nix-super/src/libexpr/primops/fetchMercurial.cc
Rebecca Turner c6a89c1a16
libexpr: Support structured error classes
While preparing PRs like #9753, I've had to change error messages in
dozens of code paths. It would be nice if instead of

    EvalError("expected 'boolean' but found '%1%'", showType(v))

we could write

    TypeError(v, "boolean")

or similar. Then, changing the error message could be a mechanical
refactor with the compiler pointing out places the constructor needs to
be changed, rather than the error-prone process of grepping through the
codebase. Structured errors would also help prevent the "same" error
from having multiple slightly different messages, and could be a first
step towards error codes / an error index.

This PR reworks the exception infrastructure in `libexpr` to
support exception types with different constructor signatures than
`BaseError`. Actually refactoring the exceptions to use structured data
will come in a future PR (this one is big enough already, as it has to
touch every exception in `libexpr`).

The core design is in `eval-error.hh`. Generally, errors like this:

    state.error("'%s' is not a string", getAttrPathStr())
      .debugThrow<TypeError>()

are transformed like this:

    state.error<TypeError>("'%s' is not a string", getAttrPathStr())
      .debugThrow()

The type annotation has moved from `ErrorBuilder::debugThrow` to
`EvalState::error`.
2024-02-01 16:39:38 -08:00

92 lines
3.5 KiB
C++

#include "primops.hh"
#include "eval-inline.hh"
#include "eval-settings.hh"
#include "store-api.hh"
#include "fetchers.hh"
#include "url.hh"
#include "url-parts.hh"
namespace nix {
static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
std::string url;
std::optional<Hash> rev;
std::optional<std::string> ref;
std::string_view name = "source";
NixStringContext context;
state.forceValue(*args[0], pos);
if (args[0]->type() == nAttrs) {
for (auto & attr : *args[0]->attrs) {
std::string_view n(state.symbols[attr.name]);
if (n == "url")
url = state.coerceToString(attr.pos, *attr.value, context,
"while evaluating the `url` attribute passed to builtins.fetchMercurial",
false, false).toOwned();
else if (n == "rev") {
// Ugly: unlike fetchGit, here the "rev" attribute can
// be both a revision or a branch/tag name.
auto value = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `rev` attribute passed to builtins.fetchMercurial");
if (std::regex_match(value.begin(), value.end(), revRegex))
rev = Hash::parseAny(value, HashAlgorithm::SHA1);
else
ref = value;
}
else if (n == "name")
name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `name` attribute passed to builtins.fetchMercurial");
else
state.error<EvalError>("unsupported argument '%s' to 'fetchMercurial'", state.symbols[attr.name]).atPos(attr.pos).debugThrow();
}
if (url.empty())
state.error<EvalError>("'url' argument required").atPos(pos).debugThrow();
} else
url = state.coerceToString(pos, *args[0], context,
"while evaluating the first argument passed to builtins.fetchMercurial",
false, false).toOwned();
// FIXME: git externals probably can be used to bypass the URI
// whitelist. Ah well.
state.checkURI(url);
if (evalSettings.pureEval && !rev)
throw Error("in pure evaluation mode, 'fetchMercurial' requires a Mercurial revision");
fetchers::Attrs attrs;
attrs.insert_or_assign("type", "hg");
attrs.insert_or_assign("url", url.find("://") != std::string::npos ? url : "file://" + url);
attrs.insert_or_assign("name", std::string(name));
if (ref) attrs.insert_or_assign("ref", *ref);
if (rev) attrs.insert_or_assign("rev", rev->gitRev());
auto input = fetchers::Input::fromAttrs(std::move(attrs));
// FIXME: use name
auto [storePath, input2] = input.fetch(state.store);
auto attrs2 = state.buildBindings(8);
state.mkStorePathString(storePath, attrs2.alloc(state.sOutPath));
if (input2.getRef())
attrs2.alloc("branch").mkString(*input2.getRef());
// Backward compatibility: set 'rev' to
// 0000000000000000000000000000000000000000 for a dirty tree.
auto rev2 = input2.getRev().value_or(Hash(HashAlgorithm::SHA1));
attrs2.alloc("rev").mkString(rev2.gitRev());
attrs2.alloc("shortRev").mkString(rev2.gitRev().substr(0, 12));
if (auto revCount = input2.getRevCount())
attrs2.alloc("revCount").mkInt(*revCount);
v.mkAttrs(attrs2);
state.allowPath(storePath);
}
static RegisterPrimOp r_fetchMercurial({
.name = "fetchMercurial",
.arity = 1,
.fun = prim_fetchMercurial
});
}