odb: refactoring out serialization code for std::variant

- Makes the code in dbScanPin more simple
- std::variant now is available to be use for serialization by others
- setting template recursion limit to 16 for std::tuple and std::variant

Signed-off-by: Felipe Garay <fgaray@google.com>

src/odb/include/odb/dbStream.h

@@ -39,6 +39,7 @@
 #include <ostream>
 #include <string>
 #include <unordered_map>
+#include <variant>
 
 #include "ZException.h"
 #include "dbObject.h"
@@ -50,6 +51,8 @@ namespace odb {
 
 class _dbDatabase;
 
+inline constexpr size_t kTemplateRecursionLimit = 16;
+
 class dbOStream
 {
   _dbDatabase* _db;
@@ -173,6 +176,9 @@ class dbOStream
   template <size_t I = 0, typename... Ts>
   constexpr dbOStream& operator<<(const std::tuple<Ts...>& tup)
   {
+    static_assert(I <= kTemplateRecursionLimit,
+                  "OpenROAD disallows of std::tuple larger than 16 "
+                  "elements. You should look into alternate solutions");
     if constexpr (I == sizeof...(Ts)) {
       return *this;
     } else {
@@ -222,6 +228,23 @@ class dbOStream
     return *this;
   }
 
+  template <uint32_t I = 0, typename... Ts>
+  dbOStream& operator<<(const std::variant<Ts...>& v)
+  {
+    static_assert(I <= kTemplateRecursionLimit,
+                  "OpenROAD disallows of std::variants larger than 16 "
+                  "elements. You should look into alternate solutions");
+    if constexpr (I == sizeof...(Ts)) {
+      return *this;
+    } else {
+      if (I == v.index()) {
+        *this << (uint32_t) v.index();
+        *this << std::get<I>(v);
+      }
+      return ((*this).operator<< <I + 1>(v));
+    }
+  }
+
   double lefarea(int value) { return ((double) value * _lef_area_factor); }
 
   double lefdist(int value) { return ((double) value * _lef_dist_factor); }
@@ -381,6 +404,9 @@ class dbIStream
   template <size_t I = 0, typename... Ts>
   constexpr dbIStream& operator>>(std::tuple<Ts...>& tup)
   {
+    static_assert(I <= kTemplateRecursionLimit,
+                  "OpenROAD disallows of std::tuple larger than 16 "
+                  "elements. You should look into alternate solutions");
     if constexpr (I == sizeof...(Ts)) {
       return *this;
     } else {
@@ -398,9 +424,34 @@ class dbIStream
     return *this;
   }
 
+  template <uint32_t I = 0, typename... Ts>
+  dbIStream& operator>>(std::variant<Ts...>& v)
+  {
+    uint32_t index = 0;
+    *this >> index;
+    return variantHelper(index, v);
+  }
+
   double lefarea(int value) { return ((double) value * _lef_area_factor); }
 
   double lefdist(int value) { return ((double) value * _lef_dist_factor); }
+
+ private:
+  template <uint32_t I = 0, typename... Ts>
+  dbIStream& variantHelper(uint32_t index, std::variant<Ts...>& v)
+  {
+    static_assert(I <= kTemplateRecursionLimit,
+                  "OpenROAD disallows of std::variants larger than 16 "
+                  "elements. You should look into alternate solutions");
+    if constexpr (I == sizeof...(Ts)) {
+      return *this;
+    } else {
+      if (I == index) {
+        *this >> std::get<I>(v);
+      }
+      return ((*this).operator>><I + 1>(v));
+    }
+  }
 };
 
 }  // namespace odb

src/odb/src/codeGenerator/schema/scan/dbScanPin.json

@@ -2,6 +2,11 @@
   "name": "dbScanPin",
   "type": "dbObject",
   "fields": [
+    {
+      "name": "pin_",
+      "type": "std::variant<dbId<_dbBTerm>, dbId<_dbITerm>>",
+      "flags": ["private", "no-template"]
+    }
   ],
   "h_includes": [
     "dbBTerm.h",

src/odb/src/db/dbScanPin.cpp

@@ -111,33 +111,13 @@ _dbScanPin::_dbScanPin(_dbDatabase* db, const _dbScanPin& r)
 
 dbIStream& operator>>(dbIStream& stream, _dbScanPin& obj)
 {
-  // User Code Begin >>
-  int index = 0;
-  stream >> index;
-  if (index == 0) {
-    dbId<_dbBTerm> bterm;
-    stream >> bterm;
-    obj.pin_ = bterm;
-  } else if (index == 1) {
-    dbId<_dbITerm> iterm;
-    stream >> iterm;
-    obj.pin_ = iterm;
-  }
-  // User Code End >>
+  stream >> obj.pin_;
   return stream;
 }
 
 dbOStream& operator<<(dbOStream& stream, const _dbScanPin& obj)
 {
-  // User Code Begin <<
-  int index = obj.pin_.index();
-  stream << index;
-  if (index == 0) {
-    stream << std::get<0>(obj.pin_);
-  } else if (index == 1) {
-    stream << std::get<1>(obj.pin_);
-  }
-  // User Code End <<
+  stream << obj.pin_;
   return stream;
 }
 

src/odb/src/db/dbScanPin.h

@@ -64,9 +64,7 @@ class _dbScanPin : public _dbObject
                    const _dbScanPin& rhs) const;
   void out(dbDiff& diff, char side, const char* field) const;
 
-  // User Code Begin Fields
   std::variant<dbId<_dbBTerm>, dbId<_dbITerm>> pin_;
-  // User Code End Fields
 };
 dbIStream& operator>>(dbIStream& stream, _dbScanPin& obj);
 dbOStream& operator<<(dbOStream& stream, const _dbScanPin& obj);