The C99 standard was released in January 1999, now 22 years ago. It provides a variety of useful features, including variadic arguments for macros, declarations after statements, designated initializers, and a wide variety of other useful features, many of which we already use.
We'd like to take advantage of these features, but we want to be cautious. As far as we know, all major compilers now support C99 or a later C standard, such as C11 or C17. POSIX has required C99 support as a requirement for the 2001 revision, so we can safely assume any POSIX system which we are interested in supporting has C99.
Even MSVC, long a holdout against modern C, now supports both C11 and C17 with an appropriate update. Moreover, even if people are using an older version of MSVC on these systems, they will generally need some implementation of the standard Unix utilities for the testsuite, and GNU coreutils, the most common option, has required C99 since 2009. Therefore, we can safely assume that a suitable version of GCC or clang is available to users even if their version of MSVC is not sufficiently capable.
Let's add a test balloon to git-compat-util.h to see if anyone is using an older compiler. We'll add a comment telling people how to enable this functionality on GCC and Clang, even though modern versions of both will automatically do the right thing, and ask people still experiencing a problem to report that to us on the list.
Note that C89 compilers don't provide the __STDC_VERSION__ macro, so we use a well-known hack of using "- 0". On compilers with this macro, it doesn't change the value, and on C89 compilers, the macro will be replaced with nothing, and our value will be 0.
For sparse, we explicitly request the gnu99 style because we've traditionally taken advantage of some GCC- and clang-specific extensions when available and we'd like to retain the ability to do that. sparse also defaults to C89 without it, so things will fail for us if we don't.
Update the cmake configuration to require C11 for MSVC. We do this because this will make MSVC to use C11, since it does not explicitly support C99. We do this with a compiler options because setting the C_STANDARD option does not work in our CI on MSVC and at the moment, we don't want to require C11 for Unix compilers.
In the Makefile, don't set any compiler flags for the compiler itself, since on some systems, such as FreeBSD, we actually need C11, and asking for C99 causes things to fail to compile. The error message should make it obvious what's going wrong and allow a user to set the appropriate option when building in the event they're using a Unix compiler that doesn't support it by default.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
Makefile | 2 +-
contrib/buildsystems/CMakeLists.txt | 2 +-
git-compat-util.h | 13 +++++++++++++
3 files changed, 15 insertions(+), 2 deletions(-)
Show changes to 3 files +15 −2
Makefile, contrib/buildsystems/CMakeLists.txt, git-compat-util.h
diff --git a/Makefile b/Makefile
index 12be39ac49..3d0ce6ddf6 100644
--- a/Makefile
+++ b/Makefile
@@ -1215,7 +1215,7 @@ ARFLAGS = rcs
PTHREAD_CFLAGS =
# For the 'sparse' target
-SPARSE_FLAGS ?=
+SPARSE_FLAGS ?= -std=gnu99
SP_EXTRA_FLAGS = -Wno-universal-initializer
# For informing GIT-BUILD-OPTIONS of the SANITIZE=leak target
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index fd1399c440..07b6c5494b 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -208,7 +208,7 @@ endif()
if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_BINARY_DIR})
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_BINARY_DIR})
- add_compile_options(/MP)
+ add_compile_options(/MP /std:c11)
endif()
#default behaviour
diff --git a/git-compat-util.h b/git-compat-util.h
index d70ce14286..ffe70b570f 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1,6 +1,19 @@
#ifndef GIT_COMPAT_UTIL_H
#define GIT_COMPAT_UTIL_H
+#if __STDC_VERSION__ - 0 < 199901L
+/*
+ * Git is in a testing period for mandatory C99 support in the compiler. If
+ * your compiler is reasonably recent, you can try to enable C99 support (or,
+ * for MSVC, C11 support). If you encounter a problem and can't enable C99
+ * support with your compiler (such as with "-std=gnu99") and don't have access
+ * to one with this support, such as GCC or Clang, you can remove this #if
+ * directive, but please report the details of your system to
+ * git@vger.kernel.org.
+ */
+#error "Required C99 support is in a test phase. Please see git-compat-util.h for more details."
+#endif
+
#ifdef USE_MSVC_CRTDBG
/*
* For these to work they must appear very early in each
brian m. carlson
