Merge pull request libgit2#6911 from libgit2/ethomson/c90-2

Configurable C standard

Author: ethomson

.github/workflows/main.yml

@@ -132,7 +132,7 @@ jobs:
           env:
             CC: clang
             CFLAGS: -fsanitize=memory -fsanitize-memory-track-origins=2 -fsanitize-blacklist=/home/libgit2/source/script/sanitizers.supp -fno-optimize-sibling-calls -fno-omit-frame-pointer
-            CMAKE_OPTIONS: -DCMAKE_PREFIX_PATH=/usr/local/msan -DUSE_HTTPS=mbedTLS -DUSE_SHA1=HTTPS -DREGEX_BACKEND=pcre -DDEPRECATE_HARD=ON -DUSE_BUNDLED_ZLIB=ON -DUSE_SSH=ON
+            CMAKE_OPTIONS: -DC_EXTENSIONS=ON -DCMAKE_PREFIX_PATH=/usr/local/msan -DUSE_HTTPS=mbedTLS -DUSE_SHA1=HTTPS -DREGEX_BACKEND=pcre -DDEPRECATE_HARD=ON -DUSE_BUNDLED_ZLIB=ON -DUSE_SSH=ON
             CMAKE_GENERATOR: Ninja
             SKIP_SSH_TESTS: true
             SKIP_NEGOTIATE_TESTS: true

CMakeLists.txt

@@ -90,6 +90,8 @@ endif()
 
 # Modules
 
+include(FeatureSummary)
+include(SetCStandard)
 include(CheckLibraryExists)
 include(CheckFunctionExists)
 include(CheckSymbolExists)
@@ -102,7 +104,6 @@ include(FindStatNsec)
 include(Findfutimens)
 include(GNUInstallDirs)
 include(IdeSplitSources)
-include(FeatureSummary)
 include(EnableWarnings)
 include(DefaultCFlags)
 include(ExperimentalFeatures)

README.md

@@ -373,11 +373,13 @@ following:
 Compiler and linker options
 ---------------------------
 
-CMake lets you specify a few variables to control the behavior of the
-compiler and linker. These flags are rarely used but can be useful for
-64-bit to 32-bit cross-compilation.
+There are several options that control the behavior of the compiler and
+linker. These flags may be useful for cross-compilation or specialized
+setups.
 
 - `CMAKE_C_FLAGS`: Set your own compiler flags
+- `C_STANDARD`: the C standard to compile against; defaults to `C90`
+- `C_EXTENSIONS`: whether compiler extensions are supported; defaults to `OFF`
 - `CMAKE_FIND_ROOT_PATH`: Override the search path for libraries
 - `ZLIB_LIBRARY`, `OPENSSL_SSL_LIBRARY` AND `OPENSSL_CRYPTO_LIBRARY`:
 Tell CMake where to find those specific libraries

cmake/SetCStandard.cmake

@@ -0,0 +1,24 @@
+if("${C_STANDARD}" STREQUAL "")
+	set(C_STANDARD "90")
+endif()
+if("${C_EXTENSIONS}" STREQUAL "")
+	set(C_EXTENSIONS OFF)
+endif()
+
+if(${C_STANDARD} MATCHES "^[Cc].*")
+	string(REGEX REPLACE "^[Cc]" "" C_STANDARD ${C_STANDARD})
+endif()
+
+if(${C_STANDARD} MATCHES ".*-strict$")
+	string(REGEX REPLACE "-strict$" "" C_STANDARD ${C_STANDARD})
+	set(C_EXTENSIONS OFF)
+
+	add_feature_info("C Standard" ON "C${C_STANDARD} (strict)")
+else()
+	add_feature_info("C Standard" ON "C${C_STANDARD}")
+endif()
+
+function(set_c_standard project)
+	set_target_properties(${project} PROPERTIES C_STANDARD ${C_STANDARD})
+	set_target_properties(${project} PROPERTIES C_EXTENSIONS ${C_EXTENSIONS})
+endfunction()