[flang-commits] [flang] [flang] Add traits to more AST nodes (PR #175566)

[Krzysztof Parzyszek via flang-commits]

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@@ -433,38 +433,6 @@ struct ParseTreeVisitorLookupScope {
         x, mutator);
   }
 
-  template <typename V> static void Walk(const CallStmt &x, V &visitor) {
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kparzysz wrote:

The parse tree defines certain traits which then impose certain properties on AST classes with these traits.  For example a class with a "TupleTrait" is expected to have a member named `t`, which is `std::tuple`.  The parse-tree-visitor uses these traits to visit all members of a given AST node "generically", so for a class with a TupleTrait it will visit all members of `t`.  This is completely generic and independent of the types contained in `t`.

Some AST classes don't follow that convention, and instead of using a tuple and getting a trait, they list members explicitly.  For those classes there has to be a specific visitor which walks the members of that class.

This series of PRs converts the majority of the non-conforming classes to conform to the trait-based convention, so that the generic "Walk" functions can be used to visit them, instead of having the specialized ones.

For example
```
struct Foo {
   A object;
   B kind;
};
```
is converted to
```
struct Foo {
  TUPLE_CLASS_BOILERPLATE(Foo);  // adds the TupleTrait + other stuff
  std::tuple<A, B> t;
};
```


https://github.com/llvm/llvm-project/pull/175566