Diagnose assignment to indexed property instead of ICE (#7160)

source/slang/slang-diagnostics.lua

@@ -4474,6 +4474,13 @@ err(
     span { loc = "location", message = "arg ~argIndex:Int in '~funcName:IRInst' is not a compile-time constant" }
 )
 
+err(
+    "unsupported-assignment-target",
+    40017,
+    "assignment target is not supported",
+    span { loc = "location", message = "this form of assignment is not currently supported; consider assigning to the whole value instead of an individual element" }
+)
+
 err(
     "cannot-unroll-loop",
     40020,

source/slang/slang-lower-to-ir.cpp

@@ -10081,7 +10081,21 @@ void assign(IRGenContext* context, LoweredValInfo const& inLeft, LoweredValInfo
         break;
 
     default:
-        SLANG_UNIMPLEMENTED_X("assignment");
+        {
+            SourceLoc loc;
+            for (auto locInfo = context->irBuilder->getSourceLocInfo(); locInfo;
+                 locInfo = locInfo->next)
+            {
+                if (locInfo->sourceLoc.getRaw() != 0)
+                {
+                    loc = locInfo->sourceLoc;
+                    break;
+                }
+            }
+            context->getSink()->diagnose(Diagnostics::UnsupportedAssignmentTarget{
+                .location = loc,
+            });
+        }
         break;
     }
 }

tests/diagnostics/indexed-property-assign.slang

@@ -0,0 +1,34 @@
+//DIAGNOSTIC_TEST:SIMPLE(diag=CHECK): -target spirv -entry computeMain
+
+// Regression test for https://github.com/shader-slang/slang/issues/7160
+// Assigning to an indexed element of an array-returning property should
+// produce a diagnostic instead of crashing with an internal error.
+
+struct Foo
+{
+    float a;
+    float _b[2];
+
+    property float b[2]
+    {
+        get { return _b; }
+        set
+        {
+            _b[0] = newValue[0];
+            _b[1] = newValue[1];
+        }
+    }
+}
+
+RWStructuredBuffer<float> output;
+
+[shader("compute")]
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    Foo c;
+    c.b[0] = 1.0;
+//CHECK:   ^ assignment target is not supported
+//CHECK:   ^ this form of assignment is not currently supported; consider assigning to the whole value instead of an individual element
+    output[0] = c.b[0];
+}