Clang shouldn't complain that C file is supplied in C++ mode when dependencies are parsed

[yurivict]

Bugzilla Link	9272
Resolution	INVALID
Resolved on	Jul 20, 2012 07:48
Version	trunk
OS	FreeBSD
CC	@DougGregor

Extended Description

When I run command like this:
clang++ -M file1.c file2.C
I get this warning:
clang: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated

Such warning should be disabled in dependency parsing mode (-M). This is because such operation doesn't depend on C/C++ differences and its very convenient to make just one call in a mixed C/C++ project instead of calling it once for all C files and once for all C++ files.

rev.126022

[lattner]

Strictly speaking, whether something is parsed as c or c++ can change what files get #included, because different macros are set, and macros can affect #includes.

[lattner]

Strictly speaking, whether something is parsed as c or c++ can change what
files get #included, because different macros are set, and macros can affect
#includes.

[llvmbot]

If clang is designed to be gcc drop in replacement. This should be allow atleast for sometime now.
Doing this will reduce the porting effort from gcc to clang.
Another reason might be any file with *cpp file compile without any warning even though functionally, it is std C. Just renaming the file to *.cpp from *c will suffice, But the effort can be saved.

[DougGregor]

If clang is designed to be gcc drop in replacement. This should be allow
atleast for sometime now.
Doing this will reduce the porting effort from gcc to clang.
Another reason might be any file with *cpp file compile without any warning
even though functionally, it is std C. Just renaming the file to *.cpp from *c
will suffice, But the effort can be saved.

Clang doesn't model every GCC quirk, and it never will. A system that depends on the use of "g++" or "clang++" to compile a ".c" file as C++ is doing something fairly odd, because it does matter which language is used, even for dependency scanning.

[llvmbot]

Clang doesn't model every GCC quirk, and it never will. A system that depends
on the use of "g++" or "clang++" to compile a ".c" file as C++ is doing
something fairly odd, because it does matter which language is used, even for
dependency scanning.

But have read as drop in replacement for gcc.

[llvmbot]

or either a option to disable this warning might be helpful.

[DougGregor]

Clang doesn't model every GCC quirk, and it never will. A system that depends
on the use of "g++" or "clang++" to compile a ".c" file as C++ is doing
something fairly odd, because it does matter which language is used, even for
dependency scanning.

But have read as drop in replacement for gcc.

"Drop-in" does not mean that Clang will model every strange GCC behavior, especially those that are dubious (like this one). It means that the vast majority of projects should "just work", or in practice, need very few tweaks to work.

It's fine to submit a separate bug requesting a way to silence this warning, but I strongly recommend that you use C file extensions for C code and C++ file extensions for C++ code. The compiler isn't the only tool that cares.

[llvmbot]

Clang doesn't model every GCC quirk, and it never will. A system that depends
on the use of "g++" or "clang++" to compile a ".c" file as C++ is doing
something fairly odd, because it does matter which language is used, even for
dependency scanning.

But have read as drop in replacement for gcc.

"Drop-in" does not mean that Clang will model every strange GCC behavior,
especially those that are dubious (like this one). It means that the vast
majority of projects should "just work", or in practice, need very few tweaks
to work.

I don't know from the compiler persepective, but from user's persepective. All the C code are legal c++ code. The uglier part is that clang does not complain if we rename *.c to *.cpp, Why so specific on a naming extension, When the importance is at the code.

[llvmbot]

Though late, But I got it. I think, This warning is wiser.
After all, What about having a option to disable this option may be as a separate bug.