fix(semantic): allow reserved keywords in typescript ambient contexts (#15495)

Reserved keywords are allowed as an identifier in ambient contexts.
```ts
declare const private: number
```
This is allowed.

Author: sapphi-red

crates/oxc_semantic/src/checker/javascript.rs

@@ -13,7 +13,7 @@ use oxc_syntax::{
     number::NumberBase,
     operator::{AssignmentOperator, UnaryOperator},
     scope::{ScopeFlags, ScopeId},
-    symbol::SymbolFlags,
+    symbol::{SymbolFlags, SymbolId},
 };
 
 use crate::{IsGlobalReference, builder::SemanticBuilder, diagnostics::redeclaration};
@@ -98,9 +98,15 @@ pub const STRICT_MODE_NAMES: Set<&'static str> = phf_set! {
     "yield",
 };
 
-pub fn check_identifier(name: &str, span: Span, ctx: &SemanticBuilder<'_>) {
-    // ts module block allows revered keywords
-    if ctx.current_scope_flags().is_ts_module_block() {
+pub fn check_identifier(
+    name: &str,
+    span: Span,
+    symbol_id: Option<SymbolId>,
+    ctx: &SemanticBuilder<'_>,
+) {
+    // reserved keywords are allowed in ambient contexts
+    if ctx.source_type.is_typescript_definition() || is_current_node_ambient_binding(symbol_id, ctx)
+    {
         return;
     }
     if name == "await" {
@@ -120,6 +126,24 @@ pub fn check_identifier(name: &str, span: Span, ctx: &SemanticBuilder<'_>) {
     }
 }
 
+fn is_current_node_ambient_binding(symbol_id: Option<SymbolId>, ctx: &SemanticBuilder<'_>) -> bool {
+    if ctx.current_scope_flags().is_ts_module_block() {
+        return true;
+    }
+
+    if let Some(symbol_id) = symbol_id
+        && ctx.scoping.symbol_flags(symbol_id).contains(SymbolFlags::Ambient)
+    {
+        true
+    } else if let AstKind::BindingIdentifier(id) = ctx.nodes.kind(ctx.current_node_id)
+        && let Some(symbol_id) = id.symbol_id.get()
+    {
+        ctx.scoping.symbol_flags(symbol_id).contains(SymbolFlags::Ambient)
+    } else {
+        false
+    }
+}
+
 fn unexpected_identifier_assign(x0: &str, span1: Span) -> OxcDiagnostic {
     OxcDiagnostic::error(format!("Cannot assign to '{x0}' in strict mode")).with_label(span1)
 }

crates/oxc_semantic/src/checker/mod.rs

@@ -16,14 +16,14 @@ pub fn check<'a>(kind: AstKind<'a>, ctx: &SemanticBuilder<'a>) {
             js::check_unresolved_exports(program, ctx);
         }
         AstKind::BindingIdentifier(ident) => {
-            js::check_identifier(&ident.name, ident.span, ctx);
+            js::check_identifier(&ident.name, ident.span, ident.symbol_id.get(), ctx);
             js::check_binding_identifier(ident, ctx);
         }
         AstKind::IdentifierReference(ident) => {
-            js::check_identifier(&ident.name, ident.span, ctx);
+            js::check_identifier(&ident.name, ident.span, None, ctx);
             js::check_identifier_reference(ident, ctx);
         }
-        AstKind::LabelIdentifier(ident) => js::check_identifier(&ident.name, ident.span, ctx),
+        AstKind::LabelIdentifier(ident) => js::check_identifier(&ident.name, ident.span, None, ctx),
         AstKind::PrivateIdentifier(ident) => js::check_private_identifier_outside_class(ident, ctx),
         AstKind::NumericLiteral(lit) => js::check_number_literal(lit, ctx),
         AstKind::StringLiteral(lit) => js::check_string_literal(lit, ctx),

tasks/coverage/misc/pass/declare-let-private.ts

@@ -0,0 +1,3 @@
+declare let private: number;
+
+export {};

tasks/coverage/snapshots/codegen_misc.snap

@@ -1,3 +1,3 @@
 codegen_misc Summary:
-AST Parsed     : 50/50 (100.00%)
-Positive Passed: 50/50 (100.00%)
+AST Parsed     : 51/51 (100.00%)
+Positive Passed: 51/51 (100.00%)

