fix: resolve compiler warnings for clean -Wall -Wextra -Wshadow build

.github/actions/build_cmake/action.yml

@@ -20,6 +20,14 @@ inputs:
     description: 'Enable SVS support.'
     required: false
     default: OFF
+  warning_level:
+    description: 'Compiler warning level (0=off, 1=basic, 2=standard, 3=strict).'
+    required: false
+    default: '0'
+  warnings_as_errors:
+    description: 'Treat compiler warnings as errors.'
+    required: false
+    default: 'false'
   setup_conda:
     description: 'Setup miniconda environment.'
     required: false
@@ -150,6 +158,8 @@ runs:
               -DFAISS_OPT_LEVEL=${{ inputs.opt_level }} \
               -DFAISS_ENABLE_SVS=${{ inputs.svs }} \
               -DFAISS_ENABLE_C_API=ON \
+              -DFAISS_WARNING_LEVEL=${{ inputs.warning_level }} \
+              -DFAISS_WARNINGS_AS_ERRORS=${{ inputs.warnings_as_errors == 'true' && 'ON' || 'OFF' }} \
               -DPYTHON_EXECUTABLE=$CONDA/bin/python \
               -DCMAKE_BUILD_TYPE=Release \
               -DBLA_VENDOR=${{ runner.arch == 'X64' && 'Intel10_64_dyn' || '' }} \

.github/workflows/build-pull-request.yml

@@ -41,6 +41,18 @@ jobs:
       - name: Build C++ demos
         run: |
           make -C build demo_diversity_result_handler
+  linux-x86_64-warnings-cmake:
+    name: Linux x86_64 warnings (cmake)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Build and Test with warnings (cmake)
+        uses: ./.github/actions/build_cmake
+        with:
+          warning_level: '1'
+          warnings_as_errors: 'true'
+          upload_artifacts: 'false'
   linux-x86_64-AVX2-cmake:
     name: Linux x86_64 AVX2 (cmake)
     needs: linux-x86_64-cmake

CMakeLists.txt

@@ -61,6 +61,10 @@ endif()
 
 list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 
+# Include compiler warnings configuration
+include(StrictCompilerWarnings)
+faiss_print_warning_config()
+
 # Valid values are "generic", "avx2", "avx512", "avx512_spr", "sve".
 option(FAISS_OPT_LEVEL "" "generic")
 option(FAISS_ENABLE_GPU "Enable support for GPU indexes." ON)
@@ -119,7 +123,13 @@ endif()
 include(CTest)
 if(BUILD_TESTING)
   add_subdirectory(tests)
-  add_subdirectory(perf_tests)
+  # perf_tests require gflags - make them optional
+  find_package(gflags QUIET)
+  if(gflags_FOUND)
+    add_subdirectory(perf_tests)
+  else()
+    message(STATUS "gflags not found, skipping perf_tests")
+  endif()
   if(FAISS_ENABLE_GPU)
     if(FAISS_ENABLE_ROCM)
       add_subdirectory(faiss/gpu/test)

CONTRIBUTING.md

@@ -46,6 +46,44 @@ outlined on that page and do not file a public issue.
 * 80 character line length (both for C++ and Python)
 * C++ language level: C++17
 
+## Compiler Warnings
+
+Faiss supports configurable compiler warning levels. We encourage contributors
+to build with warnings enabled to catch potential issues early.
+
+### Warning Levels
+
+Configure the warning level with `-DFAISS_WARNING_LEVEL=<level>`:
+
+| Level | Description | Recommended For |
+|-------|-------------|-----------------|
+| 0 | Disabled (default) | Normal builds |
+| 1 | Basic warnings (`-Wall -Wextra`) | Development builds |
+| 2 | Standard warnings (adds `-Wpedantic`, `-Wshadow`, etc.) | Code review |
+| 3 | Strict warnings (all recommended warnings) | Static analysis |
+
+### Example Usage
+
+```bash
+# Build with basic warnings
+cmake .. -DFAISS_WARNING_LEVEL=1
+
+# Build with warnings as errors (strict mode)
+cmake .. -DFAISS_WARNING_LEVEL=2 -DFAISS_WARNINGS_AS_ERRORS=ON
+```
+
+### Best Practices for New Code
+
+When writing new code:
+
+* Use `static_cast<>`, `reinterpret_cast<>`, or `const_cast<>` instead of C-style casts
+* Initialize all member variables in the member initializer list
+* Order member initializers to match declaration order
+* Use `[[maybe_unused]]` for intentionally unused parameters
+* Use `override` for virtual function overrides
+* Prefer `nullptr` over `NULL` or `0` for null pointers
+* Avoid shadowing variables in inner scopes
+
 ## License
 
