Allow sourceType: module even with ecmaVersion < 6

acorn-loose/src/statement.js

@@ -10,9 +10,7 @@ lp.parseTopLevel = function() {
   while (this.tok.type !== tt.eof) node.body.push(this.parseStatement())
   this.toks.adaptDirectivePrologue(node.body)
   this.last = this.tok
-  if (this.options.ecmaVersion >= 6) {
-    node.sourceType = this.options.sourceType
-  }
+  node.sourceType = this.options.sourceType
   return this.finishNode(node, "Program")
 }
 

acorn/README.md

@@ -64,6 +64,9 @@ an object containing any of these fields:
   either `"script"` or `"module"`. This influences global strict mode
   and parsing of `import` and `export` declarations.
 
+  **NOTE**: If set to `"module"`, then static `import` / `export` syntax
+  will be valid, even if `ecmaVersion` is less than 6.
+
 - **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/state.js

@@ -9,7 +9,7 @@ export class Parser {
   constructor(options, input, startPos) {
     this.options = options = getOptions(options)
     this.sourceFile = options.sourceFile
-    this.keywords = wordsRegexp(keywords[options.ecmaVersion >= 6 ? 6 : 5])
+    this.keywords = wordsRegexp(keywords[options.ecmaVersion >= 6 ? 6 : options.sourceType === "module" ? "5module" : 5])
     let reserved = ""
     if (options.allowReserved !== true) {
       for (let v = options.ecmaVersion;; v--)

acorn/src/statement.js

@@ -27,9 +27,7 @@ pp.parseTopLevel = function(node) {
       this.raiseRecoverable(this.undefinedExports[name].start, `Export '${name}' is not defined`)
   this.adaptDirectivePrologue(node.body)
   this.next()
-  if (this.options.ecmaVersion >= 6) {
-    node.sourceType = this.options.sourceType
-  }
+  node.sourceType = this.options.sourceType
   return this.finishNode(node, "Program")
 }
 

test/tests.js

@@ -7,6 +7,35 @@ if (typeof exports != "undefined") {
   var acorn = require("../acorn");
 }
 
+test("import ''", {
+  type: "Program",
+  start: 0,
+  end: 9,
+  body: [
+    {
+      type: "ImportDeclaration",
+      start: 0,
+      end: 9,
+      specifiers: [],
+      source: {
+        type: "Literal",
+        start: 7,
+        end: 9,
+        value: "",
+        raw: "''"
+      }
+    }
+  ]
+}, {
+  ecmaVersion: 5,
+  sourceType: "module"
+});
+
+testFail("import('')", "Unexpected token (1:6)", {
+  ecmaVersion: 5,
+  sourceType: "module"
+});
+
 test("new Object", {
   type: "Program",
   start: 0,