[flang-commits] [flang] [llvm] [flang][OpenMP] Apply modifier representation to semantic checks (PR #116658)

[Krzysztof Parzyszek via flang-commits]

================
@@ -3440,6 +3440,16 @@ struct OmpObject {
 
 WRAPPER_CLASS(OmpObjectList, std::list<OmpObject>);
 
+#define MODIFIER_BOILERPLATE(...) \
+  struct Modifier { \
+    using Variant = std::variant<__VA_ARGS__>; \
+    UNION_CLASS_BOILERPLATE(Modifier); \
+    CharBlock source; \
+    Variant u; \
+  }
+
+#define MODIFIERS() std::optional<std::list<Modifier>>
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kparzysz wrote:

The purpose of the `MODIFIERS()` macro is to hide the name "Modifier" that the boilerplate macro introduces.

The `MODIFIER_BOILERPLATE(type1, type2, ...)` macro expands to (roughly)
```
struct Modifier {
  std::variant<type1, type2, ...> u;
};
```
So inside a clause class it will be
```
struct OmpSomeClause {
  struct Modifier {
    std::variant<...> u;
  };
  std::tuple<std::optional<std::list<Modifier>>, ClauseArg1, ClauseArg2...> t;
};
```
The `std::optional<std::list<Modifier>>` here is what the `MODIFIERS()` macro inserts.  It's always the same string (hence no arguments to the macro), but the "Modifier" word in it refers to a different thing each time.

With the alias you suggested, the user would always have to say
```
struct OmpSomeClause {
   MODIFIER_BOILERPLATE(type1, type2, ...)
   std::tuple<Modifiers<Modifier>, ClauseArg1, ClauseArg2, ...> t;
};
```
and explicitly use the word "Modifier".

https://github.com/llvm/llvm-project/pull/116658