Use C++ fixed-type enumeration syntax under C23 (or higher) as well

C23 [has introduced support for enumerations with fixed underlying
type](https://open-std.org/JTC1/SC22/WG14/www/docs/n3030.htm),
matching the existing C++ syntax for this functionality.

This PR modifies cbindgen to output a header that enables this syntax if
either `__cplusplus` is defined (as before) or if the compilation is
according to C23 or later (added in this PR).

My motivation for this change is that my toolchain complained that some
names were defined twice, both as an enum and a typedef.  I [fixed the
error](https://github.com/Qiskit/Qiskit.jl/blob/73bfbb9440168dc76685632f9fb3d00d3a17bd79/gen/generator.jl#L16-L18)
by defining `__cplusplus` even thought the compiler is compiling in C
mode.  This change will allow me to remove that workaround, as long as
C23 or later is set as the C standard.

Closes #1156

Author: garrison

src/bindgen/ir/enumeration.rs

@@ -680,15 +680,20 @@ impl Enum {
                     }
                     write!(out, " {tag_name}");
 
-                    if config.cpp_compatible_c() {
-                        out.new_line();
-                        out.write("#ifdef __cplusplus");
-                        out.new_line();
-                        write!(out, "  : {prim}");
-                        out.new_line();
-                        out.write("#endif // __cplusplus");
-                        out.new_line();
-                    }
+                    // Emit typed enum syntax (valid in C23 or later or C++)
+                    let cond = if config.cpp_compatible_c() {
+                        "defined(__cplusplus) || __STDC_VERSION__ >= 202311L"
+                    } else {
+                        "__STDC_VERSION__ >= 202311L"
+                    };
+
+                    out.new_line();
+                    write!(out, "#if {cond}");
+                    out.new_line();
+                    write!(out, "  : {prim}");
+                    out.new_line();
+                    write!(out, "#endif // {cond}");
+                    out.new_line();
                 } else {
                     if config.style.generate_typedef() {
                         out.write("typedef ");
@@ -759,17 +764,39 @@ impl Enum {
         }
 
         // Emit typedef specifying the tag enum's size if necessary.
-        // In C++ enums can "inherit" from numeric types (`enum E: uint8_t { ... }`),
-        // but in C `typedef uint8_t E` is the only way to give a fixed size to `E`.
+        // In C++ or C23 enums can "inherit" from numeric types (`enum E: uint8_t { ... }`),
+        // but in older versions of C `typedef uint8_t E` is the only way to give a fixed size to `E`.
         if let Some(prim) = size {
             if config.cpp_compatible_c() {
                 out.new_line_if_not_start();
                 out.write("#ifndef __cplusplus");
             }
 
             if config.language != Language::Cxx {
+                if config.language == Language::C {
+                    out.new_line();
+                    out.write("#if __STDC_VERSION__ >= 202311L");
+
+                    out.new_line();
+                    write!(
+                        out,
+                        "{} enum {} {};",
+                        config.language.typedef(),
+                        tag_name,
+                        tag_name
+                    );
+
+                    out.new_line();
+                    out.write("#else");
+                }
+
                 out.new_line();
                 write!(out, "{} {} {};", config.language.typedef(), prim, tag_name);
+
+                if config.language == Language::C {
+                    out.new_line();
+                    out.write("#endif // __STDC_VERSION__ >= 202311L");
+                }
             }
 
             if config.cpp_compatible_c() {

tests/expectations/alias.c

@@ -3,11 +3,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-enum Status {
+enum Status
+#if __STDC_VERSION__ >= 202311L
+  : uint32_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Ok,
   Err,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct {
   int32_t a;

tests/expectations/alias.compat.c

@@ -4,15 +4,19 @@
 #include <stdlib.h>
 
 enum Status
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint32_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   Ok,
   Err,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 typedef struct {

tests/expectations/alias_both.c

@@ -3,11 +3,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-enum Status {
+enum Status
+#if __STDC_VERSION__ >= 202311L
+  : uint32_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Ok,
   Err,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct Dep {
   int32_t a;

