Fixed binding element types coming from the out of tuple bounds under noUncheckedIndexedAccess

src/compiler/checker.ts

@@ -22767,7 +22767,18 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return propType;
         }
         if (everyType(type, isTupleType)) {
-            return mapType(type, t => getRestTypeOfTupleType(t as TupleTypeReference) || undefinedType);
+            return mapType(type, t => {
+                const tupleType = t as TupleTypeReference;
+                const restType = getRestTypeOfTupleType(tupleType);
+                if (!restType) {
+                    return undefinedType;
+                }
+                if (compilerOptions.noUncheckedIndexedAccess &&
+                    index >= tupleType.target.fixedLength + getEndElementCount(tupleType.target, ElementFlags.Fixed)) {
+                    return getUnionType([restType, undefinedType]);
+                }
+                return restType;
+            });
         }
         return undefined;
     }

tests/baselines/reference/destructureTupleWithVariableElement.errors.txt

@@ -0,0 +1,31 @@
+tests/cases/compiler/destructureTupleWithVariableElement.ts(9,1): error TS18048: 's1' is possibly 'undefined'.
+tests/cases/compiler/destructureTupleWithVariableElement.ts(10,1): error TS18048: 's2' is possibly 'undefined'.
+tests/cases/compiler/destructureTupleWithVariableElement.ts(18,1): error TS18048: 's5' is possibly 'undefined'.
+
+
+==== tests/cases/compiler/destructureTupleWithVariableElement.ts (3 errors) ====
+    // repro from #52302
+
+    type NonEmptyStringArray = [string, ...Array<string>]
+
+    const strings: NonEmptyStringArray = ['one', 'two']
+    const [s0, s1, s2] = strings;
+
+    s0.toUpperCase()
+    s1.toUpperCase() 
+    ~~
+!!! error TS18048: 's1' is possibly 'undefined'.
+    s2.toUpperCase()
+    ~~
+!!! error TS18048: 's2' is possibly 'undefined'.
+
+    declare const strings2: [string, ...Array<string>, string]
+
+    const [s3, s4, s5] = strings2;
+
+    s3.toUpperCase()
+    s4.toUpperCase() 
+    s5.toUpperCase()
+    ~~
+!!! error TS18048: 's5' is possibly 'undefined'.
+

tests/baselines/reference/destructureTupleWithVariableElement.symbols

@@ -0,0 +1,57 @@
+=== tests/cases/compiler/destructureTupleWithVariableElement.ts ===
+// repro from #52302
+
+type NonEmptyStringArray = [string, ...Array<string>]
+>NonEmptyStringArray : Symbol(NonEmptyStringArray, Decl(destructureTupleWithVariableElement.ts, 0, 0))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+const strings: NonEmptyStringArray = ['one', 'two']
+>strings : Symbol(strings, Decl(destructureTupleWithVariableElement.ts, 4, 5))
+>NonEmptyStringArray : Symbol(NonEmptyStringArray, Decl(destructureTupleWithVariableElement.ts, 0, 0))
+
+const [s0, s1, s2] = strings;
+>s0 : Symbol(s0, Decl(destructureTupleWithVariableElement.ts, 5, 7))
+>s1 : Symbol(s1, Decl(destructureTupleWithVariableElement.ts, 5, 10))
+>s2 : Symbol(s2, Decl(destructureTupleWithVariableElement.ts, 5, 14))
+>strings : Symbol(strings, Decl(destructureTupleWithVariableElement.ts, 4, 5))
+
+s0.toUpperCase()
+>s0.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s0 : Symbol(s0, Decl(destructureTupleWithVariableElement.ts, 5, 7))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+s1.toUpperCase() 
+>s1.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s1 : Symbol(s1, Decl(destructureTupleWithVariableElement.ts, 5, 10))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+s2.toUpperCase()
+>s2.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s2 : Symbol(s2, Decl(destructureTupleWithVariableElement.ts, 5, 14))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+declare const strings2: [string, ...Array<string>, string]
+>strings2 : Symbol(strings2, Decl(destructureTupleWithVariableElement.ts, 11, 13))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+const [s3, s4, s5] = strings2;
+>s3 : Symbol(s3, Decl(destructureTupleWithVariableElement.ts, 13, 7))
+>s4 : Symbol(s4, Decl(destructureTupleWithVariableElement.ts, 13, 10))
+>s5 : Symbol(s5, Decl(destructureTupleWithVariableElement.ts, 13, 14))
+>strings2 : Symbol(strings2, Decl(destructureTupleWithVariableElement.ts, 11, 13))
+
+s3.toUpperCase()
+>s3.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s3 : Symbol(s3, Decl(destructureTupleWithVariableElement.ts, 13, 7))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+s4.toUpperCase() 
+>s4.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s4 : Symbol(s4, Decl(destructureTupleWithVariableElement.ts, 13, 10))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+
+s5.toUpperCase()
+>s5.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>s5 : Symbol(s5, Decl(destructureTupleWithVariableElement.ts, 13, 14))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+

