nix-super/src/libexpr/primops/fetchTree.cc

#include "primops.hh"
#include "eval-inline.hh"
#include "eval-settings.hh"
#include "store-api.hh"
#include "fetchers.hh"
#include "filetransfer.hh"
#include "registry.hh"
#include "url.hh"

#include <ctime>
#include <iomanip>
#include <regex>

namespace nix {

void emitTreeAttrs(
    EvalState & state,
    const fetchers::Tree & tree,
    const fetchers::Input & input,
    Value & v,
    bool emptyRevFallback,
    bool forceDirty)
{
    assert(input.isLocked());

    auto attrs = state.buildBindings(10);

    state.mkStorePathString(tree.storePath, attrs.alloc(state.sOutPath));

    // FIXME: support arbitrary input attributes.

    auto narHash = input.getNarHash();
    assert(narHash);
    attrs.alloc("narHash").mkString(narHash->to_string(SRI, true));

    if (input.getType() == "git")
        attrs.alloc("submodules").mkBool(
            fetchers::maybeGetBoolAttr(input.attrs, "submodules").value_or(false));

    if (!forceDirty) {

        if (auto rev = input.getRev()) {
            attrs.alloc("rev").mkString(rev->gitRev());
            attrs.alloc("shortRev").mkString(rev->gitShortRev());
        } else if (emptyRevFallback) {
            // Backwards compat for `builtins.fetchGit`: dirty repos return an empty sha1 as rev
            auto emptyHash = Hash(htSHA1);
            attrs.alloc("rev").mkString(emptyHash.gitRev());
            attrs.alloc("shortRev").mkString(emptyHash.gitShortRev());
        }

        if (auto revCount = input.getRevCount())
            attrs.alloc("revCount").mkInt(*revCount);
        else if (emptyRevFallback)
            attrs.alloc("revCount").mkInt(0);

    }

    if (auto dirtyRev = fetchers::maybeGetStrAttr(input.attrs, "dirtyRev")) {
        attrs.alloc("dirtyRev").mkString(*dirtyRev);
        attrs.alloc("dirtyShortRev").mkString(*fetchers::maybeGetStrAttr(input.attrs, "dirtyShortRev"));
    }

    if (auto lastModified = input.getLastModified()) {
        attrs.alloc("lastModified").mkInt(*lastModified);
        attrs.alloc("lastModifiedDate").mkString(
            fmt("%s", std::put_time(std::gmtime(&*lastModified), "%Y%m%d%H%M%S")));
    }

    v.mkAttrs(attrs);
}

struct FetchTreeParams {
    bool emptyRevFallback = false;
    bool allowNameArgument = false;
    bool isFetchGit = false;
};

static void fetchTree(
    EvalState & state,
    const PosIdx pos,
    Value * * args,
    Value & v,
    const FetchTreeParams & params = FetchTreeParams{}
) {
    fetchers::Input input;
    NixStringContext context;
    std::optional<std::string> type;
    if (params.isFetchGit) type = "git";

    state.forceValue(*args[0], pos);

    if (args[0]->type() == nAttrs) {
        state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.fetchTree");

        fetchers::Attrs attrs;

        if (auto aType = args[0]->attrs->get(state.sType)) {
            if (type)
                state.debugThrowLastTrace(EvalError({
                    .msg = hintfmt("unexpected attribute 'type'"),
                    .errPos = state.positions[pos]
                }));
            type = state.forceStringNoCtx(*aType->value, aType->pos, "while evaluating the `type` attribute passed to builtins.fetchTree");
        } else if (!type)
            state.debugThrowLastTrace(EvalError({
                .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
                .errPos = state.positions[pos]
            }));

        attrs.emplace("type", type.value());

        for (auto & attr : *args[0]->attrs) {
            if (attr.name == state.sType) continue;
            state.forceValue(*attr.value, attr.pos);
            if (attr.value->type() == nPath || attr.value->type() == nString) {
                auto s = state.coerceToString(attr.pos, *attr.value, context, "", false, false).toOwned();
                attrs.emplace(state.symbols[attr.name],
                    params.isFetchGit && state.symbols[attr.name] == "url"
                    ? fixGitURL(s)
                    : s);
            }
            else if (attr.value->type() == nBool)
                attrs.emplace(state.symbols[attr.name], Explicit<bool>{attr.value->boolean});
            else if (attr.value->type() == nInt)
                attrs.emplace(state.symbols[attr.name], uint64_t(attr.value->integer));
            else
                state.debugThrowLastTrace(TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
                    state.symbols[attr.name], showType(*attr.value)));
        }

