Merge pull request #9294 from obsidiansystems/minimal-git

Git object hashing in libutil

doc/manual/src/contributing/testing.md

@@ -133,17 +133,17 @@ ran test tests/functional/${testName}.sh... [PASS]
 or without `make`:
 
 ```shell-session
-$ ./mk/run-test.sh tests/functional/${testName}.sh
+$ ./mk/run-test.sh tests/functional/${testName}.sh tests/functional/init.sh
 ran test tests/functional/${testName}.sh... [PASS]
 ```
 
 To see the complete output, one can also run:
 
 ```shell-session
-$ ./mk/debug-test.sh tests/functional/${testName}.sh
+$ ./mk/debug-test.sh tests/functional/${testName}.sh tests/functional/init.sh
-+ foo
++(${testName}.sh:1) foo
 output from foo
-+ bar
++(${testName}.sh:2) bar
 output from bar
 ...
 ```
@@ -175,7 +175,7 @@ edit it like so:
 Then, running the test with `./mk/debug-test.sh` will drop you into GDB once the script reaches that point:
 
 ```shell-session
-$ ./mk/debug-test.sh tests/functional/${testName}.sh
+$ ./mk/debug-test.sh tests/functional/${testName}.sh tests/functional/init.sh
 ...
 + gdb blash blub
 GNU gdb (GDB) 12.1

mk/common-test.sh

@@ -1,15 +1,27 @@
-test_dir=tests/functional
+# Remove overall test dir (at most one of the two should match) and
+# remove file extension.
+test_name=$(echo -n "$test" | sed \
+    -e "s|^unit-test-data/||" \
+    -e "s|^tests/functional/||" \
+    -e "s|\.sh$||" \
+    )
 
-test=$(echo -n "$test" | sed -e "s|^$test_dir/||")
+TESTS_ENVIRONMENT=(
-
+    "TEST_NAME=$test_name"
-TESTS_ENVIRONMENT=("TEST_NAME=${test%.*}" 'NIX_REMOTE=')
+    'NIX_REMOTE='
+    'PS4=+(${BASH_SOURCE[0]-$0}:$LINENO) '
+)
 
 : ${BASH:=/usr/bin/env bash}
 
+run () {
+   cd "$(dirname $1)" && env "${TESTS_ENVIRONMENT[@]}" $BASH -x -e -u -o pipefail $(basename $1)
+}
+
 init_test () {
-   cd "$test_dir" && env "${TESTS_ENVIRONMENT[@]}" $BASH -e init.sh 2>/dev/null > /dev/null
+   run "$init" 2>/dev/null > /dev/null
 }
 
 run_test_proper () {
-   cd "$test_dir/$(dirname $test)" && env "${TESTS_ENVIRONMENT[@]}" $BASH -e $(basename $test)
+   run "$test"
 }

mk/debug-test.sh

@@ -3,9 +3,12 @@
 set -eu -o pipefail
 
 test=$1
+init=${2-}
 
 dir="$(dirname "${BASH_SOURCE[0]}")"
 source "$dir/common-test.sh"
 
-(init_test)
+if [ -n "$init" ]; then
+    (init_test)
+fi
 run_test_proper

mk/lib.mk

@@ -122,14 +122,15 @@ $(foreach script, $(bin-scripts), $(eval $(call install-program-in,$(script),$(b
 $(foreach script, $(bin-scripts), $(eval programs-list += $(script)))
 $(foreach script, $(noinst-scripts), $(eval programs-list += $(script)))
 $(foreach template, $(template-files), $(eval $(call instantiate-template,$(template))))
+install_test_init=tests/functional/init.sh
 $(foreach test, $(install-tests), \
-  $(eval $(call run-install-test,$(test))) \
+  $(eval $(call run-test,$(test),$(install_test_init))) \
   $(eval installcheck: $(test).test))
 $(foreach test-group, $(install-tests-groups), \
-  $(eval $(call run-install-test-group,$(test-group))) \
+  $(eval $(call run-test-group,$(test-group),$(install_test_init))) \
   $(eval installcheck: $(test-group).test-group) \
   $(foreach test, $($(test-group)-tests), \
-    $(eval $(call run-install-test,$(test))) \
+    $(eval $(call run-test,$(test),$(install_test_init))) \
     $(eval $(test-group).test-group: $(test).test)))
 
 $(foreach file, $(man-pages), $(eval $(call install-data-in, $(file), $(mandir)/man$(patsubst .%,%,$(suffix $(file))))))

mk/run-test.sh

@@ -8,6 +8,7 @@ yellow=""
 normal=""
 
 test=$1
+init=${2-}
 
 dir="$(dirname "${BASH_SOURCE[0]}")"
 source "$dir/common-test.sh"
@@ -21,7 +22,9 @@ if [ -t 1 ]; then
 fi
 
 run_test () {
-    (init_test 2>/dev/null > /dev/null)
+    if [ -n "$init" ]; then
+        (init_test 2>/dev/null > /dev/null)
+    fi
     log="$(run_test_proper 2>&1)" && status=0 || status=$?