tests/baselines/reference/destructureTupleWithVariableElement.types

@@ -0,0 +1,63 @@
+=== tests/cases/compiler/destructureTupleWithVariableElement.ts ===
+// repro from #52302
+
+type NonEmptyStringArray = [string, ...Array<string>]
+>NonEmptyStringArray : [string, ...string[]]
+
+const strings: NonEmptyStringArray = ['one', 'two']
+>strings : [string, ...string[]]
+>['one', 'two'] : [string, string]
+>'one' : "one"
+>'two' : "two"
+
+const [s0, s1, s2] = strings;
+>s0 : string
+>s1 : string | undefined
+>s2 : string | undefined
+>strings : [string, ...string[]]
+
+s0.toUpperCase()
+>s0.toUpperCase() : string
+>s0.toUpperCase : () => string
+>s0 : string
+>toUpperCase : () => string
+
+s1.toUpperCase() 
+>s1.toUpperCase() : string
+>s1.toUpperCase : () => string
+>s1 : string | undefined
+>toUpperCase : () => string
+
+s2.toUpperCase()
+>s2.toUpperCase() : string
+>s2.toUpperCase : () => string
+>s2 : string | undefined
+>toUpperCase : () => string
+
+declare const strings2: [string, ...Array<string>, string]
+>strings2 : [string, ...string[], string]
+
+const [s3, s4, s5] = strings2;
+>s3 : string
+>s4 : string | undefined
+>s5 : string | undefined
+>strings2 : [string, ...string[], string]
+
+s3.toUpperCase()
+>s3.toUpperCase() : string
+>s3.toUpperCase : () => string
+>s3 : string
+>toUpperCase : () => string
+
+s4.toUpperCase() 
+>s4.toUpperCase() : string
+>s4.toUpperCase : () => string
+>s4 : string
+>toUpperCase : () => string
+
+s5.toUpperCase()
+>s5.toUpperCase() : string
+>s5.toUpperCase : () => string
+>s5 : string | undefined
+>toUpperCase : () => string
+

tests/cases/compiler/destructureTupleWithVariableElement.ts

@@ -0,0 +1,22 @@
+// @strict: true
+// @noUncheckedIndexedAccess: true
+// @noEmit: true
+
+// repro from #52302
+
+type NonEmptyStringArray = [string, ...Array<string>]
+
+const strings: NonEmptyStringArray = ['one', 'two']
+const [s0, s1, s2] = strings;
+
+s0.toUpperCase()
+s1.toUpperCase() 
+s2.toUpperCase()
+
+declare const strings2: [string, ...Array<string>, string]
+
+const [s3, s4, s5] = strings2;
+
+s3.toUpperCase()
+s4.toUpperCase() 
+s5.toUpperCase()