lix/src/nix/eval.cc
pennae 8775be3393 store Symbols in a table as well, like positions
this slightly increases the amount of memory used for any given symbol, but this
increase is more than made up for if the symbol is referenced more than once in
the EvalState that holds it. on average every symbol should be referenced at
least twice (once to introduce a binding, once to use it), so we expect no
increase in memory on average.

symbol tables are limited to 2³² entries like position tables, and similar
arguments apply to why overflow is not likely: 2³² symbols would require as many
string instances (at 24 bytes each) and map entries (at 24 bytes or more each,
assuming that the map holds on average at most one item per bucket as the docs
say). a full symbol table would require at least 192GB of memory just for
symbols, which is well out of reach. (an ofborg eval of nixpks today creates
less than a million symbols!)
2022-04-21 21:56:31 +02:00

130 lines
3.9 KiB
C++

#include "command.hh"
#include "common-args.hh"
#include "shared.hh"
#include "store-api.hh"
#include "eval.hh"
#include "eval-inline.hh"
#include "json.hh"
#include "value-to-json.hh"
#include "progress-bar.hh"
using namespace nix;
struct CmdEval : MixJSON, InstallableCommand
{
bool raw = false;
std::optional<std::string> apply;
std::optional<Path> writeTo;
CmdEval() : InstallableCommand(true /* supportReadOnlyMode */)
{
addFlag({
.longName = "raw",
.description = "Print strings without quotes or escaping.",
.handler = {&raw, true},
});
addFlag({
.longName = "apply",
.description = "Apply the function *expr* to each argument.",
.labels = {"expr"},
.handler = {&apply},
});
addFlag({
.longName = "write-to",
.description = "Write a string or attrset of strings to *path*.",
.labels = {"path"},
.handler = {&writeTo},
});
}
std::string description() override
{
return "evaluate a Nix expression";
}
std::string doc() override
{
return
#include "eval.md"
;
}
Category category() override { return catSecondary; }
void run(ref<Store> store) override
{
if (raw && json)
throw UsageError("--raw and --json are mutually exclusive");
auto state = getEvalState();
auto [v, pos] = installable->toValue(*state);
PathSet context;
if (apply) {
auto vApply = state->allocValue();
state->eval(state->parseExprFromString(*apply, absPath(".")), *vApply);
auto vRes = state->allocValue();
state->callFunction(*vApply, *v, *vRes, noPos);
v = vRes;
}
if (writeTo) {
stopProgressBar();
if (pathExists(*writeTo))
throw Error("path '%s' already exists", *writeTo);
std::function<void(Value & v, const PosIdx pos, const Path & path)> recurse;
recurse = [&](Value & v, const PosIdx pos, const Path & path)
{
state->forceValue(v, pos);
if (v.type() == nString)
// FIXME: disallow strings with contexts?
writeFile(path, v.string.s);
else if (v.type() == nAttrs) {
if (mkdir(path.c_str(), 0777) == -1)
throw SysError("creating directory '%s'", path);
for (auto & attr : *v.attrs) {
std::string_view name = state->symbols[attr.name];
try {
if (name == "." || name == "..")
throw Error("invalid file name '%s'", name);
recurse(*attr.value, attr.pos, concatStrings(path, "/", name));
} catch (Error & e) {
e.addTrace(
state->positions[attr.pos],
hintfmt("while evaluating the attribute '%s'", name));
throw;
}
}
}
else
throw TypeError("value at '%s' is not a string or an attribute set", state->positions[pos]);
};
recurse(*v, pos, *writeTo);
}
else if (raw) {
stopProgressBar();
std::cout << *state->coerceToString(noPos, *v, context);
}
else if (json) {
JSONPlaceholder jsonOut(std::cout);
printValueAsJSON(*state, true, *v, pos, jsonOut, context);
}
else {
state->forceValueDeep(*v);
logger->cout("%s", printValue(*state, *v));
}
}
};
static auto rCmdEval = registerCommand<CmdEval>("eval");