 }
 

mk/tests.mk

@@ -2,19 +2,22 @@
 
 test-deps =
 
-define run-install-test
+define run-bash
 
-  .PHONY: $1.test
+  .PHONY: $1
-  $1.test: $1 $(test-deps)
+  $1: $2
-	@env BASH=$(bash) $(bash) mk/run-test.sh $1 < /dev/null
+	@env BASH=$(bash) $(bash) $3 < /dev/null
-
-  .PHONY: $1.test-debug
-  $1.test-debug: $1 $(test-deps)
-	@env BASH=$(bash) $(bash) mk/debug-test.sh $1 < /dev/null
 
 endef
 
-define run-install-test-group
+define run-test
+
+  $(eval $(call run-bash,$1.test,$1 $(test-deps),mk/run-test.sh $1 $2))
+  $(eval $(call run-bash,$1.test-debug,$1 $(test-deps),mk/debug-test.sh $1 $2))
+
+endef
+
+define run-test-group
 
   .PHONY: $1.test-group
 

src/libutil/experimental-features.cc

@@ -96,6 +96,14 @@ constexpr std::array<ExperimentalFeatureDetails, numXpFeatures> xpFeatureDetails
             [`nix`](@docroot@/command-ref/new-cli/nix.md) for details.
         )",
     },
+    {
+        .tag = Xp::GitHashing,
+        .name = "git-hashing",
+        .description = R"(
+            Allow creating (content-addressed) store objects which are hashed via Git's hashing algorithm.
+            These store objects will not be understandable by older versions of Nix.
+        )",
+    },
     {
         .tag = Xp::RecursiveNix,
         .name = "recursive-nix",

src/libutil/experimental-features.hh

@@ -22,6 +22,7 @@ enum struct ExperimentalFeature
     Flakes,
     FetchTree,
     NixCommand,
+    GitHashing,
     RecursiveNix,
     NoUrlLiterals,
     FetchClosure,

src/libutil/git.cc

@@ -1,9 +1,263 @@
-#include "git.hh"
+#include <cerrno>
-
+#include <algorithm>
+#include <vector>
+#include <map>
 #include <regex>
+#include <strings.h> // for strcasecmp
+
+#include "signals.hh"
+#include "config.hh"
+#include "hash.hh"
+#include "posix-source-accessor.hh"
+
+#include "git.hh"
+#include "serialise.hh"
+
+namespace nix::git {
+
+using namespace nix;
+using namespace std::string_literals;
+
+std::optional<Mode> decodeMode(RawMode m) {
+    switch (m) {
+        case (RawMode) Mode::Directory:
+        case (RawMode) Mode::Executable:
+        case (RawMode) Mode::Regular:
+        case (RawMode) Mode::Symlink:
+            return (Mode) m;
+        default:
+            return std::nullopt;
+    }
+}
+
+
+static std::string getStringUntil(Source & source, char byte)
+{
+    std::string s;
+    char n[1];
+    source(std::string_view { n, 1 });
+    while (*n != byte) {
+        s += *n;
+        source(std::string_view { n, 1 });
+    }
+    return s;
+}
+
+
+static std::string getString(Source & source, int n)
+{
+    std::string v;
+    v.resize(n);
+    source(v);
+    return v;
+}
+
+
+void parse(
+    ParseSink & sink,
+    const Path & sinkPath,
+    Source & source,
+    std::function<SinkHook> hook,
+    const ExperimentalFeatureSettings & xpSettings)
+{
+    xpSettings.require(Xp::GitHashing);
+
+    auto type = getString(source, 5);
+
+    if (type == "blob ") {
+        sink.createRegularFile(sinkPath);
+
+        unsigned long long size = std::stoi(getStringUntil(source, 0));
+
+        sink.preallocateContents(size);
+
+        unsigned long long left = size;
+        std::string buf;
+        buf.reserve(65536);
+
+        while (left) {
+            checkInterrupt();
+            buf.resize(std::min((unsigned long long)buf.capacity(), left));
+            source(buf);
+            sink.receiveContents(buf);
+            left -= buf.size();
+        }
+    } else if (type == "tree ") {
+        unsigned long long size = std::stoi(getStringUntil(source, 0));
+        unsigned long long left = size;
+
+        sink.createDirectory(sinkPath);
+
+        while (left) {
+            std::string perms = getStringUntil(source, ' ');
+            left -= perms.size();
