Generate Patches¶

Note

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This tutorial demonstrates how to generate patches for mutants. The patches can be further applied on the original source code to generate mutated version of the codebase.

This tutorial is based on the fmtlib example.

Step 1. Check out the source code¶

git clone https://github.com/fmtlib/fmt --depth 1
cd fmt

Step 2. Create config `mull.yml`¶

mutators:
  - cxx_add_to_sub
excludePaths:
  - .*gtest.*
  - .*gmock.*

Step 3. Configure and build fmtlib¶

mkdir build.dir
export CXX=clang++-18
cmake \
  -DCMAKE_CXX_FLAGS="-O0 -fpass-plugin=/usr/lib/mull-ir-frontend-18 -g -grecord-command-line" \
  -S $PWD -B build.dir
cmake --build build.dir/ -t core-test

Step 4. Run Mull against fmtlib tests¶

mull-runner-18 --reporters=Patches --report-name fmtlib --report-patch-base $PWD ./build.dir/bin/core-test

You should see similar output:

[info] Using config /workspaces/mull/tests/end2end/fmt/mull.yml
[info] Warm up run (threads: 1)
      [################################] 1/1. Finished in 186ms
[info] Filter mutants (threads: 1)
      [################################] 1/1. Finished in 0ms
[info] Baseline run (threads: 1)
      [################################] 1/1. Finished in 182ms
[info] Running mutants (threads: 8)
      [################################] 42/42. Finished in 1595ms
[info] Patchfiles can be found at './fmtlib-patches'
[info] Total execution time: 2002ms
[info] Surviving mutants: 37

Generated patches are located under fmtlib-patches:

$ ls -l fmtlib-patches/
total 168
-rw-r--r-- 1 root root 376 May 15 21:47 killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L2356-C47.patch
-rw-r--r-- 1 root root 348 May 15 21:47 killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L395-C32.patch
-rw-r--r-- 1 root root 254 May 15 21:47 killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L599-C17.patch
-rw-r--r-- 1 root root 324 May 15 21:47 killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L901-C53.patch
-rw-r--r-- 1 root root 326 May 15 21:47 killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L979-C52.patch
-rw-r--r-- 1 root root 254 May 15 21:47 survived-workspaces_mull_tests_end2end_fmt_include_fmt_core_h-cxx_add_to_sub-L279-C19.patch
-rw-r--r-- 1 root root 358 May 15 21:47 survived-workspaces_mull_tests_end2end_fmt_include_fmt_format-inl_h-cxx_add_to_sub-L449-C29.patch
# ...

The patches can be applied now:

$ patch -p1 < ./fmtlib-patches/killed-workspaces_mull_tests_end2end_fmt_include_fmt_format_h-cxx_add_to_sub-L395-C32.patch
patching file include/fmt/format.h
$ git diff

diff --git a/include/fmt/format.h b/include/fmt/format.h
index 1bb24a5..946c798 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -392,7 +392,7 @@ inline T *make_checked(T *p, std::size_t) { return p; }
template <typename T>
template <typename U>
void basic_buffer<T>::append(const U *begin, const U *end) {
-  std::size_t new_size = size_ + internal::to_unsigned(end - begin);
+  std::size_t new_size = size_ - internal::to_unsigned(end - begin);
  reserve(new_size);
  std::uninitialized_copy(begin, end,
                          internal::make_checked(ptr_, capacity_) + size_);

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