lix/src/libexpr/eval.hh

#pragma once

#include "attr-set.hh"
#include "value.hh"
#include "nixexpr.hh"
#include "symbol-table.hh"
#include "config.hh"

#include <regex>
#include <map>
#include <optional>
#include <unordered_map>
#include <mutex>


namespace nix {


class Store;
class EvalState;
struct StorePath;
enum RepairFlag : bool;


typedef void (* PrimOpFun) (EvalState & state, const Pos & pos, Value * * args, Value & v);


struct PrimOp
{
    PrimOpFun fun;
    size_t arity;
    Symbol name;
    PrimOp(PrimOpFun fun, size_t arity, Symbol name)
        : fun(fun), arity(arity), name(name) { }
};


struct Env
{
    Env * up;
    unsigned short prevWith:14; // nr of levels up to next `with' environment
    enum { Plain = 0, HasWithExpr, HasWithAttrs } type:2;
    Value * values[0];
};


Value & mkString(Value & v, std::string_view s, const PathSet & context = PathSet());

void copyContext(const Value & v, PathSet & context);


/* Cache for calls to addToStore(); maps source paths to the store
   paths. */
typedef std::map<Path, StorePath> SrcToStore;


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


typedef std::pair<std::string, std::string> SearchPathElem;
typedef std::list<SearchPathElem> SearchPath;


/* Initialise the Boehm GC, if applicable. */
void initGC();


class EvalState
{
public:
    SymbolTable symbols;

    const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
        sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
        sFile, sLine, sColumn, sFunctor, sToString,
        sRight, sWrong, sStructuredAttrs, sBuilder, sArgs,
        sOutputHash, sOutputHashAlgo, sOutputHashMode,
        sDescription, sSelf, sEpsilon, sRecurseForDerivations;
    Symbol sDerivationNix;

    /* If set, force copying files to the Nix store even if they
       already exist there. */
    RepairFlag repair;

    /* The allowed filesystem paths in restricted or pure evaluation
       mode. */
    std::optional<PathSet> allowedPaths;

    Value vEmptySet;

    const ref<Store> store;


private:
    SrcToStore srcToStore;

    /* A cache from path names to parse trees. */
#if HAVE_BOEHMGC
    typedef std::map<Path, Expr *, std::less<Path>, traceable_allocator<std::pair<const Path, Expr *> > > FileParseCache;
#else
    typedef std::map<Path, Expr *> FileParseCache;
#endif
    FileParseCache fileParseCache;

    /* A cache from path names to values. */
#if HAVE_BOEHMGC
    typedef std::map<Path, Value, std::less<Path>, traceable_allocator<std::pair<const Path, Value> > > FileEvalCache;
#else
    typedef std::map<Path, Value> FileEvalCache;
#endif
    FileEvalCache fileEvalCache;

    SearchPath searchPath;

    std::map<std::string, std::pair<bool, std::string>> searchPathResolved;

    /* Cache used by checkSourcePath(). */
    std::unordered_map<Path, Path> resolvedPaths;

    /* Cache used by prim_match(). */
    std::unordered_map<std::string, std::regex> regexCache;

public:

    EvalState(const Strings & _searchPath, ref<Store> store);
    ~EvalState();

    void addToSearchPath(const string & s);

    SearchPath getSearchPath() { return searchPath; }

    Path checkSourcePath(const Path & path);

    void checkURI(const std::string & uri);

    /* When using a diverted store and 'path' is in the Nix store, map
       'path' to the diverted location (e.g. /nix/store/foo is mapped
       to /home/alice/my-nix/nix/store/foo). However, this is only
       done if the context is not empty, since otherwise we're
       probably trying to read from the actual /nix/store. This is
       intended to distinguish between import-from-derivation and
       sources stored in the actual /nix/store. */
    Path toRealPath(const Path & path, const PathSet & context);

    /* Parse a Nix expression from the specified file. */
    Expr * parseExprFromFile(const Path & path);
    Expr * parseExprFromFile(const Path & path, StaticEnv & staticEnv);

