vbscript: Add err.source implementation.

dlls/vbscript/global.c

@@ -2500,8 +2500,8 @@ static HRESULT Err_Number(vbdisp_t *This, VARIANT *args, unsigned args_cnt, VARI
 
 static HRESULT Err_Source(vbdisp_t *This, VARIANT *args, unsigned args_cnt, VARIANT *res)
 {
-    FIXME("\n");
-    return E_NOTIMPL;
+    TRACE("\n");
+    return !This->desc ? E_UNEXPECTED : err_string_prop(&This->desc->ctx->ei.bstrSource, args, args_cnt, res);
 }
 
 static HRESULT Err_Clear(vbdisp_t *This, VARIANT *args, unsigned args_cnt, VARIANT *res)

dlls/vbscript/interp.c

@@ -2170,6 +2170,7 @@ HRESULT exec_script(script_ctx_t *ctx, function_t *func, vbdisp_t *vbthis, DISPP
                 clear_ei(&ctx->ei);
 
                 ctx->ei.scode = hres = map_hres(hres);
+                ctx->ei.bstrSource = get_vbscript_string(VBS_RUNTIME_ERROR);
                 ctx->ei.bstrDescription = get_vbscript_error_string(hres);
             }else {
                 hres = ctx->ei.scode;

dlls/vbscript/tests/api.vbs

@@ -134,6 +134,7 @@ sub testCStrError()
     Error.clear()
     CStr(null)
     call ok(Err.number = 94, "Err.number = " & Err.number)
+    if isEnglishLang then call ok(Err.source = "Microsoft VBScript runtime error", "Err.source = " & Err.source)
     if isEnglishLang then call ok(Err.description = "Invalid use of Null", "Err.description = " & Err.description)
 end sub
 call testCStrError()