Improved error messages for module loading failures.

There are several reasons why a file cannot be opened. Without
extra information, especially in containerized environments, these
problems are difficult to debug. Adding errno status to the
error output helps identify the root cause.

Additionally, error messages are now aligned between njs and QuickJS.

Author: xeioex

nginx/ngx_js.c

@@ -1979,10 +1979,15 @@ ngx_qjs_module_loader(JSContext *cx, const char *module_name, void *opaque)
     info.name.start = (u_char *) module_name;
     info.name.length = njs_strlen(module_name);
 
+    errno = 0;
     ret = ngx_js_module_lookup(conf, &info);
     if (ret != NJS_OK) {
-        JS_ThrowReferenceError(cx, "could not load module filename '%s'",
-                               module_name);
+        if (errno != 0) {
+            JS_ThrowReferenceError(cx, "Cannot load module \"%s\" "
+                                   "(%s:%s)", module_name,
+                                   njs_errno_string(errno), strerror(errno));
+        }
+
         return NULL;
     }
 
@@ -3764,8 +3769,14 @@ ngx_js_module_loader(njs_vm_t *vm, njs_external_ptr_t external, njs_str_t *name)
 
     info.name = *name;
 
+    errno = 0;
     ret = ngx_js_module_lookup(conf, &info);
     if (njs_slow_path(ret != NJS_OK)) {
+        if (errno != 0) {
+            njs_vm_ref_error(vm, "Cannot load module \"%V\" (%s:%s)", name,
+                             njs_errno_string(errno), strerror(errno));
+        }
+
         return NULL;
     }
 

src/njs.h

@@ -72,6 +72,8 @@ extern const njs_value_t            njs_value_undefined;
     njs_vm_error2(vm, 2, fmt, ##__VA_ARGS__)
 #define njs_vm_range_error(vm, fmt, ...)                                      \
     njs_vm_error2(vm, 3, fmt, ##__VA_ARGS__)
+#define njs_vm_ref_error(vm, fmt, ...)                                        \
+    njs_vm_error2(vm, 4, fmt, ##__VA_ARGS__)
 #define njs_vm_syntax_error(vm, fmt, ...)                                     \
     njs_vm_error2(vm, 5, fmt, ##__VA_ARGS__)
 #define njs_vm_type_error(vm, fmt, ...)                                       \

src/njs_module.c

@@ -148,7 +148,7 @@ njs_module_require(njs_vm_t *vm, njs_value_t *args, njs_uint_t nargs,
 
     module = njs_module_find(vm, &name, 0);
     if (njs_slow_path(module == NULL)) {
-        njs_error(vm, "Cannot find module \"%V\"", &name);
+        njs_error(vm, "Cannot load module \"%V\"", &name);
 
         return NJS_ERROR;
     }

src/njs_parser.c

@@ -8114,7 +8114,7 @@ njs_parser_module(njs_parser_t *parser, njs_str_t *name)
     vm = parser->vm;
 
     if (name->length == 0) {
-        njs_parser_syntax_error(parser, "Cannot find module \"%V\"", name);
+        njs_parser_ref_error(parser, "Cannot load module \"%V\"", name);
         return NULL;
     }
 
@@ -8124,13 +8124,16 @@ njs_parser_module(njs_parser_t *parser, njs_str_t *name)
     }
 
     if (vm->module_loader == NULL) {
-        njs_parser_syntax_error(parser, "Cannot load module \"%V\"", name);
+        njs_parser_ref_error(parser, "Module loader callback is not provided");
         return NULL;
     }
 
     module = vm->module_loader(vm, vm->module_loader_opaque, name);
     if (module == NULL) {
-        njs_parser_syntax_error(parser, "Cannot find module \"%V\"", name);
+        if (!njs_is_valid(&vm->exception)) {
+            njs_parser_ref_error(parser, "Cannot load module \"%V\"", name);
+        }
+
         return NULL;
     }
 

src/test/njs_unit_test.c

@@ -18975,7 +18975,7 @@ static njs_unit_test_t  njs_test[] =
     /* require(). */
 
     { njs_str("require('unknown_module')"),
-      njs_str("Error: Cannot find module \"unknown_module\"") },
+      njs_str("Error: Cannot load module \"unknown_module\"") },
 
     { njs_str("require()"),
       njs_str("TypeError: missing path") },
@@ -19045,7 +19045,7 @@ static njs_unit_test_t  njs_test[] =
       njs_str("SyntaxError: Unexpected token \"{\" in 1") },
 
     { njs_str("import x from ''"),
-      njs_str("SyntaxError: Cannot find module \"\" in 1") },
+      njs_str("ReferenceError: Cannot load module \"\" in 1") },
 
     { njs_str("export"),
       njs_str("SyntaxError: Illegal export statement in 1") },

test/shell_test_njs.exp

@@ -173,13 +173,13 @@ njs_test {
 # quiet mode
 
 njs_run {"-q" "test/js/import_chain.t.js"} \
-        "SyntaxError: Cannot find module \"lib2.js\" in 7"
+        "ReferenceError: Cannot load module \"lib2.js\" in 7"
 
 # sandboxing
 
 njs_test {
     {"var fs = require('fs')\r\n"
-     "Error: Cannot find module \"fs\"\r\n"}
+     "Error: Cannot load module \"fs\"\r\n"}
 } "-s"
 
 njs_test {