microsoft · rbuckton · Dec 15, 2022 · Dec 13, 2022 · rbuckton · Dec 14, 2022
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
@@ -5735,19 +5735,20 @@ export interface Symbol {
     members?: SymbolTable;                  // Class, interface or object literal instance members
     exports?: SymbolTable;                  // Module exports
     globalExports?: SymbolTable;            // Conditional global UMD exports
-    /** @internal */ id?: SymbolId;          // Unique id (used to look up SymbolLinks)
-    /** @internal */ mergeId?: number;       // Merge id (used to look up merged symbol)
-    /** @internal */ parent?: Symbol;        // Parent symbol
-    /** @internal */ exportSymbol?: Symbol;  // Exported symbol associated with this symbol
-    /** @internal */ constEnumOnlyModule?: boolean; // True if module contains only const enums or other modules with only const enums
+    /** @internal */ id: SymbolId;          // Unique id (used to look up SymbolLinks)
+    /** @internal */ mergeId: number;       // Merge id (used to look up merged symbol)
+    /** @internal */ parent?: Symbol;       // Parent symbol
+    /** @internal */ exportSymbol?: Symbol; // Exported symbol associated with this symbol
+    /** @internal */ constEnumOnlyModule: boolean | undefined; // True if module contains only const enums or other modules with only const enums
     /** @internal */ isReferenced?: SymbolFlags; // True if the symbol is referenced elsewhere. Keeps track of the meaning of a reference in case a symbol is both a type parameter and parameter.
     /** @internal */ isReplaceableByMethod?: boolean; // Can this Javascript class property be replaced by a method symbol?
-    /** @internal */ isAssigned?: boolean;   // True if the symbol is a parameter with assignments
+    /** @internal */ isAssigned?: boolean;  // True if the symbol is a parameter with assignments
     /** @internal */ assignmentDeclarationMembers?: Map<number, Declaration>; // detected late-bound assignment declarations associated with the symbol
 }
 
 /** @internal */
 export interface SymbolLinks {
+    _symbolLinksBrand: any;
     immediateTarget?: Symbol;                   // Immediate target of an alias. May be another alias. Do not access directly, use `checker.getImmediateAliasedSymbol` instead.
     aliasTarget?: Symbol,                       // Resolved (non-alias) target of an alias
     target?: Symbol;                            // Original version of an instantiated symbol
@@ -5758,7 +5759,7 @@ export interface SymbolLinks {
     declaredType?: Type;                        // Type of class, interface, enum, type alias, or type parameter
     typeParameters?: TypeParameter[];           // Type parameters of type alias (undefined if non-generic)
     outerTypeParameters?: TypeParameter[];      // Outer type parameters of anonymous object type
-    instantiations?: Map<string, Type>;       // Instantiations of generic type alias (undefined if non-generic)
+    instantiations?: Map<string, Type>;         // Instantiations of generic type alias (undefined if non-generic)
     aliasSymbol?: Symbol;                       // Alias associated with generic type alias instantiation
     aliasTypeArguments?: readonly Type[]        // Alias type arguments (if any)
     inferredClassSymbol?: Map<SymbolId, TransientSymbol>; // Symbol of an inferred ES5 constructor function
@@ -5831,23 +5832,38 @@ export const enum CheckFlags {
 }
 
 /** @internal */
-export interface TransientSymbol extends Symbol, SymbolLinks {
+export interface TransientSymbolLinks extends SymbolLinks {
     checkFlags: CheckFlags;
 }
 
 /** @internal */
-export interface MappedSymbol extends TransientSymbol {
+export interface TransientSymbol extends Symbol {
+    links: TransientSymbolLinks;
+}
+
+/** @internal */
+export interface MappedSymbolLinks extends TransientSymbolLinks {
     mappedType: MappedType;
     keyType: Type;
 }
 
 /** @internal */
-export interface ReverseMappedSymbol extends TransientSymbol {
+export interface MappedSymbol extends TransientSymbol {
+    links: MappedSymbolLinks;
+}
+
+/** @internal */
+export interface ReverseMappedSymbolLinks extends TransientSymbolLinks {
     propertyType: Type;
     mappedType: MappedType;
     constraintType: IndexType;
 }
 
