Propagate errorType in getConditionalType

src/compiler/checker.ts

@@ -17773,20 +17773,22 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         while (true) {
             if (tailCount === 1000) {
                 error(currentNode, Diagnostics.Type_instantiation_is_excessively_deep_and_possibly_infinite);
-                result = errorType;
-                break;
+                return errorType;
+            }
+            const checkType = instantiateType(getActualTypeVariable(root.checkType), mapper);
+            const extendsType = instantiateType(root.extendsType, mapper);
+            if (checkType === errorType || extendsType === errorType) {
+                return errorType;
+            }
+            if (checkType === wildcardType || extendsType === wildcardType) {
+                return wildcardType;
             }
             // When the check and extends types are simple tuple types of the same arity, we defer resolution of the
             // conditional type when any tuple elements are generic. This is such that non-distributable conditional
             // types can be written `[X] extends [Y] ? ...` and be deferred similarly to `X extends Y ? ...`.
             const checkTuples = isSimpleTupleType(root.node.checkType) && isSimpleTupleType(root.node.extendsType) &&
                 length((root.node.checkType as TupleTypeNode).elements) === length((root.node.extendsType as TupleTypeNode).elements);
-            const checkType = instantiateType(getActualTypeVariable(root.checkType), mapper);
             const checkTypeDeferred = isDeferredType(checkType, checkTuples);
-            const extendsType = instantiateType(root.extendsType, mapper);
-            if (checkType === wildcardType || extendsType === wildcardType) {
-                return wildcardType;
-            }
             let combinedMapper: TypeMapper | undefined;
             if (root.inferTypeParameters) {
                 // When we're looking at making an inference for an infer type, when we get its constraint, it'll automagically be

tests/baselines/reference/excessivelyLargeTupleSpread.errors.txt

@@ -1,19 +1,16 @@
-tests/cases/compiler/excessivelyLargeTupleSpread.ts(6,10): error TS2589: Type instantiation is excessively deep and possibly infinite.
 tests/cases/compiler/excessivelyLargeTupleSpread.ts(6,10): error TS2799: Type produces a tuple type that is too large to represent.
 tests/cases/compiler/excessivelyLargeTupleSpread.ts(22,12): error TS2799: Type produces a tuple type that is too large to represent.
 tests/cases/compiler/excessivelyLargeTupleSpread.ts(38,13): error TS2800: Expression produces a tuple type that is too large to represent.
 
 
-==== tests/cases/compiler/excessivelyLargeTupleSpread.ts (4 errors) ====
+==== tests/cases/compiler/excessivelyLargeTupleSpread.ts (3 errors) ====
     // #41771
 
     type BuildTuple<L extends number, T extends any[] = [any]> = 
         T['length'] extends L ? T : BuildTuple<L, [...T, ...T]>;
 
