Added type checks to avoid false positive results

Author: navya9singh

src/compiler/checker.ts

@@ -15589,8 +15589,8 @@ m2: ${(this.mapper2 as unknown as DebugTypeMapper).__debugToString().split("\n")
                         return accessFlags & AccessFlags.IncludeUndefined ? getUnionType([indexInfo.type, undefinedType]) : indexInfo.type;
                     }
                     errorIfWritingToReadonlyIndex(indexInfo);
-                    if (accessFlags & AccessFlags.IncludeUndefined && objectType.symbol.flags & (SymbolFlags.RegularEnum | SymbolFlags.ConstEnum)) {
-                        if(indexType.flags & TypeFlags.EnumLiteral){
+                    if (accessFlags & AccessFlags.IncludeUndefined && objectType.symbol && objectType.symbol.flags & (SymbolFlags.RegularEnum | SymbolFlags.ConstEnum)) {
+                        if (indexType.symbol && indexType.flags & TypeFlags.EnumLiteral && getParentOfSymbol(indexType.symbol) === objectType.symbol) {
                             return indexInfo.type;
                         }
                     }

tests/baselines/reference/noUncheckedIndexAccess.js

@@ -15,9 +15,17 @@ enum Meat {
   //Avoiding a false positive
   const value = Meat[0]
 
-  const t = "testing"
-  const value2 = Meat[t]
-
+  const valueUndefined = "testing"
+  const value2 = Meat[valueUndefined]
+
+  enum A {
+    a, b, c
+  }
+  enum B {
+    x, y, z
+  }
+  
+  const value3 = A[B.x];
 
 //// [noUncheckedIndexAccess.js]
 var Meat;
@@ -33,5 +41,18 @@ var union = Meat.Bacon;
 var valueUnion = Meat[union];
 //Avoiding a false positive
 var value = Meat[0];
-var t = "testing";
-var value2 = Meat[t];
+var valueUndefined = "testing";
+var value2 = Meat[valueUndefined];
+var A;
+(function (A) {
+    A[A["a"] = 0] = "a";
+    A[A["b"] = 1] = "b";
+    A[A["c"] = 2] = "c";
+})(A || (A = {}));
+var B;
+(function (B) {
+    B[B["x"] = 0] = "x";
+    B[B["y"] = 1] = "y";
+    B[B["z"] = 2] = "z";
+})(B || (B = {}));
+var value3 = A[B.x];

tests/baselines/reference/noUncheckedIndexAccess.symbols

@@ -50,11 +50,35 @@ enum Meat {
 >value : Symbol(value, Decl(noUncheckedIndexAccess.ts, 14, 7))
 >Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
 
-  const t = "testing"
->t : Symbol(t, Decl(noUncheckedIndexAccess.ts, 16, 7))
+  const valueUndefined = "testing"
+>valueUndefined : Symbol(valueUndefined, Decl(noUncheckedIndexAccess.ts, 16, 7))
 
-  const value2 = Meat[t]
+  const value2 = Meat[valueUndefined]
 >value2 : Symbol(value2, Decl(noUncheckedIndexAccess.ts, 17, 7))
 >Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
->t : Symbol(t, Decl(noUncheckedIndexAccess.ts, 16, 7))
+>valueUndefined : Symbol(valueUndefined, Decl(noUncheckedIndexAccess.ts, 16, 7))
+
+  enum A {
+>A : Symbol(A, Decl(noUncheckedIndexAccess.ts, 17, 37))
+
+    a, b, c
+>a : Symbol(A.a, Decl(noUncheckedIndexAccess.ts, 19, 10))
+>b : Symbol(A.b, Decl(noUncheckedIndexAccess.ts, 20, 6))
+>c : Symbol(A.c, Decl(noUncheckedIndexAccess.ts, 20, 9))
+  }
+  enum B {
+>B : Symbol(B, Decl(noUncheckedIndexAccess.ts, 21, 3))
+
+    x, y, z
+>x : Symbol(B.x, Decl(noUncheckedIndexAccess.ts, 22, 10))
+>y : Symbol(B.y, Decl(noUncheckedIndexAccess.ts, 23, 6))
+>z : Symbol(B.z, Decl(noUncheckedIndexAccess.ts, 23, 9))
+  }
+  
+  const value3 = A[B.x];
+>value3 : Symbol(value3, Decl(noUncheckedIndexAccess.ts, 26, 7))
+>A : Symbol(A, Decl(noUncheckedIndexAccess.ts, 17, 37))
+>B.x : Symbol(B.x, Decl(noUncheckedIndexAccess.ts, 22, 10))
+>B : Symbol(B, Decl(noUncheckedIndexAccess.ts, 21, 3))
+>x : Symbol(B.x, Decl(noUncheckedIndexAccess.ts, 22, 10))
 

tests/baselines/reference/noUncheckedIndexAccess.types

@@ -53,13 +53,38 @@ enum Meat {
 >Meat : typeof Meat
 >0 : 0
 
-  const t = "testing"
->t : "testing"
+  const valueUndefined = "testing"
+>valueUndefined : "testing"
 >"testing" : "testing"
 
-  const value2 = Meat[t]
+  const value2 = Meat[valueUndefined]
 >value2 : error
->Meat[t] : error
+>Meat[valueUndefined] : error
 >Meat : typeof Meat
->t : "testing"
+>valueUndefined : "testing"
+
+  enum A {
+>A : A
+
+    a, b, c
+>a : A.a
+>b : A.b
+>c : A.c
+  }
+  enum B {
+>B : B
+
+    x, y, z
+>x : B.x
+>y : B.y
+>z : B.z
+  }
+  
+  const value3 = A[B.x];
+>value3 : string | undefined
+>A[B.x] : string | undefined
+>A : typeof A
+>B.x : B.x
+>B : typeof B
+>x : B.x
 

tests/cases/compiler/noUncheckedIndexAccess.ts

@@ -17,5 +17,14 @@ enum Meat {
   //Avoiding a false positive
   const value = Meat[0]
 
-  const t = "testing"
-  const value2 = Meat[t]
+  const valueUndefined = "testing"
+  const value2 = Meat[valueUndefined]
+
+  enum A {
+    a, b, c
+  }
+  enum B {
+    x, y, z
+  }
+  
+  const value3 = A[B.x];