+/** @internal */
+export interface ReverseMappedSymbol extends TransientSymbol {
+    links: ReverseMappedSymbolLinks;
+}
+
 export const enum InternalSymbolName {
     Call = "__call", // Call signatures
     Constructor = "__constructor", // Constructor implementations

diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
@@ -6821,7 +6821,7 @@ export function closeFileWatcher(watcher: FileWatcher) {
 
 /** @internal */
 export function getCheckFlags(symbol: Symbol): CheckFlags {
-    return symbol.flags & SymbolFlags.Transient ? (symbol as TransientSymbol).checkFlags : 0;
+    return symbol.flags & SymbolFlags.Transient ? (symbol as TransientSymbol).links.checkFlags : 0;
 }
 
 /** @internal */
@@ -6833,7 +6833,8 @@ export function getDeclarationModifierFlagsFromSymbol(s: Symbol, isWrite = false
         return s.parent && s.parent.flags & SymbolFlags.Class ? flags : flags & ~ModifierFlags.AccessibilityModifier;
     }
     if (getCheckFlags(s) & CheckFlags.Synthetic) {
-        const checkFlags = (s as TransientSymbol).checkFlags;
+        // NOTE: potentially unchecked cast to TransientSymbol
+        const checkFlags = (s as TransientSymbol).links.checkFlags;
         const accessModifier = checkFlags & CheckFlags.ContainsPrivate ? ModifierFlags.Private :
             checkFlags & CheckFlags.ContainsPublic ? ModifierFlags.Public :
             ModifierFlags.Protected;
@@ -7262,9 +7263,16 @@ function Symbol(this: Symbol, flags: SymbolFlags, name: __String) {
     this.escapedName = name;
     this.declarations = undefined;
     this.valueDeclaration = undefined;
-    this.id = undefined;
-    this.mergeId = undefined;
+    this.id = 0;
+    this.mergeId = 0;
     this.parent = undefined;
+    this.members = undefined;
+    this.exports = undefined;
+    this.exportSymbol = undefined;
+    this.constEnumOnlyModule = undefined;
+    this.isReferenced = undefined;
+    this.isAssigned = undefined;
+    (this as any).links = undefined; // used by TransientSymbol
 }
 
 function Type(this: Type, checker: TypeChecker, flags: TypeFlags) {

diff --git a/src/services/codefixes/fixInvalidImportSyntax.ts b/src/services/codefixes/fixInvalidImportSyntax.ts
@@ -15,6 +15,7 @@ import {
     isExpression,
     isImportCall,
     isNamedDeclaration,
+    isTransientSymbol,
     makeImport,
     ModuleKind,
     NamespaceImport,
@@ -23,7 +24,6 @@ import {
     SourceFile,
     SyntaxKind,
     textChanges,
-    TransientSymbol,
 } from "../_namespaces/ts";
 import {
     createCodeFixActionWithoutFixAll,
@@ -107,11 +107,11 @@ function getActionsForInvalidImportLocation(context: CodeFixContext): CodeFixAct
 
 function getImportCodeFixesForExpression(context: CodeFixContext, expr: Node): CodeFixAction[] | undefined {
     const type = context.program.getTypeChecker().getTypeAtLocation(expr);
-    if (!(type.symbol && (type.symbol as TransientSymbol).originatingImport)) {
+    if (!(type.symbol && isTransientSymbol(type.symbol) && type.symbol.links.originatingImport)) {
         return [];
     }
     const fixes: CodeFixAction[] = [];
-    const relatedImport = (type.symbol as TransientSymbol).originatingImport!; // TODO: GH#18217
+    const relatedImport = type.symbol.links.originatingImport;
     if (!isImportCall(relatedImport)) {
         addRange(fixes, getCodeFixesForImportDeclaration(context, relatedImport));
     }