    /* Parse a Nix expression from the specified string. */
    Expr * parseExprFromString(std::string_view s, const Path & basePath, StaticEnv & staticEnv);
    Expr * parseExprFromString(std::string_view s, const Path & basePath);

    Expr * parseStdin();

    /* Evaluate an expression read from the given file to normal
       form. Optionally enforce that the top-level expression is
       trivial (i.e. doesn't require arbitrary computation). */
    void evalFile(const Path & path, Value & v, bool mustBeTrivial = false);

    void resetFileCache();

    /* Look up a file in the search path. */
    Path findFile(const string & path);
    Path findFile(SearchPath & searchPath, const string & path, const Pos & pos = noPos);

    /* If the specified search path element is a URI, download it. */
    std::pair<bool, std::string> resolveSearchPathElem(const SearchPathElem & elem);

    /* Evaluate an expression to normal form, storing the result in
       value `v'. */
    void eval(Expr * e, Value & v);

    /* Evaluation the expression, then verify that it has the expected
       type. */
    inline bool evalBool(Env & env, Expr * e);
    inline bool evalBool(Env & env, Expr * e, const Pos & pos);
    inline void evalAttrs(Env & env, Expr * e, Value & v);

    /* If `v' is a thunk, enter it and overwrite `v' with the result
       of the evaluation of the thunk.  If `v' is a delayed function
       application, call the function and overwrite `v' with the
       result.  Otherwise, this is a no-op. */
    inline void forceValue(Value & v, const Pos & pos = noPos);

    /* Force a value, then recursively force list elements and
       attributes. */
    void forceValueDeep(Value & v);

    /* Force `v', and then verify that it has the expected type. */
    NixInt forceInt(Value & v, const Pos & pos);
    NixFloat forceFloat(Value & v, const Pos & pos);
    bool forceBool(Value & v, const Pos & pos);
    inline void forceAttrs(Value & v);
    inline void forceAttrs(Value & v, const Pos & pos);
    inline void forceList(Value & v);
    inline void forceList(Value & v, const Pos & pos);
    void forceFunction(Value & v, const Pos & pos); // either lambda or primop
    string forceString(Value & v, const Pos & pos = noPos);
    string forceString(Value & v, PathSet & context, const Pos & pos = noPos);
    string forceStringNoCtx(Value & v, const Pos & pos = noPos);

    /* Return true iff the value `v' denotes a derivation (i.e. a
       set with attribute `type = "derivation"'). */
    bool isDerivation(Value & v);

    std::optional<string> tryAttrsToString(const Pos & pos, Value & v,
        PathSet & context, bool coerceMore = false, bool copyToStore = true);

    /* String coercion.  Converts strings, paths and derivations to a
       string.  If `coerceMore' is set, also converts nulls, integers,
       booleans and lists to a string.  If `copyToStore' is set,
       referenced paths are copied to the Nix store as a side effect. */
    string coerceToString(const Pos & pos, Value & v, PathSet & context,
        bool coerceMore = false, bool copyToStore = true);

    string copyPathToStore(PathSet & context, const Path & path);

    /* Path coercion.  Converts strings, paths and derivations to a
       path.  The result is guaranteed to be a canonicalised, absolute
       path.  Nothing is copied to the store. */
    Path coerceToPath(const Pos & pos, Value & v, PathSet & context);

public:

    /* The base environment, containing the builtin functions and
       values. */
    Env & baseEnv;

    /* The same, but used during parsing to resolve variables. */
    StaticEnv staticBaseEnv; // !!! should be private

private:

    unsigned int baseEnvDispl = 0;

    void createBaseEnv();

    Value * addConstant(const string & name, Value & v);

    Value * addPrimOp(const string & name,
        size_t arity, PrimOpFun primOp);

public:

    Value & getBuiltin(const string & name);

private:

    inline Value * lookupVar(Env * env, const ExprVar & var, bool noEval);

    friend struct ExprVar;
    friend struct ExprAttrs;
    friend struct ExprLet;

    Expr * parse(const char * text, const Path & path,
        const Path & basePath, StaticEnv & staticEnv);

public:

