fix(47508): noUncheckedIndexedAccess with enums Type narrowed

src/compiler/checker.ts

@@ -15589,7 +15589,18 @@ m2: ${(this.mapper2 as unknown as DebugTypeMapper).__debugToString().split("\n")
                         return accessFlags & AccessFlags.IncludeUndefined ? getUnionType([indexInfo.type, undefinedType]) : indexInfo.type;
                     }
                     errorIfWritingToReadonlyIndex(indexInfo);
-                    return accessFlags & AccessFlags.IncludeUndefined ? getUnionType([indexInfo.type, undefinedType]) : indexInfo.type;
+                    // When accessing an enum object with its own type,
+                    // e.g. E[E.A] for enum E { A }, undefined shouldn't
+                    // be included in the result type
+                    if ((accessFlags & AccessFlags.IncludeUndefined) &&
+                        !(objectType.symbol &&
+                            objectType.symbol.flags & (SymbolFlags.RegularEnum | SymbolFlags.ConstEnum) &&
+                            (indexType.symbol &&
+                            indexType.flags & TypeFlags.EnumLiteral &&
+                            getParentOfSymbol(indexType.symbol) === objectType.symbol))) {
+                        return getUnionType([indexInfo.type, undefinedType]);
+                    }
+                    return indexInfo.type;
                 }
                 if (indexType.flags & TypeFlags.Never) {
                     return neverType;

tests/baselines/reference/noUncheckedIndexAccess.js

@@ -0,0 +1,58 @@
+//// [noUncheckedIndexAccess.ts]
+enum Meat {
+    Sausage,
+    Bacon
+  }
+  const sausage = Meat.Sausage
+  const valueSausage = Meat[sausage]
+
+  const bacon = Meat.Bacon
+  const valueBacon = Meat[bacon]
+
+  const union: Meat.Bacon | Meat.Sausage = Meat.Bacon
+  const valueUnion = Meat[union]
+
+  //Avoiding a false positive
+  const value = Meat[0]
+
+  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;
+(function (Meat) {
+    Meat[Meat["Sausage"] = 0] = "Sausage";
+    Meat[Meat["Bacon"] = 1] = "Bacon";
+})(Meat || (Meat = {}));
+var sausage = Meat.Sausage;
+var valueSausage = Meat[sausage];
+var bacon = Meat.Bacon;
+var valueBacon = Meat[bacon];
+var union = Meat.Bacon;
+var valueUnion = Meat[union];
+//Avoiding a false positive
+var value = Meat[0];
+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

@@ -0,0 +1,84 @@
+=== tests/cases/compiler/noUncheckedIndexAccess.ts ===
+enum Meat {
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+
+    Sausage,
+>Sausage : Symbol(Meat.Sausage, Decl(noUncheckedIndexAccess.ts, 0, 11))
+
+    Bacon
+>Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+  }
+  const sausage = Meat.Sausage
+>sausage : Symbol(sausage, Decl(noUncheckedIndexAccess.ts, 4, 7))
+>Meat.Sausage : Symbol(Meat.Sausage, Decl(noUncheckedIndexAccess.ts, 0, 11))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>Sausage : Symbol(Meat.Sausage, Decl(noUncheckedIndexAccess.ts, 0, 11))
+
+  const valueSausage = Meat[sausage]
+>valueSausage : Symbol(valueSausage, Decl(noUncheckedIndexAccess.ts, 5, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>sausage : Symbol(sausage, Decl(noUncheckedIndexAccess.ts, 4, 7))
+
+  const bacon = Meat.Bacon
+>bacon : Symbol(bacon, Decl(noUncheckedIndexAccess.ts, 7, 7))
+>Meat.Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+
+  const valueBacon = Meat[bacon]
+>valueBacon : Symbol(valueBacon, Decl(noUncheckedIndexAccess.ts, 8, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>bacon : Symbol(bacon, Decl(noUncheckedIndexAccess.ts, 7, 7))
+
+  const union: Meat.Bacon | Meat.Sausage = Meat.Bacon
+>union : Symbol(union, Decl(noUncheckedIndexAccess.ts, 10, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>Sausage : Symbol(Meat.Sausage, Decl(noUncheckedIndexAccess.ts, 0, 11))
+>Meat.Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>Bacon : Symbol(Meat.Bacon, Decl(noUncheckedIndexAccess.ts, 1, 12))
+
+  const valueUnion = Meat[union]
+>valueUnion : Symbol(valueUnion, Decl(noUncheckedIndexAccess.ts, 11, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>union : Symbol(union, Decl(noUncheckedIndexAccess.ts, 10, 7))
+
+  //Avoiding a false positive
+  const value = Meat[0]
+>value : Symbol(value, Decl(noUncheckedIndexAccess.ts, 14, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+
+  const valueUndefined = "testing"
+>valueUndefined : Symbol(valueUndefined, Decl(noUncheckedIndexAccess.ts, 16, 7))
+
+  const value2 = Meat[valueUndefined]
+>value2 : Symbol(value2, Decl(noUncheckedIndexAccess.ts, 17, 7))
+>Meat : Symbol(Meat, Decl(noUncheckedIndexAccess.ts, 0, 0))
+>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

