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85 lines
3.8 KiB
Markdown
<a id="top"></a>
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# Migrating from v2 to v3
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v3 is the next major version of Catch2 and brings three significant changes:
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* Catch2 is now split into multiple headers
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* Catch2 is now compiled as a static library
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* C++14 is the minimum required C++ version
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There are many reasons why we decided to go from the old single-header
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distribution model to a more standard library distribution model. The
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big one is compile-time performance, but moving over to a split header
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distribution model also improves the future maintainability and
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extendability of the codebase. For example v3 adds a new kind of matchers
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without impacting the compilation times of users that do not use matchers
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in their tests. The new model is also more friendly towards package
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managers, such as vcpkg and Conan.
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The result of this move is a significant improvement in compilation
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times, e.g. the inclusion overhead of Catch2 in the common case has been
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reduced by roughly 80%. The improved ease of maintenance also led to
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various runtime performance improvements and the introduction of new features.
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For details, look at [the release notes of 3.0.1](release-notes.md#301).
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_Note that we still provide one header + one TU distribution but do
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not consider it the primarily supported option. You should also expect
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that the compilation times will be worse if you use this option._
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## How to migrate projects from v2 to v3
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To migrate to v3, there are two basic approaches to do so.
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1. Use `catch_amalgamated.hpp` and `catch_amalgamated.cpp`.
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2. Build Catch2 as a proper (static) library, and move to piecewise headers
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Doing 1 means downloading the [amalgamated header](/extras/catch_amalgamated.hpp)
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and the [amalgamated sources](/extras/catch_amalgamated.cpp) from `extras`,
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dropping them into your test project, and rewriting your includes from
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`<catch2/catch.hpp>` to `"catch_amalgamated.hpp"` (or something similar,
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based on how you set up your paths).
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The disadvantage of using this approach are increased compilation times,
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at least compared to the second approach, but it does let you avoid
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dealing with consuming libraries in your build system of choice.
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However, we recommend doing 2, and taking extra time to migrate to v3
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properly. This lets you reap the benefits of significantly improved
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compilation times in the v3 version. The basic steps to do so are:
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1. Change your CMakeLists.txt to link against `Catch2WithMain` target if
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you use Catch2's default main. (If you do not, keep linking against
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the `Catch2` target.)
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2. Delete TU with `CATCH_CONFIG_RUNNER` or `CATCH_CONFIG_MAIN` defined,
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as it is no longer needed.
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3. Change `#include <catch2/catch.hpp>` to `#include <catch2/catch_all.hpp>`
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4. Check that everything compiles. You might have to modify namespaces,
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or perform some other changes (see the
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[Things that can break during porting](#things-that-can-break-during-porting)
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section for the most common things).
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5. Start migrating your test TUs from including `<catch2/catch_all.hpp>`
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to piecemeal includes. You will likely want to start by including
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`<catch2/catch_test_macros.hpp>`, and then go from there. (see
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[other notes](#other-notes) for further ideas)
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## Other notes
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* The main test include is now `<catch2/catch_test_macros.hpp>`
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* Big "subparts" like Matchers, or Generators, have their own folder, and
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also their own "big header", so if you just want to include all matchers,
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you can include `<catch2/matchers/catch_matchers_all.hpp>`,
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or `<catch2/generators/catch_generators_all.hpp>`
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## Things that can break during porting
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* The namespace on Matchers were cleaned up, they are no longer first declared
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deep within an internal namespace and then brought up. All Matchers now live
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in `Catch::Matchers`.
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* The reporter interfaces changed in a breaking manner. If you wrote custom
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reporter or listener, you might need to modify them a bit.
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---
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[Home](Readme.md#top)
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