        if (!params.allowNameArgument)
            if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
                state.debugThrowLastTrace(EvalError({
                    .msg = hintfmt("attribute 'name' isn’t supported in call to 'fetchTree'"),
                    .errPos = state.positions[pos]
                }));

        input = fetchers::Input::fromAttrs(std::move(attrs));
    } else {
        auto url = state.coerceToString(pos, *args[0], context,
                "while evaluating the first argument passed to the fetcher",
                false, false).toOwned();

        if (params.isFetchGit) {
            fetchers::Attrs attrs;
            attrs.emplace("type", "git");
            attrs.emplace("url", fixGitURL(url));
            input = fetchers::Input::fromAttrs(std::move(attrs));
        } else {
            if (!experimentalFeatureSettings.isEnabled(Xp::Flakes))
                state.debugThrowLastTrace(EvalError({
                    .msg = hintfmt("passing a string argument to 'fetchTree' requires the 'flakes' experimental feature"),
                    .errPos = state.positions[pos]
                }));
            input = fetchers::Input::fromURL(url);
        }
    }

    if (!evalSettings.pureEval && !input.isDirect() && experimentalFeatureSettings.isEnabled(Xp::Flakes))
        input = lookupInRegistries(state.store, input).first;

    if (evalSettings.pureEval && !input.isLocked())
        state.debugThrowLastTrace(EvalError("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", state.positions[pos]));

    state.checkURI(input.toURLString());

    auto [tree, input2] = input.fetch(state.store);

    state.allowPath(tree.storePath);

    emitTreeAttrs(state, tree, input2, v, params.emptyRevFallback, false);
}

static void prim_fetchTree(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
    fetchTree(state, pos, args, v, { });
}

static RegisterPrimOp primop_fetchTree({
    .name = "fetchTree",
    .args = {"input"},
    .doc = R"(
      Fetch a source tree or a plain file using one of the supported backends.
      *input* must be a [flake reference](@docroot@/command-ref/new-cli/nix3-flake.md#flake-references), either in attribute set representation or in the URL-like syntax.
      The input should be "locked", that is, it should contain a commit hash or content hash unless impure evaluation (`--impure`) is enabled.

      > **Note**
      >
      > The URL-like syntax requires the [`flakes` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-flakes) to be enabled.

      Here are some examples of how to use `fetchTree`:

      - Fetch a GitHub repository using the attribute set representation:

          ```nix
          builtins.fetchTree {
            type = "github";
            owner = "NixOS";
            repo = "nixpkgs";
            rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
          }
          ```

        This evaluates to the following attribute set:

          ```
          {
            lastModified = 1686503798;
            lastModifiedDate = "20230611171638";
            narHash = "sha256-rA9RqKP9OlBrgGCPvfd5HVAXDOy8k2SmPtB/ijShNXc=";
            outPath = "/nix/store/l5m6qlvfs9sdw14ja3qbzpglcjlb6j1x-source";
            rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
            shortRev = "ae2e6b3";
          }
          ```

      - Fetch the same GitHub repository using the URL-like syntax:

          ```
          builtins.fetchTree "github:NixOS/nixpkgs/ae2e6b3958682513d28f7d633734571fb18285dd"
          ```
    )",
    .fun = prim_fetchTree,
});

static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v,
    const std::string & who, bool unpack, std::string name)
{
    std::optional<std::string> url;
    std::optional<Hash> expectedHash;

