From 6e519c59c13e4e99da0bf779a1f2bbee232cf7a1 Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Wed, 25 Jun 2025 14:29:50 -0700
Subject: [PATCH] Fix BigInt literal error in ambient contexts when targeting <
 ES2020 (#61935)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>
---
 src/compiler/checker.ts                       |  3 +-
 .../reference/bigintAmbientMinimal.errors.txt | 17 +++++++++
 .../reference/bigintAmbientMinimal.js         | 18 ++++++++++
 .../reference/bigintAmbientMinimal.symbols    | 22 ++++++++++++
 .../reference/bigintAmbientMinimal.types      | 35 +++++++++++++++++++
 tests/cases/compiler/bigintAmbientMinimal.ts  | 14 ++++++++
 6 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/bigintAmbientMinimal.errors.txt
 create mode 100644 tests/baselines/reference/bigintAmbientMinimal.js
 create mode 100644 tests/baselines/reference/bigintAmbientMinimal.symbols
 create mode 100644 tests/baselines/reference/bigintAmbientMinimal.types
 create mode 100644 tests/cases/compiler/bigintAmbientMinimal.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 5614da35039..e66a209af81 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -53188,7 +53188,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const literalType = isLiteralTypeNode(node.parent) ||
             isPrefixUnaryExpression(node.parent) && isLiteralTypeNode(node.parent.parent);
         if (!literalType) {
-            if (languageVersion < ScriptTarget.ES2020) {
+            // Don't error on BigInt literals in ambient contexts
+            if (!(node.flags & NodeFlags.Ambient) && languageVersion < ScriptTarget.ES2020) {
                 if (grammarErrorOnNode(node, Diagnostics.BigInt_literals_are_not_available_when_targeting_lower_than_ES2020)) {
                     return true;
                 }
diff --git a/tests/baselines/reference/bigintAmbientMinimal.errors.txt b/tests/baselines/reference/bigintAmbientMinimal.errors.txt
new file mode 100644
index 00000000000..e95b511da01
--- /dev/null
+++ b/tests/baselines/reference/bigintAmbientMinimal.errors.txt
@@ -0,0 +1,17 @@
+/main.ts(5,17): error TS2737: BigInt literals are not available when targeting lower than ES2020.
+
+
+==== /ambient.d.ts (0 errors) ====
+    declare const fromDts = 789n;
+    declare namespace Lib {
+        const value = 999n;
+    }
+    
+==== /main.ts (1 errors) ====
+    // Minimal repro from issue
+    declare const n = 123n;
+    
+    // Non-ambient for comparison
+    const regular = 456n;
+                    ~~~~
+!!! error TS2737: BigInt literals are not available when targeting lower than ES2020.
\ No newline at end of file
diff --git a/tests/baselines/reference/bigintAmbientMinimal.js b/tests/baselines/reference/bigintAmbientMinimal.js
new file mode 100644
index 00000000000..d2147fb7d30
--- /dev/null
+++ b/tests/baselines/reference/bigintAmbientMinimal.js
@@ -0,0 +1,18 @@
+//// [tests/cases/compiler/bigintAmbientMinimal.ts] ////
+
+//// [ambient.d.ts]
+declare const fromDts = 789n;
+declare namespace Lib {
+    const value = 999n;
+}
+
+//// [main.ts]
+// Minimal repro from issue
+declare const n = 123n;
+
+// Non-ambient for comparison
+const regular = 456n;
+
+//// [main.js]
+// Non-ambient for comparison
+var regular = 456n;
diff --git a/tests/baselines/reference/bigintAmbientMinimal.symbols b/tests/baselines/reference/bigintAmbientMinimal.symbols
new file mode 100644
index 00000000000..d438ba12359
--- /dev/null
+++ b/tests/baselines/reference/bigintAmbientMinimal.symbols
@@ -0,0 +1,22 @@
+//// [tests/cases/compiler/bigintAmbientMinimal.ts] ////
+
+=== /ambient.d.ts ===
+declare const fromDts = 789n;
+>fromDts : Symbol(fromDts, Decl(ambient.d.ts, 0, 13))
+
+declare namespace Lib {
+>Lib : Symbol(Lib, Decl(ambient.d.ts, 0, 29))
+
+    const value = 999n;
+>value : Symbol(value, Decl(ambient.d.ts, 2, 9))
+}
+
+=== /main.ts ===
+// Minimal repro from issue
+declare const n = 123n;
+>n : Symbol(n, Decl(main.ts, 1, 13))
+
+// Non-ambient for comparison
+const regular = 456n;
+>regular : Symbol(regular, Decl(main.ts, 4, 5))
+
diff --git a/tests/baselines/reference/bigintAmbientMinimal.types b/tests/baselines/reference/bigintAmbientMinimal.types
new file mode 100644
index 00000000000..086ac1d5676
--- /dev/null
+++ b/tests/baselines/reference/bigintAmbientMinimal.types
@@ -0,0 +1,35 @@
+//// [tests/cases/compiler/bigintAmbientMinimal.ts] ////
+
+=== /ambient.d.ts ===
+declare const fromDts = 789n;
+>fromDts : 789n
+>        : ^^^^
+>789n : 789n
+>     : ^^^^
+
+declare namespace Lib {
+>Lib : typeof Lib
+>    : ^^^^^^^^^^
+
+    const value = 999n;
+>value : 999n
+>      : ^^^^
+>999n : 999n
+>     : ^^^^
+}
+
+=== /main.ts ===
+// Minimal repro from issue
+declare const n = 123n;
+>n : 123n
+>  : ^^^^
+>123n : 123n
+>     : ^^^^
+
+// Non-ambient for comparison
+const regular = 456n;
+>regular : 456n
+>        : ^^^^
+>456n : 456n
+>     : ^^^^
+
diff --git a/tests/cases/compiler/bigintAmbientMinimal.ts b/tests/cases/compiler/bigintAmbientMinimal.ts
new file mode 100644
index 00000000000..4bad00279bc
--- /dev/null
+++ b/tests/cases/compiler/bigintAmbientMinimal.ts
@@ -0,0 +1,14 @@
+// @target: ES5
+
+// @Filename: /ambient.d.ts
+declare const fromDts = 789n;
+declare namespace Lib {
+    const value = 999n;
+}
+
+// @Filename: /main.ts
+// Minimal repro from issue
+declare const n = 123n;
+
+// Non-ambient for comparison
+const regular = 456n;
\ No newline at end of file