fix(parser): support top-level await detection in unambiguous mode

crates/oxc_linter/src/snapshots/unicorn_prefer_logical_operator_over_ternary.snap

@@ -99,26 +99,19 @@ source: crates/oxc_linter/src/tester.rs
    ╰────
   help: Either remove this `await` or add the `async` keyword to the enclosing function
 
-  × `await` is only allowed within async functions and at the top levels of modules
+  ⚠ eslint-plugin-unicorn(prefer-logical-operator-over-ternary): Prefer using a logical operator over a ternary.
    ╭─[prefer_logical_operator_over_ternary.tsx:1:1]
  1 │ await a ? await a : foo
-   · ─────
-   ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
-
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[prefer_logical_operator_over_ternary.tsx:1:11]
- 1 │ await a ? await a : foo
-   ·           ─────
+   · ───────────────────────
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Switch to "||" or "??" operator
 
-  × `await` is only allowed within async functions and at the top levels of modules
+  ⚠ eslint-plugin-unicorn(prefer-logical-operator-over-ternary): Prefer using a logical operator over a ternary.
    ╭─[prefer_logical_operator_over_ternary.tsx:1:1]
  1 │ await a ? (await (a)) : (foo)
-   · ─────
+   · ─────────────────────────────
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Switch to "||" or "??" operator
 
   × `await` is only allowed within async functions and at the top levels of modules
    ╭─[prefer_logical_operator_over_ternary.tsx:1:2]

crates/oxc_linter/src/snapshots/unicorn_prefer_node_protocol.snap

@@ -105,9 +105,9 @@ source: crates/oxc_linter/src/tester.rs
    ·        ──
    ╰────
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[prefer_node_protocol.tsx:1:1]
+  ⚠ eslint-plugin-unicorn(prefer-node-protocol): Prefer using the `node:` protocol when importing Node.js builtin modules.
+   ╭─[prefer_node_protocol.tsx:1:14]
  1 │ await import('assert/strict')
-   · ─────
+   ·              ───────────────
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Prefer `node:assert/strict` over `assert/strict`.

crates/oxc_parser/src/js/expression.rs

@@ -1476,7 +1476,7 @@ impl<'a> ParserImpl<'a> {
 
     /// ``AwaitExpression`[Yield]` :
     ///     await `UnaryExpression`[?Yield, +Await]
-    fn parse_await_expression(&mut self, lhs_span: u32) -> Expression<'a> {
+    pub(crate) fn parse_await_expression(&mut self, lhs_span: u32) -> Expression<'a> {
         let span = self.start_span();
         if !self.ctx.has_await() {
             // For `ModuleKind::Unambiguous`, defer the error until we know whether
@@ -1542,6 +1542,11 @@ impl<'a> ParserImpl<'a> {
             if self.ctx.has_await() {
                 return true;
             }
+            // In Script mode (not module, not unambiguous), `await` at top level is just an identifier.
+            // Only check lookahead for Module (top-level await) or Unambiguous mode (detection).
+            if !self.source_type.is_module() && !self.source_type.is_unambiguous() {
+                return false;
+            }
             return self.lookahead(|p| {
                 Self::next_token_is_identifier_or_keyword_or_literal_on_same_line(p, true)
             });

crates/oxc_parser/src/js/statement.rs

@@ -155,6 +155,13 @@ impl<'a> ParserImpl<'a> {
             Kind::Const => self.parse_const_statement(stmt_ctx),
             Kind::Using if self.is_using_declaration() => self.parse_using_statement(stmt_ctx),
             Kind::Await if self.is_using_statement() => self.parse_using_statement(stmt_ctx),
+            Kind::Await
+                if stmt_ctx.is_top_level()
+                    && self.source_type.is_unambiguous()
+                    && self.is_unambiguous_await_statement() =>
+            {
+                self.parse_await_statement()
+            }
             Kind::Interface
             | Kind::Type
             | Kind::Module
@@ -234,6 +241,73 @@ impl<'a> ParserImpl<'a> {
         self.parse_expression_statement(span, expr)
     }
 
