Add support for retrieving generator's element as string

src/CMakeLists.txt

@@ -184,6 +184,7 @@ set(IMPL_SOURCES
     ${SOURCES_DIR}/internal/catch_istream.cpp
     ${SOURCES_DIR}/generators/internal/catch_generators_combined_tu.cpp
     ${SOURCES_DIR}/interfaces/catch_interfaces_combined_tu.cpp
+    ${SOURCES_DIR}/interfaces/catch_interfaces_generatortracker.cpp
     ${SOURCES_DIR}/interfaces/catch_interfaces_reporter.cpp
     ${SOURCES_DIR}/internal/catch_list.cpp
     ${SOURCES_DIR}/matchers/catch_matchers_floating_point.cpp

src/catch2/generators/catch_generators.hpp

@@ -8,6 +8,7 @@
 #ifndef CATCH_GENERATORS_HPP_INCLUDED
 #define CATCH_GENERATORS_HPP_INCLUDED
 
+#include <catch2/catch_tostring.hpp>
 #include <catch2/interfaces/catch_interfaces_generatortracker.hpp>
 #include <catch2/internal/catch_source_line_info.hpp>
 #include <catch2/internal/catch_stringref.hpp>
@@ -32,6 +33,10 @@ namespace Detail {
 
     template<typename T>
     class IGenerator : public GeneratorUntypedBase {
+        std::string stringifyImpl() const override {
+            return ::Catch::Detail::stringify( get() );
+        }
+
     public:
         ~IGenerator() override = default;
         IGenerator() = default;

src/catch2/interfaces/catch_interfaces_generatortracker.cpp

@@ -0,0 +1,32 @@
+
+//              Copyright Catch2 Authors
+// Distributed under the Boost Software License, Version 1.0.
+//   (See accompanying file LICENSE_1_0.txt or copy at
+//        https://www.boost.org/LICENSE_1_0.txt)
+
+// SPDX-License-Identifier: BSL-1.0
+
+#include <catch2/interfaces/catch_interfaces_generatortracker.hpp>
+#include <string>
+
+namespace Catch {
+    namespace Generators {
+
+        bool GeneratorUntypedBase::countedNext() {
+            auto ret = next();
+            if ( ret ) {
+                m_stringReprCache.clear();
+                ++m_currentElementIndex;
+            }
+            return ret;
+        }
+
+        StringRef GeneratorUntypedBase::currentElementAsString() const {
+            if ( m_stringReprCache.empty() ) {
+                m_stringReprCache = stringifyImpl();
+            }
+            return m_stringReprCache;
+        }
+
+    } // namespace Generators
+} // namespace Catch

src/catch2/interfaces/catch_interfaces_generatortracker.hpp

@@ -9,11 +9,18 @@
 #define CATCH_INTERFACES_GENERATORTRACKER_HPP_INCLUDED
 
 #include <catch2/internal/catch_unique_ptr.hpp>
+#include <catch2/internal/catch_stringref.hpp>
+
+#include <string>
 
 namespace Catch {
 
     namespace Generators {
         class GeneratorUntypedBase {
+            // Caches result from `toStringImpl`, assume that when it is an
+            // empty string, the cache is invalidated.
+            mutable std::string m_stringReprCache;
+
             // Counts based on `next` returning true
             std::size_t m_currentElementIndex = 0;
 
@@ -25,6 +32,9 @@ namespace Catch {
              */
             virtual bool next() = 0;
 
+            //! Customization point for `currentElementAsString`
+            virtual std::string stringifyImpl() const = 0;
+
         public:
             GeneratorUntypedBase() = default;
             // Generation of copy ops is deprecated (and Clang will complain)
@@ -44,15 +54,24 @@ namespace Catch {
              * As with `next`, returns true iff the move succeeded and
              * the generator has new valid element to provide.
              */
-            bool countedNext() {
+            bool countedNext();
-                auto ret = next();
-                if ( ret ) {
-                    ++m_currentElementIndex;
-                }
-                return ret;
-            }
 
             std::size_t currentElementIndex() const { return m_currentElementIndex; }
+
+            /**
+             * Returns generator's current element as user-friendly string.
+             *
+             * By default returns string equivalent to calling
+             * `Catch::Detail::stringify` on the current element, but generators
+             * can customize their implementation as needed.
+             *
+             * Not thread-safe due to internal caching.
+             *
+             * The returned ref is valid only until the generator instance
+             * is destructed, or it moves onto the next element, whichever
+             * comes first.
+             */
+            StringRef currentElementAsString() const;
         };
         using GeneratorBasePtr = Catch::Detail::unique_ptr<GeneratorUntypedBase>;
 

tests/SelfTest/IntrospectiveTests/GeneratorsImpl.tests.cpp

@@ -424,3 +424,92 @@ TEST_CASE("Generators count returned elements", "[generators][approvals]") {
     REQUIRE_FALSE( generator.countedNext() );
     REQUIRE( generator.currentElementIndex() == 2 );
 }
+
+TEST_CASE( "Generators can stringify their elements",
+           "[generators][approvals]" ) {
+    auto generator =
+        Catch::Generators::FixedValuesGenerator<int>( { 1, 2, 3 } );
+
+    REQUIRE( generator.currentElementAsString() == "1"_catch_sr );
+    REQUIRE( generator.countedNext() );
+    REQUIRE( generator.currentElementAsString() == "2"_catch_sr );
+    REQUIRE( generator.countedNext() );
+    REQUIRE( generator.currentElementAsString() == "3"_catch_sr );
+}
+
+namespace {
+    class CustomStringifyGenerator
+        : public Catch::Generators::IGenerator<bool> {
+        bool m_first = true;
+
+        std::string stringifyImpl() const override {
+            return m_first ? "first" : "second";
+        }
+
+        bool next() override {
+            if ( m_first ) {
+                m_first = false;
+                return true;
+            }
+            return false;
+        }
+
+    public:
+        bool const& get() const override;
+    };
+
+    // Avoids -Wweak-vtables
+    bool const& CustomStringifyGenerator::get() const { return m_first; }
+} // namespace
+
+TEST_CASE( "Generators can override element stringification",
+           "[generators][approvals]" ) {
+    CustomStringifyGenerator generator;
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+    REQUIRE( generator.countedNext() );
+    REQUIRE( generator.currentElementAsString() == "second"_catch_sr );
+}
+
+namespace {
+    class StringifyCountingGenerator
+        : public Catch::Generators::IGenerator<bool> {
+        bool m_first = true;
+        mutable size_t m_stringificationCalls = 0;
+
+        std::string stringifyImpl() const override {
+            ++m_stringificationCalls;
+            return m_first ? "first" : "second";
+        }
+
+        bool next() override {
+            if ( m_first ) {
+                m_first = false;
+                return true;
+            }
+            return false;
+        }
+
+    public:
+
+        bool const& get() const override;
+        size_t stringificationCalls() const { return m_stringificationCalls; }
+    };
+
+    // Avoids -Wweak-vtables
+    bool const& StringifyCountingGenerator::get() const { return m_first; }
+
+} // namespace
+
+TEST_CASE( "Generator element stringification is cached",
+           "[generators][approvals]" ) {
+    StringifyCountingGenerator generator;
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+    REQUIRE( generator.currentElementAsString() == "first"_catch_sr );
+
+    REQUIRE( generator.stringificationCalls() == 1 );
+}
+
+// caching?