C90 standard compliance #4700
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C90 standard compliance #4700
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ISO C90 does not specify the `inline` attribute, and as such we cannot use it in our code. While we already use `__inline` when building in Microsoft Visual Studio, we should also be using the `__inline__` attribute from GCC/Clang. Otherwise, if we're using neither MSVC nor GCC/Clang, we should simply avoid using `inline` at all and just define functions as static. This commit adjusts our own `GIT_INLINE` macro as well as the inline macros specified by khash and xdiff. This allows us to enable strict C90 mode in a later commit.
C++ style comment ("//") are not specified by the ISO C90 standard and
thus do not conform to it. While libgit2 aims to conform to C90, we did
not enforce it until now, which is why quite a lot of these
non-conforming comments have snuck into our codebase. Do a tree-wide
conversion of all C++ style comments to the supported C style comments
to allow us enforcing strict C90 compliance in a later commit.
While we want to enforce strict C90 mode, this may cause issues with system provided header files which are themselves not strictly conforming. E.g. if a system header has C++ style comments, a compiler in strict C90 mode would produce an error and abort the build. As the user most likely doesn't want to change the system header, this would completely break the build on such systems. One example of this is mbedtls, which provides such header files. The problem can be worked around by distinguishing between system-provided and project-provided include directories. When adding include directories via "-isystem" instead of "-I", the compiler will skip certain checks and print out less warnings. To use system includes, we can simply add the "SYSTEM" flag to CMake's `INCLUDE_DIRECTORIES` and `TARGET_INCLUDE_DIRECTORIES` functions. Note that we have to split the include directories into two variables because of this, as we definitely still want to check for all warnings produced by our own header files.
The mbedtls headers make direct use of the `inline` attribute to instruct the compiler to inline functions. As this function is not C90 compliant, this can cause the compiler to error as soon as any of these files is included and the `-std=c90` flag is being added. The mbedtls headers declaring functions as inline always have a prelude which define `inline` as a macro in case it is not yet defined. Thus, we can easily replace their define with our own define, which simply copies the logic of our own `GIT_INLINE` macro.
While the aim of libgit2 was to conform to C90 code, we never instructed the compiler to enforce C90 compliance. Thus, quite a few violations were able to get into our code base, which have been removed with the previous commits. As we are now able to build libgit2 with C90 enforced, we can set the C_STANDARD property for our own build targets. Note that we explicitly avoid setting the C standard for our third-party dependencies. At least the zlib target does not build with C90 enforced, and we do not want to fix them by deviating from upstream. Thus we simply enforce no standard for them.
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This PR is finally ready to be merged, opinions would be appreciated :) |
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As noted in #4689, we currently do not enforce compliance with ISO C90. This PR fixes that for Unix platforms by first fixing all non-compliant code and then adding
-std=c90to the compiler flags.