@@ -0,0 +1,90 @@
+=== tests/cases/compiler/noUncheckedIndexAccess.ts ===
+enum Meat {
+>Meat : Meat
+
+    Sausage,
+>Sausage : Meat.Sausage
+
+    Bacon
+>Bacon : Meat.Bacon
+  }
+  const sausage = Meat.Sausage
+>sausage : Meat.Sausage
+>Meat.Sausage : Meat.Sausage
+>Meat : typeof Meat
+>Sausage : Meat.Sausage
+
+  const valueSausage = Meat[sausage]
+>valueSausage : string
+>Meat[sausage] : string
+>Meat : typeof Meat
+>sausage : Meat.Sausage
+
+  const bacon = Meat.Bacon
+>bacon : Meat.Bacon
+>Meat.Bacon : Meat.Bacon
+>Meat : typeof Meat
+>Bacon : Meat.Bacon
+
+  const valueBacon = Meat[bacon]
+>valueBacon : string
+>Meat[bacon] : string
+>Meat : typeof Meat
+>bacon : Meat.Bacon
+
+  const union: Meat.Bacon | Meat.Sausage = Meat.Bacon
+>union : Meat
+>Meat : any
+>Meat : any
+>Meat.Bacon : Meat.Bacon
+>Meat : typeof Meat
+>Bacon : Meat.Bacon
+
+  const valueUnion = Meat[union]
+>valueUnion : string
+>Meat[union] : string
+>Meat : typeof Meat
+>union : Meat.Bacon
+
+  //Avoiding a false positive
+  const value = Meat[0]
+>value : string | undefined
+>Meat[0] : string | undefined
+>Meat : typeof Meat
+>0 : 0
+
+  const valueUndefined = "testing"
+>valueUndefined : "testing"
+>"testing" : "testing"
+
+  const value2 = Meat[valueUndefined]
+>value2 : error
+>Meat[valueUndefined] : error
+>Meat : typeof Meat
+>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

@@ -0,0 +1,30 @@
+//@noUncheckedIndexedAccess: true
+//@strictNullChecks: true
+
+enum Meat {
+    Sausage,
+    Bacon
+  }
+  const sausage = Meat.Sausage
+  const valueSausage = Meat[sausage]
+
+  const bacon = Meat.Bacon
+  const valueBacon = Meat[bacon]
+
+  const union: Meat.Bacon | Meat.Sausage = Meat.Bacon
+  const valueUnion = Meat[union]
+
+  //Avoiding a false positive
+  const value = Meat[0]
+
+  const valueUndefined = "testing"
+  const value2 = Meat[valueUndefined]
+
+  enum A {
+    a, b, c
+  }
+  enum B {
+    x, y, z
+  }
+
+  const value3 = A[B.x];