lix/src/libexpr/eval.hh
Eelco Dolstra d4dcffd643
Add pure evaluation mode
In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
2018-01-16 19:23:18 +01:00

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#pragma once
#include "attr-set.hh"
#include "value.hh"
#include "nixexpr.hh"
#include "symbol-table.hh"
#include "hash.hh"
#include <map>
namespace nix {
class Store;
class EvalState;
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 size; // used by valueSize
unsigned short prevWith:15; // nr of levels up to next `with' environment
unsigned short haveWithAttrs:1;
Value * values[0];
};
Value & mkString(Value & v, const string & 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, Path> 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;
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::experimental::optional<PathSet> allowedPaths;
Value vEmptySet;
const ref<Store> store;
private:
SrcToStore srcToStore;
/* 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;
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(const string & s, const Path & basePath, StaticEnv & staticEnv);
Expr * parseExprFromString(const string & s, const Path & basePath);
Expr * parseStdin();
/* Evaluate an expression read from the given file to normal
form. */
void evalFile(const Path & path, Value & v);
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);
/* 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();
void addConstant(const string & name, Value & v);
Value * addPrimOp(const string & name,
unsigned int 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(unsigned int size);
Value * allocAttr(Value & vAttrs, const Symbol & name);
Bindings * allocBindings(Bindings::size_t capacity);
void mkList(Value & v, unsigned int length);
void mkAttrs(Value & v, unsigned int capacity);
void mkThunk_(Value & v, Expr * expr);
void mkPos(Value & v, Pos * pos);
void concatLists(Value & v, unsigned int 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, unsigned int> PrimOpCalls;
PrimOpCalls primOpCalls;
typedef std::map<ExprLambda *, unsigned int> FunctionCalls;
FunctionCalls functionCalls;
void incrFunctionCall(ExprLambda * fun);
typedef std::map<Pos, unsigned int> 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);
};
/* Return a string representing the type of the value `v'. */
string showType(const Value & v);
/* 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
};
}