test(3p/nix): Port language test suite to Googletest r/1390

This moves the language test suite into Googletest by constructing
parameterised tests out of the same language snippets used for the
previous lang.sh evaluation.

So far this includes support for about 3/4 of all tests, specifically:

* all parser success/failure tests
* all evaluator failure tests

The evaluator success tests will be implemented in a subsequent commit,
because the output comparison contains a whole bunch of additional
logic that I did not want to cram in here.

Change-Id: Icec9f368366cdbaa53b4c7e4472b8b6e8dd72eba
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1278
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: isomer <isomer@tvl.fyi>
Tested-by: BuildkiteCI

3 files changed, 200 insertions, 0 deletions

diff --git a/third_party/nix/src/tests/CMakeLists.txt b/third_party/nix/src/tests/CMakeLists.txt
index 0cbb8c7747e8..81ccf95b7840 100644
--- a/third_party/nix/src/tests/CMakeLists.txt
+++ b/third_party/nix/src/tests/CMakeLists.txt
@@ -9,3 +9,12 @@ target_link_libraries(value-to-json
 )
 
 gtest_discover_tests(value-to-json)
+
+add_executable(language-tests language-tests.cc)
+target_link_libraries(language-tests
+  nixexpr
+  nixstore
+  GTest::gtest_main
+)
+
+gtest_discover_tests(language-tests)
diff --git a/third_party/nix/src/tests/dummy-store.hh b/third_party/nix/src/tests/dummy-store.hh
index d0f8bf14b60f..b2c49364b741 100644
--- a/third_party/nix/src/tests/dummy-store.hh
+++ b/third_party/nix/src/tests/dummy-store.hh
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <filesystem>
+
 #include "libstore/store-api.hh"
 