tests/expectations/alias_both.compat.c

@@ -4,15 +4,19 @@
 #include <stdlib.h>
 
 enum Status
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint32_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   Ok,
   Err,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 typedef struct Dep {

tests/expectations/alias_tag.c

@@ -3,11 +3,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-enum Status {
+enum Status
+#if __STDC_VERSION__ >= 202311L
+  : uint32_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Ok,
   Err,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 
 struct Dep {
   int32_t a;

tests/expectations/alias_tag.compat.c

@@ -4,15 +4,19 @@
 #include <stdlib.h>
 
 enum Status
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint32_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   Ok,
   Err,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum Status Status;
+#else
 typedef uint32_t Status;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 struct Dep {

tests/expectations/annotation.c

@@ -3,11 +3,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-enum C {
+enum C
+#if __STDC_VERSION__ >= 202311L
+  : uint32_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   X = 2,
   Y,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum C C;
+#else
 typedef uint32_t C;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct {
   int32_t m0;
@@ -18,12 +26,20 @@ typedef struct {
   float y;
 } B;
 
-enum F_Tag {
+enum F_Tag
+#if __STDC_VERSION__ >= 202311L
+  : uint8_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Foo,
   Bar,
   Baz,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum F_Tag F_Tag;
+#else
 typedef uint8_t F_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct {
   F_Tag tag;
@@ -40,12 +56,20 @@ typedef union {
   Bar_Body bar;
 } F;
 
-enum H_Tag {
+enum H_Tag
+#if __STDC_VERSION__ >= 202311L
+  : uint8_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Hello,
   There,
   Everyone,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum H_Tag H_Tag;
+#else
 typedef uint8_t H_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct {
   uint8_t x;

tests/expectations/annotation.compat.c

@@ -4,15 +4,19 @@
 #include <stdlib.h>
 
 enum C
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint32_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   X = 2,
   Y,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum C C;
+#else
 typedef uint32_t C;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 typedef struct {
@@ -25,16 +29,20 @@ typedef struct {
 } B;
 
 enum F_Tag
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint8_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   Foo,
   Bar,
   Baz,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum F_Tag F_Tag;
+#else
 typedef uint8_t F_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 typedef struct {
@@ -53,16 +61,20 @@ typedef union {
 } F;
 
 enum H_Tag
-#ifdef __cplusplus
+#if defined(__cplusplus) || __STDC_VERSION__ >= 202311L
   : uint8_t
-#endif // __cplusplus
+#endif // defined(__cplusplus) || __STDC_VERSION__ >= 202311L
  {
   Hello,
   There,
   Everyone,
 };
 #ifndef __cplusplus
+#if __STDC_VERSION__ >= 202311L
+typedef enum H_Tag H_Tag;
+#else
 typedef uint8_t H_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 #endif // __cplusplus
 
 typedef struct {

tests/expectations/annotation_both.c

@@ -3,11 +3,19 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-enum C {
+enum C
+#if __STDC_VERSION__ >= 202311L
+  : uint32_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   X = 2,
   Y,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum C C;
+#else
 typedef uint32_t C;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct A {
   int32_t m0;
@@ -18,12 +26,20 @@ typedef struct B {
   float y;
 } B;
 
-enum F_Tag {
+enum F_Tag
+#if __STDC_VERSION__ >= 202311L
+  : uint8_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Foo,
   Bar,
   Baz,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum F_Tag F_Tag;
+#else
 typedef uint8_t F_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct Bar_Body {
   F_Tag tag;
@@ -40,12 +56,20 @@ typedef union F {
   Bar_Body bar;
 } F;
 
-enum H_Tag {
+enum H_Tag
+#if __STDC_VERSION__ >= 202311L
+  : uint8_t
+#endif // __STDC_VERSION__ >= 202311L
+ {
   Hello,
   There,
   Everyone,
 };
+#if __STDC_VERSION__ >= 202311L
+typedef enum H_Tag H_Tag;
+#else
 typedef uint8_t H_Tag;
+#endif // __STDC_VERSION__ >= 202311L
 
 typedef struct There_Body {
   uint8_t x;