Make -D- option for compiled datalog behave same as if interpreted

cmake/SouffleTests.cmake

@@ -144,7 +144,7 @@ function(SOUFFLE_RUN_TEST_HELPER)
 #Usually just "facts" but can be different when running multi - tests
     cmake_parse_arguments(
         PARAM
-        "COMPILED;COMPILED_SPLITTED;FUNCTORS;NEGATIVE;MULTI_TEST;NO_PREPROCESSOR" # Options
+        "COMPILED;COMPILED_SPLITTED;FUNCTORS;NEGATIVE;MULTI_TEST;NO_PREPROCESSOR;OUTPUT_STDOUT" # Options
         "TEST_NAME;CATEGORY;FACTS_DIR_NAME;EXTRA_DATA" #Single valued options
         "INCLUDE_DIRS" # Multi-valued options
         ${ARGV}
@@ -226,7 +226,11 @@ function(SOUFFLE_RUN_TEST_HELPER)
                                        FIXTURE_NAME ${FIXTURE_NAME}
                                        TEST_LABELS ${TEST_LABELS})
 
-    set(SOUFFLE_PARAMS "-D" "." "-F" "${FACTS_DIR}")
+    if(PARAM_OUTPUT_STDOUT)
+      set(SOUFFLE_PARAMS "-D-" "-F" "${FACTS_DIR}")
+    else()
+      set(SOUFFLE_PARAMS "-D" "." "-F" "${FACTS_DIR}")
+    endif()
     list(PREPEND SOUFFLE_PARAMS ${EXTRA_FLAGS})
 
     if (OPENMP_FOUND)

src/include/souffle/CompiledOptions.h

@@ -151,7 +151,7 @@ class CmdOptions {
                     break;
                 /* Output directory for resulting .csv files */
                 case 'D':
-                    if (*optarg && !existDir(optarg)) {
+                    if (*optarg && !existDir(optarg) && !dirIsStdout(optarg)) {
                         printf("Output directory %s does not exists!\n", optarg);
                         ok = false;
                     }
@@ -258,6 +258,13 @@ class CmdOptions {
         }
         return false;
     }
+
+    /**
+     *  Check whether the output is "-", for which the output should be stdout
+     */
+    bool dirIsStdout(const std::string& name) const {
+        return name == "-";
+    }
 };
 
 }  // end of namespace souffle

src/synthesiser/Synthesiser.cpp

@@ -376,7 +376,10 @@ void Synthesiser::emitCode(std::ostream& out, const Statement& stmt) {
                 out << "std::map<std::string, std::string> directiveMap(";
                 printDirectives(directives);
                 out << ");\n";
-                out << R"_(if (!outputDirectory.empty()) {)_";
+                out << R"_(if (outputDirectory == "-"){)_";
+                out << R"_(directiveMap["IO"] = "stdout"; directiveMap["headers"] = "true";)_";
+                out << "}\n";
+                out << R"_(else if (!outputDirectory.empty()) {)_";
                 out << R"_(directiveMap["output-dir"] = outputDirectory;)_";
                 out << "}\n";
                 out << "IOSystem::getInstance().getWriter(";

tests/semantic/CMakeLists.txt

@@ -18,6 +18,11 @@ function(positive_test NAME)
     souffle_positive_test(${NAME} semantic ${ARGN})
 endfunction()
 
+function(positive_output_stdout_test NAME)
+    souffle_run_test_helper(TEST_NAME ${NAME} CATEGORY semantic OUTPUT_STDOUT ${ARGV})
+    souffle_run_test_helper(TEST_NAME ${NAME} CATEGORY semantic OUTPUT_STDOUT ${ARGV} COMPILED)
+endfunction()
+
 function(negative_test NAME)
     souffle_negative_test(${NAME} semantic)
 endfunction()
@@ -259,4 +264,5 @@ positive_test(underscore5)
 negative_test(mutually_dependent_aggregate)
 positive_test(independent_aggregate)
 positive_test(independent_aggregate2)
-souffle_positive_functor_test(issue2373 CATEGORY semantic)
+souffle_positive_functor_test(issue2373 CATEGORY semantic)
+positive_output_stdout_test(output_stdout)

tests/semantic/output_stdout/output_stdout.dl

@@ -0,0 +1,9 @@
+// Souffle - A Datalog Compiler
+// Copyright (c) 2023, The Souffle Developers. All rights reserved
+// Licensed under the Universal Permissive License v 1.0 as shown at:
+// - https://opensource.org/licenses/UPL
+// - <souffle root>/licenses/SOUFFLE-UPL.txt
+
+.decl foo(a: symbol)
+.output foo
+foo("bar").

tests/semantic/output_stdout/output_stdout.out

@@ -0,0 +1,6 @@
+---------------
+foo
+a
+===============
+bar
+===============