+            left -= 1;
+
+            RawMode rawMode = std::stoi(perms, 0, 8);
+            auto modeOpt = decodeMode(rawMode);
+            if (!modeOpt)
+                throw Error("Unknown Git permission: %o", perms);
+            auto mode = std::move(*modeOpt);
+
+            std::string name = getStringUntil(source, '\0');
+            left -= name.size();
+            left -= 1;
+
+            std::string hashs = getString(source, 20);
+            left -= 20;
+
+            Hash hash(htSHA1);
+            std::copy(hashs.begin(), hashs.end(), hash.hash);
+
+            hook(name, TreeEntry {
+                .mode = mode,
+                .hash = hash,
+            });
+
+            if (mode == Mode::Executable)
+                sink.isExecutable();
+        }
+    } else throw Error("input doesn't look like a Git object");
+}
+
+
+std::optional<Mode> convertMode(SourceAccessor::Type type)
+{
+    switch (type) {
+    case SourceAccessor::tSymlink:   return Mode::Symlink;
+    case SourceAccessor::tRegular:   return Mode::Regular;
+    case SourceAccessor::tDirectory: return Mode::Directory;
+    case SourceAccessor::tMisc:      return std::nullopt;
+    default: abort();
+    }
+}
+
+
+void restore(ParseSink & sink, Source & source, std::function<RestoreHook> hook)
+{
+    parse(sink, "", source, [&](Path name, TreeEntry entry) {
+        auto [accessor, from] = hook(entry.hash);
+        auto stat = accessor->lstat(from);
+        auto gotOpt = convertMode(stat.type);
+        if (!gotOpt)
+            throw Error("file '%s' (git hash %s) has an unsupported type",
+                from,
+                entry.hash.to_string(HashFormat::Base16, false));
+        auto & got = *gotOpt;
+        if (got != entry.mode)
+            throw Error("git mode of file '%s' (git hash %s) is %o but expected %o",
+                from,
+                entry.hash.to_string(HashFormat::Base16, false),
+                (RawMode) got,
+                (RawMode) entry.mode);
+        copyRecursive(
+            *accessor, from,
+            sink, name);
+    });
+}
+
+
+void dumpBlobPrefix(
+    uint64_t size, Sink & sink,
+    const ExperimentalFeatureSettings & xpSettings)
+{
+    xpSettings.require(Xp::GitHashing);
+    auto s = fmt("blob %d\0"s, std::to_string(size));
+    sink(s);
+}
+
+
+void dumpTree(const Tree & entries, Sink & sink,
+    const ExperimentalFeatureSettings & xpSettings)
+{
+    xpSettings.require(Xp::GitHashing);
+
+    std::string v1;
+
+    for (auto & [name, entry] : entries) {
+        auto name2 = name;
+        if (entry.mode == Mode::Directory) {
+            assert(name2.back() == '/');
+            name2.pop_back();
+        }
+        v1 += fmt("%o %s\0"s, static_cast<RawMode>(entry.mode), name2);
+        std::copy(entry.hash.hash, entry.hash.hash + entry.hash.hashSize, std::back_inserter(v1));
+    }
+
+    {
+        auto s = fmt("tree %d\0"s, v1.size());
+        sink(s);
+    }
+
+    sink(v1);
+}
+
+
+Mode dump(
+    SourceAccessor & accessor, const CanonPath & path,
+    Sink & sink,
+    std::function<DumpHook> hook,
+    PathFilter & filter,
+    const ExperimentalFeatureSettings & xpSettings)
+{
+    auto st = accessor.lstat(path);
+
+    switch (st.type) {
+    case SourceAccessor::tRegular:
+    {
+        accessor.readFile(path, sink, [&](uint64_t size) {
+            dumpBlobPrefix(size, sink, xpSettings);
+        });
+        return st.isExecutable
+            ? Mode::Executable
+            : Mode::Regular;
+    }
+
+    case SourceAccessor::tDirectory:
+    {
+        Tree entries;
+        for (auto & [name, _] : accessor.readDirectory(path)) {
+            auto child = path + name;
+            if (!filter(child.abs())) continue;
