Nested GENERATEs cause Catch2 to loop indefinitely

Author: ptc-dshakirCreated Aug 21, 2023Updated Aug 10, 2026

Describe the bug Using nested GENERATEs inside a SECTION together with raw values causes Catch2 to loop indefinitely.

Expected behavior Catch2 should finish without going into an infinite loop.

To be fair, I'm not sure whether this is a supported use case. Perhaps nested GENERATE statements are not supported, or perhaps we are nesting them incorrectly. I haven't been able to find any explicit documentation about this, but if I've missed something, please refer me to it.

Reproduction steps I've managed to reproduce this using the following minimal example:

cpp

#include <catch_amalgamated.hpp>


TEST_CASE("Explicitly nested GENERATEs", "[explicit][infinite]")
{
    SECTION("Inside section 1")
    {
        SECTION("Inside section 2")
        {
            const auto& [str1, str2] = GENERATE(table<std::string, std::string>({
                { "myStr0.1", "myStr0.2" }, // Removing this line lets Catch2 finish
                { GENERATE("myStr1.1", "myStr1.2"), "myStr2.1" }
            }));
            CHECK(str1 == "myStr1.1");
        }
    }
}


TEST_CASE("Implicitly nested GENERATEs with copy", "[implicit][copy][fine]")
{
    const auto& myStr1 = GENERATE("myStr1.1", "myStr1.2");
    const auto& [str1, str2] = GENERATE_COPY(table<std::string, std::string>({
        { "myStr0.1", "myStr0.2" },
        { myStr1, "myStr2.1" }
    }));
    CHECK(str1 == "myStr1.1");
}


TEST_CASE("Implicitly nested GENERATEs with ref", "[implicit][ref][fine]")
{
    const auto& myStr1 = GENERATE("myStr1.1", "myStr1.2");
    const auto& [str1, str2] = GENERATE_REF(table<std::string, std::string>({
        { "myStr0.1", "myStr0.2" },
        { myStr1, "myStr2.1" }
    }));
    CHECK(str1 == "myStr1.1");
}


TEST_CASE("No nested GENERATEs", "[fine]")
{
    const auto& [str1, str2] = GENERATE(table<std::string, std::string>({
        { "myStr1.1", "myStr2.1" },
        { "myStr1.2", "myStr2.1" }
    }));
    CHECK(str1 == "myStr1.1");
}

I'm compiling the code using:

bash

clang++ infinitegenerate.cpp <path-to-catch2-srcs>/catch_amalgamated.cpp <path-to-catch2-srcs>/catch_amalgamated.hpp -I<path-to-catch2-srcs> -std=c++17

The [fine] test cases finish normally. The [infinite] test case seems to run indefinitely, i.e. just keeps printing:

bash

-------------------------------------------------------------------------------
Explicitly nested GENERATEs
  Inside section 1
  Inside section 2
-------------------------------------------------------------------------------
infinitegenerate.cpp:8
...............................................................................

infinitegenerate.cpp:14: FAILED:
  CHECK( str1 == "myStr1.1" )
with expansion:
  "myStr0.1" == "myStr1.1"

Please note that I've indicated a line within this test case, which, if removed, the test case runs fine.

Platform information:

OS: macOS 13.4.1
Compiler+version: Clang v14.0.0
Catch version: v3.4.0

Additional context It's worth noting that we haven't observed this issue when using the same code with Catch2 v2.13.10.

I've found the following old bug, which seems to be talking about a similar issue: https://github.com/catchorg/Catch2/issues/2025 Not sure it's related, though, as it was fixed quite a while ago.

Source: catchorg/Catch2

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