+    /// Check if `await` starts an unambiguous await statement.
+    ///
+    /// Returns true if:
+    /// - We're at `await`
+    /// - Not in await context (not already in async/module)
+    /// - Next token is NOT ambiguous (not +, -, (, [, /, template, of, using, newline)
+    ///
+    /// This is used in unambiguous mode to detect that `await expr` at top level
+    /// definitively makes this file an ES module.
+    pub(crate) fn is_unambiguous_await_statement(&mut self) -> bool {
+        debug_assert!(self.at(Kind::Await));
+        if self.ctx.has_await() {
+            return false;
+        }
+        self.lookahead(Self::peek_is_unambiguous_await_argument)
+    }
+
+    /// Check if the token following `await` is unambiguous (not ambiguous).
+    ///
+    /// Ambiguous tokens are those that could produce different ASTs depending on whether
+    /// the file is parsed as a script or module:
+    /// - Line break: `await\n0` could be two expression statements
+    /// - `+` / `-`: `await + 0` could be binary expression or await of unary
+    /// - `(`: `await(0)` could be call expression or await of parenthesized
+    /// - `[`: `await[0]` could be member expression or await of array
+    /// - `/`: `await /x/` could be division or await of regex
+    /// - Template: `await\`\`` could be tagged template or await of template
+    /// - `of`: `for (await of [])` ambiguity
+    /// - `using`: `await using` has special declaration semantics
+    /// - `%`: `await %x(0)` is always modulo in script mode (`await % x(0)`)
+    /// - `;`: `await;` is identifier statement, not await expression (await needs argument)
+    fn peek_is_unambiguous_await_argument(&mut self) -> bool {
+        self.bump_any(); // skip `await`
+        let token = self.cur_token();
+        if token.is_on_new_line() {
+            return false;
+        }
+        !matches!(
+            token.kind(),
+            Kind::Plus
+                | Kind::Minus
+                | Kind::LParen
+                | Kind::LBrack
+                | Kind::Slash
+                | Kind::Percent
+                | Kind::Semicolon
+                | Kind::TemplateHead
+                | Kind::NoSubstitutionTemplate
+                | Kind::Of
+                | Kind::Using
+        )
+    }
+
+    /// Parse a top-level await statement in unambiguous mode.
+    ///
+    /// This marks the file as ESM (since unambiguous await proves this is a module)
+    /// and parses the full expression (which starts with await) as an expression statement.
+    pub(crate) fn parse_await_statement(&mut self) -> Statement<'a> {
+        let span = self.start_span();
+        // Mark as ESM - unambiguous await proves this is a module
+        self.module_record_builder.found_unambiguous_await();
+        // Enable await context and parse the full expression (not just the await part)
+        // This handles cases like `await a ? b : c` where the await is part of a larger expression
+        let expr = self.context_add(Context::Await, Self::parse_expr);
+        self.parse_expression_statement(span, expr)
+    }
+
     /// Section 14.2 Block Statement
     pub(crate) fn parse_block(&mut self) -> Box<'a, BlockStatement<'a>> {
         let span = self.start_span();

crates/oxc_parser/src/module_record.rs

@@ -199,6 +199,14 @@ impl<'a> ModuleRecordBuilder<'a> {
         self.module_record.import_metas.push(span);
     }
 
+    /// Mark as ESM when an unambiguous top-level await is encountered.
+    ///
+    /// In unambiguous mode, `await expr` where `expr` is clearly an expression (not ambiguous
+    /// like `+`, `-`, `(`, `[`, etc.) indicates this is definitely an ES module.
+    pub fn found_unambiguous_await(&mut self) {
+        self.module_record.has_module_syntax = true;
+    }
+
     pub fn visit_import_declaration(&mut self, decl: &ImportDeclaration<'a>) {
         let module_request = NameSpan::new(decl.source.value, decl.source.span);
 

tasks/coverage/snapshots/codegen_babel.snap

@@ -1,5 +1,5 @@
 commit: 6ef16ca4
 
 codegen_babel Summary:
-AST Parsed     : 2221/2221 (100.00%)
-Positive Passed: 2221/2221 (100.00%)
+AST Parsed     : 2225/2225 (100.00%)
+Positive Passed: 2225/2225 (100.00%)

tasks/coverage/snapshots/formatter_babel.snap

@@ -1,8 +1,8 @@
 commit: 6ef16ca4
 
 formatter_babel Summary:
-AST Parsed     : 2221/2221 (100.00%)
-Positive Passed: 2215/2221 (99.73%)
+AST Parsed     : 2225/2225 (100.00%)
+Positive Passed: 2219/2225 (99.73%)
 Mismatch: tasks/coverage/babel/packages/babel-parser/test/fixtures/comments/basic/async-arrow-function/input.js
 