+
+            auto entry = hook(child);
+
+            auto name2 = name;
+            if (entry.mode == Mode::Directory)
+                name2 += "/";
+
+            entries.insert_or_assign(std::move(name2), std::move(entry));
+        }
+        dumpTree(entries, sink, xpSettings);
+        return Mode::Directory;
+    }
+
+    case SourceAccessor::tSymlink:
+    case SourceAccessor::tMisc:
+    default:
+        throw Error("file '%1%' has an unsupported type", path);
+    }
+}
+
+
+TreeEntry dumpHash(
+    HashType ht,
+    SourceAccessor & accessor, const CanonPath & path, PathFilter & filter)
+{
+    std::function<DumpHook> hook;
+    hook = [&](const CanonPath & path) -> TreeEntry {
+        auto hashSink = HashSink(ht);
+        auto mode = dump(accessor, path, hashSink, hook, filter);
+        auto hash = hashSink.finish().first;
+        return {
+            .mode = mode,
+            .hash = hash,
+        };
+    };
+
+    return hook(path);
+}
 
-namespace nix {
-namespace git {
 
 std::optional<LsRemoteRefLine> parseLsRemoteLine(std::string_view line)
 {
@@ -22,4 +276,3 @@ std::optional<LsRemoteRefLine> parseLsRemoteLine(std::string_view line)
 }
 
 }
-}

src/libutil/git.hh

@@ -5,9 +5,127 @@
 #include <string_view>
 #include <optional>
 
-namespace nix {
+#include "types.hh"
+#include "serialise.hh"
+#include "hash.hh"
+#include "source-accessor.hh"
+#include "fs-sink.hh"
 
-namespace git {
+namespace nix::git {
+
+using RawMode = uint32_t;
+
+enum struct Mode : RawMode {
+    Directory = 0040000,
+    Executable = 0100755,
+    Regular = 0100644,
+    Symlink = 0120000,
+};
+
+std::optional<Mode> decodeMode(RawMode m);
+
+/**
+ * An anonymous Git tree object entry (no name part).
+ */
+struct TreeEntry
+{
+    Mode mode;
+    Hash hash;
+
+    GENERATE_CMP(TreeEntry, me->mode, me->hash);
+};
+
+/**
+ * A Git tree object, fully decoded and stored in memory.
+ *
+ * Directory names must end in a `/` for sake of sorting. See
+ * https://github.com/mirage/irmin/issues/352
+ */
+using Tree = std::map<std::string, TreeEntry>;
+
+/**
+ * Callback for processing a child hash with `parse`
+ *
+ * The function should
+ *
+ * 1. Obtain the file system objects denoted by `gitHash`
+ *
+ * 2. Ensure they match `mode`
+ *
+ * 3. Feed them into the same sink `parse` was called with
+ *
+ * Implementations may seek to memoize resources (bandwidth, storage,
+ * etc.) for the same Git hash.
+ */
+using SinkHook = void(const Path & name, TreeEntry entry);
+
+void parse(
+    ParseSink & sink, const Path & sinkPath,
+    Source & source,
+    std::function<SinkHook> hook,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
+
+/**
+ * Assists with writing a `SinkHook` step (2).
+ */
+std::optional<Mode> convertMode(SourceAccessor::Type type);
+
+/**
+ * Simplified version of `SinkHook` for `restore`.
+ *
+ * Given a `Hash`, return a `SourceAccessor` and `CanonPath` pointing to
+ * the file system object with that path.
+ */
+using RestoreHook = std::pair<SourceAccessor *, CanonPath>(Hash);
+
+/**
+ * Wrapper around `parse` and `RestoreSink`
+ */
+void restore(ParseSink & sink, Source & source, std::function<RestoreHook> hook);
+
+/**
+ * Dumps a single file to a sink
+ *
+ * @param xpSettings for testing purposes
+ */
+void dumpBlobPrefix(
+    uint64_t size, Sink & sink,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
+
+/**
+ * Dumps a representation of a git tree to a sink
+ */
+void dumpTree(
+    const Tree & entries, Sink & sink,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
+
+/**
+ * Callback for processing a child with `dump`
+ *
+ * The function should return the Git hash and mode of the file at the
+ * given path in the accessor passed to `dump`.