    /* Do a deep equality test between two values.  That is, list
       elements and attributes are compared recursively. */
    bool eqValues(Value & v1, Value & v2);

    bool isFunctor(Value & fun);

    void callFunction(Value & fun, Value & arg, Value & v, const Pos & pos);
    void callPrimOp(Value & fun, Value & arg, Value & v, const Pos & pos);

    /* Automatically call a function for which each argument has a
       default value or has a binding in the `args' map. */
    void autoCallFunction(Bindings & args, Value & fun, Value & res);

    /* Allocation primitives. */
    Value * allocValue();
    Env & allocEnv(size_t size);

    Value * allocAttr(Value & vAttrs, const Symbol & name);
    Value * allocAttr(Value & vAttrs, const std::string & name);

    Bindings * allocBindings(size_t capacity);

    void mkList(Value & v, size_t length);
    void mkAttrs(Value & v, size_t capacity);
    void mkThunk_(Value & v, Expr * expr);
    void mkPos(Value & v, Pos * pos);

    void concatLists(Value & v, size_t nrLists, Value * * lists, const Pos & pos);

    /* Print statistics. */
    void printStats();

    void realiseContext(const PathSet & context);

private:

    unsigned long nrEnvs = 0;
    unsigned long nrValuesInEnvs = 0;
    unsigned long nrValues = 0;
    unsigned long nrListElems = 0;
    unsigned long nrAttrsets = 0;
    unsigned long nrAttrsInAttrsets = 0;
    unsigned long nrOpUpdates = 0;
    unsigned long nrOpUpdateValuesCopied = 0;
    unsigned long nrListConcats = 0;
    unsigned long nrPrimOpCalls = 0;
    unsigned long nrFunctionCalls = 0;

    bool countCalls;

    typedef std::map<Symbol, size_t> PrimOpCalls;
    PrimOpCalls primOpCalls;

    typedef std::map<ExprLambda *, size_t> FunctionCalls;
    FunctionCalls functionCalls;

    void incrFunctionCall(ExprLambda * fun);

    typedef std::map<Pos, size_t> AttrSelects;
    AttrSelects attrSelects;

    friend struct ExprOpUpdate;
    friend struct ExprOpConcatLists;
    friend struct ExprSelect;
    friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
    friend void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v);
};


/* Return a string representing the type of the value `v'. */
string showType(ValueType type);
string showType(const Value & v);

/* Decode a context string ‘!<name>!<path>’ into a pair <path,
   name>. */
std::pair<string, string> decodeContext(const string & s);

/* If `path' refers to a directory, then append "/default.nix". */
Path resolveExprPath(Path path);

struct InvalidPathError : EvalError
{
    Path path;
    InvalidPathError(const Path & path);
#ifdef EXCEPTION_NEEDS_THROW_SPEC
    ~InvalidPathError() throw () { };
#endif
};

struct EvalSettings : Config
{
    EvalSettings();

    static Strings getDefaultNixPath();

    Setting<bool> enableNativeCode{this, false, "allow-unsafe-native-code-during-evaluation",
        "Whether builtin functions that allow executing native code should be enabled."};

    Setting<Strings> nixPath{this, getDefaultNixPath(), "nix-path",
        "List of directories to be searched for <...> file references."};

    Setting<bool> restrictEval{this, false, "restrict-eval",
        "Whether to restrict file system access to paths in $NIX_PATH, "
        "and network access to the URI prefixes listed in 'allowed-uris'."};

    Setting<bool> pureEval{this, false, "pure-eval",
        "Whether to restrict file system and network access to files specified by cryptographic hash."};

    Setting<bool> enableImportFromDerivation{this, true, "allow-import-from-derivation",
        "Whether the evaluator allows importing the result of a derivation."};

    Setting<Strings> allowedUris{this, {}, "allowed-uris",
        "Prefixes of URIs that builtin functions such as fetchurl and fetchGit are allowed to fetch."};

    Setting<bool> traceFunctionCalls{this, false, "trace-function-calls",
        "Emit log messages for each function entry and exit at the 'vomit' log level (-vvvv)."};
};

extern EvalSettings evalSettings;

}