builder,pref: allow thirdparty objects compilation with CPP compiler (#19124)

cmd/tools/modules/testing/common.v

@@ -187,6 +187,7 @@ pub fn new_test_session(_vargs string, will_compile bool) TestSession {
 		skip_files << 'examples/coroutines/simple_coroutines.v'
 		$if msvc {
 			skip_files << 'vlib/v/tests/const_comptime_eval_before_vinit_test.v' // _constructor used
+			skip_files << 'vlib/v/tests/project_with_cpp_code/compiling_cpp_files_with_a_cplusplus_compiler_test.v'
 		}
 		$if solaris {
 			skip_files << 'examples/gg/gg2.v'

cmd/tools/vtest-self.v

@@ -170,6 +170,7 @@ const (
 		'vlib/orm/orm_insert_reserved_name_test.v',
 		'vlib/v/tests/orm_sub_array_struct_test.v',
 		'vlib/v/tests/orm_handle_error_for_select_from_not_created_table_test.v',
+		'vlib/v/tests/project_with_cpp_code/compiling_cpp_files_with_a_cplusplus_compiler_test.v', // fails compilation with: undefined reference to vtable for __cxxabiv1::__function_type_info'
 	]
 	skip_with_werror              = [
 		'do_not_remove',
@@ -243,6 +244,7 @@ const (
 		'vlib/v/tests/const_fixed_array_containing_references_to_itself_test.v', // error C2099: initializer is not a constant
 		'vlib/v/tests/const_and_global_with_same_name_test.v', // error C2099: initializer is not a constant
 		'vlib/v/tests/sumtype_as_cast_test.v', // error: cannot support compound statement expression ({expr; expr; expr;})
+		'vlib/v/tests/project_with_cpp_code/compiling_cpp_files_with_a_cplusplus_compiler_test.v', // TODO
 	]
 	skip_on_windows               = [
 		'do_not_remove',
@@ -333,6 +335,7 @@ fn main() {
 	}
 
 	if github_job == 'windows-tcc' {
+		tsession.skip_files << 'vlib/v/tests/project_with_cpp_code/compiling_cpp_files_with_a_cplusplus_compiler_test.v'
 		// TODO: fix these ASAP
 		tsession.skip_files << 'vlib/net/tcp_test.v'
 		tsession.skip_files << 'vlib/net/udp_test.v'

vlib/v/builder/cc.v

@@ -10,6 +10,13 @@ import v.util
 import v.vcache
 import term
 
+const (
+	c_std       = 'c99'
+	c_std_gnu   = 'gnu99'
+	cpp_std     = 'c++17'
+	cpp_std_gnu = 'gnu++17'
+)
+
 const c_verror_message_marker = 'VERROR_MESSAGE '
 
 const c_error_info = '
@@ -131,13 +138,6 @@ fn (mut v Builder) setup_ccompiler_options(ccompiler string) {
 	// arguments for the C compiler
 	ccoptions.args = [v.pref.cflags]
 	ccoptions.ldflags = [v.pref.ldflags]
-	if !v.pref.no_std {
-		if v.pref.os == .linux {
-			ccoptions.args << '-std=gnu99 -D_DEFAULT_SOURCE'
-		} else {
-			ccoptions.args << '-std=c99 -D_DEFAULT_SOURCE'
-		}
-	}
 	ccoptions.wargs = [
 		'-Wall',
 		'-Wextra',
@@ -343,6 +343,14 @@ fn (mut v Builder) setup_ccompiler_options(ccompiler string) {
 	if v.pref.os == .macos {
 		ccoptions.source_args << '-x none'
 	}
+	if !v.pref.no_std {
+		if v.pref.os == .linux {
+			ccoptions.source_args << '-std=${builder.c_std_gnu}'
+		} else {
+			ccoptions.source_args << '-std=${builder.c_std}'
+		}
+		ccoptions.source_args << '-D_DEFAULT_SOURCE'
+	}
 	// Min macos version is mandatory I think?
 	if v.pref.os == .macos {
 		ccoptions.post_args << '-mmacosx-version-min=10.7'
@@ -396,7 +404,7 @@ fn (mut v Builder) setup_ccompiler_options(ccompiler string) {
 	// setup the cache too, so that different compilers/options do not interfere:
 	v.pref.cache_manager.set_temporary_options(v.thirdparty_object_args(v.ccoptions, [
 		ccoptions.guessed_compiler,
-	]))
+	], false))
 }
 
 fn (v &Builder) all_args(ccoptions CcompilerOptions) []string {
@@ -437,8 +445,26 @@ fn (v &Builder) all_args(ccoptions CcompilerOptions) []string {
 	return all
 }
 