diff --git a/src/services/codefixes/inferFromUsage.ts b/src/services/codefixes/inferFromUsage.ts
@@ -53,6 +53,7 @@ import {
     isRestParameter,
     isRightSideOfQualifiedNameOrPropertyAccess,
     isSetAccessorDeclaration,
+    isTransientSymbol,
     isVariableDeclaration,
     isVariableStatement,
     LanguageServiceHost,
@@ -88,7 +89,6 @@ import {
     SourceFile,
     Symbol,
     SymbolFlags,
-    SymbolLinks,
     SyntaxKind,
     textChanges,
     Token,
@@ -1045,7 +1045,7 @@ function inferTypeFromReferences(program: Program, references: readonly Identifi
         const members = mapEntries(props, (name, types) => {
             const isOptional = types.length < anons.length ? SymbolFlags.Optional : 0;
             const s = checker.createSymbol(SymbolFlags.Property | isOptional, name as __String);
-            s.type = checker.getUnionType(types);
+            s.links.type = checker.getUnionType(types);
             return [name, s];
         });
         const indexInfos = [];
@@ -1080,7 +1080,7 @@ function inferTypeFromReferences(program: Program, references: readonly Identifi
 
         const candidateTypes = (usage.candidateTypes || []).map(t => checker.getBaseTypeOfLiteralType(t));
         const callsType = usage.calls?.length ? inferStructuralType(usage) : undefined;
-        if (callsType && candidateTypes) {
+        if (callsType && candidateTypes) { // TODO: should this be `some(candidateTypes)`?
             types.push(checker.getUnionType([callsType, ...candidateTypes], UnionReduction.Subtype));
         }
         else {
@@ -1101,7 +1101,7 @@ function inferTypeFromReferences(program: Program, references: readonly Identifi
         if (usage.properties) {
             usage.properties.forEach((u, name) => {
                 const symbol = checker.createSymbol(SymbolFlags.Property, name);
-                symbol.type = combineFromUsage(u);
+                symbol.links.type = combineFromUsage(u);
                 members.set(name, symbol);
             });
         }
@@ -1202,7 +1202,7 @@ function inferTypeFromReferences(program: Program, references: readonly Identifi
             if (elementType) {
                 genericParamType = elementType;
             }
-            const targetType = (usageParam as SymbolLinks).type
+            const targetType = tryCast(usageParam, isTransientSymbol)?.links.type
                 || (usageParam.valueDeclaration ? checker.getTypeOfSymbolAtLocation(usageParam, usageParam.valueDeclaration) : checker.getAnyType());
             types.push(...inferTypeParameters(genericParamType, targetType, typeParameter));
         }
@@ -1221,7 +1221,7 @@ function inferTypeFromReferences(program: Program, references: readonly Identifi
         const length = Math.max(...calls.map(c => c.argumentTypes.length));
         for (let i = 0; i < length; i++) {
             const symbol = checker.createSymbol(SymbolFlags.FunctionScopedVariable, escapeLeadingUnderscores(`arg${i}`));
-            symbol.type = combineTypes(calls.map(call => call.argumentTypes[i] || checker.getUndefinedType()));
+            symbol.links.type = combineTypes(calls.map(call => call.argumentTypes[i] || checker.getUndefinedType()));
             if (calls.some(call => call.argumentTypes[i] === undefined)) {
                 symbol.flags |= SymbolFlags.Optional;
             }

diff --git a/src/services/codefixes/returnValueCorrect.ts b/src/services/codefixes/returnValueCorrect.ts
@@ -120,7 +120,7 @@ registerCodeFix({
 
 function createObjectTypeFromLabeledExpression(checker: TypeChecker, label: Identifier, expression: Expression) {
     const member = checker.createSymbol(SymbolFlags.Property, label.escapedText);
-    member.type = checker.getTypeAtLocation(expression);
+    member.links.type = checker.getTypeAtLocation(expression);
     const members = createSymbolTable([member]);
     return checker.createAnonymousType(/*symbol*/ undefined, members, [], [], []);
 }

