Properly parse export default from when exportDefaultFrom is not enabled (#11676)

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

packages/babel-parser/src/parser/error-message.js

@@ -42,6 +42,8 @@ export const ErrorMessages = Object.freeze({
   DuplicateRegExpFlags: "Duplicate regular expression flag",
   ElementAfterRest: "Rest element must be last element",
   EscapedCharNotAnIdentifier: "Invalid Unicode escape",
+  ExportDefaultFromAsIdentifier:
+    "'from' is not allowed as an identifier after 'export default'",
   ForInOfLoopInitializer:
     "%0 loop variable declaration may not have an initializer",
   GeneratorInSingleStatementContext:

packages/babel-parser/src/parser/statement.js

@@ -1857,10 +1857,24 @@ export default class StatementParser extends ExpressionParser {
     }
 
     const next = this.nextTokenStart();
-    return (
+    const hasFrom = this.isUnparsedContextual(next, "from");
+    if (
       this.input.charCodeAt(next) === charCodes.comma ||
-      this.isUnparsedContextual(next, "from")
+      (this.match(tt.name) && hasFrom)
-    );
+    ) {
+      return true;
+    }
+    // lookahead again when `export default from` is seen
+    if (this.match(tt._default) && hasFrom) {
+      const nextAfterFrom = this.input.charCodeAt(
+        this.nextTokenStartSince(next + 4),
+      );
+      return (
+        nextAfterFrom === charCodes.quotationMark ||
+        nextAfterFrom === charCodes.apostrophe
+      );
+    }
+    return false;
   }
 
   parseExportFrom(node: N.ExportNamedDeclaration, expect?: boolean): void {
@@ -1911,6 +1925,18 @@ export default class StatementParser extends ExpressionParser {
       if (isDefault) {
         // Default exports
         this.checkDuplicateExports(node, "default");
+        if (this.hasPlugin("exportDefaultFrom")) {
+          const declaration = ((node: any): N.ExportDefaultDeclaration)
+            .declaration;
+          if (
+            declaration.type === "Identifier" &&
+            declaration.name === "from" &&
+            declaration.end - declaration.start === 4 && // does not contain escape
+            !declaration.extra?.parenthesized
+          ) {
+            this.raise(declaration.start, Errors.ExportDefaultFromAsIdentifier);
+          }
+        }
       } else if (node.specifiers && node.specifiers.length) {
         // Named exports
         for (const specifier of node.specifiers) {

packages/babel-parser/src/plugins/placeholders.js

@@ -251,6 +251,23 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return super.parseExport(node);
     }
 
+    isExportDefaultSpecifier(): boolean {
+      if (this.match(tt._default)) {
+        const next = this.nextTokenStart();
+        if (this.isUnparsedContextual(next, "from")) {
+          if (
+            this.input.startsWith(
+              tt.placeholder.label,
+              this.nextTokenStartSince(next + 4),
+            )
+          ) {
+            return true;
+          }
+        }
+      }
+      return super.isExportDefaultSpecifier();
+    }
+
     maybeParseExportDefaultSpecifier(node: N.Node): boolean {
       if (node.specifiers && node.specifiers.length > 0) {
         // "export %%NAME%%" has already been parsed by #parseExport.

packages/babel-parser/src/tokenizer/index.js

@@ -190,11 +190,14 @@ export default class Tokenizer extends ParserErrors {
   }
 
   nextTokenStart(): number {
-    const thisTokEnd = this.state.pos;
+    return this.nextTokenStartSince(this.state.pos);
-    skipWhiteSpace.lastIndex = thisTokEnd;
+  }
+
+  nextTokenStartSince(pos: number): number {
+    skipWhiteSpace.lastIndex = pos;
     const skip = skipWhiteSpace.exec(this.input);
     // $FlowIgnore: The skipWhiteSpace ensures to match any string
-    return thisTokEnd + skip[0].length;
+    return pos + skip[0].length;
   }
 
   lookaheadCharCode(): number {

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier-2/input.js

@@ -0,0 +1 @@
+export default from (bar);

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier-2/output.json

@@ -0,0 +1,33 @@
+{
+  "type": "File",
+  "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+        "declaration": {
+          "type": "CallExpression",
+          "start":15,"end":25,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":25}},
+          "callee": {
+            "type": "Identifier",
+            "start":15,"end":19,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":19},"identifierName":"from"},
+            "name": "from"
+          },
+          "arguments": [
+            {
+              "type": "Identifier",
+              "start":21,"end":24,"loc":{"start":{"line":1,"column":21},"end":{"line":1,"column":24},"identifierName":"bar"},
+              "name": "bar"
+            }
+          ]
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier-3/input.js

