Make ecmaVersion a required option

(With a warning that defaults it to 2020 for the time being.)

acorn-loose/README.md

@@ -52,7 +52,7 @@ on the `acorn` package, because it uses the same tokenizer.
 
 ```javascript
 var acornLoose = require("acorn-loose");
-console.log(acornLoose.parse("1 / * 4 )[2]"));
+console.log(acornLoose.parse("1 / * 4 )[2]", {ecmaVersion: 2020}));
 ```
 
 Like the regular parser, the loose parser supports plugins. You can

acorn/README.md

@@ -32,14 +32,14 @@ npm install
 ## Interface
 
 **parse**`(input, options)` is the main interface to the library. The
-`input` parameter is a string, `options` can be undefined or an object
-setting some of the options listed below. The return value will be an
-abstract syntax tree object as specified by the [ESTree
+`input` parameter is a string, `options` must be an object setting
+some of the options listed below. The return value will be an abstract
+syntax tree object as specified by the [ESTree
 spec](https://github.com/estree/estree).
 
 ```javascript
 let acorn = require("acorn");
-console.log(acorn.parse("1 + 1"));
+console.log(acorn.parse("1 + 1", {ecmaVersion: 2020}));
 ```
 
 When encountering a syntax error, the parser will raise a
@@ -48,18 +48,19 @@ have a `pos` property that indicates the string offset at which the
 error occurred, and a `loc` object that contains a `{line, column}`
 object referring to that same position.
 
-Options can be provided by passing a second argument, which should be
-an object containing any of these fields:
+Options are provided by in a second argument, which should be an
+object containing any of these fields (only `ecmaVersion` is
+required):
 
 - **ecmaVersion**: Indicates the ECMAScript version to parse. Must be
-  either 3, 5, 6 (2015), 7 (2016), 8 (2017), 9 (2018), 10 (2019) or 11
-  (2020, partial support). This influences support for strict mode,
-  the set of reserved words, and support for new syntax features.
-  Default is 10.
+  either 3, 5, 6 (or 2015), 7 (2016), 8 (2017), 9 (2018), 10 (2019),
+  11 (2020), or 12 (2021, partial support), or `"latest"` (the latest
+  the library supports). This influences support for strict mode, the
+  set of reserved words, and support for new syntax features.
 
   **NOTE**: Only 'stage 4' (finalized) ECMAScript features are being
-  implemented by Acorn. Other proposed new features can be implemented
-  through plugins.
+  implemented by Acorn. Other proposed new features must be
+  implemented through plugins.
 
 - **sourceType**: Indicate the mode the code should be parsed in. Can be
   either `"script"` or `"module"`. This influences global strict mode
@@ -224,7 +225,7 @@ you can use its static `extend` method.
 var acorn = require("acorn");
 var jsx = require("acorn-jsx");
 var JSXParser = acorn.Parser.extend(jsx());
-JSXParser.parse("foo(<bar/>)");
+JSXParser.parse("foo(<bar/>)", {ecmaVersion: 2020});
 ```
 
 The `extend` method takes any number of plugin values, and returns a

acorn/src/.eslintrc

@@ -12,6 +12,7 @@
         "new-parens": "off",
         "no-case-declarations": "off",
         "no-cond-assign": "off",
+        "no-console": ["error", { allow: ["warn", "error"] }],
         "no-fallthrough": "off",
         "no-labels": "off",
         "no-mixed-operators": "off",

acorn/src/options.js

@@ -1,16 +1,16 @@
 import {has, isArray} from "./util"
 import {SourceLocation} from "./locutil"
 
-// A second optional argument can be given to further configure
-// the parser process. These options are recognized:
+// A second argument must be given to configure the parser process.
+// These options are recognized (only `ecmaVersion` is required):
 
 export const defaultOptions = {
   // `ecmaVersion` indicates the ECMAScript version to parse. Must be
-  // either 3, 5, 6 (2015), 7 (2016), 8 (2017), 9 (2018), or 10
-  // (2019). This influences support for strict mode, the set of
-  // reserved words, and support for new syntax features. The default
-  // is 10.
-  ecmaVersion: 10,
+  // either 3, 5, 6 (or 2015), 7 (2016), 8 (2017), 9 (2018), 10
+  // (2019), 11 (2020), 12 (2021), or `"latest"` (the latest version
+  // the library supports). This influences support for strict mode,
+  // the set of reserved words, and support for new syntax features.
+  ecmaVersion: null,
   // `sourceType` indicates the mode the code should be parsed in.
   // Can be either `"script"` or `"module"`. This influences global
   // strict mode and parsing of `import` and `export` declarations.
@@ -91,14 +91,25 @@ export const defaultOptions = {
 
 // Interpret and default an options object
 
+let warnedAboutEcmaVersion = false
+
 export function getOptions(opts) {
   let options = {}
 
   for (let opt in defaultOptions)
     options[opt] = opts && has(opts, opt) ? opts[opt] : defaultOptions[opt]
 
-  if (options.ecmaVersion >= 2015)
+  if (options.ecmaVersion === "latest") {
+    options.ecmaVersion = 1e8
+  } else if (options.ecmaVersion == null) {
+    if (!warnedAboutEcmaVersion && typeof console === "object" && console.warn) {
+      warnedAboutEcmaVersion = true
+      console.warn("Since Acorn 8.0.0, options.ecmaVersion is required.\nDefaulting to 2020, but this will stop working in the future.")
+    }
+    options.ecmaVersion = 11
+  } else if (options.ecmaVersion >= 2015) {
     options.ecmaVersion -= 2009
+  }
 
   if (options.allowReserved == null)
     options.allowReserved = options.ecmaVersion < 5