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;
-    skipWhiteSpace.lastIndex = thisTokEnd;
+    return this.nextTokenStartSince(this.state.pos);
+  }
+
+  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 {