 Mismatch: tasks/coverage/babel/packages/babel-parser/test/fixtures/comments/basic/class-method/input.js

tasks/coverage/snapshots/minifier_babel.snap

@@ -1,5 +1,5 @@
 commit: 6ef16ca4
 
 minifier_babel Summary:
-AST Parsed     : 1783/1783 (100.00%)
-Positive Passed: 1783/1783 (100.00%)
+AST Parsed     : 1787/1787 (100.00%)
+Positive Passed: 1787/1787 (100.00%)

tasks/coverage/snapshots/parser_babel.snap

@@ -1,8 +1,8 @@
 commit: 6ef16ca4
 
 parser_babel Summary:
-AST Parsed     : 2217/2221 (99.82%)
-Positive Passed: 2204/2221 (99.23%)
+AST Parsed     : 2221/2225 (99.82%)
+Positive Passed: 2208/2225 (99.24%)
 Negative Passed: 1654/1689 (97.93%)
 Expect Syntax Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/es2026/explicit-resource-management/invalid-for-using-of-no-initializer/input.js
 
@@ -1186,12 +1186,12 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: In strict mode code, functions can only be declared at top level or inside a block
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/core/sourcetype-commonjs/invalid-top-level-await/input.js:1:1]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[babel/packages/babel-parser/test/fixtures/core/sourcetype-commonjs/invalid-top-level-await/input.js:1:6]
  1 │ await Promise.resolve();
-   · ─────
+   ·      ▲
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
   × A 'yield' expression is only allowed in a generator body.
    ╭─[babel/packages/babel-parser/test/fixtures/core/sourcetype-commonjs/invalid-top-level-yield/input.js:1:1]
@@ -5128,21 +5128,21 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Try inserting a semicolon here
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/9/input.js:1:25]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/9/input.js:1:30]
  1 │ function foo(promise) { await promise; }
-   ·                         ─────
+   ·                              ▲
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/allow-await-outside-function-throw/input.js:2:10]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/allow-await-outside-function-throw/input.js:2:15]
  1 │ function a() {
  2 │   return await 1
-   ·          ─────
+   ·               ▲
  3 │ }
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
   × Cannot use `await` as an identifier in an async context
    ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/async-await-as-arrow-binding-identifier/input.js:1:7]
@@ -5186,12 +5186,12 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  3 │ }
    ╰────
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-arrow-expression-disallowed/input.js:1:9]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-arrow-expression-disallowed/input.js:1:14]
  1 │ () => { await x }
-   ·         ─────
+   ·              ▲
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
   × await expression not allowed in formal parameter
    ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-parameters/input.js:1:23]
@@ -5225,21 +5225,13 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
  3 │ }
    ╰────
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-parameters-of-nested-function/input.js:2:20]
+  × Expected `,` or `)` but found `decimal`
+   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-parameters-of-nested-function/input.js:2:26]
  1 │ async function foo() {
  2 │   function bar(x = await 2) {}
-   ·                    ─────
- 3 │ }
-   ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
-
-  × await expression not allowed in formal parameter
-   ╭─[babel/packages/babel-parser/test/fixtures/es2017/async-functions/await-inside-parameters-of-nested-function/input.js:2:20]
- 1 │ async function foo() {
- 2 │   function bar(x = await 2) {}
-   ·                    ───┬───
-   ·                       ╰── await expression not allowed in formal parameter
+   ·               ┬          ┬
+   ·               │          ╰── `,` or `)` expected
+   ·               ╰── Opened here
  3 │ }
    ╰────
 