 namespace nix::tests {
diff --git a/third_party/nix/src/tests/language-tests.cc b/third_party/nix/src/tests/language-tests.cc
new file mode 100644
index 000000000000..7e53cd8f5eaa
--- /dev/null
+++ b/third_party/nix/src/tests/language-tests.cc
@@ -0,0 +1,190 @@
+// This file defines the language test suite. Language tests are run
+// by evaluating a small snippet of Nix code (against a fake store),
+// serialising it to a string and comparing that to a known output.
+//
+// This test suite is a port of the previous language integration test
+// suite, and it's previous structure is retained.
+//
+// Test cases are written in nix files under lang/, following one of
+// four possible filename patterns which trigger different behaviours:
+//
+// 1. parse-fail-*.nix: These files contain expressions which should
+//    cause a parser failure.
+//
+// 2. parse-okay-*.nix: These files contain expressions which should
+//    parse fine.
+//
+// 3. eval-fail-*.nix: These files contain expressions which should
+//    parse, but fail to evaluate.
+//
+// 4. eval-okay-*.nix: These files contain expressions which should
+//    parse and evaluate fine. They have accompanying .exp files which
+//    contain the expected string representation of the evaluation.
+
+#include <algorithm>
+#include <filesystem>
+#include <iostream>
+#include <memory>
+#include <optional>
+#include <string>
+
+#include <absl/strings/ascii.h>
+#include <absl/strings/match.h>
+#include <absl/strings/str_cat.h>
+#include <absl/strings/str_split.h>
+#include <absl/strings/string_view.h>
+#include <glog/logging.h>
+#include <gtest/gtest-param-test.h>
+#include <gtest/gtest.h>
+#include <gtest/internal/gtest-param-util.h>
+
+#include "libexpr/eval-inline.hh"
+#include "libexpr/eval.hh"
+#include "libexpr/nixexpr.hh"
+#include "nix_config.h"
+#include "tests/dummy-store.hh"
+
+namespace nix::tests {
+namespace {
+
+// List all the language test .nix files matching the given prefix.
+std::vector<std::filesystem::path> TestFilesFor(absl::string_view prefix) {
+  std::vector<std::filesystem::path> matching_files;
+
+  auto dir_iter =
+      std::filesystem::directory_iterator(NIX_SRC_DIR "/src/tests/lang");
+
+  for (auto& entry : dir_iter) {
+    if (!entry.is_regular_file()) {
+      continue;
+    }
+
+    auto filename = entry.path().filename().string();
+    if (absl::StartsWith(filename, prefix) &&
+        absl::EndsWith(filename, ".nix")) {
+      matching_files.push_back(entry.path());
+    }
+  }
+
+  std::sort(matching_files.begin(), matching_files.end());
+  return matching_files;
+}
+
+// Construct a test name from a path parameter, re-casing its name to
+// PascalCase. Googletest only accepts alphanumeric test-names, but
+// the file names are in kebab-case.
+std::string TestNameFor(
+    const testing::TestParamInfo<std::filesystem::path>& info) {
+  std::string name;
+
+  for (auto part : absl::StrSplit(info.param.stem().string(), '-')) {
+    std::string part_owned(part);
+    part_owned[0] = absl::ascii_toupper(part_owned[0]);
+    absl::StrAppend(&name, part_owned);
+  }
+
+  return name;
+}
+
+}  // namespace
+
+using nix::tests::DummyStore;
+
+class NixEnvironment : public testing::Environment {
+ public:
+  void SetUp() override {
+    google::InitGoogleLogging("--logtostderr=false");
+    nix::initGC();
+  }
+};
+
+::testing::Environment* const nix_env =
+    ::testing::AddGlobalTestEnvironment(new NixEnvironment);
+
+class ParserFailureTest : public testing::TestWithParam<std::filesystem::path> {
+};
+
+// Test pattern for files that should fail to parse.
+TEST_P(ParserFailureTest, Fails) {
+  std::shared_ptr<Store> store = std::make_shared<DummyStore>();
+  EvalState state({}, ref<Store>(store));
+  auto path = GetParam();
+
+  // There are multiple types of exceptions that the parser can throw,
+  // and the tests don't define which one they expect, so we need to
+  // allow all of these - but fail on other errors.
+  try {
+    state.parseExprFromFile(GetParam().string());
+    FAIL() << path.stem().string() << ": parsing should not succeed";
+  } catch (ParseError e) {
+    SUCCEED();
+  } catch (UndefinedVarError e) {
+    SUCCEED();
+  } catch (const std::exception& e) {
+    FAIL() << path.stem().string()
+           << ": unexpected parser exception: " << e.what();
+  }
+}
+
+INSTANTIATE_TEST_SUITE_P(Parser, ParserFailureTest,
+                         testing::ValuesIn(TestFilesFor("parse-fail-")),
+                         TestNameFor);
+
+class ParserSuccessTest : public testing::TestWithParam<std::filesystem::path> {
+};
+
+// Test pattern for files that should parse successfully.
+TEST_P(ParserSuccessTest, Parses) {
+  std::shared_ptr<Store> store = std::make_shared<DummyStore>();
+  EvalState state({}, ref<Store>(store));
+  auto path = GetParam();
+
+  EXPECT_NO_THROW(state.parseExprFromFile(GetParam().string()))
+      << path.stem().string() << ": parsing should succeed";
+
+  SUCCEED();
+}
+
+INSTANTIATE_TEST_SUITE_P(Parser, ParserSuccessTest,
+                         testing::ValuesIn(TestFilesFor("parse-okay-")),
+                         TestNameFor);
+
+class EvalFailureTest : public testing::TestWithParam<std::filesystem::path> {};
+
+// Test pattern for files that should fail to evaluate.
+TEST_P(EvalFailureTest, Fails) {
+  std::shared_ptr<Store> store = std::make_shared<DummyStore>();
+  EvalState state({}, ref<Store>(store));
+  auto path = GetParam();
+
+  Expr* expr;
+  EXPECT_NO_THROW(expr = state.parseExprFromFile(GetParam().string()))
+      << path.stem().string() << ": should parse successfully";
+
+  // Again, there are multiple expected exception types and the tests
+  // don't specify which ones they are looking for.
+  try {
+    Value result;
+    state.eval(expr, result);
+    state.forceValue(result);
+    std::cout << result;
+    FAIL() << path.stem().string() << ": evaluating should not succeed";
+  } catch (AssertionError e) {
+    SUCCEED();
+  } catch (EvalError e) {
+    SUCCEED();
+  } catch (SysError e) {
+    SUCCEED();
+  } catch (ParseError /* sic! */ e) {
+    SUCCEED();
+  } catch (const std::exception& e) {
+    FAIL() << path.stem().string()
+           << ": unexpected evaluator exception: " << e.what();
+  }
+}
+
+INSTANTIATE_TEST_SUITE_P(Eval, EvalFailureTest,
+                         testing::ValuesIn(TestFilesFor("eval-fail-")),
+                         TestNameFor);
+
+}  // namespace nix::tests