+ *
+ * Note that if the child is a directory, its child in must also be so
+ * processed in order to compute this information.
+ */
+using DumpHook = TreeEntry(const CanonPath & path);
+
+Mode dump(
+    SourceAccessor & accessor, const CanonPath & path,
+    Sink & sink,
+    std::function<DumpHook> hook,
+    PathFilter & filter = defaultPathFilter,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
+
+/**
+ * Recursively dumps path, hashing as we go.
+ *
+ * A smaller wrapper around `dump`.
+ */
+TreeEntry dumpHash(
+    HashType ht,
+    SourceAccessor & accessor, const CanonPath & path,
+    PathFilter & filter = defaultPathFilter);
 
 /**
  * A line from the output of `git ls-remote --symref`.
@@ -16,15 +134,17 @@ namespace git {
  *
  * - Symbolic references of the form
  *
- *      ref: {target}	{reference}
+ *   ```
- *
+ *   ref: {target} {reference}
- *    where {target} is itself a reference and {reference} is optional
+ *   ```
+ *   where {target} is itself a reference and {reference} is optional
  *
  * - Object references of the form
  *
- *      {target}	{reference}
+ *   ```
- *
+ *   {target}  {reference}
- *    where {target} is a commit id and {reference} is mandatory
+ *   ```
+ *   where {target} is a commit id and {reference} is mandatory
  */
 struct LsRemoteRefLine {
     enum struct Kind {
@@ -36,8 +156,9 @@ struct LsRemoteRefLine {
     std::optional<std::string> reference;
 };
 
+/**
+ * Parse an `LsRemoteRefLine`
+ */
 std::optional<LsRemoteRefLine> parseLsRemoteLine(std::string_view line);
 
 }
-
-}

src/libutil/memory-source-accessor.cc

@@ -121,4 +121,60 @@ CanonPath MemorySourceAccessor::addFile(CanonPath path, std::string && contents)
     return path;
 }
 
+
+using File = MemorySourceAccessor::File;
+
+void MemorySink::createDirectory(const Path & path)
+{
+    auto * f = dst.open(CanonPath{path}, File { File::Directory { } });
+    if (!f)
+        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
+
+    if (!std::holds_alternative<File::Directory>(f->raw))
+        throw Error("file '%s' is not a directory", path);
+};
+
+void MemorySink::createRegularFile(const Path & path)
+{
+    auto * f = dst.open(CanonPath{path}, File { File::Regular {} });
+    if (!f)
+        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
+    if (!(r = std::get_if<File::Regular>(&f->raw)))
+        throw Error("file '%s' is not a regular file", path);
+}
+
+void MemorySink::closeRegularFile()
+{
+    r = nullptr;
+}
+
+void MemorySink::isExecutable()
+{
+    assert(r);
+    r->executable = true;
+}
+
+void MemorySink::preallocateContents(uint64_t len)
+{
+    assert(r);
+    r->contents.reserve(len);
+}
+
+void MemorySink::receiveContents(std::string_view data)
+{
+    assert(r);
+    r->contents += data;
+}
+
+void MemorySink::createSymlink(const Path & path, const std::string & target)
+{
+    auto * f = dst.open(CanonPath{path}, File { File::Symlink { } });
+    if (!f)
+        throw Error("file '%s' cannot be made because some parent file is not a directory", path);
+    if (auto * s = std::get_if<File::Symlink>(&f->raw))
+        s->target = target;
+    else
+        throw Error("file '%s' is not a symbolic link", path);
+}
+
 }

src/libutil/memory-source-accessor.hh

@@ -1,4 +1,5 @@
 #include "source-accessor.hh"
+#include "fs-sink.hh"
 #include "variant-wrapper.hh"
 
 namespace nix {
@@ -71,4 +72,28 @@ struct MemorySourceAccessor : virtual SourceAccessor
     CanonPath addFile(CanonPath path, std::string && contents);
 };
 
+/**
+ * Write to a `MemorySourceAccessor` at the given path
+ */
+struct MemorySink : ParseSink
+{
+    MemorySourceAccessor & dst;
+
+    MemorySink(MemorySourceAccessor & dst) : dst(dst) { }
+
+    void createDirectory(const Path & path) override;
+
+    void createRegularFile(const Path & path) override;
+    void receiveContents(std::string_view data) override;
+    void isExecutable() override;
+    void closeRegularFile() override;
+
+    void createSymlink(const Path & path, const std::string & target) override;
+
+    void preallocateContents(uint64_t size) override;
+
+private:
+    MemorySourceAccessor::File::Regular * r;
+};
+
 }

src/libutil/serialise.cc

@@ -74,6 +74,10 @@ void Source::operator () (char * data, size_t len)
     }
 }
 
+void Source::operator () (std::string_view data)
+{
+    (*this)((char *)data.data(), data.size());
+}
 
 void Source::drainInto(Sink & sink)
 {

src/libutil/serialise.hh

@@ -73,6 +73,7 @@ struct Source
      * an error if it is not going to be available.
