Fixes #5104.

src/compiler/core.ts

@@ -437,8 +437,12 @@ namespace ts {
     }
 
     export function concatenateDiagnosticMessageChains(headChain: DiagnosticMessageChain, tailChain: DiagnosticMessageChain): DiagnosticMessageChain {
-        Debug.assert(!headChain.next);
-        headChain.next = tailChain;
+        let lastChain = headChain;
+        while (lastChain.next) {
+            lastChain = lastChain.next;
+        }
+
+        lastChain.next = tailChain;
         return headChain;
     }
 

tests/baselines/reference/decoratorCallGeneric.errors.txt

@@ -0,0 +1,22 @@
+tests/cases/conformance/decorators/decoratorCallGeneric.ts(7,2): error TS1238: Unable to resolve signature of class decorator when called as an expression.
+  The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+    Type argument candidate 'C' is not a valid type argument because it is not a supertype of candidate 'void'.
+
+
+==== tests/cases/conformance/decorators/decoratorCallGeneric.ts (1 errors) ====
+    interface I<T> {
+        prototype: T,
+        m: () => T
+    }
+    function dec<T>(c: I<T>) { }
+    
+    @dec
+     ~~~
+!!! error TS1238: Unable to resolve signature of class decorator when called as an expression.
+!!! error TS1238:   The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly.
+!!! error TS1238:     Type argument candidate 'C' is not a valid type argument because it is not a supertype of candidate 'void'.
+    class C {
+        _brand: any;
+        static m() {}
+    }
+    

tests/baselines/reference/decoratorCallGeneric.js

@@ -0,0 +1,31 @@
+//// [decoratorCallGeneric.ts]
+interface I<T> {
+    prototype: T,
+    m: () => T
+}
+function dec<T>(c: I<T>) { }
+
+@dec
+class C {
+    _brand: any;
+    static m() {}
+}
+
+
+//// [decoratorCallGeneric.js]
+var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
+    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
+    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
+    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
+    return c > 3 && r && Object.defineProperty(target, key, r), r;
+};
+function dec(c) { }
+var C = (function () {
+    function C() {
+    }
+    C.m = function () { };
+    C = __decorate([
+        dec
+    ], C);
+    return C;
+})();

tests/cases/conformance/decorators/decoratorCallGeneric.ts

@@ -0,0 +1,12 @@
+// @experimentalDecorators: true
+interface I<T> {
+    prototype: T,
+    m: () => T
+}
+function dec<T>(c: I<T>) { }
+
+@dec
+class C {
+    _brand: any;
+    static m() {}
+}