Merge pull request #12301 from Microsoft/recursiveMappedTypes

Fix recursive mapped types

src/compiler/checker.ts

@@ -4489,6 +4489,8 @@ namespace ts {
             const members: SymbolTable = createMap<Symbol>();
             let stringIndexInfo: IndexInfo;
             let numberIndexInfo: IndexInfo;
+            // Resolve upfront such that recursive references see an empty object type.
+            setStructuredTypeMembers(type, emptySymbols, emptyArray, emptyArray, undefined, undefined);
             // In { [P in K]: T }, we refer to P as the type parameter type, K as the constraint type,
             // and T as the template type.
             const typeParameter = getTypeParameterFromMappedType(type);

tests/baselines/reference/recursiveMappedTypes.js

@@ -0,0 +1,30 @@
+//// [recursiveMappedTypes.ts]
+
+// Recursive mapped types simply appear empty
+
+type Recurse = {
+    [K in keyof Recurse]: Recurse[K]
+}
+
+type Recurse1 = {
+    [K in keyof Recurse2]: Recurse2[K]
+}
+
+type Recurse2 = {
+    [K in keyof Recurse1]: Recurse1[K]
+}
+
+//// [recursiveMappedTypes.js]
+// Recursive mapped types simply appear empty
+
+
+//// [recursiveMappedTypes.d.ts]
+declare type Recurse = {
+    [K in keyof Recurse]: Recurse[K];
+};
+declare type Recurse1 = {
+    [K in keyof Recurse2]: Recurse2[K];
+};
+declare type Recurse2 = {
+    [K in keyof Recurse1]: Recurse1[K];
+};

tests/baselines/reference/recursiveMappedTypes.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/conformance/types/mapped/recursiveMappedTypes.ts ===
+
+// Recursive mapped types simply appear empty
+
+type Recurse = {
+>Recurse : Symbol(Recurse, Decl(recursiveMappedTypes.ts, 0, 0))
+
+    [K in keyof Recurse]: Recurse[K]
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 4, 5))
+>Recurse : Symbol(Recurse, Decl(recursiveMappedTypes.ts, 0, 0))
+>Recurse : Symbol(Recurse, Decl(recursiveMappedTypes.ts, 0, 0))
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 4, 5))
+}
+
+type Recurse1 = {
+>Recurse1 : Symbol(Recurse1, Decl(recursiveMappedTypes.ts, 5, 1))
+
+    [K in keyof Recurse2]: Recurse2[K]
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 8, 5))
+>Recurse2 : Symbol(Recurse2, Decl(recursiveMappedTypes.ts, 9, 1))
+>Recurse2 : Symbol(Recurse2, Decl(recursiveMappedTypes.ts, 9, 1))
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 8, 5))
+}
+
+type Recurse2 = {
+>Recurse2 : Symbol(Recurse2, Decl(recursiveMappedTypes.ts, 9, 1))
+
+    [K in keyof Recurse1]: Recurse1[K]
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 12, 5))
+>Recurse1 : Symbol(Recurse1, Decl(recursiveMappedTypes.ts, 5, 1))
+>Recurse1 : Symbol(Recurse1, Decl(recursiveMappedTypes.ts, 5, 1))
+>K : Symbol(K, Decl(recursiveMappedTypes.ts, 12, 5))
+}

tests/baselines/reference/recursiveMappedTypes.types

@@ -0,0 +1,33 @@
+=== tests/cases/conformance/types/mapped/recursiveMappedTypes.ts ===
+
+// Recursive mapped types simply appear empty
+
+type Recurse = {
+>Recurse : Recurse
+
+    [K in keyof Recurse]: Recurse[K]
+>K : K
+>Recurse : Recurse
+>Recurse : Recurse
+>K : K
+}
+
+type Recurse1 = {
+>Recurse1 : Recurse1
+
+    [K in keyof Recurse2]: Recurse2[K]
+>K : K
+>Recurse2 : Recurse2
+>Recurse2 : Recurse2
+>K : K
+}
+
+type Recurse2 = {
+>Recurse2 : Recurse2
+
+    [K in keyof Recurse1]: Recurse1[K]
+>K : K
+>Recurse1 : Recurse1
+>Recurse1 : Recurse1
+>K : K
+}

tests/cases/conformance/types/mapped/recursiveMappedTypes.ts

@@ -0,0 +1,15 @@
+// @declaration: true
+
+// Recursive mapped types simply appear empty
+
+type Recurse = {
+    [K in keyof Recurse]: Recurse[K]
+}
+
+type Recurse1 = {
+    [K in keyof Recurse2]: Recurse2[K]
+}
+
+type Recurse2 = {
+    [K in keyof Recurse1]: Recurse1[K]
+}