      */
     void operator () (char * data, size_t len);
+    void operator () (std::string_view data);
 
     /**
      * Store up to ‘len’ in the buffer pointed to by ‘data’, and

src/libutil/tests/git.cc

@@ -1,33 +1,236 @@
-#include "git.hh"
 #include <gtest/gtest.h>
 
+#include "git.hh"
+#include "memory-source-accessor.hh"
+
+#include "tests/characterization.hh"
+
 namespace nix {
 
-    TEST(GitLsRemote, parseSymrefLineWithReference) {
+using namespace git;
-        auto line = "ref: refs/head/main	HEAD";
+
-        auto res = git::parseLsRemoteLine(line);
+class GitTest : public CharacterizationTest
-        ASSERT_TRUE(res.has_value());
+{
-        ASSERT_EQ(res->kind, git::LsRemoteRefLine::Kind::Symbolic);
+    Path unitTestData = getUnitTestData() + "/libutil/git";
-        ASSERT_EQ(res->target, "refs/head/main");
+
-        ASSERT_EQ(res->reference, "HEAD");
+public:
+
+    Path goldenMaster(std::string_view testStem) const override {
+        return unitTestData + "/" + testStem;
     }
 
-    TEST(GitLsRemote, parseSymrefLineWithNoReference) {
+    /**
-        auto line = "ref: refs/head/main";
+     * We set these in tests rather than the regular globals so we don't have
-        auto res = git::parseLsRemoteLine(line);
+     * to worry about race conditions if the tests run concurrently.
-        ASSERT_TRUE(res.has_value());
+     */
-        ASSERT_EQ(res->kind, git::LsRemoteRefLine::Kind::Symbolic);
+    ExperimentalFeatureSettings mockXpSettings;
-        ASSERT_EQ(res->target, "refs/head/main");
-        ASSERT_EQ(res->reference, std::nullopt);
-    }
 
-    TEST(GitLsRemote, parseObjectRefLine) {
+private:
-        auto line = "abc123	refs/head/main";
+
-        auto res = git::parseLsRemoteLine(line);
+    void SetUp() override
-        ASSERT_TRUE(res.has_value());
+    {
-        ASSERT_EQ(res->kind, git::LsRemoteRefLine::Kind::Object);
+        mockXpSettings.set("experimental-features", "git-hashing");
-        ASSERT_EQ(res->target, "abc123");
-        ASSERT_EQ(res->reference, "refs/head/main");
     }
+};
+
+TEST(GitMode, gitMode_directory) {
+    Mode m = Mode::Directory;
+    RawMode r = 0040000;
+    ASSERT_EQ(static_cast<RawMode>(m), r);
+    ASSERT_EQ(decodeMode(r), std::optional { m });
+};
+
+TEST(GitMode, gitMode_executable) {
+    Mode m = Mode::Executable;
+    RawMode r = 0100755;
+    ASSERT_EQ(static_cast<RawMode>(m), r);
+    ASSERT_EQ(decodeMode(r), std::optional { m });
+};
+
+TEST(GitMode, gitMode_regular) {
+    Mode m = Mode::Regular;
+    RawMode r = 0100644;
+    ASSERT_EQ(static_cast<RawMode>(m), r);
+    ASSERT_EQ(decodeMode(r), std::optional { m });
+};
+
+TEST(GitMode, gitMode_symlink) {
+    Mode m = Mode::Symlink;
+    RawMode r = 0120000;
+    ASSERT_EQ(static_cast<RawMode>(m), r);
+    ASSERT_EQ(decodeMode(r), std::optional { m });
+};
+
+TEST_F(GitTest, blob_read) {
+    readTest("hello-world-blob.bin", [&](const auto & encoded) {
+        StringSource in { encoded };
+        StringSink out;
+        RegularFileSink out2 { out };
+        parse(out2, "", in, [](auto &, auto) {}, mockXpSettings);
+
+        auto expected = readFile(goldenMaster("hello-world.bin"));
+
+        ASSERT_EQ(out.s, expected);
+    });
 }
 
+TEST_F(GitTest, blob_write) {
+    writeTest("hello-world-blob.bin", [&]() {
+        auto decoded = readFile(goldenMaster("hello-world.bin"));
+        StringSink s;
+        dumpBlobPrefix(decoded.size(), s, mockXpSettings);
+        s(decoded);
+        return s.s;
+    });
+}
+
+/**
+ * This data is for "shallow" tree tests. However, we use "real" hashes
+ * so that we can check our test data in the corresponding functional
+ * test (`git-hashing/unit-test-data`).
