Add CMake clang-tidy integration, enable in CI, and fix all clang-tidy errors

[Copilot]

Adds idiomatic CMake support for running clang-tidy during builds via per-target CXX_CLANG_TIDY properties, activates it in CI, and fixes all resulting clang-tidy errors across the codebase.

• CMakeLists.txt: New CLANG_TIDY option (default OFF). When enabled, uses find_program to locate clang-tidy and sets the CXX_CLANG_TIDY property per-target via add_unit_test(), avoiding running clang-tidy on third-party sources (e.g., EverCrypt).
• .github/workflows/ci.yml: Install clang-tidy on Ubuntu runners; pass -DCLANG_TIDY=ON and -DCMAKE_EXPORT_COMPILE_COMMANDS=ON for all Linux builds. Added a dedicated "Clang-Tidy Header" CI step that runs clang-tidy directly on merklecpp.h using the compile database, since the header-only library is not compiled as a translation unit.
• .clang-tidy: New configuration file with curated check categories, treating all warnings as errors (WarningsAsErrors: '*'), and using the existing .clang-format for formatting (FormatStyle: file). Enables broadly applicable categories (bugprone-*, cert-*, clang-analyzer-*, concurrency-*, cppcoreguidelines-*, hicpp-*, misc-*, modernize-*, performance-*, portability-*, readability-*) while excluding project/company/platform-specific and overly opinionated checks.
• merklecpp.h: Fixed all clang-tidy findings including braces, const-correctness, using instead of typedef, [[nodiscard]], noexcept on move constructors, std::move for rvalue ref params, null-pointer guard, and more.
• Test files: Fixed all clang-tidy errors across all test files (#define→constexpr, std::endl→'\n', braces, const, static_cast, split declarations, nullptr, narrowing/widening conversions, etc.). Fixed a real bug in retract.cpp: a std::runtime_error was constructed but never thrown.
• past_root() verification: Investigated a reviewer concern about past_root() only handling PATH_LEFT direction elements. Confirmed this is intentionally correct: PATH_LEFT elements represent sibling subtrees from the past state, while PATH_RIGHT elements represent future state and must be skipped. Added a deterministic test verifying past_root() at every leaf index for trees of size 2–64.

cmake -DTESTS=ON -DCLANG_TIDY=ON ..

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[achamayou]

@copilot add a .clang-tidy configuration that enables warnings as errors, uses FormatStyle "file", and enables all categories of errors.

[Copilot]

@copilot add a .clang-tidy configuration that enables warnings as errors, uses FormatStyle "file", and enables all categories of errors.

Added .clang-tidy in 129d9b4 with Checks: '*', WarningsAsErrors: '*', and FormatStyle: file. Note that enabling all checks will cause build failures on the existing codebase (e.g., llvmlibc-*, fuchsia-*, altera-* checks). You may want to selectively disable non-applicable checks with -checkname entries.

[achamayou]

@copilot you make a good point, can you enable all the sensible checks you can think of then, and not the ones that are project or company dependent?

Note that enabling all checks will cause build failures on the existing codebase (e.g., llvmlibc-, fuchsia-, altera-* checks). You may want to selectively disable non-applicable checks with -checkname entries.

[Copilot]

@copilot you make a good point, can you enable all the sensible checks you can think of then, and not the ones that are project or company dependent?

Note that enabling all checks will cause buil...

Updated in 02e2456. The .clang-tidy now enables only broadly applicable categories: bugprone-*, cert-*, clang-analyzer-*, concurrency-*, cppcoreguidelines-*, hicpp-*, misc-*, modernize-*, performance-*, portability-*, readability-*.

Excluded project/company/platform-specific categories: abseil-*, altera-*, android-*, boost-*, darwin-*, fuchsia-*, google-*, linuxkernel-*, llvm-*, llvmlibc-*, mpi-*, objc-*, openmp-*, zircon-*.

[achamayou]

@copilot great, now run the build step you have modified to add clang tidy, look a errors it produces, and makes the necessary changes to the code to fix them.

[Copilot]

Pull request overview

This PR adds first-class clang-tidy support to the CMake build and CI pipeline, introduces a repository .clang-tidy configuration, and updates the library header and multiple test programs to satisfy clang-tidy checks.

Changes:

• Add a CLANG_TIDY CMake option and enable clang-tidy in Ubuntu CI builds.
• Add a curated .clang-tidy config and a CI step to run clang-tidy on merklecpp.h.
• Refactor/fix various test and header code patterns to address clang-tidy findings (casts, const-correctness, braces, iostream usage, etc.).

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
CMakeLists.txt	Adds CLANG_TIDY option and wires clang-tidy into CMake builds.
.github/workflows/ci.yml	Installs clang-tidy on Ubuntu and runs it in CI (including a header check).
.clang-tidy	Adds project-wide clang-tidy ruleset with warnings-as-errors.
merklecpp.h	Multiple clang-tidy-driven refactors and safety checks in core types/algorithms.
test/time_large_trees.cpp	Modernizes constants/printing/casts and timing calculations.
test/serialise_to_file.cpp	Updates constants/loops and file I/O style.
test/serialisation.cpp	Refactors constants/casts/printing; minor structural changes.
test/retract.cpp	Refactors constants/casts/printing; adjusts a retract invariant check.
test/paths.cpp	Refactors constants/casts/printing and adds explicit error branches.
test/past_root.cpp	Refactors constants/casts/printing and adds braces.
test/past_paths.cpp	Refactors constants/casts/printing; removes unused main args; adds braces.
test/partial_serialisation.cpp	Refactors constants/casts/printing; adds braces.
test/flush.cpp	Refactors constants/casts/printing; updates insertion loop.
test/demo_tree.cpp	Refactors constants/printing and adds braces for single-line conditionals.
test/compare_hash_functions.cpp	Refactors constants/printing/typedefs and improves const-correctness.

Comments suppressed due to low confidence (1)

test/serialise_to_file.cpp:63

• The file read loop uses while (!f.eof()) and unconditionally push_back(t) after read(). This commonly appends an extra byte (the last value of t) when the final read() fails. Prefer a loop that only pushes when the read succeeds (e.g., while (f.read(&t, 1))).

        while (!f.eof())
        {
          f.read(&t, 1);
          bytes.push_back(t);
        }

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[Copilot]

@achamayou Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: 1c09f2e7-c3ef-4d80-8f68-1dad7d7f7e58

Sorry for the inconvenience!

[achamayou]

@copilot try again

[Copilot]

@copilot try again

Ran the full build with clang-tidy in both Debug and Release modes (-DTESTS=ON -DOPENSSL=ON -DCLANG_TIDY=ON), plus the header scan. Zero clang-tidy errors across all configurations and all 11 tests pass. The codebase is clean as of 0957e5e.