lix/src/libexpr/value.hh

#pragma once
///@file

#include <cassert>
#include <climits>

#include "gc-alloc.hh"
#include "symbol-table.hh"
#include "value/context.hh"
#include "input-accessor.hh"
#include "source-path.hh"
#include "print-options.hh"
#include "checked-arithmetic.hh"

#include <nlohmann/json_fwd.hpp>

namespace nix {

class BindingsBuilder;


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

/**
 * This type abstracts over all actual value types in the language,
 * grouping together implementation details like tList*, different function
 * types, and types in non-normal form (so thunks and co.)
 */
typedef enum {
    nThunk,
    nInt,
    nFloat,
    nBool,
    nString,
    nPath,
    nNull,
    nAttrs,
    nList,
    nFunction,
    nExternal
} ValueType;

class Bindings;
struct Env;
struct Expr;
struct ExprLambda;
struct ExprBlackHole;
struct PrimOp;
class Symbol;
class PosIdx;
struct Pos;
class StorePath;
class Store;
class EvalState;
class XMLWriter;
class Printer;

using NixInt = checked::Checked<int64_t>;
using NixFloat = double;

/**
 * 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);
    friend class Printer;
    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;

    /**
     * Coerce the value to a string. Defaults to uncoercable, i.e. throws an
     * error.
     */
    virtual std::string coerceToString(EvalState & state, const PosIdx & pos, NixStringContext & 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 nlohmann::json printValueAsJSON(EvalState & state, bool strict,
        NixStringContext & context, bool copyToStore = true) const;

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

    virtual ~ExternalValueBase()
    {
    };
};

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


struct Value
{
private:
    InternalType internalType;

    friend std::string showType(const Value & v);

public:

    void print(EvalState &state, std::ostream &str, PrintOptions options = PrintOptions {});

    // Functions needed to distinguish the type
    // These should be removed eventually, by putting the functionality that's
    // needed by callers into methods of this type

    // type() == nThunk
    inline bool isThunk() const { return internalType == tThunk; };
    inline bool isApp() const { return internalType == tApp; };
    inline bool isBlackhole() const;

    // type() == nFunction
    inline bool isLambda() const { return internalType == tLambda; };
    inline bool isPrimOp() const { return internalType == tPrimOp; };
    inline bool isPrimOpApp() const { return internalType == tPrimOpApp; };

    union
    {
        NixInt integer;
        bool boolean;

        /**
         * 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 {
            const char * s;
            const char * * context; // must be in sorted order
        } string;

        const char * _path;
        Bindings * attrs;
        struct {
            size_t size;
            Value * * elems;
        } bigList;
        Value * smallList[2];
        struct {
            Env * env;
            Expr * expr;
        } thunk;
        struct {
            Value * left, * right;
        } app;
        struct {
            Env * env;
            ExprLambda * fun;
        } lambda;
        PrimOp * primOp;
        struct {
            Value * left, * right;
        } primOpApp;
        ExternalValueBase * external;
        NixFloat fpoint;
    };

    /**
     * Returns the normal type of a Value. This only returns nThunk if
     * the Value hasn't been forceValue'd
     *
     * @param invalidIsThunk Instead of aborting an an invalid (probably
     * 0, so uninitialized) internal type, return `nThunk`.
     */
    inline ValueType type(bool invalidIsThunk = false) const
    {
        switch (internalType) {
            case tInt: return nInt;
            case tBool: return nBool;
            case tString: return nString;
            case tPath: return nPath;
            case tNull: return nNull;
            case tAttrs: return nAttrs;
            case tList1: case tList2: case tListN: return nList;
            case tLambda: case tPrimOp: case tPrimOpApp: return nFunction;
            case tExternal: return nExternal;
            case tFloat: return nFloat;
            case tThunk: case tApp: return nThunk;
        }
        if (invalidIsThunk)
            return nThunk;
        else
            abort();
    }

