lix/src/libexpr/eval.hh

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#pragma once
#include "attr-set.hh"
#include "value.hh"
#include "nixexpr.hh"
#include "symbol-table.hh"
#include "config.hh"
#include <map>
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#include <optional>
#include <unordered_map>
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#include <mutex>
namespace nix {
class Store;
class EvalState;
class 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;
std::vector<std::string> args;
const char * doc = nullptr;
};
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());
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void copyContext(const Value & v, PathSet & context);
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/* 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();
struct RegexCache;
std::shared_ptr<RegexCache> makeRegexCache();
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class EvalState
{
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public:
SymbolTable symbols;
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const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
sFile, sLine, sColumn, sFunctor, sToString,
sRight, sWrong, sStructuredAttrs, sBuilder, sArgs,
sContentAddressed,
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sOutputHash, sOutputHashAlgo, sOutputHashMode,
sRecurseForDerivations,
sDescription, sSelf, sEpsilon;
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. */
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std::optional<PathSet> allowedPaths;
Value vEmptySet;
const ref<Store> store;
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private:
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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::shared_ptr<RegexCache> regexCache;
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public:
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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);
Add primop ‘scopedImport’ ‘scopedImport’ works like ‘import’, except that it takes a set of attributes to be added to the lexical scope of the expression, essentially extending or overriding the builtin variables. For instance, the expression scopedImport { x = 1; } ./foo.nix where foo.nix contains ‘x’, will evaluate to 1. This has a few applications: * It allows getting rid of function argument specifications in package expressions. For instance, a package expression like: { stdenv, fetchurl, libfoo }: stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } can now we written as just stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } and imported in all-packages.nix as: bar = scopedImport pkgs ./bar.nix; So whereas we once had dependencies listed in three places (buildInputs, the function, and the call site), they now only need to appear in one place. * It allows overriding builtin functions. For instance, to trace all calls to ‘map’: let overrides = { map = f: xs: builtins.trace "map called!" (map f xs); # Ensure that our override gets propagated by calls to # import/scopedImport. import = fn: scopedImport overrides fn; scopedImport = attrs: fn: scopedImport (overrides // attrs) fn; # Also update ‘builtins’. builtins = builtins // overrides; }; in scopedImport overrides ./bla.nix * Similarly, it allows extending the set of builtin functions. For instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library functions could be added to the default scope. There is a downside: calls to scopedImport are not memoized, unlike import. So importing a file multiple times leads to multiple parsings / evaluations. It would be possible to construct the AST only once, but that would require careful handling of variables/environments.
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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);
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Expr * parseStdin();
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/* 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);
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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
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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. */
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NixInt forceInt(Value & v, const Pos & pos);
NixFloat forceFloat(Value & v, const Pos & pos);
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bool forceBool(Value & v, const Pos & pos);
inline void forceAttrs(Value & v);
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inline void forceAttrs(Value & v, const Pos & pos);
inline void forceList(Value & v);
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inline void forceList(Value & v, const Pos & pos);
void forceFunction(Value & v, const Pos & pos); // either lambda or primop
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string forceString(Value & v, const Pos & pos = noPos);
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string forceString(Value & v, PathSet & context, const Pos & pos = noPos);
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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);
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std::optional<string> tryAttrsToString(const Pos & pos, Value & v,
PathSet & context, bool coerceMore = false, bool copyToStore = true);
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/* 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,
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referenced paths are copied to the Nix store as a side effect. */
string coerceToString(const Pos & pos, Value & v, PathSet & context,
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bool coerceMore = false, bool copyToStore = true);
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string copyPathToStore(PathSet & context, const Path & path);
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/* 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);
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public:
/* The base environment, containing the builtin functions and
values. */
Env & baseEnv;
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/* The same, but used during parsing to resolve variables. */
StaticEnv staticBaseEnv; // !!! should be private
private:
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unsigned int baseEnvDispl = 0;
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void createBaseEnv();
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Value * addConstant(const string & name, Value & v);
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Value * addPrimOp(const string & name,
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size_t arity, PrimOpFun primOp);
Value * addPrimOp(PrimOp && primOp);
public:
Value & getBuiltin(const string & name);
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struct Doc
{
Pos pos;
std::optional<Symbol> name;
size_t arity;
std::vector<std::string> args;
const char * doc;
};
std::optional<Doc> getDoc(Value & v);
private:
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inline Value * lookupVar(Env * env, const ExprVar & var, bool noEval);
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friend struct ExprVar;
friend struct ExprAttrs;
friend struct ExprLet;
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Expr * parse(const char * text, FileOrigin origin, const Path & path,
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const Path & basePath, StaticEnv & staticEnv);
public:
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/* Do a deep equality test between two values. That is, list
elements and attributes are compared recursively. */
bool eqValues(Value & v1, Value & v2);
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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);
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/* Allocation primitives. */
Value * allocValue();
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Env & allocEnv(size_t size);
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Value * allocAttr(Value & vAttrs, const Symbol & name);
Value * allocAttr(Value & vAttrs, const std::string & name);
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Bindings * allocBindings(size_t capacity);
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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);
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void concatLists(Value & v, size_t nrLists, Value * * lists, const Pos & pos);
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/* Print statistics. */
void printStats();
void realiseContext(const PathSet & context);
private:
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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;
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typedef std::map<Symbol, size_t> PrimOpCalls;
PrimOpCalls primOpCalls;
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typedef std::map<ExprLambda *, size_t> FunctionCalls;
FunctionCalls functionCalls;
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void incrFunctionCall(ExprLambda * fun);
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typedef std::map<Pos, size_t> AttrSelects;
AttrSelects attrSelects;
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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);
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string showType(const Value & v);
/* Decode a context string !<name>!<path> into a pair <path,
name>. */
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std::pair<string, string> decodeContext(std::string_view s);
/* If `path' refers to a directory, then append "/default.nix". */
Path resolveExprPath(Path path);
struct InvalidPathError : EvalError
{
Path path;
InvalidPathError(const Path & path);
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#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",
R"(
If set to `true`, the Nix evaluator will not allow access to any
files outside of the Nix search path (as set via the `NIX_PATH`
environment variable or the `-I` option), or to URIs outside of
`allowed-uri`. The default is `false`.
)"};
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",
R"(
By default, Nix allows you to `import` from a derivation, allowing
building at evaluation time. With this option set to false, Nix will
throw an error when evaluating an expression that uses this feature,
allowing users to ensure their evaluation will not require any
builds to take place.
)"};
Setting<Strings> allowedUris{this, {}, "allowed-uris",
R"(
A list of URI prefixes to which access is allowed in restricted
evaluation mode. For example, when set to
`https://github.com/NixOS`, builtin functions such as `fetchGit` are
allowed to access `https://github.com/NixOS/patchelf.git`.
)"};
Setting<bool> traceFunctionCalls{this, false, "trace-function-calls",
R"(
If set to `true`, the Nix evaluator will trace every function call.
Nix will print a log message at the "vomit" level for every function
entrance and function exit.
function-trace entered undefined position at 1565795816999559622
function-trace exited undefined position at 1565795816999581277
function-trace entered /nix/store/.../example.nix:226:41 at 1565795253249935150
function-trace exited /nix/store/.../example.nix:226:41 at 1565795253249941684
The `undefined position` means the function call is a builtin.
Use the `contrib/stack-collapse.py` script distributed with the Nix
source code to convert the trace logs in to a format suitable for
`flamegraph.pl`.
)"};
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Setting<bool> useEvalCache{this, true, "eval-cache",
"Whether to use the flake evaluation cache."};
};
extern EvalSettings evalSettings;
}