\./, '')}`
 }
 
@@ -58,6 +66,21 @@ const HANDLEBARS_PATH = 'handlebars/lib/handlebars.runtime'
 const IMPORT_HANDLEBARS = `import Handlebars from '${HANDLEBARS_PATH}'`
 const IMPORT_HELPERS = `import Render from '${PLUGIN_ID}'`
 
+/**
+ * @callback CompilerOpts
+ * @param {string} id - import ID of module to compile
+ * @returns {object} - Handlebars compiler options based on id
+ */
+
+/**
+ * @callback AdjustSourceMap
+ * @param {string} map - the Handlebars source map as a JSON string
+ * @param {number} numLinesBeforeTmpl - number of empty lines to add to the
+ *   beginning of the source mappings to account for the generated code before
+ *   the precompiled template
+ * @returns {SourceMap} - potentially modified Handlebars source map
+ */
+
 /**
  * Rollup Handlebars precompiler implementation
  */
@@ -67,10 +90,15 @@ export default class PluginImpl {
   #isPartial
   #partialName
   #partialPath
+  /** @type {CompilerOpts} */
   #compilerOpts
+  /** @type {AdjustSourceMap} */
   #adjustSourceMap
 
-  constructor(options = {}) {
+  /**
+   * @param {PluginOptions} options - plugin configuration options
+   */
+  constructor(options = /** @type {PluginOptions} */ ({})) {
     this.#helpers = options.helpers || []
     this.#isTemplate = createFilter(
       options.include || DEFAULT_INCLUDE,
@@ -101,6 +129,10 @@ export default class PluginImpl {
     }
   }
 
+  /**
+   * @param {string} id - import identifier
+   * @returns {boolean} - true if id is the plugin's import identifier
+   */
   shouldEmitHelpersModule(id) { return id === PLUGIN_ID }
 
   helpersModule() {
@@ -118,12 +150,17 @@ export default class PluginImpl {
     ].join('\n')
   }
 
+  /**
+   * @param {string} id - import identifier
+   * @returns {boolean} - true if id matches the filter for template files
+   */
   isTemplate(id) { return this.#isTemplate(id) }
 
+  /** @type {Transform} */
   compile(code, id) {
     const opts = this.#compilerOpts(id)
     const ast = Handlebars.parse(code, opts)
-    const compiled = Handlebars.precompile(ast, opts)
+    const compiled = /** @type {Compiled} */ (Handlebars.precompile(ast, opts))
     const { code: tmpl = compiled, map: srcMap } = compiled
 
     const beforeTmpl = [
@@ -143,6 +180,10 @@ export default class PluginImpl {
     }
   }
 
+  /**
+   * @param {string} id - id of the partial to register
+   * @returns {string} - Handlebars.registerPartial statement for the partial
+   */
   #partialRegistration(id) {
     return `Handlebars.registerPartial('${this.#partialName(id)}', RawTemplate)`
   }

lib/partials.js

@@ -43,18 +43,28 @@ import Handlebars from 'handlebars'
  * @see https://github.com/handlebars-lang/handlebars.js/blob/master/docs/compiler-api.md
  */
 class PartialCollector extends Handlebars.Visitor {
+  /** @type {string[]} */
   partials = []
 
+  /**
+   * @param {hbs.AST.PartialStatement} partial - partial name to evaluate
+   */
   PartialStatement(partial) {
     this.collect(partial.name)
-    return super.PartialStatement(partial)
+    super.PartialStatement(partial)
   }
-
+  /**
+   * @param {hbs.AST.PartialBlockStatement} partial - partial name to evaluate
+   */
   PartialBlockStatement(partial) {
     this.collect(partial.name)
-    return super.PartialBlockStatement(partial)
+    super.PartialBlockStatement(partial)
   }
 
+  /**
+   * @param {hbs.AST.PathExpression | hbs.AST.SubExpression} n - potential
+   *   partial name to collect
+   */
   collect(n) {
     if (n.type === 'PathExpression' && n.original !== '@partial-block') {
       this.partials.push(n.original)
@@ -64,11 +74,11 @@ class PartialCollector extends Handlebars.Visitor {
 
 /**
  * Returns the partial names parsed from a Handlebars template
+ * @param {hbs.AST.Program} ast - abstract syntax tree for a Handlebars template
+ *   returned by Handlebars.parse()
+ * @returns {string[]} - a list of partial names parsed from the template
  * @see https://handlebarsjs.com/guide/partials.html
  * @see https://github.com/handlebars-lang/handlebars.js/blob/master/docs/compiler-api.md
- * @param {object} ast - abstract syntax tree for a Handlebars template returned
- *   by Handlebars.parse()
- * @returns {string[]} - a list of partial names parsed from the template
  */
 export default function collectPartials(ast) {
   const collector = new PartialCollector()