path: root/third_party/nix/src/libexpr/value.hh

#pragma once

#include <gc/gc_allocator.h>

#include "libexpr/symbol-table.hh"
#include "libutil/types.hh"

namespace nix {

typedef enum {
  tInt = 1,
  tBool,
  tString,
  tPath,
  tNull,
  tAttrs,
  tList1,
  tList2,
  tListN,
  tThunk,
  tApp,
  tLambda,
  tBlackhole,
  tPrimOp,
  tPrimOpApp,
  tExternal,
  tFloat
} ValueType;

class Bindings;
struct Env;
struct Expr;
struct ExprLambda;
struct PrimOp;
struct PrimOp;
class Symbol;
struct Pos;
class EvalState;
class XMLWriter;
class JSONPlaceholder;

typedef int64_t NixInt;
typedef double NixFloat;

/* External values must descend from ExternalValueBase, so that
 * type-agnostic nix functions (e.g. showType) can be implemented
 */
class ExternalValueBase {
  friend std::ostream& operator<<(std::ostream& str,
                                  const ExternalValueBase& v);

 protected:
  /* Print out the value */
  virtual std::ostream& print(std::ostream& str) const = 0;

 public:
  /* Return a simple string describing the type */
  virtual std::string showType() const = 0;

  /* Return a string to be used in builtins.typeOf */
  virtual std::string typeOf() const = 0;

  /* How much space does this value take up */
  virtual size_t valueSize(std::set<const void*>& seen) const = 0;

  /* Coerce the value to a string. Defaults to uncoercable, i.e. throws an
   * error
   */
  virtual std::string coerceToString(const Pos& pos, PathSet& context,
                                     bool copyMore, bool copyToStore) const;

  /* Compare to another value of the same type. Defaults to uncomparable,
   * i.e. always false.
   */
  virtual bool operator==(const ExternalValueBase& b) const;

  /* Print the value as JSON. Defaults to unconvertable, i.e. throws an error */
  virtual void printValueAsJSON(EvalState& state, bool strict,
                                JSONPlaceholder& out, PathSet& context) const;

  /* Print the value as XML. Defaults to unevaluated */
  virtual void printValueAsXML(EvalState& state, bool strict, bool location,
                               XMLWriter& doc, PathSet& context,
                               PathSet& drvsSeen) const;

  virtual ~ExternalValueBase(){};
};

std::ostream& operator<<(std::ostream& str, const ExternalValueBase& v);

// Forward declaration of Value is required because the following
// types are mutually recursive.
//
// TODO(tazjin): Really, these types need some serious refactoring.
struct Value;

/* Strings in the evaluator carry a so-called `context' which
   is a list of strings representing store paths.  This is to
   allow users to write things like

   "--with-freetype2-library=" + freetype + "/lib"

   where `freetype' is a derivation (or a source to be copied
   to the store).  If we just concatenated the strings without
   keeping track of the referenced store paths, then if the
   string is used as a derivation attribute, the derivation
   will not have the correct dependencies in its inputDrvs and
   inputSrcs.

   The semantics of the context is as follows: when a string
   with context C is used as a derivation attribute, then the
   derivations in C will be added to the inputDrvs of the
   derivation, and the other store paths in C will be added to
   the inputSrcs of the derivations.

   For canonicity, the store paths should be in sorted order. */
struct NixString {
  const char* s;
  const char** context;  // must be in sorted order
};

struct NixBigList {
  size_t size;
  Value** elems;
};

struct NixThunk {
  Env* env;
  Expr* expr;
};

struct NixApp {
  Value *left, *right;
};

struct NixLambda {
  Env* env;
  ExprLambda* fun;
};

struct NixPrimOpApp {
  Value *left, *right;
};

struct Value {
  ValueType type;
  union {  // TODO(tazjin): std::variant
    NixInt integer;
    bool boolean;
    NixString string;
    const char* path;
    Bindings* attrs;
    NixBigList bigList;
    Value* smallList[2];
    NixThunk thunk;
    NixApp app;  // TODO(tazjin): "app"?
    NixLambda lambda;
    PrimOp* primOp;
    NixPrimOpApp primOpApp;
    ExternalValueBase* external;
    NixFloat fpoint;
  };

  bool isList() const {
    return type == tList1 || type == tList2 || type == tListN;
  }

  Value** listElems() {
    return type == tList1 || type == tList2 ? smallList : bigList.elems;
  }

  const Value* const* listElems() const {
    return type == tList1 || type == tList2 ? smallList : bigList.elems;
  }

  size_t listSize() const {
    return type == tList1 ? 1 : type == tList2 ? 2 : bigList.size;
  }
};

/* After overwriting an app node, be sure to clear pointers in the
   Value to ensure that the target isn't kept alive unnecessarily. */
static inline void clearValue(Value& v) { v.app.left = v.app.right = 0; }

static inline void mkInt(Value& v, NixInt n) {
  clearValue(v);
  v.type = tInt;
  v.integer = n;
}

static inline void mkFloat(Value& v, NixFloat n) {
  clearValue(v);
  v.type = tFloat;
  v.fpoint = n;
}

static inline void mkBool(Value& v, bool b) {
  clearValue(v);
  v.type = tBool;
  v.boolean = b;
}

static inline void mkNull(Value& v) {
  clearValue(v);
  v.type = tNull;
}

static inline void mkApp(Value& v, Value& left, Value& right) {
  v.type = tApp;
  v.app.left = &left;
  v.app.right = &right;
}

static inline void mkPrimOpApp(Value& v, Value& left, Value& right) {
  v.type = tPrimOpApp;
  v.app.left = &left;
  v.app.right = &right;
}

static inline void mkStringNoCopy(Value& v, const char* s) {
  v.type = tString;
  v.string.s = s;
  v.string.context = 0;
}

static inline void mkString(Value& v, const Symbol& s) {
  mkStringNoCopy(v, ((const std::string&)s).c_str());
}

void mkString(Value& v, const char* s);

static inline void mkPathNoCopy(Value& v, const char* s) {
  clearValue(v);
  v.type = tPath;
  v.path = s;
}

void mkPath(Value& v, const char* s);

/* Compute the size in bytes of the given value, including all values
   and environments reachable from it. Static expressions (Exprs) are
   not included. */
size_t valueSize(Value& v);

typedef std::vector<Value*, gc_allocator<Value*> > ValueVector;
typedef std::map<Symbol, Value*, std::less<Symbol>,
                 gc_allocator<std::pair<const Symbol, Value*> > >
    ValueMap;

}  // namespace nix