Add unit tests for libexpr (#5377)

* libexpr: fix builtins.split example

The example was previously indicating that multiple whitespaces would be
collapsed into a single captured whitespace. That isn't true and was
likely a mistake when being documented initially.

* Fix segfault on unitilized list when printing value

Since lists are just chunks of memory the individual elements in the
list might be unitilized when a programming error happens within Nix.

In this case the values are null-initialized (at least with Boehm GC)
and we can avoid a nullptr deref when printing them.

I ran into this issue while ensuring that new expression tests would
show the actual value on an assertion failure.

This is unlikely to cause any runtime performance regressions as
printing values is not really in the hot path (unless the repl is the
primary use case).

* Add operator<< for ValueTypes

* Add libexpr tests

This introduces tests for libexpr that evalulate various trivial Nix
language expressions and primop invocations that should be good smoke
tests wheter or not the implementation is behaving as expected.

.gitignore

@@ -35,6 +35,7 @@ perl/Makefile.config
 /src/libexpr/parser-tab.hh
 /src/libexpr/parser-tab.output
 /src/libexpr/nix.tbl
+/src/libexpr/tests/libexpr-tests
 
 # /src/libstore/
 *.gen.*

Makefile

@@ -8,6 +8,7 @@ makefiles = \
  src/libfetchers/local.mk \
  src/libmain/local.mk \
  src/libexpr/local.mk \
+ src/libexpr/tests/local.mk \
  src/libcmd/local.mk \
  src/nix/local.mk \
  src/resolve-system-dependencies/local.mk \

src/libexpr/eval.cc

@@ -147,7 +147,10 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
  else {
  str << "[ ";
  for (auto v2 : listItems()) {
- v2->print(symbols, str, seen);
+ if (v2)
+ v2->print(symbols, str, seen);
+ else
+ str << "(nullptr)";
  str << " ";
  }
  str << "]";
@@ -184,6 +187,11 @@ void Value::print(const SymbolTable & symbols, std::ostream & str, bool showRepe
  print(symbols, str, showRepeated ? nullptr : &seen);
 }
 
+// Pretty print types for assertion errors
+std::ostream & operator << (std::ostream & os, const ValueType t) {
+ os << showType(t);
+ return os;
+}
 
 std::string printValue(const EvalState & state, const Value & v)
 {

src/libexpr/eval.hh

@@ -55,6 +55,7 @@ typedef std::map<Path, StorePath> SrcToStore;
 
 std::ostream & printValue(const EvalState & state, std::ostream & str, const Value & v);
 std::string printValue(const EvalState & state, const Value & v);
+std::ostream & operator << (std::ostream & os, const ValueType t);
 
 
 typedef std::pair<std::string, std::string> SearchPathElem;

src/libexpr/primops.cc

@@ -3632,7 +3632,7 @@ static RegisterPrimOp primop_split({
  Evaluates to `[ "" [ "a" null ] "b" [ null "c" ] "" ]`.
 
  ```nix
- builtins.split "([[:upper:]]+)" "  FOO  "
+ builtins.split "([[:upper:]]+)" " FOO "
  ```
 
  Evaluates to `[ " " [ "FOO" ] " " ]`.

src/libexpr/tests/json.cc

@@ -0,0 +1,68 @@
+#include "libexprtests.hh"
+#include "value-to-json.hh"
+
+namespace nix {
+// Testing the conversion to JSON
+
+ class JSONValueTest : public LibExprTest {
+ protected:
+ std::string getJSONValue(Value& value) {
+ std::stringstream ss;
+ PathSet ps;
+ printValueAsJSON(state, true, value, noPos, ss, ps);
+ return ss.str();
+ }
+ };
+
+ TEST_F(JSONValueTest, null) {
+ Value v;
+ v.mkNull();
+ ASSERT_EQ(getJSONValue(v), "null");
+ }
+
+ TEST_F(JSONValueTest, BoolFalse) {
+ Value v;
+ v.mkBool(false);
+ ASSERT_EQ(getJSONValue(v),"false");
+ }
+
+ TEST_F(JSONValueTest, BoolTrue) {
+ Value v;
+ v.mkBool(true);
+ ASSERT_EQ(getJSONValue(v), "true");
+ }
+
+ TEST_F(JSONValueTest, IntPositive) {
+ Value v;
+ v.mkInt(100);
+ ASSERT_EQ(getJSONValue(v), "100");
+ }
+
+ TEST_F(JSONValueTest, IntNegative) {
+ Value v;
+ v.mkInt(-100);
+ ASSERT_EQ(getJSONValue(v), "-100");
+ }
+
+ TEST_F(JSONValueTest, String) {
+ Value v;
+ v.mkString("test");
+ ASSERT_EQ(getJSONValue(v), "\"test\"");
+ }
+
+ TEST_F(JSONValueTest, StringQuotes) {
+ Value v;
+
+ v.mkString("test\"");
+ ASSERT_EQ(getJSONValue(v), "\"test\\\"\"");
+ }
+
+ // The dummy store doesn't support writing files. Fails with this exception message:
+ // C++ exception with description "error: operation 'addToStoreFromDump' is
+ // not supported by store 'dummy'" thrown in the test body.
+ TEST_F(JSONValueTest, DISABLED_Path) {
+ Value v;
+ v.mkPath("test");
+ ASSERT_EQ(getJSONValue(v), "\"/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x\"");
+ }
+} /* namespace nix */

