sccache chooses the -x flag to the compiler based on extension only

[mathstuf]

I'm seeing this affecting a line like this:

sccache /usr/bin/c++    -o CMakeFiles/SetLang.dir/bar.c.o -c "/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c"
/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c:4:1: error: unknown type name 'class'
    4 | class A
      | ^~~~~
/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c:5:1: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token
    5 | {
      | ^
/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c: In function 'main':
/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c:13:3: error: unknown type name 'A'
   13 |   A a;
      |   ^
/builds/gitlab-kitware-cmake ci/Tests/SetLang/bar.c:14:8: error: request for member 'i' in something not a structure or union
   14 |   if (a.i == 21) {
      |        ^

Should sccache choose the -x flag based on the compiler used rather than the extension? If the compiler is ambiguous or unknown to be a specific language, the extension can then be used.

Related: #163 (@luser @glandium @mikeconley @rillian)
Related: ee10eae

Full log of the test: https://open.cdash.org/testDetails.php?test=883197977&build=6530941

[froydnj]

g++ seems to always compile as C++; clang++ gives a warning (clang 9.0-ish), but compiles as C++ anyway. I guess we should be compatible with this behavior, then.

[robertmaynard]

Should this be closed now that #803 has been closed?

[monsdar]

I'm having a thirdparty code generator that generates a C++ library for me. Unfortunately the files getting generated are named like C-files: generated_akm.c etc.

So far we've worked around this by setting the file properties using CMake like so: set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/generated_akm.c PROPERTIES GENERATED true LANGUAGE CXX). This builds as it should, though admittedly it's a dirty hack.

Now when turning on sccache we're not able to compile anymore. sccache is ignoring what CMake sets for us and tries to compile the sources with the C compiler.

Is there an easy way around this? It'd be very helpful if there's a way to make sscache use the correct compiler instead of having to touch a lot of legacy code.

[robertmaynard]

This builds as it should, though admittedly it's a dirty hack.

FYI, this isn't a dirty hack but the intended way for CMake projects to state that the language extension of a file should be ignored

[froydnj]

Is there an easy way around this? It'd be very helpful if there's a way to make sscache use the correct compiler instead of having to touch a lot of legacy code.

Does this behavior still happen with sccache compiled from git?

[mathstuf]

I think #803 might have fixed the C/C++ confusion, but I suspect this is a larger problem than just that. I haven't tested since #803 was closed though.

[robertmaynard]

You might also need to wait for CMake 3.19 ( https://gitlab.kitware.com/cmake/cmake/-/merge_requests/4780 ). Before 3.19 when compiling a file with a C extension for C++ CMake would presume that calling g++ || clang++ was sufficient. Starting in 3.19 we will add an explicit -x c++ to the command line.

Note: This -x c++ is only added when somebody has explicitly specified the LANGUAGE property

[froydnj]

I think #803 might have fixed the C/C++ confusion, but I suspect this is a larger problem than just that.

What is the "larger problem" here? I guess that sccache only implements the language-switching behavior for clang and gcc and not for other compilers? Or something else?

[monsdar]

I'll check with latest revision of sccache. Thanks for the fast responses!

[monsdar]

Before setting up a Rust toolchain etc: Is there a prebuilt master available somewhere? Is travis only building releases?
/update: Using the official Rust Docker image works like a charm, sccache master is building right now

[cr1901]

I'm still having problems compiling based on file extension as of 6628e1f:

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/build-rv32i/build-gcc-newlib-stage1/build-x86_64-w64-mingw32/libcpp
$ sccache g++  -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp -I. -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/../include -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include  -g -O2 -W -Wall -Wno-narrowing -Wwrite-strings -Wmissing-format-attribute -pedantic -Wno-long-long  -fno-exceptions -fno-rtti -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp -I. -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/../include -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include   -c -o directives.o -MT directives.o -MMD -MP -MF .deps/directives.Tpo ../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/directives.c
cc1.exe: warning: command line option '-fno-rtti' is valid for C++/D/ObjC++ but not for C In file included from ../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include/cpplib.h:27,
                 from ../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/directives.c:23:
../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include/line-map.h:329:3: error: expected specifier-qualifier-list before 'static'
  329 |   static source_range from_location (location_t loc)
      |   ^~~~~~
../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include/line-map.h:402:43: error: expected identifier or '(' before ':' token
  402 | struct GTY((tag ("1"))) line_map_ordinary : public line_map {
      |                                           ^
../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include/line-map.h:446:2: warning: ISO C does not allow extra ';' outside of a function [-Wpedantic]
  446 | };

Source file compiles successfully if I remove the sccache invocation:

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/build-rv32i/build-gcc-newlib-stage1/build-x86_64-w64-mingw32/libcpp
$ g++  -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp -I. -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/../include -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include  -g -O2 -W -Wall -Wno-narrowing -Wwrite-strings -Wmissing-format-attribute -pedantic -Wno-long-long  -fno-exceptions -fno-rtti -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp -I. -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/../include -I../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/include   -c -o directives.o -MT directives.o -MMD -MP -MF .deps/directives.Tpo ../../../../riscv-gnu-toolchain/riscv-gcc/libcpp/directives.c

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/build-rv32i/build-gcc-newlib-stage1/build-x86_64-w64-mingw32/libcpp

EDIT: To duplicate this, checkout the riscv-gnu-toolchain repo, export CC="sccache gcc" and export CXX="sccache g++" and configure in another directory using something like: ../riscv-gnu-toolchain/configure --with-arch=rv32i --prefix=/opt/riscv32i. The binutils build will succeed, but the gcc build will choke due to numerous C++ files having a .c extension. More than I can manually alter, unfortunately.