From a6f8898ee59302e2557f554c06b45fa2b5fff654 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 25 Sep 2025 21:18:08 +0000
Subject: [PATCH] Add test case for readonly property assignment via type
 assertion per jakebailey feedback

Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>
---
 ...usedBeforeAssignedTypeAssertion.errors.txt | 20 ++++++++-
 .../usedBeforeAssignedTypeAssertion.js        | 20 +++++++++
 .../usedBeforeAssignedTypeAssertion.symbols   | 32 +++++++++++--
 .../usedBeforeAssignedTypeAssertion.types     | 45 +++++++++++++++++++
 .../usedBeforeAssignedTypeAssertion.ts        | 13 ++++++
 5 files changed, 125 insertions(+), 5 deletions(-)

diff --git a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.errors.txt b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.errors.txt
index 2bd93515b3f..4cecead9a16 100644
--- a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.errors.txt
+++ b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.errors.txt
@@ -1,8 +1,9 @@
 usedBeforeAssignedTypeAssertion.ts(28,6): error TS2588: Cannot assign to 'm' because it is a constant.
-usedBeforeAssignedTypeAssertion.ts(34,12): error TS2454: Variable 'uninitialized' is used before being assigned.
+usedBeforeAssignedTypeAssertion.ts(41,10): error TS2540: Cannot assign to 'prop' because it is a read-only property.
+usedBeforeAssignedTypeAssertion.ts(47,12): error TS2454: Variable 'uninitialized' is used before being assigned.
 
 
-==== usedBeforeAssignedTypeAssertion.ts (2 errors) ====
+==== usedBeforeAssignedTypeAssertion.ts (3 errors) ====
     // Test case for type assertion (angle bracket syntax) - assignment should not error
     function testTypeAssertion() {
         let x: number;
@@ -35,6 +36,21 @@ usedBeforeAssignedTypeAssertion.ts(34,12): error TS2454: Variable 'uninitialized
 !!! error TS2588: Cannot assign to 'm' because it is a constant.
     }
     
