maint: Avoid g_once_init_enter error in GCC 11

On platforms where g_once_init_enter() is defined to use C11 atomic
builtins, passing a pointer to a volatile value is an error in GCC 11 and
later, in C++.

More info about the GCC change:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95378
https://gcc.gnu.org/pipermail/gcc-patches/2020-June/548283.html

However, it's my understanding that in modern C++ there is no longer a
need to guard the initialization of these variables. Since C++11, static
local variables in a function are guaranteed to be initialized only once,
the first time control passes through that function. So we can just remove
the g_once_init_enter guard.

More info:
https://en.cppreference.com/w/cpp/language/storage_duration#Static_local_variables

Stack Overflow answers with quotations from the C++ standard:
https://stackoverflow.com/a/58804/172999
https://stackoverflow.com/a/8102145/172999

Closes: #376

1 files changed, 13 insertions, 19 deletions

diff --git a/gjs/error-types.cpp b/gjs/error-types.cpp
index cdfd7fa3..4c652da4 100644
--- a/gjs/error-types.cpp
+++ b/gjs/error-types.cpp
@@ -12,24 +12,18 @@ G_DEFINE_QUARK(gjs-js-error-quark, gjs_js_error)
 // clang-format on
 
 GType gjs_js_error_get_type(void) {
-    static volatile GType g_type_id;
-
-    if (g_once_init_enter(&g_type_id)) {
-        static GEnumValue errors[] = {
-            { GJS_JS_ERROR_ERROR, "Error", "error" },
-            { GJS_JS_ERROR_EVAL_ERROR, "EvalError", "eval-error" },
-            { GJS_JS_ERROR_INTERNAL_ERROR, "InternalError", "internal-error" },
-            { GJS_JS_ERROR_RANGE_ERROR, "RangeError", "range-error" },
-            { GJS_JS_ERROR_REFERENCE_ERROR, "ReferenceError", "reference-error" },
-            { GJS_JS_ERROR_STOP_ITERATION, "StopIteration", "stop-iteration" },
-            { GJS_JS_ERROR_SYNTAX_ERROR, "SyntaxError", "syntax-error" },
-            { GJS_JS_ERROR_TYPE_ERROR, "TypeError", "type-error" },
-            { GJS_JS_ERROR_URI_ERROR, "URIError", "uri-error" },
-            { 0, nullptr, nullptr }
-        };
-
-        g_type_id = g_enum_register_static("GjsJSError", errors);
-    }
-
+    static const GEnumValue errors[] = {
+        {GJS_JS_ERROR_ERROR, "Error", "error"},
+        {GJS_JS_ERROR_EVAL_ERROR, "EvalError", "eval-error"},
+        {GJS_JS_ERROR_INTERNAL_ERROR, "InternalError", "internal-error"},
+        {GJS_JS_ERROR_RANGE_ERROR, "RangeError", "range-error"},
+        {GJS_JS_ERROR_REFERENCE_ERROR, "ReferenceError", "reference-error"},
+        {GJS_JS_ERROR_STOP_ITERATION, "StopIteration", "stop-iteration"},
+        {GJS_JS_ERROR_SYNTAX_ERROR, "SyntaxError", "syntax-error"},
+        {GJS_JS_ERROR_TYPE_ERROR, "TypeError", "type-error"},
+        {GJS_JS_ERROR_URI_ERROR, "URIError", "uri-error"},
+        {0, nullptr, nullptr}};
+    // Initialization of static local variable guaranteed only once in C++11
+    static GType g_type_id = g_enum_register_static("GjsJSError", errors);
     return g_type_id;
 }