Add slightly modified example from microsoft#25413

Author: weswigham

src/compiler/checker.ts

@@ -13495,9 +13495,9 @@ namespace ts {
 
                     // TODO: Find a nice way to include potential conditional type breakdowns in error output, if those seems good (they usually don't)
                     let localResult: Ternary | undefined;
-                    if (skipTrue || (localResult = isRelatedTo(source, instantiateType(c.trueType, distributionMapper), /*reportErrors*/ false))) {
+                    if (skipTrue || (localResult = isRelatedTo(source, instantiateType(getTrueTypeFromConditionalType(c), distributionMapper), /*reportErrors*/ false))) {
                         if (!skipFalse) {
-                            localResult = (localResult || Ternary.Maybe) & isRelatedTo(source, instantiateType(c.falseType, distributionMapper), /*reportErrors*/ false);
+                            localResult = (localResult || Ternary.Maybe) & isRelatedTo(source, instantiateType(getFalseTypeFromConditionalType(c), distributionMapper), /*reportErrors*/ false);
                         }
                     }
                     if (localResult) {

tests/baselines/reference/conditionalTypeSubclassExtendsTypeParam.js

@@ -0,0 +1,9 @@
+//// [conditionalTypeSubclassExtendsTypeParam.ts]
+declare class Model<M extends MR, MR extends {}> {
+    public getField2<K extends keyof M>(): Field<M[K], [K] extends [keyof MR] ? MR[K] : M[K]>
+}
+
+declare class Field<T extends TR, TR> {
+}
+
+//// [conditionalTypeSubclassExtendsTypeParam.js]

tests/baselines/reference/conditionalTypeSubclassExtendsTypeParam.symbols

@@ -0,0 +1,28 @@
+=== tests/cases/compiler/conditionalTypeSubclassExtendsTypeParam.ts ===
+declare class Model<M extends MR, MR extends {}> {
+>Model : Symbol(Model, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 0))
+>M : Symbol(M, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 20))
+>MR : Symbol(MR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 33))
+>MR : Symbol(MR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 33))
+
+    public getField2<K extends keyof M>(): Field<M[K], [K] extends [keyof MR] ? MR[K] : M[K]>
+>getField2 : Symbol(Model.getField2, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 50))
+>K : Symbol(K, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 1, 21))
+>M : Symbol(M, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 20))
+>Field : Symbol(Field, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 2, 1))
+>M : Symbol(M, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 20))
+>K : Symbol(K, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 1, 21))
+>K : Symbol(K, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 1, 21))
+>MR : Symbol(MR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 33))
+>MR : Symbol(MR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 33))
+>K : Symbol(K, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 1, 21))
+>M : Symbol(M, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 0, 20))
+>K : Symbol(K, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 1, 21))
+}
+
+declare class Field<T extends TR, TR> {
+>Field : Symbol(Field, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 2, 1))
+>T : Symbol(T, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 4, 20))
+>TR : Symbol(TR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 4, 33))
+>TR : Symbol(TR, Decl(conditionalTypeSubclassExtendsTypeParam.ts, 4, 33))
+}

tests/baselines/reference/conditionalTypeSubclassExtendsTypeParam.types

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/conditionalTypeSubclassExtendsTypeParam.ts ===
+declare class Model<M extends MR, MR extends {}> {
+>Model : Model<M, MR>
+
+    public getField2<K extends keyof M>(): Field<M[K], [K] extends [keyof MR] ? MR[K] : M[K]>
+>getField2 : <K extends keyof M>() => Field<M[K], [K] extends [keyof MR] ? MR[K] : M[K]>
+}
+
+declare class Field<T extends TR, TR> {
+>Field : Field<T, TR>
+}

tests/cases/compiler/conditionalTypeSubclassExtendsTypeParam.ts

@@ -0,0 +1,6 @@
+declare class Model<M extends MR, MR extends {}> {
+    public getField2<K extends keyof M>(): Field<M[K], [K] extends [keyof MR] ? MR[K] : M[K]>
+}
+
+declare class Field<T extends TR, TR> {
+}