Fixed string completions from generic conditional types that match typed argument against template literal type

Author: Andarist

src/services/stringCompletions.ts

@@ -485,7 +485,7 @@ function getStringLiteralCompletionsFromSignature(call: CallLikeExpression, arg:
             }
         }
         isNewIdentifier = isNewIdentifier || !!(type.flags & TypeFlags.String);
-        return getStringLiteralTypes(type, uniques);
+        return getStringLiteralTypes(type, uniques, arg.text);
     });
     return length(types) ? { kind: StringLiteralCompletionKind.Types, types, isNewIdentifier } : undefined;
 }
@@ -517,11 +517,11 @@ function stringLiteralCompletionsForObjectLiteral(checker: TypeChecker, objectLi
     };
 }
 
-function getStringLiteralTypes(type: Type | undefined, uniques = new Map<string, true>()): readonly StringLiteralType[] {
+function getStringLiteralTypes(type: Type | undefined, uniques = new Map<string, true>(), alreadyTyped = ""): readonly StringLiteralType[] {
     if (!type) return emptyArray;
     type = skipConstraint(type);
-    return type.isUnion() ? flatMap(type.types, t => getStringLiteralTypes(t, uniques)) :
-        type.isStringLiteral() && !(type.flags & TypeFlags.EnumLiteral) && addToSeen(uniques, type.value) ? [type] : emptyArray;
+    return type.isUnion() ? flatMap(type.types, t => getStringLiteralTypes(t, uniques, alreadyTyped)) :
+        type.isStringLiteral() && !(type.flags & TypeFlags.EnumLiteral) && type.value.startsWith(alreadyTyped) && addToSeen(uniques, type.value) ? [type] : emptyArray;
 }
 
 interface NameAndKind {

tests/cases/fourslash/stringCompletionsFromGenericConditionalTypesUsingTemplateLiteralTypes.ts

@@ -0,0 +1,13 @@
+/// <reference path="fourslash.ts" />
+
+// @Filename: /a.tsx
+//// type PathOf<T, K extends string, P extends string = ""> =
+////   K extends `${infer U}.${infer V}`
+////     ? U extends keyof T ? PathOf<T[U], V, `${P}${U}.`> : `${P}${keyof T & (string | number)}`
+////     : K extends keyof T ? `${P}${K}` : `${P}${keyof T & (string | number)}`;
+////
+//// declare function consumer<K extends string>(path: PathOf<{a: string, b: {c: string}}, K>) : number;
+////
+//// consumer('b./*ts*/')
+
+verify.completions({ marker: ["ts"], exact: ["b.c"] });