@@ -8422,12 +8414,12 @@ Expect to Parse: tasks/coverage/babel/packages/babel-parser/test/fixtures/typesc
    ╰────
   help: Either remove this `await` or add the `async` keyword to the enclosing function
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[babel/packages/babel-parser/test/fixtures/es2022/top-level-await-script/top-level/input.js:1:1]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[babel/packages/babel-parser/test/fixtures/es2022/top-level-await-script/top-level/input.js:1:6]
  1 │ await 0;
-   · ─────
+   ·      ▲
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
   × Invalid regular expression: Invalid unicode flags combination `u` and `v`
    ╭─[babel/packages/babel-parser/test/fixtures/es2024/regexp-unicode-sets/uv-error/input.js:1:6]

tasks/coverage/snapshots/parser_misc.snap

@@ -72,13 +72,13 @@ Negative Passed: 131/131 (100.00%)
    · ──────
    ╰────
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[misc/fail/commonjs-top-level-await.cjs:2:1]
+  × Expected a semicolon or an implicit semicolon after a statement, but found none
+   ╭─[misc/fail/commonjs-top-level-await.cjs:2:6]
  1 │ // CommonJS does NOT allow top-level await (only ES modules do)
  2 │ await Promise.resolve();
-   · ─────
+   ·      ▲
    ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
+  help: Try inserting a semicolon here
 
   × Encountered diff marker
     ╭─[misc/fail/diff-markers.js:10:1]

tasks/coverage/snapshots/parser_typescript.snap

@@ -3,7 +3,7 @@ commit: 7f6a8467
 parser_typescript Summary:
 AST Parsed     : 9842/9843 (99.99%)
 Positive Passed: 9837/9843 (99.94%)
-Negative Passed: 1500/2555 (58.71%)
+Negative Passed: 1499/2555 (58.67%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/FunctionDeclaration3.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/FunctionDeclaration4.ts
@@ -1484,6 +1484,8 @@ Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/externalM
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/rewriteRelativeImportExtensions/emit.ts
 
+Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/topLevelAwaitNonModule.ts
+
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/topLevelModuleDeclarationAndFile.ts
 
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/typeOnly/chained2.ts
@@ -19784,23 +19786,6 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/statements/Va
    ·          ─────
    ╰────
 
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[typescript/tests/cases/conformance/externalModules/topLevelAwaitNonModule.ts:1:1]
- 1 │ await x;
-   · ─────
- 2 │ 
-   ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
-
-  × `await` is only allowed within async functions and at the top levels of modules
-   ╭─[typescript/tests/cases/conformance/externalModules/topLevelAwaitNonModule.ts:5:5]
- 4 │ 
- 5 │ for await (const item of arr) {
-   ·     ─────
- 6 │   item;
-   ╰────
-  help: Either remove this `await` or add the `async` keyword to the enclosing function
-
   × Expected `=` but found `;`
     ╭─[typescript/tests/cases/conformance/externalModules/typeOnly/exportDeclaration_missingBraces.ts:11:16]
  10 │ namespace ns {

tasks/coverage/snapshots/semantic_babel.snap

@@ -1,8 +1,8 @@
 commit: 6ef16ca4
 
 semantic_babel Summary:
-AST Parsed     : 2221/2221 (100.00%)
-Positive Passed: 2022/2221 (91.04%)
+AST Parsed     : 2225/2225 (100.00%)
+Positive Passed: 2026/2225 (91.06%)
 semantic Error: tasks/coverage/babel/packages/babel-parser/test/fixtures/comments/decorators/decorators-after-export/input.js
 Symbol span mismatch for "C":
 after transform: SymbolId(0): Span { start: 65, end: 66 }

tasks/coverage/snapshots/transformer_babel.snap

@@ -1,7 +1,7 @@
 commit: 6ef16ca4
 
 transformer_babel Summary:
-AST Parsed     : 2221/2221 (100.00%)
-Positive Passed: 2220/2221 (99.95%)
+AST Parsed     : 2225/2225 (100.00%)
+Positive Passed: 2224/2225 (99.96%)
 Mismatch: tasks/coverage/babel/packages/babel-parser/test/fixtures/core/opts/allowYieldOutsideFunction-true-2/input.js