Preserve input key style when writing mapped type keys in declaration emit (microsoft#50781)

Author: weswigham

src/compiler/checker.ts

@@ -7735,23 +7735,23 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
 
         function getPropertyNameNodeForSymbol(symbol: Symbol, context: NodeBuilderContext) {
+            const stringNamed = !!length(symbol.declarations) && every(symbol.declarations, isStringNamed);
             const singleQuote = !!length(symbol.declarations) && every(symbol.declarations, isSingleQuotedStringNamed);
-            const fromNameType = getPropertyNameNodeForSymbolFromNameType(symbol, context, singleQuote);
+            const fromNameType = getPropertyNameNodeForSymbolFromNameType(symbol, context, singleQuote, stringNamed);
             if (fromNameType) {
                 return fromNameType;
             }
             const rawName = unescapeLeadingUnderscores(symbol.escapedName);
-            const stringNamed = !!length(symbol.declarations) && every(symbol.declarations, isStringNamed);
             return createPropertyNameNodeForIdentifierOrLiteral(rawName, getEmitScriptTarget(compilerOptions), singleQuote, stringNamed);
         }
 
         // See getNameForSymbolFromNameType for a stringy equivalent
-        function getPropertyNameNodeForSymbolFromNameType(symbol: Symbol, context: NodeBuilderContext, singleQuote?: boolean) {
+        function getPropertyNameNodeForSymbolFromNameType(symbol: Symbol, context: NodeBuilderContext, singleQuote?: boolean, stringNamed?: boolean) {
             const nameType = getSymbolLinks(symbol).nameType;
             if (nameType) {
                 if (nameType.flags & TypeFlags.StringOrNumberLiteral) {
                     const name = "" + (nameType as StringLiteralType | NumberLiteralType).value;
-                    if (!isIdentifierText(name, getEmitScriptTarget(compilerOptions)) && !isNumericLiteralName(name)) {
+                    if (!isIdentifierText(name, getEmitScriptTarget(compilerOptions)) && (stringNamed || !isNumericLiteralName(name))) {
                         return factory.createStringLiteral(name, !!singleQuote);
                     }
                     if (isNumericLiteralName(name) && startsWith(name, "-")) {

tests/baselines/reference/declarationEmitMappedTypePropertyFromNumericStringKey.js

@@ -0,0 +1,14 @@
+//// [declarationEmitMappedTypePropertyFromNumericStringKey.ts]
+export const f = (<T>(arg: {[K in keyof T]: T[K] | string}) => arg)({'0': 0}); // Original prop uses string syntax
+
+//// [declarationEmitMappedTypePropertyFromNumericStringKey.js]
+"use strict";
+exports.__esModule = true;
+exports.f = void 0;
+exports.f = (function (arg) { return arg; })({ '0': 0 }); // Original prop uses string syntax
+
+
+//// [declarationEmitMappedTypePropertyFromNumericStringKey.d.ts]
+export declare const f: {
+    '0': string | number;
+};

tests/baselines/reference/declarationEmitMappedTypePropertyFromNumericStringKey.symbols

@@ -0,0 +1,12 @@
+=== tests/cases/compiler/declarationEmitMappedTypePropertyFromNumericStringKey.ts ===
+export const f = (<T>(arg: {[K in keyof T]: T[K] | string}) => arg)({'0': 0}); // Original prop uses string syntax
+>f : Symbol(f, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 12))
+>T : Symbol(T, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 19))
+>arg : Symbol(arg, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 22))
+>K : Symbol(K, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 29))
+>T : Symbol(T, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 19))
+>T : Symbol(T, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 19))
+>K : Symbol(K, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 29))
+>arg : Symbol(arg, Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 22))
+>'0' : Symbol('0', Decl(declarationEmitMappedTypePropertyFromNumericStringKey.ts, 0, 69))
+

tests/baselines/reference/declarationEmitMappedTypePropertyFromNumericStringKey.types

@@ -0,0 +1,12 @@
+=== tests/cases/compiler/declarationEmitMappedTypePropertyFromNumericStringKey.ts ===
+export const f = (<T>(arg: {[K in keyof T]: T[K] | string}) => arg)({'0': 0}); // Original prop uses string syntax
+>f : { '0': string | number; }
+>(<T>(arg: {[K in keyof T]: T[K] | string}) => arg)({'0': 0}) : { '0': string | number; }
+>(<T>(arg: {[K in keyof T]: T[K] | string}) => arg) : <T>(arg: { [K in keyof T]: string | T[K]; }) => { [K in keyof T]: string | T[K]; }
+><T>(arg: {[K in keyof T]: T[K] | string}) => arg : <T>(arg: { [K in keyof T]: string | T[K]; }) => { [K in keyof T]: string | T[K]; }
+>arg : { [K in keyof T]: string | T[K]; }
+>arg : { [K in keyof T]: string | T[K]; }
+>{'0': 0} : { '0': number; }
+>'0' : number
+>0 : 0
+

tests/cases/compiler/declarationEmitMappedTypePropertyFromNumericStringKey.ts

@@ -0,0 +1,2 @@
+// @declaration: true
+export const f = (<T>(arg: {[K in keyof T]: T[K] | string}) => arg)({'0': 0}); // Original prop uses string syntax