diff --git a/src/services/refactors/extractSymbol.ts b/src/services/refactors/extractSymbol.ts
@@ -2124,7 +2124,7 @@ function collectReadsAndWrites(
             const decl = find(visibleDeclarationsInExtractedRange, d => d.symbol === sym);
             if (decl) {
                 if (isVariableDeclaration(decl)) {
-                    const idString = decl.symbol.id!.toString();
+                    const idString = decl.symbol.id.toString();
                     if (!exposedVariableSymbolSet.has(idString)) {
                         exposedVariableDeclarations.push(decl);
                         exposedVariableSymbolSet.set(idString, true);

diff --git a/src/services/services.ts b/src/services/services.ts
@@ -183,8 +183,9 @@ import {
     isTagName,
     isTextWhiteSpaceLike,
     isThisTypeParameter,
-    JSDoc,
+    isTransientSymbol,
     JsDoc,
+    JSDoc,
     JSDocContainer,
     JSDocTagInfo,
     JsonSourceFile,
@@ -304,7 +305,6 @@ import {
     toPath,
     tracing,
     TransformFlags,
-    TransientSymbol,
     Type,
     TypeChecker,
     TypeFlags,
@@ -615,6 +615,9 @@ class SymbolObject implements Symbol {
     escapedName: __String;
     declarations!: Declaration[];
     valueDeclaration!: Declaration;
+    id = 0;
+    mergeId = 0;
+    constEnumOnlyModule: boolean | undefined;
 
     // Undefined is used to indicate the value has not been computed. If, after computing, the
     // symbol has no doc comment, then the empty array will be returned.
@@ -656,8 +659,8 @@ class SymbolObject implements Symbol {
         if (!this.documentationComment) {
             this.documentationComment = emptyArray; // Set temporarily to avoid an infinite loop finding inherited docs
 
-            if (!this.declarations && (this as Symbol as TransientSymbol).target && ((this as Symbol as TransientSymbol).target as TransientSymbol).tupleLabelDeclaration) {
-                const labelDecl = ((this as Symbol as TransientSymbol).target as TransientSymbol).tupleLabelDeclaration!;
+            if (!this.declarations && isTransientSymbol(this) && this.links.target && isTransientSymbol(this.links.target) && this.links.target.links.tupleLabelDeclaration) {
+                const labelDecl = this.links.target.links.tupleLabelDeclaration;
                 this.documentationComment = getDocumentationComment([labelDecl], checker);
             }
             else {

diff --git a/src/services/signatureHelp.ts b/src/services/signatureHelp.ts
@@ -49,6 +49,7 @@ import {
     isTemplateLiteralToken,
     isTemplateSpan,
     isTemplateTail,
+    isTransientSymbol,
     last,
     lastOrUndefined,
     ListFormat,
@@ -77,7 +78,6 @@ import {
     TaggedTemplateExpression,
     TemplateExpression,
     TextSpan,
-    TransientSymbol,
     tryCast,
     Type,
     TypeChecker,
@@ -724,7 +724,7 @@ function itemInfoForParameters(candidateSignature: Signature, checker: TypeCheck
     const isVariadic: (parameterList: readonly Symbol[]) => boolean =
         !checker.hasEffectiveRestParameter(candidateSignature) ? _ => false
         : lists.length === 1 ? _ => true
-        : pList => !!(pList.length && (pList[pList.length - 1] as TransientSymbol).checkFlags & CheckFlags.RestParameter);
+        : pList => !!(pList.length && tryCast(pList[pList.length - 1], isTransientSymbol)?.links.checkFlags! & CheckFlags.RestParameter);
     return lists.map(parameterList => ({
         isVariadic: isVariadic(parameterList),
         parameters: parameterList.map(p => createSignatureHelpParameterForParameter(p, checker, enclosingDeclaration, sourceFile, printer)),
@@ -739,7 +739,7 @@ function createSignatureHelpParameterForParameter(parameter: Symbol, checker: Ty
         printer.writeNode(EmitHint.Unspecified, param, sourceFile, writer);
     });
     const isOptional = checker.isOptionalParameter(parameter.valueDeclaration as ParameterDeclaration);
-    const isRest = !!((parameter as TransientSymbol).checkFlags & CheckFlags.RestParameter);
+    const isRest = isTransientSymbol(parameter) && !!(parameter.links.checkFlags & CheckFlags.RestParameter);
     return { name: parameter.name, documentation: parameter.getDocumentationComment(checker), displayParts, isOptional, isRest };
 }
 

