C++ Core Guidelines Setup

-Wall -Wextra -Wpedantic
-Werror          # promote all warnings to errors once the codebase is clean
-std=c++17       # minimum standard recommended by the guidelines (c++20 preferred)

# Forbid C-style casts; use static_cast/dynamic_cast/const_cast/reinterpret_cast
-Wold-style-cast

# Drop cv-qualifiers only deliberately
-Wcast-qual

# Warn on alignment-unsafe casts
-Wcast-align=strict          # GCC >= 8
-Wcast-align                 # earlier GCC / Clang

# Warn on reinterpret-cast-equivalent pointer conversions (Clang)
-Wundefined-reinterpret-cast # Clang

# Warn when a cast converts to a type with smaller range
-Wfloat-conversion
-Wdouble-promotion
-Wconversion
-Wsign-conversion
-Wsign-compare
-Wshorten-64-to-32           # Clang
-Warith-conversion           # GCC >= 10

# Varargs are banned (Type.8)
# (enforced by cppcoreguidelines-pro-type-vararg in clang-tidy)

# Pointer arithmetic warnings
-Wpointer-arith

# Array-to-pointer decay
# (enforced by cppcoreguidelines-pro-bounds-array-to-pointer-decay in clang-tidy)

# Out-of-bounds detection at compile time
-Warray-bounds=2             # GCC; =2 enables more checks via value range
-Wstringop-overflow=4        # GCC >= 7
-Wstringop-overread          # GCC >= 11
-Wstringop-truncation        # GCC >= 8

# Zero-length and flexible array bounds
-Wzero-length-bounds         # GCC >= 10 (enabled by -Warray-bounds)

# Use-after-move / dangling references
# (runtime: see Sanitizers section below)
-Wnull-dereference           # GCC >= 6, Clang
-Winit-self
-Wuninitialized
-Wmissing-field-initializers

# Strict aliasing enables the compiler to catch type-pun UB
-Wstrict-aliasing=3  -fstrict-aliasing

# Stack allocation limits (tune to your target)
-Wstack-usage=16384  -fstack-usage
-Walloca                     # GCC >= 7: flag alloca() use
-Wvla                        # warn on variable-length arrays (Clang -Wvla)

# Dynamic memory
# (enforced by cppcoreguidelines-no-malloc / cppcoreguidelines-owning-memory)

# Object slicing
# (enforced by cppcoreguidelines-slicing in clang-tidy)

# RAII: warn on unused [[nodiscard]] results
-Wunused-result              # implicit; explicit with [[nodiscard]]

# Control flow clarity
-Wimplicit-fallthrough       # GCC >= 7, Clang: require [[fallthrough]] annotation
-Wswitch-enum                # all enum values must be handled or have a default
-Wswitch-default             # always require a default case

# Avoid uninitialised values
-Wconditional-uninitialized  # Clang: warns in conditional branches
-Wmaybe-uninitialized        # GCC

# Shadowing (ES.12)
-Wshadow

# Misleading formatting (ES.47)
-Wmisleading-indentation     # GCC >= 6, Clang

# Avoid goto (ES.76)
# (enforced by cppcoreguidelines-avoid-goto in clang-tidy)

# Integer overflow / shift (ES.103, ES.104)
-Wshift-overflow=2           # GCC >= 6
-Wshift-negative-value       # GCC >= 6
-Wsign-conversion

# Redundant / tautological expressions
-Wduplicated-cond            # GCC >= 6
-Wduplicated-branches        # GCC >= 7
-Wlogical-op                 # GCC: catch | used where || intended

# Floating-point
-Wfloat-equal                # ES.100

# Missing declarations (I.2: avoid non-const global variables)
-Wmissing-declarations
-Wmissing-variable-declarations  # Clang

# Non-null contract enforcement at compile time
-Wnonnull

# Format string safety (I.13)
-Wformat=2
-Wformat-security
-Wformat-nonliteral
-Wformat-signedness          # Clang >= 19, GCC

# Rule of 0/5 (C.21, C.67)
# (enforced by cppcoreguidelines-special-member-functions in clang-tidy)

# Virtual function safety
-Wnon-virtual-dtor           # base class with virtual functions needs virtual dtor
-Woverloaded-virtual         # C.128

# Suggest final (C.139)
-Wsuggest-final-types        # GCC >= 5
-Wsuggest-final-methods      # GCC >= 5
-Wsuggest-override           # GCC >= 5; require 'override' keyword

# Keep functions small (F.4)
# (enforced by readability-function-size in clang-tidy)

# Always-inline / never-inline hints
-Winline

# Stack protection for unsafe functions
-Wstack-protector  -fstack-protector-strong

# Thread safety annotations (Clang)
-Wthread-safety
-Wthread-safety-analysis     # Clang: static analysis of mutex guards

# Data races (GCC, runtime)
# (use -fsanitize=thread at test time; see Sanitizers below)

# Exception-related
-Wterminate                  # GCC: warn when noexcept function may throw
-Wnoexcept                   # GCC: suggest noexcept

# Require handling of [[nodiscard]] return values
-Wunused-result

-Wwrite-strings              # string literals are const char[]
-Wformat-overflow=2          # GCC >= 7
-Wformat-truncation=2        # GCC >= 7

# Stack canary
-fstack-protector-strong

# Fortify glibc wrappers (catches unsafe buffer functions at compile time)
-D_FORTIFY_SOURCE=3

# Prevent UB from signed overflow being optimised away
-fno-strict-overflow         # or: -ftrapv to trap on signed overflow

# Control-flow integrity (Clang; link with -flto)
-fsanitize=cfi-icall
-fsanitize=cfi-vcall

# Unsafe-buffer-usage (Clang >= 19)
-Wunsafe-buffer-usage

# Bidirectional control characters in source (CVE-2021-42574)
-Wbidi-chars=any             # GCC >= 12, Clang