🤖 Pick PR #59232 (Fixed regression in reverse mapped ...) into release-5.5 (#59258)

Co-authored-by: Mateusz Burzyński <[email protected]>

Author: TypeScript Bot

src/compiler/checker.ts

@@ -2193,6 +2193,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     /** Key is "/path/to/a.ts|/path/to/b.ts". */
     var amalgamatedDuplicates: Map<string, DuplicateInfoForFiles> | undefined;
     var reverseMappedCache = new Map<string, Type | undefined>();
+    var reverseHomomorphicMappedCache = new Map<string, Type | undefined>();
     var ambientModulesCache: Symbol[] | undefined;
     /**
      * List of every ambient module with a "*" wildcard.
@@ -7003,20 +7004,38 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
 
         function shouldUsePlaceholderForProperty(propertySymbol: Symbol, context: NodeBuilderContext) {
-            // Use placeholders for reverse mapped types we've either already descended into, or which
-            // are nested reverse mappings within a mapping over a non-anonymous type. The later is a restriction mostly just to
+            // Use placeholders for reverse mapped types we've either
+            // (1) already descended into, or
+            // (2) are nested reverse mappings within a mapping over a non-anonymous type, or
+            // (3) are deeply nested properties that originate from the same mapped type.
+            // Condition (2) is a restriction mostly just to
             // reduce the blowup in printback size from doing, eg, a deep reverse mapping over `Window`.
             // Since anonymous types usually come from expressions, this allows us to preserve the output
             // for deep mappings which likely come from expressions, while truncating those parts which
             // come from mappings over library functions.
+            // Condition (3) limits printing of possibly infinitely deep reverse mapped types.
+            const depth = 3;
             return !!(getCheckFlags(propertySymbol) & CheckFlags.ReverseMapped)
                 && (
                     contains(context.reverseMappedStack, propertySymbol as ReverseMappedSymbol)
                     || (
                         context.reverseMappedStack?.[0]
                         && !(getObjectFlags(last(context.reverseMappedStack).links.propertyType) & ObjectFlags.Anonymous)
                     )
+                    || isDeeplyNestedReverseMappedTypeProperty()
                 );
+            function isDeeplyNestedReverseMappedTypeProperty() {
+                if ((context.reverseMappedStack?.length ?? 0) < depth) {
+                    return false;
+                }
+                for (let i = 0; i < depth; i++) {
+                    const prop = context.reverseMappedStack![context.reverseMappedStack!.length - 1 - i];
+                    if (prop.links.mappedType.symbol !== (propertySymbol as ReverseMappedSymbol).links.mappedType.symbol) {
+                        return false;
+                    }
+                }
+                return true;
+            }
         }
 
         function addPropertyToElementList(propertySymbol: Symbol, context: NodeBuilderContext, typeElements: TypeElement[]) {
@@ -25604,11 +25623,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
      */
     function inferTypeForHomomorphicMappedType(source: Type, target: MappedType, constraint: IndexType): Type | undefined {
         const cacheKey = source.id + "," + target.id + "," + constraint.id;
-        if (reverseMappedCache.has(cacheKey)) {
-            return reverseMappedCache.get(cacheKey);
+        if (reverseHomomorphicMappedCache.has(cacheKey)) {
+            return reverseHomomorphicMappedCache.get(cacheKey);
         }
         const type = createReverseMappedType(source, target, constraint);
-        reverseMappedCache.set(cacheKey, type);
+        reverseHomomorphicMappedCache.set(cacheKey, type);
         return type;
     }