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

    inline void mkInt(NixInt::Inner n)
    {
        mkInt(NixInt{n});
    }

    inline void mkInt(NixInt n)
    {
        clearValue();
        internalType = tInt;
        integer = n;
    }

    inline void mkBool(bool b)
    {
        clearValue();
        internalType = tBool;
        boolean = b;
    }

    inline void mkString(const char * s, const char * * context = 0)
    {
        internalType = tString;
        string.s = s;
        string.context = context;
    }

    void mkString(std::string_view s);

    void mkString(std::string_view s, const NixStringContext & context);

    void mkStringMove(const char * s, const NixStringContext & context);

    inline void mkString(const Symbol & s)
    {
        mkString(((const std::string &) s).c_str());
    }

    void mkPath(const SourcePath & path);

    inline void mkPath(const char * path)
    {
        clearValue();
        internalType = tPath;
        _path = path;
    }

    inline void mkNull()
    {
        clearValue();
        internalType = tNull;
    }

    inline void mkAttrs(Bindings * a)
    {
        clearValue();
        internalType = tAttrs;
        attrs = a;
    }

    Value & mkAttrs(BindingsBuilder & bindings);

    inline void mkList(size_t size)
    {
        clearValue();
        if (size == 1)
            internalType = tList1;
        else if (size == 2)
            internalType = tList2;
        else {
            internalType = tListN;
            bigList.size = size;
        }
    }

    inline void mkThunk(Env * e, Expr & ex)
    {
        internalType = tThunk;
        thunk.env = e;
        thunk.expr = &ex;
    }

    inline void mkApp(Value * l, Value * r)
    {
        internalType = tApp;
        app.left = l;
        app.right = r;
    }

    inline void mkLambda(Env * e, ExprLambda * f)
    {
        internalType = tLambda;
        lambda.env = e;
        lambda.fun = f;
    }

    inline void mkBlackhole();

    void mkPrimOp(PrimOp * p);

    inline void mkPrimOpApp(Value * l, Value * r)
    {
        internalType = tPrimOpApp;
        primOpApp.left = l;
        primOpApp.right = r;
    }

    /**
     * For a `tPrimOpApp` value, get the original `PrimOp` value.
     */
    PrimOp * primOpAppPrimOp() const;

    inline void mkExternal(ExternalValueBase * e)
    {
        clearValue();
        internalType = tExternal;
        external = e;
    }

    inline void mkFloat(NixFloat n)
    {
        clearValue();
        internalType = tFloat;
        fpoint = n;
    }

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

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

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

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

    PosIdx determinePos(const PosIdx pos) const;

    /**
     * Check whether forcing this value requires a trivial amount of
     * computation. In particular, function applications are
     * non-trivial.
     */
    bool isTrivial() const;

    auto listItems()
    {
        struct ListIterable
        {
            typedef Value * const * iterator;
            iterator _begin, _end;
            iterator begin() const { return _begin; }
            iterator end() const { return _end; }
        };
        assert(isList());
        auto begin = listElems();
        return ListIterable { begin, begin + listSize() };
    }

    auto listItems() const
    {
        struct ConstListIterable
        {
            typedef const Value * const * iterator;
            iterator _begin, _end;
            iterator begin() const { return _begin; }
            iterator end() const { return _end; }
        };
        assert(isList());
        auto begin = listElems();
        return ConstListIterable { begin, begin + listSize() };
    }

    SourcePath path() const
    {
        assert(internalType == tPath);
        return SourcePath{CanonPath(_path)};
    }

    std::string_view str() const
    {
        assert(internalType == tString);
        return std::string_view(string.s);
    }
};


extern ExprBlackHole eBlackHole;

bool Value::isBlackhole() const
{
    return internalType == tThunk && thunk.expr == (Expr*) &eBlackHole;
}

void Value::mkBlackhole()
{
    internalType = tThunk;
    thunk.expr = (Expr*) &eBlackHole;
}

using ValueVector = GcVector<Value *>;
using ValueMap = GcMap<Symbol, Value *>;
using ValueVectorMap = std::map<Symbol, ValueVector>;

/**
 * A value allocated in traceable memory.
 */
typedef std::shared_ptr<Value *> RootValue;

RootValue allocRootValue(Value * v);

}