 By contributing to Faiss, you agree that your contributions will be licensed

benchs/CMakeLists.txt

@@ -10,8 +10,10 @@ find_package(OpenMP REQUIRED)
 add_executable(bench_ivf_selector EXCLUDE_FROM_ALL bench_ivf_selector.cpp)
 target_link_libraries(bench_ivf_selector PRIVATE faiss_avx512 ${BLAS_LIBRARIES} ${LAPACK_LIBRARIES} OpenMP::OpenMP_CXX)
 target_compile_options(bench_ivf_selector PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-mavx2 -mfma -mf16c -mavx512f -mavx512cd -mavx512vl -mavx512dq -mavx512bw -mpopcnt>)
+faiss_add_warnings(bench_ivf_selector)
 
 add_executable(bench_result_handler_overhead EXCLUDE_FROM_ALL
   bench_result_handler_overhead.cpp)
 target_link_libraries(bench_result_handler_overhead PRIVATE faiss_avx512 ${BLAS_LIBRARIES} ${LAPACK_LIBRARIES} OpenMP::OpenMP_CXX)
 target_compile_options(bench_result_handler_overhead PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-mavx2 -mfma -mf16c -mavx512f -mavx512cd -mavx512vl -mavx512dq -mavx512bw -mpopcnt>)
+faiss_add_warnings(bench_result_handler_overhead)

c_api/CMakeLists.txt

@@ -82,6 +82,13 @@ endif()
 
 add_library(faiss_c_sve ${FAISS_C_SRC})
 target_link_libraries(faiss_c_sve PRIVATE faiss_sve)
+
+# Apply compiler warnings
+faiss_add_warnings(faiss_c)
+faiss_add_warnings(faiss_c_avx2)
+faiss_add_warnings(faiss_c_avx512)
+faiss_add_warnings(faiss_c_avx512_spr)
+faiss_add_warnings(faiss_c_sve)
 if(NOT FAISS_OPT_LEVEL STREQUAL "sve")
   set_target_properties(faiss_c_sve PROPERTIES EXCLUDE_FROM_ALL TRUE)
 endif()

c_api/impl/AuxIndexStructures_c.cpp

@@ -280,7 +280,7 @@ int faiss_RangeSearchPartialResult_new_result(
         idx_t qno,
         FaissRangeQueryResult** qr) {
     try {
-        auto q = &reinterpret_cast<RangeSearchPartialResult*>(res)->new_result(
+        auto& q = reinterpret_cast<RangeSearchPartialResult*>(res)->new_result(
                 qno);
         if (qr) {
             *qr = reinterpret_cast<FaissRangeQueryResult*>(&q);

