[flang] Start on f90_correct. Incorporate review comments.

Original-commit: flang-compiler/f18@3f8cecef8e
Reviewed-on: https://github.com/flang-compiler/f18/pull/25
Tree-same-pre-rewrite: false

flang/lib/parser/characters.cc

@@ -58,11 +58,11 @@ std::optional<size_t> CountCharacters(
   const char *limit{p + bytes};
   while (p < limit) {
     ++chars;
-    if (std::optional<int> cb{cbf(p)}) {
-      p += *cb;
-    } else {
+    std::optional<int> cb{cbf(p)};
+    if (!cb.has_value()) {
       return {};
     }
+    p += *cb;
   }
   return {chars};
 }

flang/lib/parser/unparse.cc

@@ -435,6 +435,18 @@ public:
     Put(' '), Walk(std::get<std::list<EntityDecl>>(x.t), ", ");
     return false;
   }
+  bool Pre(const AttrSpec &x) {  // R802
+    std::visit(visitors{[&](const CoarraySpec &y) { Put("CODIMENSION["); },
+                   [&](const ArraySpec &y) { Put("DIMENSION("); },
+                   [&](const auto &) {}},
+        x.u);
+    return true;
+  }
+  void Post(const AttrSpec &x) {
+    std::visit(visitors{[&](const CoarraySpec &y) { Put(']'); },
+                   [&](const ArraySpec &y) { Put(')'); }, [&](const auto &) {}},
+        x.u);
+  }
   bool Pre(const EntityDecl &x) {  // R803
     Walk(std::get<ObjectName>(x.t));
     Walk("(", std::get<std::optional<ArraySpec>>(x.t), ")");