nlohmann::json instance and JSON Schema for MemorySourceAccessor

Also do a better JSON and testing for deep and shallow NAR listings.

As documented, this for file system objects themselves, since
`MemorySourceAccessor` is an implementation detail.

src/libutil-tests/data/memory-source-accessor/complex.json

@@ -0,0 +1,24 @@
+{
+  "entries": {
+    "bar": {
+      "entries": {
+        "baz": {
+          "contents": "good day,\n\u0000\n\tworld!",
+          "executable": true,
+          "type": "regular"
+        },
+        "quux": {
+          "target": "/over/there",
+          "type": "symlink"
+        }
+      },
+      "type": "directory"
+    },
+    "foo": {
+      "contents": "hello\n\u0000\n\tworld!",
+      "executable": false,
+      "type": "regular"
+    }
+  },
+  "type": "directory"
+}

src/libutil-tests/data/memory-source-accessor/simple.json

@@ -0,0 +1,5 @@
+{
+  "contents": "asdf",
+  "executable": false,
+  "type": "regular"
+}

src/libutil-tests/data/nar-listing/deep.json

@@ -0,0 +1,23 @@
+{
+  "entries": {
+    "bar": {
+      "entries": {
+        "baz": {
+          "executable": true,
+          "size": 19,
+          "type": "regular"
+        },
+        "quux": {
+          "target": "/over/there",
+          "type": "symlink"
+        }
+      },
+      "type": "directory"
+    },
+    "foo": {
+      "size": 15,
+      "type": "regular"
+    }
+  },
+  "type": "directory"
+}

src/libutil-tests/data/nar-listing/shallow.json

@@ -0,0 +1,7 @@
+{
+  "entries": {
+    "bar": {},
+    "foo": {}
+  },
+  "type": "directory"
+}

src/libutil-tests/git.cc

@@ -224,42 +224,15 @@ TEST_F(GitTest, tree_sha256_write)
     });
 }
 
+namespace memory_source_accessor {
+
+extern ref<MemorySourceAccessor> exampleComplex();
+
+}
+
 TEST_F(GitTest, both_roundrip)
 {
-    using File = MemorySourceAccessor::File;
-
-    auto files = make_ref<MemorySourceAccessor>();
-    files->root = File::Directory{
-        .entries{
-            {
-                "foo",
-                File::Regular{
-                    .contents = "hello\n\0\n\tworld!",
-                },
-            },
-            {
-                "bar",
-                File::Directory{
-                    .entries =
-                        {
-                            {
-                                "baz",
-                                File::Regular{
-                                    .executable = true,
-                                    .contents = "good day,\n\0\n\tworld!",
-                                },
-                            },
-                            {
-                                "quux",
-                                File::Symlink{
-                                    .target = "/over/there",
-                                },
-                            },
-                        },
-                },
-            },
-        },
-    };
+    auto files = memory_source_accessor::exampleComplex();
 
     for (const auto hashAlgo : {HashAlgorithm::SHA1, HashAlgorithm::SHA256}) {
         std::map<Hash, std::string> cas;