@@ -0,0 +1 @@
+export default from ?? 42;

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier-3/output.json

@@ -0,0 +1,36 @@
+{
+  "type": "File",
+  "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":26}},
+        "declaration": {
+          "type": "LogicalExpression",
+          "start":15,"end":25,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":25}},
+          "left": {
+            "type": "Identifier",
+            "start":15,"end":19,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":19},"identifierName":"from"},
+            "name": "from"
+          },
+          "operator": "??",
+          "right": {
+            "type": "NumericLiteral",
+            "start":23,"end":25,"loc":{"start":{"line":1,"column":23},"end":{"line":1,"column":25}},
+            "extra": {
+              "rawValue": 42,
+              "raw": "42"
+            },
+            "value": 42
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier/input.js

@@ -0,0 +1 @@
+export default from;

packages/babel-parser/test/fixtures/esprima/es2015-export-declaration/export-default-from-as-identifier/output.json

@@ -0,0 +1,22 @@
+{
+  "type": "File",
+  "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+        "declaration": {
+          "type": "Identifier",
+          "start":15,"end":19,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":19},"identifierName":"from"},
+          "name": "from"
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-default-asi/input.js

@@ -0,0 +1,2 @@
+export default from
+"bar";

packages/babel-parser/test/fixtures/experimental/export-extensions/default-default-asi/options.json

@@ -0,0 +1,4 @@
+{
+  "sourceType": "module",
+  "plugins": ["exportDefaultFrom"]
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-default-asi/output.json

@@ -0,0 +1,37 @@
+{
+  "type": "File",
+  "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":6}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":6}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportNamedDeclaration",
+        "start":0,"end":26,"loc":{"start":{"line":1,"column":0},"end":{"line":2,"column":6}},
+        "specifiers": [
+          {
+            "type": "ExportDefaultSpecifier",
+            "start":7,"end":14,"loc":{"start":{"line":1,"column":7},"end":{"line":1,"column":14}},
+            "exported": {
+              "type": "Identifier",
+              "start":7,"end":14,"loc":{"start":{"line":1,"column":7},"end":{"line":1,"column":14},"identifierName":"default"},
+              "name": "default"
+            }
+          }
+        ],
+        "source": {
+          "type": "StringLiteral",
+          "start":20,"end":25,"loc":{"start":{"line":2,"column":0},"end":{"line":2,"column":5}},
+          "extra": {
+            "rawValue": "bar",
+            "raw": "\"bar\""
+          },
+          "value": "bar"
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/input.js

@@ -0,0 +1 @@
+export default \u{66}rom;

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": ["exportDefaultFrom"],
+  "sourceType": "module"
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-escaped/output.json

@@ -0,0 +1,22 @@
+{
+  "type": "File",
+  "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":25,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":25}},
+        "declaration": {
+          "type": "Identifier",
+          "start":15,"end":24,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":24},"identifierName":"from"},
+          "name": "from"
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-parenthesized/input.js

@@ -0,0 +1 @@
+export default (from);

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-parenthesized/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": ["exportDefaultFrom"],
+  "sourceType": "module"
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/default-from-identifier-parenthesized/output.json

@@ -0,0 +1,26 @@
+{
+  "type": "File",
+  "start":0,"end":22,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":22}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":22,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":22}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":22,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":22}},
+        "declaration": {
+          "type": "Identifier",
+          "start":16,"end":20,"loc":{"start":{"line":1,"column":16},"end":{"line":1,"column":20},"identifierName":"from"},
+          "name": "from",
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 15
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/invalid-default-from-identifier/input.js

@@ -0,0 +1 @@
+export default from;

packages/babel-parser/test/fixtures/experimental/export-extensions/invalid-default-from-identifier/options.json

@@ -0,0 +1,4 @@
+{
+  "plugins": ["exportDefaultFrom"],
+  "sourceType": "module"
+}

packages/babel-parser/test/fixtures/experimental/export-extensions/invalid-default-from-identifier/output.json

@@ -0,0 +1,25 @@
+{
+  "type": "File",
+  "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+  "errors": [
+    "SyntaxError: 'from' is not allowed as an identifier after 'export default' (1:15)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExportDefaultDeclaration",
+        "start":0,"end":20,"loc":{"start":{"line":1,"column":0},"end":{"line":1,"column":20}},
+        "declaration": {
+          "type": "Identifier",
+          "start":15,"end":19,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":19},"identifierName":"from"},
+          "name": "from"
+        }
+      }
+    ],
+    "directives": []
+  }
+}