+ */
+const static Tree tree = {
+    {
+        "Foo",
+        {
+            .mode = Mode::Regular,
+            // hello world with special chars from above
+            .hash = Hash::parseAny("63ddb340119baf8492d2da53af47e8c7cfcd5eb2", htSHA1),
+        },
+    },
+    {
+        "bAr",
+        {
+            .mode = Mode::Executable,
+            // ditto
+            .hash = Hash::parseAny("63ddb340119baf8492d2da53af47e8c7cfcd5eb2", htSHA1),
+        },
+    },
+    {
+        "baZ/",
+        {
+            .mode = Mode::Directory,
+            // Empty directory hash
+            .hash = Hash::parseAny("4b825dc642cb6eb9a060e54bf8d69288fbee4904", htSHA1),
+        },
+    },
+};
+
+TEST_F(GitTest, tree_read) {
+    readTest("tree.bin", [&](const auto & encoded) {
+        StringSource in { encoded };
+        NullParseSink out;
+        Tree got;
+        parse(out, "", in, [&](auto & name, auto entry) {
+            auto name2 = name;
+            if (entry.mode == Mode::Directory)
+                name2 += '/';
+            got.insert_or_assign(name2, std::move(entry));
+        }, mockXpSettings);
+
+        ASSERT_EQ(got, tree);
+    });
+}
+
+TEST_F(GitTest, tree_write) {
+    writeTest("tree.bin", [&]() {
+        StringSink s;
+        dumpTree(tree, s, mockXpSettings);
+        return s.s;
+    });
+}
+
+TEST_F(GitTest, both_roundrip) {
+    using File = MemorySourceAccessor::File;
+
+    MemorySourceAccessor files;
+    files.root = File::Directory {
+        .contents {
+            {
+                "foo",
+                File::Regular {
+                    .contents = "hello\n\0\n\tworld!",
+                },
+            },
+            {
+                "bar",
+                File::Directory {
+                    .contents = {
+                        {
+                            "baz",
+                            File::Regular {
+                                .executable = true,
+                                .contents = "good day,\n\0\n\tworld!",
+                            },
+                        },
+                    },
+                },
+            },
+        },
+    };
+
+    std::map<Hash, std::string> cas;
+
+    std::function<DumpHook> dumpHook;
+    dumpHook = [&](const CanonPath & path) {
+        StringSink s;
+        HashSink hashSink { htSHA1 };
+        TeeSink s2 { s, hashSink };
+        auto mode = dump(
+            files, path, s2, dumpHook,
+            defaultPathFilter, mockXpSettings);
+        auto hash = hashSink.finish().first;
+        cas.insert_or_assign(hash, std::move(s.s));
+        return TreeEntry {
+            .mode = mode,
+            .hash = hash,
+        };
+    };
+
+    auto root = dumpHook(CanonPath::root);
+
+    MemorySourceAccessor files2;
+
+    MemorySink sinkFiles2 { files2 };
+
+    std::function<void(const Path, const Hash &)> mkSinkHook;
+    mkSinkHook = [&](const Path prefix, const Hash & hash) {
+        StringSource in { cas[hash] };
+        parse(sinkFiles2, prefix, in, [&](const Path & name, const auto & entry) {
+            mkSinkHook(prefix + "/" + name, entry.hash);
