[llvm] [llvm] Add a tool to check mustache compliance against the public spec (PR #142813)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-debian-cpp20` running on `clang-debian-cpp20` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/108/builds/13950

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (build-unified-tree) failure: build (failure)
...
3.088 [5444/17/657] Building COFFOptions.inc...
3.096 [5443/17/658] Building arm_mve.h...
3.121 [5442/17/659] Building arm_sve.h...
3.130 [5441/17/660] Building riscv_vector_builtins.inc...
3.162 [5440/17/661] Building riscv_vector_builtin_sema.inc...
3.171 [5439/17/662] Building riscv_vector_builtin_cg.inc...
3.208 [5438/17/663] Building arm_neon.h...
3.218 [5437/17/664] Linking CXX executable bin/llvm-opt-report
3.397 [5436/17/665] Building AArch64TargetParserDef.inc...
3.888 [5435/17/666] Building CXX object utils/llvm-test-mustache-spec/CMakeFiles/llvm-test-mustache-spec.dir/llvm-test-mustache-spec.cpp.o
FAILED: utils/llvm-test-mustache-spec/CMakeFiles/llvm-test-mustache-spec.dir/llvm-test-mustache-spec.cpp.o 
ccache /usr/bin/clang++-17 -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/utils/llvm-test-mustache-spec -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/include -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/include -Wno-deprecated-enum-enum-conversion -Wno-deprecated-declarations -Wno-deprecated-anon-enum-enum-conversion -Wno-ambiguous-reversed-operator -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++20  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -MD -MT utils/llvm-test-mustache-spec/CMakeFiles/llvm-test-mustache-spec.dir/llvm-test-mustache-spec.cpp.o -MF utils/llvm-test-mustache-spec/CMakeFiles/llvm-test-mustache-spec.dir/llvm-test-mustache-spec.cpp.o.d -o utils/llvm-test-mustache-spec/CMakeFiles/llvm-test-mustache-spec.dir/llvm-test-mustache-spec.cpp.o -c /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec/llvm-test-mustache-spec.cpp
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec/llvm-test-mustache-spec.cpp:160:12: error: no matching constructor for initialization of 'TestData'
  160 |     return TestData{TestCase->getString("template").value(),
      |            ^       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  161 |                     TestCase->getString("expected").value(),
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  162 |                     TestCase->getString("name").value(), TestCase->get("data"),
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  163 |                     TestCase->get("partials")};
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec/llvm-test-mustache-spec.cpp:148:8: note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 5 were provided
  148 | struct TestData {
      |        ^~~~~~~~
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec/llvm-test-mustache-spec.cpp:148:8: note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 5 were provided
  148 | struct TestData {
      |        ^~~~~~~~
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/utils/llvm-test-mustache-spec/llvm-test-mustache-spec.cpp:166:3: note: candidate constructor not viable: requires 0 arguments, but 5 were provided
  166 |   TestData() = default;
      |   ^
1 error generated.
4.492 [5435/16/667] Building AArch64GenExegesis.inc...
4.660 [5435/15/668] Building AArch64GenMCPseudoLowering.inc...
4.723 [5435/14/669] Building AArch64GenCallingConv.inc...
4.929 [5435/13/670] Building AArch64GenPostLegalizeGICombiner.inc...
4.965 [5435/12/671] Building AArch64GenDisassemblerTables.inc...
4.998 [5435/11/672] Building AArch64GenPostLegalizeGILowering.inc...
5.024 [5435/10/673] Building AArch64GenAsmWriter.inc...
5.039 [5435/9/674] Building AArch64GenAsmWriter1.inc...
5.068 [5435/8/675] Building AArch64GenMCCodeEmitter.inc...
5.135 [5435/7/676] Building RISCVTargetParserDef.inc...
5.147 [5435/6/677] Building AArch64GenO0PreLegalizeGICombiner.inc...
5.209 [5435/5/678] Building AArch64GenAsmMatcher.inc...
5.891 [5435/4/679] Building AArch64GenFastISel.inc...
6.573 [5435/3/680] Building AArch64GenGlobalISel.inc...
7.111 [5435/2/681] Building AArch64GenDAGISel.inc...
11.020 [5435/1/682] Building AArch64GenInstrInfo.inc...
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/142813