    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.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the url we should fetch");
            else if (n == "sha256")
                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the sha256 of the content we should fetch"), htSHA256);
            else if (n == "name")
                name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the name of the content we should fetch");
            else
                state.debugThrowLastTrace(EvalError({
                    .msg = hintfmt("unsupported argument '%s' to '%s'", n, who),
                    .errPos = state.positions[attr.pos]
                }));
        }

        if (!url)
            state.debugThrowLastTrace(EvalError({
                .msg = hintfmt("'url' argument required"),
                .errPos = state.positions[pos]
            }));
    } else
        url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");

    if (who == "fetchTarball")
        url = evalSettings.resolvePseudoUrl(*url);

    state.checkURI(*url);

    if (name == "")
        name = baseNameOf(*url);

    if (evalSettings.pureEval && !expectedHash)
        state.debugThrowLastTrace(EvalError("in pure evaluation mode, '%s' requires a 'sha256' argument", who));

    // early exit if pinned and already in the store
    if (expectedHash && expectedHash->type == htSHA256) {
        auto expectedPath = state.store->makeFixedOutputPath(
            name,
            FixedOutputInfo {
                .method = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat,
                .hash = *expectedHash,
                .references = {}
            });

        if (state.store->isValidPath(expectedPath)) {
            state.allowAndSetStorePathString(expectedPath, v);
            return;
        }
    }

    // TODO: fetching may fail, yet the path may be substitutable.
    //       https://github.com/NixOS/nix/issues/4313
    auto storePath =
        unpack
        ? fetchers::downloadTarball(state.store, *url, name, (bool) expectedHash).tree.storePath
        : fetchers::downloadFile(state.store, *url, name, (bool) expectedHash).storePath;

    if (expectedHash) {
        auto hash = unpack
            ? state.store->queryPathInfo(storePath)->narHash
            : hashFile(htSHA256, state.store->toRealPath(storePath));
        if (hash != *expectedHash)
            state.debugThrowLastTrace(EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true)));
    }

    state.allowAndSetStorePathString(storePath, v);
}

static void prim_fetchurl(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
    fetch(state, pos, args, v, "fetchurl", false, "");
}

static RegisterPrimOp primop_fetchurl({
    .name = "__fetchurl",
    .args = {"url"},
    .doc = R"(
      Download the specified URL and return the path of the downloaded file.

      Not available in [restricted evaluation mode](@docroot@/command-ref/conf-file.md#conf-restrict-eval).
    )",
    .fun = prim_fetchurl,
});

static void prim_fetchTarball(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
    fetch(state, pos, args, v, "fetchTarball", true, "source");
}

static RegisterPrimOp primop_fetchTarball({
    .name = "fetchTarball",
    .args = {"args"},
    .doc = R"(
      Download the specified URL, unpack it and return the path of the
      unpacked tree. The file must be a tape archive (`.tar`) compressed
      with `gzip`, `bzip2` or `xz`. The top-level path component of the
      files in the tarball is removed, so it is best if the tarball
      contains a single directory at top level. The typical use of the
      function is to obtain external Nix expression dependencies, such as
      a particular version of Nixpkgs, e.g.

      ```nix
      with import (fetchTarball https://github.com/NixOS/nixpkgs/archive/nixos-14.12.tar.gz) {};

      stdenv.mkDerivation { … }
      ```

      The fetched tarball is cached for a certain amount of time (1
      hour by default) in `~/.cache/nix/tarballs/`. You can change the
      cache timeout either on the command line with `--tarball-ttl`
      *number-of-seconds* or in the Nix configuration file by adding
      the line `tarball-ttl = ` *number-of-seconds*.

      Note that when obtaining the hash with `nix-prefetch-url` the
      option `--unpack` is required.

      This function can also verify the contents against a hash. In that
      case, the function takes a set instead of a URL. The set requires
      the attribute `url` and the attribute `sha256`, e.g.

      ```nix
      with import (fetchTarball {
        url = "https://github.com/NixOS/nixpkgs/archive/nixos-14.12.tar.gz";
        sha256 = "1jppksrfvbk5ypiqdz4cddxdl8z6zyzdb2srq8fcffr327ld5jj2";
      }) {};

      stdenv.mkDerivation { … }
      ```

      Not available in [restricted evaluation mode](@docroot@/command-ref/conf-file.md#conf-restrict-eval).
    )",
    .fun = prim_fetchTarball,
});

static void prim_fetchGit(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
    fetchTree(state, pos, args, v,
        FetchTreeParams {
            .emptyRevFallback = true,
            .allowNameArgument = true,
            .isFetchGit = true
        });
}

static RegisterPrimOp primop_fetchGit({
    .name = "fetchGit",
    .args = {"args"},
    .doc = R"(
      Fetch a path from git. *args* can be a URL, in which case the HEAD
      of the repo at that URL is fetched. Otherwise, it can be an
      attribute with the following attributes (all except `url` optional):

      - `url`

        The URL of the repo.

