Improve computed base constraint for Index type on generic IndexedAccess

src/compiler/checker.ts

@@ -13765,6 +13765,21 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     undefined;
             }
             if (t.flags & TypeFlags.Index) {
+                if ((t as IndexType).type.flags & TypeFlags.IndexedAccess) {
+                    const indexedAccess = (t as IndexType).type as IndexedAccessType;
+                    // generic objects can always be instantiated with more keys so we can't narrow down those cases
+                    if (!isGenericObjectType(indexedAccess.objectType)) {
+                        const baseIndexType = getBaseConstraint(indexedAccess.indexType);
+                        const indexedAccessType = baseIndexType && getIndexedAccessTypeOrUndefined(indexedAccess.objectType, baseIndexType);
+                        const mappedIndexTypeOfIndexedAccess = indexedAccessType && mapType(indexedAccessType, getIndexType);
+                        const narrowed = mappedIndexTypeOfIndexedAccess && filterType(keyofConstraintType, t => {
+                            return !(getIntersectionType([t, mappedIndexTypeOfIndexedAccess]).flags & TypeFlags.Never);
+                        });
+                        if (narrowed) {
+                            return narrowed;
+                        }
+                    }
+                }
                 return keyofConstraintType;
             }
             if (t.flags & TypeFlags.TemplateLiteral) {

tests/baselines/reference/keyofAndGenericIndexedAccessNarrowableConstraint.errors.txt

@@ -0,0 +1,33 @@
+keyofAndGenericIndexedAccessNarrowableConstraint.ts(15,15): error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+keyofAndGenericIndexedAccessNarrowableConstraint.ts(15,20): error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+keyofAndGenericIndexedAccessNarrowableConstraint.ts(19,16): error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+
+
+==== keyofAndGenericIndexedAccessNarrowableConstraint.ts (3 errors) ====
+    export type Context = {
+        V1: { a: string },
+        V2: { b: string },
+    }
+
+    export function path<V extends keyof Context, K extends keyof Context[V]>(v: V, k: K)  {
+        return `${v}.${k}` // ok
+    }
+
+    export function path2<K extends keyof Context[keyof Context]>(k: K)  {
+        return `.${k}` // ok
+    }
+
+    export function path3<O extends Context, V extends keyof O, K extends keyof O[V]>(v: V, k: K)  {
+        return `${v}.${k}` // error
+                  ~
+!!! error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+                       ~
+!!! error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+    }
+
+    export function path4<O extends Context[keyof Context], K extends keyof O>(k: K)  {
+        return `.${k}` // error
+                   ~
+!!! error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.
+    }
+

tests/baselines/reference/keyofAndGenericIndexedAccessNarrowableConstraint.symbols

@@ -0,0 +1,77 @@
+//// [tests/cases/conformance/types/keyof/keyofAndGenericIndexedAccessNarrowableConstraint.ts] ////
+
+=== keyofAndGenericIndexedAccessNarrowableConstraint.ts ===
+export type Context = {
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+
+    V1: { a: string },
+>V1 : Symbol(V1, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 23))
+>a : Symbol(a, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 1, 9))
+
+    V2: { b: string },
+>V2 : Symbol(V2, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 1, 22))
+>b : Symbol(b, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 2, 9))
+}
+
+export function path<V extends keyof Context, K extends keyof Context[V]>(v: V, k: K)  {
+>path : Symbol(path, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 3, 1))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 21))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 45))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 21))
+>v : Symbol(v, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 74))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 21))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 79))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 45))
+
+    return `${v}.${k}` // ok
+>v : Symbol(v, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 74))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 5, 79))
+}
+
+export function path2<K extends keyof Context[keyof Context]>(k: K)  {
+>path2 : Symbol(path2, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 7, 1))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 9, 22))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 9, 62))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 9, 22))
+
+    return `.${k}` // ok
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 9, 62))
+}
+
+export function path3<O extends Context, V extends keyof O, K extends keyof O[V]>(v: V, k: K)  {
+>path3 : Symbol(path3, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 11, 1))
+>O : Symbol(O, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 22))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 40))
+>O : Symbol(O, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 22))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 59))
+>O : Symbol(O, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 22))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 40))
+>v : Symbol(v, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 82))
+>V : Symbol(V, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 40))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 87))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 59))
+
+    return `${v}.${k}` // error
+>v : Symbol(v, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 82))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 13, 87))
+}
+
+export function path4<O extends Context[keyof Context], K extends keyof O>(k: K)  {
+>path4 : Symbol(path4, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 15, 1))
+>O : Symbol(O, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 22))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>Context : Symbol(Context, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 0, 0))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 55))
+>O : Symbol(O, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 22))
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 75))
+>K : Symbol(K, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 55))
+
+    return `.${k}` // error
+>k : Symbol(k, Decl(keyofAndGenericIndexedAccessNarrowableConstraint.ts, 17, 75))
+}
+

tests/baselines/reference/keyofAndGenericIndexedAccessNarrowableConstraint.types

@@ -0,0 +1,55 @@
+//// [tests/cases/conformance/types/keyof/keyofAndGenericIndexedAccessNarrowableConstraint.ts] ////
+
+=== keyofAndGenericIndexedAccessNarrowableConstraint.ts ===
+export type Context = {
+>Context : { V1: {    a: string;}; V2: {    b: string;}; }
+
+    V1: { a: string },
+>V1 : { a: string; }
+>a : string
+
+    V2: { b: string },
+>V2 : { b: string; }
+>b : string
+}
+
+export function path<V extends keyof Context, K extends keyof Context[V]>(v: V, k: K)  {
+>path : <V extends keyof Context, K extends keyof Context[V]>(v: V, k: K) => string
+>v : V
+>k : K
+
+    return `${v}.${k}` // ok
+>`${v}.${k}` : string
+>v : V
+>k : K
+}
+
+export function path2<K extends keyof Context[keyof Context]>(k: K)  {
+>path2 : <K extends never>(k: K) => string
+>k : K
+
+    return `.${k}` // ok
+>`.${k}` : string
+>k : K
+}
+
+export function path3<O extends Context, V extends keyof O, K extends keyof O[V]>(v: V, k: K)  {
+>path3 : <O extends Context, V extends keyof O, K extends keyof O[V]>(v: V, k: K) => string
+>v : V
+>k : K
+
+    return `${v}.${k}` // error
+>`${v}.${k}` : string
+>v : V
+>k : K
+}
+
+export function path4<O extends Context[keyof Context], K extends keyof O>(k: K)  {
+>path4 : <O extends { a: string; } | { b: string; }, K extends keyof O>(k: K) => string
+>k : K
+
+    return `.${k}` // error
+>`.${k}` : string
+>k : K
+}
+

tests/cases/conformance/types/keyof/keyofAndGenericIndexedAccessNarrowableConstraint.ts

@@ -0,0 +1,23 @@
+// @noEmit: true
+// @strict: true
+
+export type Context = {
+    V1: { a: string },
+    V2: { b: string },
+}
+
+export function path<V extends keyof Context, K extends keyof Context[V]>(v: V, k: K)  {
+    return `${v}.${k}` // ok
+}
+
+export function path2<K extends keyof Context[keyof Context]>(k: K)  {
+    return `.${k}` // ok
+}
+
+export function path3<O extends Context, V extends keyof O, K extends keyof O[V]>(v: V, k: K)  {
+    return `${v}.${k}` // error
+}
+
+export function path4<O extends Context[keyof Context], K extends keyof O>(k: K)  {
+    return `.${k}` // error
+}