Retrieve type parameter constraint using getConstraintFromTypeParameter

Author: amcasey

src/compiler/checker.ts

@@ -205,7 +205,7 @@ namespace ts {
             getEmitResolver,
             getExportsOfModule: getExportsOfModuleAsArray,
             getExportsAndPropertiesOfModule,
-            getSymbolWalker: createGetSymbolWalker(getRestTypeOfSignature, getReturnTypeOfSignature, getBaseTypes, resolveStructuredTypeMembers, getTypeOfSymbol, getResolvedSymbol, getIndexTypeOfStructuredType),
+            getSymbolWalker: createGetSymbolWalker(getRestTypeOfSignature, getReturnTypeOfSignature, getBaseTypes, resolveStructuredTypeMembers, getTypeOfSymbol, getResolvedSymbol, getIndexTypeOfStructuredType, getConstraintFromTypeParameter),
             getAmbientModules,
             getAllAttributesTypeFromJsxOpeningLikeElement: node => {
                 node = getParseTreeNode(node, isJsxOpeningLikeElement);

src/compiler/symbolWalker.ts

@@ -7,7 +7,8 @@ namespace ts {
         resolveStructuredTypeMembers: (type: ObjectType) => ResolvedType,
         getTypeOfSymbol: (sym: Symbol) => Type,
         getResolvedSymbol: (node: Node) => Symbol,
-        getIndexTypeOfStructuredType: (type: Type, kind: IndexKind) => Type) {
+        getIndexTypeOfStructuredType: (type: Type, kind: IndexKind) => Type,
+        getConstraintFromTypeParameter: (typeParameter: TypeParameter) => Type) {
 
         return getSymbolWalker;
 
@@ -92,7 +93,7 @@ namespace ts {
             }
 
             function visitTypeParameter(type: TypeParameter): void {
-                visitType(type.constraint);
+                visitType(getConstraintFromTypeParameter(type));
             }
 
             function visitUnionOrIntersectionType(type: UnionOrIntersectionType): void {

src/compiler/types.ts

@@ -3376,6 +3376,7 @@ namespace ts {
 
     // Type parameters (TypeFlags.TypeParameter)
     export interface TypeParameter extends TypeVariable {
+        /** Retrieve using getConstraintFromTypeParameter */
         constraint: Type;        // Constraint
         default?: Type;
         /* @internal */