src/libutil-tests/memory-source-accessor.cc

@@ -0,0 +1,116 @@
+#include <string_view>
+
+#include "nix/util/memory-source-accessor.hh"
+#include "nix/util/tests/json-characterization.hh"
+
+namespace nix {
+
+namespace memory_source_accessor {
+
+using namespace std::literals;
+using File = MemorySourceAccessor::File;
+
+ref<MemorySourceAccessor> exampleSimple()
+{
+    auto sc = make_ref<MemorySourceAccessor>();
+    sc->root = File{File::Regular{
+        .executable = false,
+        .contents = "asdf",
+    }};
+    return sc;
+}
+
+ref<MemorySourceAccessor> exampleComplex()
+{
+    auto files = make_ref<MemorySourceAccessor>();
+    files->root = File::Directory{
+        .entries{
+            {
+                "foo",
+                File::Regular{
+                    .contents = "hello\n\0\n\tworld!"s,
+                },
+            },
+            {
+                "bar",
+                File::Directory{
+                    .entries =
+                        {
+                            {
+                                "baz",
+                                File::Regular{
+                                    .executable = true,
+                                    .contents = "good day,\n\0\n\tworld!"s,
+                                },
+                            },
+                            {
+                                "quux",
+                                File::Symlink{
+                                    .target = "/over/there",
+                                },
+                            },
+                        },
+                },
+            },
+        },
+    };
+    return files;
+}
+
+} // namespace memory_source_accessor
+
+/* ----------------------------------------------------------------------------
+ * JSON
+ * --------------------------------------------------------------------------*/
+
+class MemorySourceAccessorTest : public virtual CharacterizationTest
+{
+    std::filesystem::path unitTestData = getUnitTestData() / "memory-source-accessor";
+
+public:
+
+    std::filesystem::path goldenMaster(std::string_view testStem) const override
+    {
+        return unitTestData / testStem;
+    }
+};
+
+using nlohmann::json;
+
+struct MemorySourceAccessorJsonTest : MemorySourceAccessorTest,
+                                      JsonCharacterizationTest<MemorySourceAccessor>,
+                                      ::testing::WithParamInterface<std::pair<std::string_view, MemorySourceAccessor>>
+{};
+
+TEST_P(MemorySourceAccessorJsonTest, from_json)
+{
+    auto & [name, expected] = GetParam();
+    /* Cannot use `readJsonTest` because need to compare `root` field of
+       the source accessors for equality. */
+    readTest(Path{name} + ".json", [&](const auto & encodedRaw) {
+        auto encoded = json::parse(encodedRaw);
+        auto decoded = static_cast<MemorySourceAccessor>(encoded);
+        ASSERT_EQ(decoded.root, expected.root);
+    });
+}
+
+TEST_P(MemorySourceAccessorJsonTest, to_json)
+{
+    auto & [name, value] = GetParam();
+    writeJsonTest(name, value);
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    MemorySourceAccessorJSON,
+    MemorySourceAccessorJsonTest,
+    ::testing::Values(
+        std::pair{
+            "simple",
+            *memory_source_accessor::exampleSimple(),
+        },
+        std::pair{
+            "complex",
+            *memory_source_accessor::exampleComplex(),
+        }));
+
+} // namespace nix

src/libutil-tests/meson.build

@@ -63,7 +63,9 @@ sources = files(
   'json-utils.cc',
   'logging.cc',
   'lru-cache.cc',
+  'memory-source-accessor.cc',
   'monitorfdhup.cc',
+  'nar-listing.cc',
   'nix_api_util.cc',
   'nix_api_util_internal.cc',
   'pool.cc',

src/libutil-tests/nar-listing.cc

@@ -0,0 +1,83 @@
+#include <string_view>
+
+#include "nix/util/nar-accessor.hh"
+#include "nix/util/tests/json-characterization.hh"
+
+namespace nix {
+
+// Forward declaration from memory-source-accessor.cc
+namespace memory_source_accessor {
+ref<MemorySourceAccessor> exampleComplex();
+}
+
+/* ----------------------------------------------------------------------------
+ * JSON
+ * --------------------------------------------------------------------------*/
+
+class NarListingTest : public virtual CharacterizationTest
+{
+    std::filesystem::path unitTestData = getUnitTestData() / "nar-listing";
+
+public:
+
+    std::filesystem::path goldenMaster(std::string_view testStem) const override
+    {
+        return unitTestData / testStem;
+    }
+};
+
+using nlohmann::json;
+
+struct NarListingJsonTest : NarListingTest,
+                            JsonCharacterizationTest<NarListing>,
+                            ::testing::WithParamInterface<std::pair<std::string_view, NarListing>>
+{};
+
+TEST_P(NarListingJsonTest, from_json)
+{
+    auto & [name, expected] = GetParam();
+    readJsonTest(name, expected);
+}
+
+TEST_P(NarListingJsonTest, to_json)
+{
+    auto & [name, value] = GetParam();
+    writeJsonTest(name, value);
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    NarListingJSON,
+    NarListingJsonTest,
+    ::testing::Values(
+        std::pair{
+            "deep",
+            listNarDeep(*memory_source_accessor::exampleComplex(), CanonPath::root),
+        }));
+
+struct ShallowNarListingJsonTest : NarListingTest,
+                                   JsonCharacterizationTest<ShallowNarListing>,
+                                   ::testing::WithParamInterface<std::pair<std::string_view, ShallowNarListing>>
+{};
+
+TEST_P(ShallowNarListingJsonTest, from_json)
+{
+    auto & [name, expected] = GetParam();
+    readJsonTest(name, expected);
+}
+
+TEST_P(ShallowNarListingJsonTest, to_json)
+{
+    auto & [name, value] = GetParam();
+    writeJsonTest(name, value);
+}
+
+INSTANTIATE_TEST_SUITE_P(
+    ShallowNarListingJSON,
+    ShallowNarListingJsonTest,
+    ::testing::Values(
+        std::pair{
+            "shallow",
+            listNarShallow(*memory_source_accessor::exampleComplex(), CanonPath::root),
+        }));
+
+} // namespace nix