fix(formatter): should treat TSMappedType as a complex type in assignment-like formatting

crates/oxc_formatter/src/utils/assignment_like.rs

@@ -994,7 +994,13 @@ fn is_complex_type_arguments(type_arguments: &TSTypeParameterInstantiation) -> b
     let is_first_argument_complex = ts_type_argument_list.first().is_some_and(|first_argument| {
         matches!(
             first_argument,
-            TSType::TSUnionType(_) | TSType::TSIntersectionType(_) | TSType::TSTypeLiteral(_)
+            TSType::TSUnionType(_)
+                | TSType::TSIntersectionType(_)
+                | TSType::TSTypeLiteral(_)
+                // TODO: This is not part of Prettier's logic, but it makes sense to consider mapped types as
+                // complex because it is the same as type literals in terms of structure.
+                // NOTE: Once the `will_break` logic is added, this will have to be revisited.
+                | TSType::TSMappedType(_)
         )
     });
 

crates/oxc_formatter/tests/fixtures/ts/assignments/complex-type-arguments.ts

@@ -0,0 +1,9 @@
+// Type argument is a `TSMappedType`
+const emitter = createGlobalEmitter<{
+  [key in Event["type"]]: Extract<Event, { type: key }>
+}>()
+
+// Type argument is a `TSTypeLiteral`
+const emitter2 = createGlobalEmitter<{
+  longlonglonglongKey: Extract<Event, { type: key }>
+}>()

crates/oxc_formatter/tests/fixtures/ts/assignments/complex-type-arguments.ts.snap

@@ -0,0 +1,42 @@
+---
+source: crates/oxc_formatter/tests/fixtures/mod.rs
+---
+==================== Input ====================
+// Type argument is a `TSMappedType`
+const emitter = createGlobalEmitter<{
+  [key in Event["type"]]: Extract<Event, { type: key }>
+}>()
+
+// Type argument is a `TSTypeLiteral`
+const emitter2 = createGlobalEmitter<{
+  longlonglonglongKey: Extract<Event, { type: key }>
+}>()
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+// Type argument is a `TSMappedType`
+const emitter = createGlobalEmitter<{
+  [key in Event["type"]]: Extract<Event, { type: key }>;
+}>();
+
+// Type argument is a `TSTypeLiteral`
+const emitter2 = createGlobalEmitter<{
+  longlonglonglongKey: Extract<Event, { type: key }>;
+}>();
+
+-------------------
+{ printWidth: 100 }
+-------------------
+// Type argument is a `TSMappedType`
+const emitter = createGlobalEmitter<{
+  [key in Event["type"]]: Extract<Event, { type: key }>;
+}>();
+
+// Type argument is a `TSTypeLiteral`
+const emitter2 = createGlobalEmitter<{
+  longlonglonglongKey: Extract<Event, { type: key }>;
+}>();
+
+===================== End =====================