Merge pull request #31150 from Microsoft/fixReadonlyIndexedAccess

Fix readonly indexed access used in indexed access type

Author: ahejlsberg

src/compiler/checker.ts

@@ -10083,7 +10083,7 @@ namespace ts {
                         error(indexNode, Diagnostics.Type_0_cannot_be_used_as_an_index_type, typeToString(indexType));
                         return indexInfo.type;
                     }
-                    if (indexInfo.isReadonly && (accessFlags & AccessFlags.Writing || accessExpression && (isAssignmentTarget(accessExpression) || isDeleteTarget(accessExpression)))) {
+                    if (indexInfo.isReadonly && accessExpression && (isAssignmentTarget(accessExpression) || isDeleteTarget(accessExpression))) {
                         if (accessExpression) {
                             error(accessExpression, Diagnostics.Index_signature_in_type_0_only_permits_reading, typeToString(objectType));
                             return indexInfo.type;

tests/baselines/reference/keyofAndIndexedAccess2.errors.txt

@@ -204,4 +204,15 @@ tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts(108,5): error TS23
     function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
         cb(param[0]);
     }
+    
+    // Repro from #31149
+    
+    function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
+        cb(param[0]);
+    }
+    
+    function fn4<K extends number>() {
+        let x: Array<string>[K] = 'abc';
+        let y: ReadonlyArray<string>[K] = 'abc';
+    }
 

tests/baselines/reference/keyofAndIndexedAccess2.js

@@ -125,6 +125,17 @@ function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(par
 function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
     cb(param[0]);
 }
+
+// Repro from #31149
+
+function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
+    cb(param[0]);
+}
+
+function fn4<K extends number>() {
+    let x: Array<string>[K] = 'abc';
+    let y: ReadonlyArray<string>[K] = 'abc';
+}
 
 
 //// [keyofAndIndexedAccess2.js]
@@ -207,3 +218,11 @@ function fn(param, cb) {
 function fn2(param, cb) {
     cb(param[0]);
 }
+// Repro from #31149
+function fn3(param, cb) {
+    cb(param[0]);
+}
+function fn4() {
+    let x = 'abc';
+    let y = 'abc';
+}

tests/baselines/reference/keyofAndIndexedAccess2.symbols

@@ -471,3 +471,35 @@ function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void
 >param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 123, 38))
 }
 
+// Repro from #31149
+
+function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
+>fn3 : Symbol(fn3, Decl(keyofAndIndexedAccess2.ts, 125, 1))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 129, 13))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 129, 46))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 129, 13))
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 129, 55))
+>element : Symbol(element, Decl(keyofAndIndexedAccess2.ts, 129, 61))
+>T : Symbol(T, Decl(keyofAndIndexedAccess2.ts, 129, 13))
+
+    cb(param[0]);
+>cb : Symbol(cb, Decl(keyofAndIndexedAccess2.ts, 129, 55))
+>param : Symbol(param, Decl(keyofAndIndexedAccess2.ts, 129, 46))
+}
+
+function fn4<K extends number>() {
+>fn4 : Symbol(fn4, Decl(keyofAndIndexedAccess2.ts, 131, 1))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
+
+    let x: Array<string>[K] = 'abc';
+>x : Symbol(x, Decl(keyofAndIndexedAccess2.ts, 134, 7))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 2 more)
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
+
+    let y: ReadonlyArray<string>[K] = 'abc';
+>y : Symbol(y, Decl(keyofAndIndexedAccess2.ts, 135, 7))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2016.array.include.d.ts, --, --), Decl(lib.es2019.array.d.ts, --, --))
+>K : Symbol(K, Decl(keyofAndIndexedAccess2.ts, 133, 13))
+}
+

tests/baselines/reference/keyofAndIndexedAccess2.types

@@ -471,3 +471,31 @@ function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void
 >0 : 0
 }
 
+// Repro from #31149
+
+function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
+>fn3 : <T extends readonly string[]>(param: T, cb: (element: T[number]) => void) => void
+>param : T
+>cb : (element: T[number]) => void
+>element : T[number]
+
+    cb(param[0]);
+>cb(param[0]) : void
+>cb : (element: T[number]) => void
+>param[0] : string
+>param : T
+>0 : 0
+}
+
+function fn4<K extends number>() {
+>fn4 : <K extends number>() => void
+
+    let x: Array<string>[K] = 'abc';
+>x : string[][K]
+>'abc' : "abc"
+
+    let y: ReadonlyArray<string>[K] = 'abc';
+>y : readonly string[][K]
+>'abc' : "abc"
+}
+

tests/cases/conformance/types/keyof/keyofAndIndexedAccess2.ts

@@ -127,3 +127,14 @@ function fn<T extends {elements: Array<string>} | {elements: Array<number>}>(par
 function fn2<T extends Array<string>>(param: T, cb: (element: T[number]) => void) {
     cb(param[0]);
 }
+
+// Repro from #31149
+
+function fn3<T extends ReadonlyArray<string>>(param: T, cb: (element: T[number]) => void) {
+    cb(param[0]);
+}
+
+function fn4<K extends number>() {
+    let x: Array<string>[K] = 'abc';
+    let y: ReadonlyArray<string>[K] = 'abc';
+}