tasks/coverage/snapshots/formatter_misc.snap

@@ -1,3 +1,3 @@
 formatter_misc Summary:
-AST Parsed     : 50/50 (100.00%)
-Positive Passed: 50/50 (100.00%)
+AST Parsed     : 51/51 (100.00%)
+Positive Passed: 51/51 (100.00%)

tasks/coverage/snapshots/parser_misc.snap

@@ -1,6 +1,6 @@
 parser_misc Summary:
-AST Parsed     : 50/50 (100.00%)
-Positive Passed: 50/50 (100.00%)
+AST Parsed     : 51/51 (100.00%)
+Positive Passed: 51/51 (100.00%)
 Negative Passed: 118/118 (100.00%)
 
   × Cannot assign to 'arguments' in strict mode

tasks/coverage/snapshots/parser_typescript.snap

@@ -2,7 +2,7 @@ commit: cc2610fd
 
 parser_typescript Summary:
 AST Parsed     : 9821/9822 (99.99%)
-Positive Passed: 9809/9822 (99.87%)
+Positive Passed: 9810/9822 (99.88%)
 Negative Passed: 1455/2545 (57.17%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/ExportAssignment7.ts
 
@@ -2365,23 +2365,6 @@ Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/es6/moduleExp
  65 │     var y = _;
     ╰────
 
-Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/externalModules/topLevelAwait.3.ts
-
-  × The keyword 'await' is reserved
-   ╭─[typescript/tests/cases/conformance/externalModules/topLevelAwait.3.ts:3:15]
- 2 │ export {};
- 3 │ declare const await: any;
-   ·               ──────────
- 4 │ declare class C extends await {}
-   ╰────
-
-  × The keyword 'await' is reserved
-   ╭─[typescript/tests/cases/conformance/externalModules/topLevelAwait.3.ts:4:25]
- 3 │ declare const await: any;
- 4 │ declare class C extends await {}
-   ·                         ─────
-   ╰────
-
 Expect to Parse: tasks/coverage/typescript/tests/cases/conformance/parser/ecmascript5/ComputedPropertyNames/parserES5ComputedPropertyName11.ts
 
   × Function implementation is missing or not immediately following the declaration.

tasks/coverage/snapshots/semantic_misc.snap

@@ -1,6 +1,11 @@
 semantic_misc Summary:
-AST Parsed     : 50/50 (100.00%)
-Positive Passed: 32/50 (64.00%)
+AST Parsed     : 51/51 (100.00%)
+Positive Passed: 32/51 (62.75%)
+semantic Error: tasks/coverage/misc/pass/declare-let-private.ts
+Bindings mismatch:
+after transform: ScopeId(0): ["private"]
+rebuilt        : ScopeId(0): []
+
 semantic Error: tasks/coverage/misc/pass/oxc-11593.ts
 Scope children mismatch:
 after transform: ScopeId(0): [ScopeId(1)]

tasks/coverage/snapshots/semantic_typescript.snap

@@ -2,7 +2,7 @@ commit: cc2610fd
 
 semantic_typescript Summary:
 AST Parsed     : 6148/6148 (100.00%)
-Positive Passed: 2661/6148 (43.28%)
+Positive Passed: 2662/6148 (43.30%)
 semantic Error: tasks/coverage/typescript/tests/cases/compiler/2dArrays.ts
 Symbol reference IDs mismatch for "Cell":
 after transform: SymbolId(0): [ReferenceId(1)]
@@ -42824,10 +42824,6 @@ Scope children mismatch:
 after transform: ScopeId(0): [ScopeId(1)]
 rebuilt        : ScopeId(0): []
 
-semantic Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/topLevelAwait.3.ts
-The keyword 'await' is reserved
-The keyword 'await' is reserved
-
 semantic Error: tasks/coverage/typescript/tests/cases/conformance/externalModules/typeAndNamespaceExportMerge.ts
 Scope children mismatch:
 after transform: ScopeId(0): [ScopeId(1)]

tasks/coverage/snapshots/transformer_misc.snap

@@ -1,3 +1,3 @@
 transformer_misc Summary:
-AST Parsed     : 50/50 (100.00%)
-Positive Passed: 50/50 (100.00%)
+AST Parsed     : 51/51 (100.00%)
+Positive Passed: 51/51 (100.00%)