+        }, mockXpSettings);
+    };
+
+    mkSinkHook("", root.hash);
+
+    ASSERT_EQ(files, files2);
+}
+
+TEST(GitLsRemote, parseSymrefLineWithReference) {
+    auto line = "ref: refs/head/main	HEAD";
+    auto res = parseLsRemoteLine(line);
+    ASSERT_TRUE(res.has_value());
+    ASSERT_EQ(res->kind, LsRemoteRefLine::Kind::Symbolic);
+    ASSERT_EQ(res->target, "refs/head/main");
+    ASSERT_EQ(res->reference, "HEAD");
+}
+
+TEST(GitLsRemote, parseSymrefLineWithNoReference) {
+    auto line = "ref: refs/head/main";
+    auto res = parseLsRemoteLine(line);
+    ASSERT_TRUE(res.has_value());
+    ASSERT_EQ(res->kind, LsRemoteRefLine::Kind::Symbolic);
+    ASSERT_EQ(res->target, "refs/head/main");
+    ASSERT_EQ(res->reference, std::nullopt);
+}
+
+TEST(GitLsRemote, parseObjectRefLine) {
+    auto line = "abc123	refs/head/main";
+    auto res = parseLsRemoteLine(line);
+    ASSERT_TRUE(res.has_value());
+    ASSERT_EQ(res->kind, LsRemoteRefLine::Kind::Object);
+    ASSERT_EQ(res->target, "abc123");
+    ASSERT_EQ(res->reference, "refs/head/main");
+}
+
+}

src/libutil/tests/local.mk

@@ -27,3 +27,7 @@ libutil-tests_CXXFLAGS += -I src/libutil
 libutil-tests_LIBS = libutil
 
 libutil-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)
+
+check: unit-test-data/libutil/git/check-data.sh.test
+
+$(eval $(call run-test,unit-test-data/libutil/git/check-data.sh))

tests/functional/common/vars-and-functions.sh.in

@@ -4,7 +4,7 @@ if [[ -z "${COMMON_VARS_AND_FUNCTIONS_SH_SOURCED-}" ]]; then
 
 COMMON_VARS_AND_FUNCTIONS_SH_SOURCED=1
 
-export PS4='+(${BASH_SOURCE[0]-$0}:$LINENO) '
+set +x
 
 export TEST_ROOT=$(realpath ${TMPDIR:-/tmp}/nix-test)/${TEST_NAME:-default/tests\/functional//}
 export NIX_STORE_DIR

unit-test-data/libutil/git/check-data.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+set -eu -o pipefail
+
+export TEST_ROOT=$(realpath ${TMPDIR:-/tmp}/nix-test)/git-hashing/unit-test-data
+mkdir -p $TEST_ROOT
+
+repo="$TEST_ROOT/scratch"
+git init "$repo"
+
+git -C "$repo" config user.email "you@example.com"
+git -C "$repo" config user.name "Your Name"
+
+# `-w` to write for tree test
+freshlyAddedHash=$(git -C "$repo" hash-object -w -t blob --stdin < "./hello-world.bin")
+encodingHash=$(sha1sum -b < "./hello-world-blob.bin" | head -c 40)
+
+# If the hashes match, then `hello-world-blob.bin` must be the encoding
+# of `hello-world.bin`.
+[[ "$encodingHash" == "$freshlyAddedHash" ]]
+
+# Create empty directory object for tree test
+echo -n | git -C "$repo" hash-object -w -t tree --stdin
+
+# Relies on both child hashes already existing in the git store
+freshlyAddedHash=$(git -C "$repo" mktree < "./tree.txt")
+encodingHash=$(sha1sum -b < "./tree.bin" | head -c 40)
+
+# If the hashes match, then `tree.bin` must be the encoding of the
+# directory denoted by `tree.txt` interpreted as git directory listing.
+[[ "$encodingHash" == "$freshlyAddedHash" ]]

unit-test-data/libutil/git/tree.txt

@@ -0,0 +1,3 @@
+100644 blob 63ddb340119baf8492d2da53af47e8c7cfcd5eb2	Foo
+100755 blob 63ddb340119baf8492d2da53af47e8c7cfcd5eb2	bAr
+040000 tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904	baZ