      - `name` (default: *basename of the URL*)

        The name of the directory the repo should be exported to in the store.

      - `rev` (default: *the tip of `ref`*)

        The [Git revision] to fetch.
        This is typically a commit hash.

        [Git revision]: https://git-scm.com/docs/git-rev-parse#_specifying_revisions

      - `ref` (default: `HEAD`)

        The [Git reference] under which to look for the requested revision.
        This is often a branch or tag name.

        [Git reference]: https://git-scm.com/book/en/v2/Git-Internals-Git-References

        By default, the `ref` value is prefixed with `refs/heads/`.
        As of 2.3.0, Nix will not prefix `refs/heads/` if `ref` starts with `refs/`.

      - `submodules` (default: `false`)

        A Boolean parameter that specifies whether submodules should be checked out.

      - `shallow` (default: `false`)

        A Boolean parameter that specifies whether fetching a shallow clone is allowed.

      - `allRefs`

        Whether to fetch all references of the repository.
        With this argument being true, it's possible to load a `rev` from *any* `ref`
        (by default only `rev`s from the specified `ref` are supported).

      Here are some examples of how to use `fetchGit`.

        - To fetch a private repository over SSH:

          ```nix
          builtins.fetchGit {
            url = "git@github.com:my-secret/repository.git";
            ref = "master";
            rev = "adab8b916a45068c044658c4158d81878f9ed1c3";
          }
          ```

        - To fetch an arbitrary reference:

          ```nix
          builtins.fetchGit {
            url = "https://github.com/NixOS/nix.git";
            ref = "refs/heads/0.5-release";
          }
          ```

        - If the revision you're looking for is in the default branch of
          the git repository you don't strictly need to specify the branch
          name in the `ref` attribute.

          However, if the revision you're looking for is in a future
          branch for the non-default branch you will need to specify the
          the `ref` attribute as well.

          ```nix
          builtins.fetchGit {
            url = "https://github.com/nixos/nix.git";
            rev = "841fcbd04755c7a2865c51c1e2d3b045976b7452";
            ref = "1.11-maintenance";
          }
          ```

          > **Note**
          >
          > It is nice to always specify the branch which a revision
          > belongs to. Without the branch being specified, the fetcher
          > might fail if the default branch changes. Additionally, it can
          > be confusing to try a commit from a non-default branch and see
          > the fetch fail. If the branch is specified the fault is much
          > more obvious.

        - If the revision you're looking for is in the default branch of
          the git repository you may omit the `ref` attribute.

          ```nix
          builtins.fetchGit {
            url = "https://github.com/nixos/nix.git";
            rev = "841fcbd04755c7a2865c51c1e2d3b045976b7452";
          }
          ```

        - To fetch a specific tag:

          ```nix
          builtins.fetchGit {
            url = "https://github.com/nixos/nix.git";
            ref = "refs/tags/1.9";
          }
          ```

        - To fetch the latest version of a remote branch:

          ```nix
          builtins.fetchGit {
            url = "ssh://git@github.com/nixos/nix.git";
            ref = "master";
          }
          ```

          Nix will refetch the branch according to the [`tarball-ttl`](@docroot@/command-ref/conf-file.md#conf-tarball-ttl) setting.

          This behavior is disabled in [pure evaluation mode](@docroot@/command-ref/conf-file.md#conf-pure-eval).

        - To fetch the content of a checked-out work directory:

          ```nix
          builtins.fetchGit ./work-dir
          ```

      If the URL points to a local directory, and no `ref` or `rev` is
      given, `fetchGit` will use the current content of the checked-out
      files, even if they are not committed or added to Git's index. It will
      only consider files added to the Git repository, as listed by `git ls-files`.
    )",
    .fun = prim_fetchGit,
});

}