+    // Test case for readonly property assignment via type assertion - should error
+    function testReadonlyPropertyAssignment() {
+        interface ReadonlyInterface {
+            readonly prop: number;
+        }
+        
+        let obj: ReadonlyInterface;
+        obj = { prop: 42 };
+        
+        // Should error - cannot assign to readonly property, even through type assertion
+        (obj.prop as any) = 100;
+             ~~~~
+!!! error TS2540: Cannot assign to 'prop' because it is a read-only property.
+    }
+    
     // Test cases that should still produce errors for proper context
     function shouldStillError() {
         let uninitialized: number;
diff --git a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.js b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.js
index d434d100a23..1f389b350d6 100644
--- a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.js
+++ b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.js
@@ -31,6 +31,19 @@ function testConstAssignment() {
     (m as any) = 16; // Should error - cannot assign to const
 }
 
+// Test case for readonly property assignment via type assertion - should error
+function testReadonlyPropertyAssignment() {
+    interface ReadonlyInterface {
+        readonly prop: number;
+    }
+    
+    let obj: ReadonlyInterface;
+    obj = { prop: 42 };
+    
+    // Should error - cannot assign to readonly property, even through type assertion
+    (obj.prop as any) = 100;
+}
+
 // Test cases that should still produce errors for proper context
 function shouldStillError() {
     let uninitialized: number;
@@ -64,6 +77,13 @@ function testConstAssignment() {
     var m = 32;
     m = 16; // Should error - cannot assign to const
 }
+// Test case for readonly property assignment via type assertion - should error
+function testReadonlyPropertyAssignment() {
+    var obj;
+    obj = { prop: 42 };
+    // Should error - cannot assign to readonly property, even through type assertion
+    obj.prop = 100;
+}
 // Test cases that should still produce errors for proper context
 function shouldStillError() {
     var uninitialized;
diff --git a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.symbols b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.symbols
index c4c3f7923fb..5a7306690f2 100644
--- a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.symbols
+++ b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.symbols
@@ -56,13 +56,39 @@ function testConstAssignment() {
 >m : Symbol(m, Decl(usedBeforeAssignedTypeAssertion.ts, 26, 9))
 }
 
+// Test case for readonly property assignment via type assertion - should error
+function testReadonlyPropertyAssignment() {
+>testReadonlyPropertyAssignment : Symbol(testReadonlyPropertyAssignment, Decl(usedBeforeAssignedTypeAssertion.ts, 28, 1))
+
+    interface ReadonlyInterface {
+>ReadonlyInterface : Symbol(ReadonlyInterface, Decl(usedBeforeAssignedTypeAssertion.ts, 31, 43))
+
+        readonly prop: number;
+>prop : Symbol(ReadonlyInterface.prop, Decl(usedBeforeAssignedTypeAssertion.ts, 32, 33))
+    }
+    
+    let obj: ReadonlyInterface;
+>obj : Symbol(obj, Decl(usedBeforeAssignedTypeAssertion.ts, 36, 7))
+>ReadonlyInterface : Symbol(ReadonlyInterface, Decl(usedBeforeAssignedTypeAssertion.ts, 31, 43))
+
+    obj = { prop: 42 };
+>obj : Symbol(obj, Decl(usedBeforeAssignedTypeAssertion.ts, 36, 7))
+>prop : Symbol(prop, Decl(usedBeforeAssignedTypeAssertion.ts, 37, 11))
+    
+    // Should error - cannot assign to readonly property, even through type assertion
+    (obj.prop as any) = 100;
+>obj.prop : Symbol(ReadonlyInterface.prop, Decl(usedBeforeAssignedTypeAssertion.ts, 32, 33))
+>obj : Symbol(obj, Decl(usedBeforeAssignedTypeAssertion.ts, 36, 7))
+>prop : Symbol(ReadonlyInterface.prop, Decl(usedBeforeAssignedTypeAssertion.ts, 32, 33))
+}
+
 // Test cases that should still produce errors for proper context
 function shouldStillError() {
->shouldStillError : Symbol(shouldStillError, Decl(usedBeforeAssignedTypeAssertion.ts, 28, 1))
+>shouldStillError : Symbol(shouldStillError, Decl(usedBeforeAssignedTypeAssertion.ts, 41, 1))
 
     let uninitialized: number;
->uninitialized : Symbol(uninitialized, Decl(usedBeforeAssignedTypeAssertion.ts, 32, 7))
+>uninitialized : Symbol(uninitialized, Decl(usedBeforeAssignedTypeAssertion.ts, 45, 7))
 
     return uninitialized; // Should error - never assigned
->uninitialized : Symbol(uninitialized, Decl(usedBeforeAssignedTypeAssertion.ts, 32, 7))
+>uninitialized : Symbol(uninitialized, Decl(usedBeforeAssignedTypeAssertion.ts, 45, 7))
 }
diff --git a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.types b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.types
index da01dc01ab2..7c8511bff5a 100644
--- a/tests/baselines/reference/usedBeforeAssignedTypeAssertion.types
+++ b/tests/baselines/reference/usedBeforeAssignedTypeAssertion.types
@@ -115,6 +115,51 @@ function testConstAssignment() {
 >   : ^^
 }
 
+// Test case for readonly property assignment via type assertion - should error
+function testReadonlyPropertyAssignment() {
+>testReadonlyPropertyAssignment : () => void
+>                               : ^^^^^^^^^^
+
+    interface ReadonlyInterface {
+        readonly prop: number;
+>prop : number
+>     : ^^^^^^
+    }
+    
+    let obj: ReadonlyInterface;
+>obj : ReadonlyInterface
+>    : ^^^^^^^^^^^^^^^^^
+
+    obj = { prop: 42 };
+>obj = { prop: 42 } : { prop: number; }
+>                   : ^^^^^^^^^^^^^^^^^
+>obj : ReadonlyInterface
+>    : ^^^^^^^^^^^^^^^^^
+>{ prop: 42 } : { prop: number; }
+>             : ^^^^^^^^^^^^^^^^^
+>prop : number
+>     : ^^^^^^
+>42 : 42
+>   : ^^
+    
+    // Should error - cannot assign to readonly property, even through type assertion
+    (obj.prop as any) = 100;
+>(obj.prop as any) = 100 : 100
+>                        : ^^^
+>(obj.prop as any) : any
+>                  : ^^^
+>obj.prop as any : any
+>                : ^^^
+>obj.prop : any
+>         : ^^^
+>obj : ReadonlyInterface
+>    : ^^^^^^^^^^^^^^^^^
+>prop : any
+>     : ^^^
+>100 : 100
+>    : ^^^
+}
+
 // Test cases that should still produce errors for proper context
 function shouldStillError() {
 >shouldStillError : () => number
diff --git a/tests/cases/compiler/usedBeforeAssignedTypeAssertion.ts b/tests/cases/compiler/usedBeforeAssignedTypeAssertion.ts
index d187950789a..77be4e15d79 100644
--- a/tests/cases/compiler/usedBeforeAssignedTypeAssertion.ts
+++ b/tests/cases/compiler/usedBeforeAssignedTypeAssertion.ts
@@ -30,6 +30,19 @@ function testConstAssignment() {
     (m as any) = 16; // Should error - cannot assign to const
 }
 
+// Test case for readonly property assignment via type assertion - should error
+function testReadonlyPropertyAssignment() {
+    interface ReadonlyInterface {
+        readonly prop: number;
+    }
+    
+    let obj: ReadonlyInterface;
+    obj = { prop: 42 };
+    
+    // Should error - cannot assign to readonly property, even through type assertion
+    (obj.prop as any) = 100;
+}
+
 // Test cases that should still produce errors for proper context
 function shouldStillError() {
     let uninitialized: number;