Add a strict option to turn on strict mode for scripts

FEATURE: The new `strict` option can be used to start script sources in
strict mode.

Issue #1439

Author: marijnh

acorn/README.md

@@ -86,6 +86,9 @@ required):
   will be valid, even if `ecmaVersion` is less than 6. If set to `"commonjs"`,
   it is the same as `"script"` except that the top-level scope behaves like a function.
 
+- **strict**: When set to true, enable strict parsing mode even if
+  `sourceType` is `"script"`.
+
 - **onInsertedSemicolon**: If given a callback, that callback will be
   called whenever a missing semicolon is inserted by the parser. The
   callback will be given the character offset of the point where the

acorn/src/acorn.d.ts

@@ -619,6 +619,12 @@ export interface Options {
    */
   sourceType?: "script" | "module" | "commonjs"
 
+  /**
+   * When set to true, enable strict parsing mode even if `sourceType`
+   * is `"script"`.
+   */
+  strict?: boolean
+
   /**
    * a callback that will be called when a semicolon is automatically inserted.
    * @param lastTokEnd the position of the comma as an offset

acorn/src/options.js

@@ -16,6 +16,9 @@ export const defaultOptions = {
   // Can be either `"script"`, `"module"` or `"commonjs"`. This influences global
   // strict mode and parsing of `import` and `export` declarations.
   sourceType: "script",
+  // When set to true, enable strict parsing mode even if `sourceType`
+  // is `"script"`.
+  strict: false,
   // `onInsertedSemicolon` can be a callback that will be called when
   // a semicolon is automatically inserted. It will be passed the
   // position of the inserted semicolon as an offset, and if

acorn/src/state.js

@@ -64,7 +64,7 @@ export class Parser {
 
     // Figure out if it's a module code.
     this.inModule = options.sourceType === "module"
-    this.strict = this.inModule || this.strictDirective(this.pos)
+    this.strict = this.inModule || options.strict == true || this.strictDirective(this.pos)
 
     // Used to signify the start of a potential arrow function
     this.potentialArrowAt = -1