cmake/StrictCompilerWarnings.cmake

@@ -0,0 +1,114 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+# Strict compiler warnings module for code quality enforcement
+# This module provides functions to enable compiler warnings at various levels
+
+# Warning levels:
+#   0 = Disabled (default for normal builds)
+#   1 = Basic warnings (Wall, Wextra) - Recommended minimum
+#   2 = Standard warnings (adds Wpedantic, Wshadow, etc.)
+#   3 = Strict warnings (all recommended warnings)
+set(FAISS_WARNING_LEVEL "0" CACHE STRING "Warning level: 0=off, 1=basic, 2=standard, 3=strict")
+set_property(CACHE FAISS_WARNING_LEVEL PROPERTY STRINGS "0" "1" "2" "3")
+
+option(FAISS_WARNINGS_AS_ERRORS "Treat warnings as errors (-Werror)" OFF)
+
+# Function to apply warnings to a target based on the warning level
+function(faiss_add_warnings target)
+    if(FAISS_WARNING_LEVEL EQUAL 0)
+        return()
+    endif()
+
+    # Level 1: Basic warnings
+    if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+        target_compile_options(${target} PRIVATE
+            $<$<COMPILE_LANGUAGE:CXX>:
+                -Wall
+                -Wextra
+            >
+        )
+    elseif(MSVC)
+        target_compile_options(${target} PRIVATE
+            $<$<COMPILE_LANGUAGE:CXX>:/W3>
+        )
+    endif()
+
+    # Level 2: Standard warnings
+    if(FAISS_WARNING_LEVEL GREATER_EQUAL 2)
+        if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:
+                    -Wpedantic
+                    -Wshadow
+                    -Wnon-virtual-dtor
+                    -Wunused
+                    -Woverloaded-virtual
+                    -Wformat=2
+                    -Wimplicit-fallthrough
+                >
+            )
+        elseif(MSVC)
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:/W4 /permissive->
+            )
+        endif()
+    endif()
+
+    # Level 3: Strict warnings
+    if(FAISS_WARNING_LEVEL GREATER_EQUAL 3)
+        if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:
+                    -Wold-style-cast
+                    -Wcast-align
+                    -Wconversion
+                    -Wsign-conversion
+                    -Wnull-dereference
+                    -Wdouble-promotion
+                    -Wmisleading-indentation
+                    -Wduplicated-cond
+                    -Wduplicated-branches
+                    -Wlogical-op
+                    -Wuseless-cast
+                >
+            )
+        elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:
+                    -Wold-style-cast
+                    -Wcast-align
+                    -Wconversion
+                    -Wsign-conversion
+                    -Wnull-dereference
+                    -Wdouble-promotion
+                >
+            )
+        endif()
+    endif()
+
+    # Warnings as errors
+    if(FAISS_WARNINGS_AS_ERRORS)
+        if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:-Werror>
+            )
+        elseif(MSVC)
+            target_compile_options(${target} PRIVATE
+                $<$<COMPILE_LANGUAGE:CXX>:/WX>
+            )
+        endif()
+    endif()
+endfunction()
+
+# Print warning configuration
+function(faiss_print_warning_config)
+    if(FAISS_WARNING_LEVEL GREATER 0)
+        message(STATUS "FAISS Warning Level: ${FAISS_WARNING_LEVEL}")
+        if(FAISS_WARNINGS_AS_ERRORS)
+            message(STATUS "FAISS Warnings as Errors: ON")
+        endif()
+    endif()
+endfunction()

demos/CMakeLists.txt

@@ -24,4 +24,12 @@ target_link_libraries(demo_weighted_kmeans PRIVATE faiss)
 add_executable(demo_residual_quantizer EXCLUDE_FROM_ALL demo_residual_quantizer.cpp)
 target_link_libraries(demo_residual_quantizer PRIVATE faiss)
 
+faiss_add_warnings(demo_imi_flat)
+faiss_add_warnings(demo_imi_pq)
+faiss_add_warnings(demo_ivfpq_indexing)
+faiss_add_warnings(demo_nndescent)
+faiss_add_warnings(demo_sift1M)
+faiss_add_warnings(demo_weighted_kmeans)
+faiss_add_warnings(demo_residual_quantizer)
+
 add_subdirectory(diversity_filter)

demos/diversity_filter/CMakeLists.txt

@@ -6,3 +6,4 @@
 add_executable(demo_diversity_result_handler EXCLUDE_FROM_ALL
   demo_diversity_result_handler.cpp)
 target_link_libraries(demo_diversity_result_handler PRIVATE faiss)
+faiss_add_warnings(demo_diversity_result_handler)