src/libexpr/tests/libexprtests.hh

@@ -0,0 +1,136 @@
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+
+#include "value.hh"
+#include "nixexpr.hh"
+#include "eval.hh"
+#include "eval-inline.hh"
+#include "store-api.hh"
+
+
+namespace nix {
+ class LibExprTest : public ::testing::Test {
+ public:
+ static void SetUpTestSuite() {
+ initGC();
+ }
+
+ protected:
+ LibExprTest()
+ : store(openStore("dummy:https://"))
+ , state({}, store)
+ {
+ }
+ Value eval(std::string input, bool forceValue = true) {
+ Value v;
+ Expr * e = state.parseExprFromString(input, "");
+ assert(e);
+ state.eval(e, v);
+ if (forceValue)
+ state.forceValue(v, noPos);
+ return v;
+ }
+
+ Symbol createSymbol(const char * value) {
+ return state.symbols.create(value);
+ }
+
+ ref<Store> store;
+ EvalState state;
+ };
+
+ MATCHER(IsListType, "") {
+ return arg != nList;
+ }
+
+ MATCHER(IsList, "") {
+ return arg.type() == nList;
+ }
+
+ MATCHER(IsString, "") {
+ return arg.type() == nString;
+ }
+
+ MATCHER(IsNull, "") {
+ return arg.type() == nNull;
+ }
+
+ MATCHER(IsThunk, "") {
+ return arg.type() == nThunk;
+ }
+
+ MATCHER(IsAttrs, "") {
+ return arg.type() == nAttrs;
+ }
+
+ MATCHER_P(IsStringEq, s, fmt("The string is equal to \"%1%\"", s)) {
+ if (arg.type() != nString) {
+ return false;
+ }
+ return std::string_view(arg.string.s) == s;
+ }
+
+ MATCHER_P(IsIntEq, v, fmt("The string is equal to \"%1%\"", v)) {
+ if (arg.type() != nInt) {
+ return false;
+ }
+ return arg.integer == v;
+ }
+
+ MATCHER_P(IsFloatEq, v, fmt("The float is equal to \"%1%\"", v)) {
+ if (arg.type() != nFloat) {
+ return false;
+ }
+ return arg.fpoint == v;
+ }
+
+ MATCHER(IsTrue, "") {
+ if (arg.type() != nBool) {
+ return false;
+ }
+ return arg.boolean == true;
+ }
+
+ MATCHER(IsFalse, "") {
+ if (arg.type() != nBool) {
+ return false;
+ }
+ return arg.boolean == false;
+ }
+
+ MATCHER_P(IsPathEq, p, fmt("Is a path equal to \"%1%\"", p)) {
+ if (arg.type() != nPath) {
+ *result_listener << "Expected a path got " << arg.type();
+ return false;
+ } else if (std::string_view(arg.string.s) != p) {
+ *result_listener << "Expected a path that equals \"" << p << "\" but got: " << arg.string.s;
+ return false;
+ }
+ return true;
+ }
+
+
+ MATCHER_P(IsListOfSize, n, fmt("Is a list of size [%1%]", n)) {
+ if (arg.type() != nList) {
+ *result_listener << "Expected list got " << arg.type();
+ return false;
+ } else if (arg.listSize() != (size_t)n) {
+ *result_listener << "Expected as list of size " << n << " got " << arg.listSize();
+ return false;
+ }
+ return true;
+ }
+
+ MATCHER_P(IsAttrsOfSize, n, fmt("Is a set of size [%1%]", n)) {
+ if (arg.type() != nAttrs) {
+ *result_listener << "Expexted set got " << arg.type();
+ return false;
+ } else if (arg.attrs->size() != (size_t)n) {
+ *result_listener << "Expected a set with " << n << " attributes but got " << arg.attrs->size();
+ return false;
+ }
+ return true;
+ }
+
+
+} /* namespace nix */

src/libexpr/tests/local.mk

@@ -0,0 +1,15 @@
+check: libexpr-tests_RUN
+
+programs += libexpr-tests
+
+libexpr-tests_DIR := $(d)
+
+libexpr-tests_INSTALL_DIR :=
+
+libexpr-tests_SOURCES := $(wildcard $(d)/*.cc)
+
+libexpr-tests_CXXFLAGS += -I src/libexpr -I src/libutil -I src/libstore -I src/libexpr/tests
+
+libexpr-tests_LIBS = libexpr libutil libstore
+
+libexpr-tests_LDFLAGS := $(GTEST_LIBS) -lgmock