diff --git a/src/services/symbolDisplay.ts b/src/services/symbolDisplay.ts
@@ -58,6 +58,7 @@ import {
     isObjectBindingPattern,
     isTaggedTemplateExpression,
     isThisInTypeQuery,
+    isTransientSymbol,
     isTypeAliasDeclaration,
     isVarConst,
     JSDocTagInfo,
@@ -176,7 +177,7 @@ function getSymbolKindOfConstructorPropertyMethodAccessorFunctionOrVar(typeCheck
     if (flags & SymbolFlags.Signature) return ScriptElementKind.indexSignatureElement;
 
     if (flags & SymbolFlags.Property) {
-        if (flags & SymbolFlags.Transient && (symbol as TransientSymbol).checkFlags & CheckFlags.Synthetic) {
+        if (flags & SymbolFlags.Transient && (symbol as TransientSymbol).links.checkFlags & CheckFlags.Synthetic) {
             // If union property is result of union of non method (property/accessors/variables), it is labeled as property
             const unionPropertyKind = forEach(typeChecker.getRootSymbols(symbol), rootSymbol => {
                 const rootSymbolFlags = rootSymbol.getFlags();
@@ -645,8 +646,8 @@ export function getSymbolDisplayPartsDocumentationAndSymbolKind(typeChecker: Typ
                     else {
                         addRange(displayParts, typeToDisplayParts(typeChecker, type, enclosingDeclaration));
                     }
-                    if ((symbol as TransientSymbol).target && ((symbol as TransientSymbol).target as TransientSymbol).tupleLabelDeclaration) {
-                        const labelDecl = ((symbol as TransientSymbol).target as TransientSymbol).tupleLabelDeclaration!;
+                    if (isTransientSymbol(symbol) && symbol.links.target && isTransientSymbol(symbol.links.target) && symbol.links.target.links.tupleLabelDeclaration) {
+                        const labelDecl = symbol.links.target.links.tupleLabelDeclaration;
                         Debug.assertNode(labelDecl.name, isIdentifier);
                         displayParts.push(spacePart());
                         displayParts.push(punctuationPart(SyntaxKind.OpenParenToken));

diff --git a/src/services/utilities.ts b/src/services/utilities.ts
@@ -225,6 +225,7 @@ import {
     isTaggedTemplateExpression,
     isTemplateLiteralKind,
     isToken,
+    isTransientSymbol,
     isTypeAliasDeclaration,
     isTypeElement,
     isTypeNode,
@@ -336,7 +337,6 @@ import {
     textSpanEnd,
     Token,
     tokenToString,
-    TransientSymbol,
     tryCast,
     Type,
     TypeChecker,
@@ -3003,9 +3003,9 @@ export function getScriptKind(fileName: string, host: LanguageServiceHost): Scri
 /** @internal */
 export function getSymbolTarget(symbol: Symbol, checker: TypeChecker): Symbol {
     let next: Symbol = symbol;
-    while (isAliasSymbol(next) || (isTransientSymbol(next) && next.target)) {
-        if (isTransientSymbol(next) && next.target) {
-            next = next.target;
+    while (isAliasSymbol(next) || (isTransientSymbol(next) && next.links.target)) {
+        if (isTransientSymbol(next) && next.links.target) {
+            next = next.links.target;
         }
         else {
             next = skipAlias(next, checker);
@@ -3014,10 +3014,6 @@ export function getSymbolTarget(symbol: Symbol, checker: TypeChecker): Symbol {
     return next;
 }
 
-function isTransientSymbol(symbol: Symbol): symbol is TransientSymbol {
-    return (symbol.flags & SymbolFlags.Transient) !== 0;
-}
-
 function isAliasSymbol(symbol: Symbol): boolean {
     return (symbol.flags & SymbolFlags.Alias) !== 0;
 }