Implement a parser for a literate testing system for the repl

This parser can be reused for other purposes. It's inspired by
https://bitheap.org/cram/

Although eelco's impostor exists https://github.com/mobusoperandi/eelco,
it is not very nice to depend on out of tree testing frameworks with no
way to customize them.

Change-Id: Ifca50177e09730182baf0ebf829c3505bbb0274a

tests/functional/local.mk

@@ -131,7 +131,7 @@ ifeq ($(HAVE_LIBCPUID), 1)
 endif
 
 ifeq ($(ENABLE_BUILD), yes)
-	nix_tests += test-libstoreconsumer.sh
+	nix_tests += test-libstoreconsumer.sh test-repl-characterization.sh
 
 	ifeq ($(BUILD_SHARED_LIBS), 1)
 		nix_tests += plugins.sh
@@ -142,6 +142,8 @@ $(d)/test-libstoreconsumer.sh.test $(d)/test-libstoreconsumer.sh.test-debug: \
   $(buildprefix)$(d)/test-libstoreconsumer/test-libstoreconsumer
 $(d)/plugins.sh.test $(d)/plugins.sh.test-debug: \
   $(buildprefix)$(d)/plugins/libplugintest.$(SO_EXT)
+$(d)/test-repl-characterization.sh.test $(d)/test-repl-characterization.sh.test-debug: \
+  $(buildprefix)$(d)/repl_characterization/test-repl-characterization
 
 install-tests += $(foreach x, $(nix_tests), $(d)/$(x))
 

tests/functional/repl_characterization/.gitignore

@@ -0,0 +1 @@
+test-repl-characterization

tests/functional/repl_characterization/data/basic.ast

@@ -0,0 +1,11 @@
+Commentary "meow meow meow"
+Command "command"
+Output "output output one"
+Output ""
+Output ""
+Output "output output two"
+Commentary "meow meow"
+Command "command two"
+Output "output output output"
+Commentary "commentary"
+Output "output output output"

tests/functional/repl_characterization/data/basic.test

@@ -0,0 +1,11 @@
+meow meow meow
+  nix-repl> command
+  output output one
+
+
+  output output two
+meow meow
+  nix-repl> command two
+  output output output
+commentary
+  output output output

tests/functional/repl_characterization/local.mk

@@ -0,0 +1,15 @@
+programs += test-repl-characterization
+
+test-repl-characterization_DIR := $(d)
+
+# do not install
+test-repl-characterization_INSTALL_DIR :=
+
+test-repl-characterization_SOURCES := \
+  $(wildcard $(d)/*.cc) \
+
+test-repl-characterization_CXXFLAGS += -I src/libutil -I tests/unit/libutil-support -DNIX_BIN_DIR="\"$(bindir)\""
+
+test-repl-characterization_LIBS = libutil libutil-test-support
+
+test-repl-characterization_LDFLAGS = $(THREAD_LDFLAGS) $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) $(LOWDOWN_LIBS) $(GTEST_LIBS)

tests/functional/repl_characterization/repl_characterization.cc

@@ -0,0 +1,42 @@
+#include <gtest/gtest.h>
+
+#include <string>
+#include <string_view>
+#include <optional>
+#include <unistd.h>
+
+#include "tests/characterization.hh"
+#include "tests/cli-literate-parser.hh"
+
+using namespace std::string_literals;
+
+namespace nix {
+
+static constexpr const char * REPL_PROMPT = "nix-repl> ";
+
+class ReplSessionTest : public CharacterizationTest
+{
+    Path unitTestData = getUnitTestData();
+
+public:
+    Path goldenMaster(std::string_view testStem) const override
+    {
+        return unitTestData + "/" + testStem;
+    }
+};
+
+TEST_F(ReplSessionTest, parses)
+{
+    writeTest("basic.ast", [this]() {
+        const std::string content = readFile(goldenMaster("basic.test"));
+        auto parser = CLILiterateParser{REPL_PROMPT};
+        parser.feed(content);
+
+        std::ostringstream out{};
+        for (auto & bit : parser.syntax()) {
+            out << bit.print() << "\n";
+        }
+        return out.str();
+    });
+}
+};

tests/functional/test-repl-characterization.sh

@@ -0,0 +1,7 @@
+source common.sh
+
+# You might think that this can trivially be moved into a makefile, however,
+# there is various environmental initialization of this shell framework that
+# seems load bearing and seemingly prevents the tests working inside the
+# builder.
+_NIX_TEST_UNIT_DATA=$(pwd)/repl_characterization/data ./repl_characterization/test-repl-characterization