.clang-tidy

# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
# Exceptions. See /LICENSE for license information.
# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

---
# Get colors when outputting through `bazel build --config=clang-tidy`.
UseColor: true
# This is necessary for `--config=clang-tidy` to catch errors.
WarningsAsErrors: '*'

# We turn on all `bugprone`, `google`, `modernize`, `performance`, and
# `readability` by default. A few `misc` are selectively enabled, and a few
# other checks are selectively disabled.
#
# Checks with nuanced reasons for disabling are:
#
# - `bugprone-branch-clone` warns when we have multiple empty cases in switches,
#    which we do for comment reasons.
# - `bugprone-easily-swappable-parameters` frequently warns on multiple
#   parameters of the same type.
# - `bugprone-exception-escape` finds issues like out-of-memory in main(). We
#   don't use exceptions, so it's unlikely to find real issues.
# - `bugprone-macro-parentheses` has false positives in places such as using an
#   argument to declare a name, which cannot have parentheses. For our limited
#   use of macros, this is a common conflict.
# - `bugprone-narrowing-conversions` conflicts with integer type C++ style.
# - `google-readability-todo` suggests usernames on TODOs, which we don't want.
# - `bugprone-switch-missing-default-case` has false positives for
#   `enum_base.h`. Clang's built-in switch warnings cover most of our risk of
#   bugs here.
# - `bugprone-unchecked-optional-access` in clang-tidy 16 has false positives on
#   code like:
#     while (auto name_ref = insts().Get(inst_id).TryAs<SemIR::NameRef>()) {
#       inst_id = name_ref->value_id;
#                 ^ unchecked access to optional value
#     }
# - `google-readability-function-size` overlaps with
#   `readability-function-size`.
# - `modernize-avoid-c-arrays` suggests `std::array`, which we could migrate to,
#   but conflicts with the status quo.
# - `modernize-use-designated-initializers` fires on creation of SemIR typed
#   insts, for which we do not currently want to use designated initialization.
# - `modernize-use-nodiscard` is disabled because it only fixes const methods,
#   not non-const, which yields distracting results on accessors.
# - `performance-unnecessary-value-param` duplicates `modernize-pass-by-value`.
# - `readability-enum-initial-value` warns on enums which use the
#   `LastValue = Value` pattern if all the other discriminants aren't given an
#   explicit value.
# - `readability-function-cognitive-complexity` warns too frequently.
# - `readability-magic-numbers` warns in reasonably documented situations.
# - `readability-redundant-member-init` warns on `= {}` which is also used to
#   indicate which fields do not need to be explicitly initialized in aggregate
#   initialization.
# - `readability-suspicious-call-argument` warns when callers use similar names
#   as different parameters.
#
# Checks that are essentially style choices we don't apply are:
#
# - `modernize-return-braced-init-list`
# - `modernize-use-default-member-init`
# - `modernize-use-emplace`
# - `readability-convert-member-functions-to-static`
# - `readability-else-after-return`
# - `readability-identifier-length`
# - `readability-implicit-bool-conversion`
# - `readability-make-member-function-const`
# - `readability-static-definition-in-anonymous-namespace`
# - `readability-use-anyofallof`
Checks:
  -*, bugprone-*, -bugprone-branch-clone, -bugprone-easily-swappable-parameters,
  -bugprone-exception-escape, -bugprone-macro-parentheses,
  -bugprone-narrowing-conversions, -bugprone-switch-missing-default-case,
  -bugprone-unchecked-optional-access, google-*,
  -google-readability-function-size, -google-readability-todo,
  misc-definitions-in-headers, misc-misplaced-const, misc-redundant-expression,
  misc-static-assert, misc-unconventional-assign-operator,
  misc-uniqueptr-reset-release, misc-unused-*, modernize-*,
  -modernize-avoid-c-arrays, -modernize-return-braced-init-list,
  -modernize-use-default-member-init, -modernize-use-designated-initializers,
  -modernize-use-emplace, -modernize-use-nodiscard, performance-*,
  -performance-unnecessary-value-param, readability-*,
  -readability-convert-member-functions-to-static,
  -readability-else-after-return, -readability-enum-initial-value,
  -readability-function-cognitive-complexity, -readability-identifier-length,
  -readability-implicit-bool-conversion, -readability-magic-numbers,
  -readability-make-member-function-const, -readability-redundant-member-init,
  -readability-static-definition-in-anonymous-namespace,
  -readability-suspicious-call-argument, -readability-use-anyofallof
CheckOptions:
  - { key: readability-identifier-naming.ClassCase, value: CamelCase }
  - { key: readability-identifier-naming.ClassConstantCase, value: CamelCase }
  - {
      key: readability-identifier-naming.ConstexprVariableCase,
      value: CamelCase,
    }
  - { key: readability-identifier-naming.NamespaceCase, value: CamelCase }
  - { key: readability-identifier-naming.StructCase, value: CamelCase }
  - {
      key: readability-identifier-naming.TemplateParameterCase,
      value: CamelCase,
    }
  - { key: readability-identifier-naming.TypeAliasCase, value: CamelCase }
  - { key: readability-identifier-naming.TypedefCase, value: CamelCase }
  - { key: readability-identifier-naming.UnionCase, value: CamelCase }
  - { key: readability-identifier-naming.VariableCase, value: lower_case }
  - { key: readability-identifier-naming.ParameterCase, value: lower_case }
  - { key: readability-identifier-naming.ClassMemberCase, value: lower_case }
  - {
      key: readability-identifier-naming.MethodIgnoredRegexp,
      value: '^classof$',
    }
  - {
      # This erroneously fires in C++20 mode with LLVM 16 clang-tidy, due to:
      # https://github.com/llvm/llvm-project/issues/46097
      key: readability-identifier-naming.TemplateParameterIgnoredRegexp,
      value: '^expr-type$',
    }