     type A = BuildTuple<3>
              ~~~~~~~~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
-             ~~~~~~~~~~~~~
 !!! error TS2799: Type produces a tuple type that is too large to represent.
 
     type T0 = [any];

tests/baselines/reference/recursiveConditionalCrash4.errors.txt

@@ -0,0 +1,42 @@
+tests/cases/compiler/recursiveConditionalCrash4.ts(7,16): error TS2503: Cannot find namespace 'StrIter'.
+tests/cases/compiler/recursiveConditionalCrash4.ts(8,5): error TS2503: Cannot find namespace 'StrIter'.
+tests/cases/compiler/recursiveConditionalCrash4.ts(9,25): error TS2304: Cannot find name 'Add'.
+tests/cases/compiler/recursiveConditionalCrash4.ts(9,37): error TS2503: Cannot find namespace 'StrIter'.
+tests/cases/compiler/recursiveConditionalCrash4.ts(10,7): error TS2589: Type instantiation is excessively deep and possibly infinite.
+tests/cases/compiler/recursiveConditionalCrash4.ts(10,31): error TS2503: Cannot find namespace 'StrIter'.
+tests/cases/compiler/recursiveConditionalCrash4.ts(16,7): error TS2589: Type instantiation is excessively deep and possibly infinite.
+
+
+==== tests/cases/compiler/recursiveConditionalCrash4.ts (7 errors) ====
+    // Repros from #53783
+
+    type LengthDown<
+      Str extends string,
+      Length extends number | bigint,
+      It
+    > = It extends StrIter.Iterator
+                   ~~~~~~~
+!!! error TS2503: Cannot find namespace 'StrIter'.
+      ? StrIter.CutAt<Str, It> extends `${infer $Rest}`
+        ~~~~~~~
+!!! error TS2503: Cannot find namespace 'StrIter'.
+        ? LengthDown<$Rest, Add<Length, StrIter.Value<It>>, It>
+                            ~~~
+!!! error TS2304: Cannot find name 'Add'.
+                                        ~~~~~~~
+!!! error TS2503: Cannot find namespace 'StrIter'.
+        : LengthDown<Str, Length, StrIter.Prev<It>>
+          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
+                                  ~~~~~~~
+!!! error TS2503: Cannot find namespace 'StrIter'.
+      : Length;
+
+    type Foo<T> = T extends unknown
+      ? unknown extends `${infer $Rest}`
+        ? Foo<T>
+        : Foo<unknown>
+          ~~~~~~~~~~~~
+!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
+      : unknown;
+

tests/baselines/reference/recursiveConditionalCrash4.symbols

@@ -0,0 +1,65 @@
+=== tests/cases/compiler/recursiveConditionalCrash4.ts ===
+// Repros from #53783
+
+type LengthDown<
+>LengthDown : Symbol(LengthDown, Decl(recursiveConditionalCrash4.ts, 0, 0))
+
+  Str extends string,
+>Str : Symbol(Str, Decl(recursiveConditionalCrash4.ts, 2, 16))
+
+  Length extends number | bigint,
+>Length : Symbol(Length, Decl(recursiveConditionalCrash4.ts, 3, 21))
+
+  It
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+
+> = It extends StrIter.Iterator
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+>StrIter : Symbol(StrIter)
+>Iterator : Symbol(StrIter.Iterator)
+
+  ? StrIter.CutAt<Str, It> extends `${infer $Rest}`
+>StrIter : Symbol(StrIter)
+>CutAt : Symbol(StrIter.CutAt)
+>Str : Symbol(Str, Decl(recursiveConditionalCrash4.ts, 2, 16))
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+>$Rest : Symbol($Rest, Decl(recursiveConditionalCrash4.ts, 7, 43))
+
+    ? LengthDown<$Rest, Add<Length, StrIter.Value<It>>, It>
+>LengthDown : Symbol(LengthDown, Decl(recursiveConditionalCrash4.ts, 0, 0))
+>$Rest : Symbol($Rest, Decl(recursiveConditionalCrash4.ts, 7, 43))
+>Add : Symbol(Add)
+>Length : Symbol(Length, Decl(recursiveConditionalCrash4.ts, 3, 21))
+>StrIter : Symbol(StrIter)
+>Value : Symbol(StrIter.Value)
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+
+    : LengthDown<Str, Length, StrIter.Prev<It>>
+>LengthDown : Symbol(LengthDown, Decl(recursiveConditionalCrash4.ts, 0, 0))
+>Str : Symbol(Str, Decl(recursiveConditionalCrash4.ts, 2, 16))
+>Length : Symbol(Length, Decl(recursiveConditionalCrash4.ts, 3, 21))
+>StrIter : Symbol(StrIter)
+>Prev : Symbol(StrIter.Prev)
+>It : Symbol(It, Decl(recursiveConditionalCrash4.ts, 4, 33))
+
+  : Length;
+>Length : Symbol(Length, Decl(recursiveConditionalCrash4.ts, 3, 21))
+
+type Foo<T> = T extends unknown
+>Foo : Symbol(Foo, Decl(recursiveConditionalCrash4.ts, 10, 11))
+>T : Symbol(T, Decl(recursiveConditionalCrash4.ts, 12, 9))
+>T : Symbol(T, Decl(recursiveConditionalCrash4.ts, 12, 9))
+
+  ? unknown extends `${infer $Rest}`
+>$Rest : Symbol($Rest, Decl(recursiveConditionalCrash4.ts, 13, 28))
+
+    ? Foo<T>
+>Foo : Symbol(Foo, Decl(recursiveConditionalCrash4.ts, 10, 11))
+>T : Symbol(T, Decl(recursiveConditionalCrash4.ts, 12, 9))
+
+    : Foo<unknown>
+>Foo : Symbol(Foo, Decl(recursiveConditionalCrash4.ts, 10, 11))
+
+  : unknown;
+

tests/baselines/reference/recursiveConditionalCrash4.types

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/recursiveConditionalCrash4.ts ===
+// Repros from #53783
+
+type LengthDown<
+>LengthDown : LengthDown<Str, Length, It>
+
+  Str extends string,
+  Length extends number | bigint,
+  It
+> = It extends StrIter.Iterator
+>StrIter : any
+
+  ? StrIter.CutAt<Str, It> extends `${infer $Rest}`
+>StrIter : any
+
+    ? LengthDown<$Rest, Add<Length, StrIter.Value<It>>, It>
+>StrIter : any
+
+    : LengthDown<Str, Length, StrIter.Prev<It>>
+>StrIter : any
+
+  : Length;
+
+type Foo<T> = T extends unknown
+>Foo : Foo<T>
+
+  ? unknown extends `${infer $Rest}`
+    ? Foo<T>
+    : Foo<unknown>
+  : unknown;
+

tests/cases/compiler/recursiveConditionalCrash4.ts

@@ -0,0 +1,20 @@
+// @strict: true
+// @noEmit: true
+
+// Repros from #53783
+
+type LengthDown<
+  Str extends string,
+  Length extends number | bigint,
+  It
+> = It extends StrIter.Iterator
+  ? StrIter.CutAt<Str, It> extends `${infer $Rest}`
+    ? LengthDown<$Rest, Add<Length, StrIter.Value<It>>, It>
+    : LengthDown<Str, Length, StrIter.Prev<It>>
+  : Length;
+
+type Foo<T> = T extends unknown
+  ? unknown extends `${infer $Rest}`
+    ? Foo<T>
+    : Foo<unknown>
+  : unknown;