-fn (v &Builder) thirdparty_object_args(ccoptions CcompilerOptions, middle []string) []string {
+fn (v &Builder) thirdparty_object_args(ccoptions CcompilerOptions, middle []string, cpp_file bool) []string {
 	mut all := []string{}
+
+	if !v.pref.no_std {
+		if v.pref.os == .linux {
+			if cpp_file {
+				all << '-std=${builder.cpp_std_gnu}'
+			} else {
+				all << '-std=${builder.c_std_gnu}'
+			}
+		} else {
+			if cpp_file {
+				all << '-std=${builder.cpp_std}'
+			} else {
+				all << '-std=${builder.c_std}'
+			}
+		}
+		all << '-D_DEFAULT_SOURCE'
+	}
+
 	all << ccoptions.env_cflags
 	all << ccoptions.args
 	all << middle
@@ -888,7 +914,13 @@ fn (mut b Builder) build_thirdparty_obj_files() {
 
 fn (mut v Builder) build_thirdparty_obj_file(mod string, path string, moduleflags []cflag.CFlag) {
 	obj_path := os.real_path(path)
-	cfile := '${obj_path[..obj_path.len - 2]}.c'
+	mut cfile := '${obj_path[..obj_path.len - 2]}.c'
+	mut cpp_file := false
+	if !os.exists(cfile) {
+		// Guessed C file does not exist, so it may be a CPP file
+		cfile += 'pp'
+		cpp_file = true
+	}
 	opath := v.pref.cache_manager.mod_postfix_with_key2cpath(mod, '.o', obj_path)
 	mut rebuild_reason_message := '${obj_path} not found, building it in ${opath} ...'
 	if os.exists(opath) {
@@ -918,8 +950,17 @@ fn (mut v Builder) build_thirdparty_obj_file(mod string, path string, moduleflag
 	all_options << moduleflags.c_options_before_target()
 	all_options << '-o ${os.quoted_path(opath)}'
 	all_options << '-c ${os.quoted_path(cfile)}'
-	cc_options := v.thirdparty_object_args(v.ccoptions, all_options).join(' ')
-	cmd := '${v.quote_compiler_name(v.pref.ccompiler)} ${cc_options}'
+	cc_options := v.thirdparty_object_args(v.ccoptions, all_options, cpp_file).join(' ')
+
+	// If the third party object file requires a CPP file compilation, switch to a CPP compiler
+	mut ccompiler := v.pref.ccompiler
+	if cpp_file {
+		$if trace_thirdparty_obj_files ? {
+			println('>>> build_thirdparty_obj_files switched from compiler "${ccompiler}" to "${v.pref.cppcompiler}"')
+		}
+		ccompiler = v.pref.cppcompiler
+	}
+	cmd := '${v.quote_compiler_name(ccompiler)} ${cc_options}'
 	$if trace_thirdparty_obj_files ? {
 		println('>>> build_thirdparty_obj_files cmd: ${cmd}')
 	}

vlib/v/pref/default.v

@@ -119,6 +119,9 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	if p.ccompiler == '' {
 		p.default_c_compiler()
 	}
+	if p.cppcompiler == '' {
+		p.default_cpp_compiler()
+	}
 	p.find_cc_if_cross_compiling()
 	p.ccompiler_type = cc_from_string(p.ccompiler)
 	p.is_test = p.path.ends_with('_test.v') || p.path.ends_with('_test.vv')
@@ -244,6 +247,14 @@ pub fn (mut p Preferences) default_c_compiler() {
 	return
 }
 
+pub fn (mut p Preferences) default_cpp_compiler() {
+	if p.ccompiler.contains('clang') {
+		p.cppcompiler = 'clang++'
+		return
+	}
+	p.cppcompiler = 'c++'
+}
+
 pub fn vexe_path() string {
 	vexe := os.getenv('VEXE')
 	if vexe != '' {

vlib/v/pref/pref.v

@@ -163,6 +163,7 @@ pub mut:
 	m64                bool         // true = generate 64-bit code, defaults to x64
 	ccompiler          string       // the name of the C compiler used
 	ccompiler_type     CompilerType // the type of the C compiler used
+	cppcompiler        string       // the name of the CPP compiler used
 	third_party_option string
 	building_v         bool
 	no_bounds_checking bool // `-no-bounds-checking` turns off *all* bounds checks for all functions at runtime, as if they all had been tagged with `[direct_array_access]`
@@ -738,6 +739,10 @@ pub fn parse_args_and_show_errors(known_external_commands []string, args []strin
 				res.build_options << '${arg} "${res.ccompiler}"'
 				i++
 			}
+			'-c++' {
+				res.cppcompiler = cmdline.option(current_args, '-c++', 'c++')
+				i++
+			}
 			'-checker-match-exhaustive-cutoff-limit' {
 				res.checker_match_exhaustive_cutoff_limit = cmdline.option(current_args,
 					arg, '10').int()

vlib/v/tests/project_with_cpp_code/compiling_cpp_files_with_a_cplusplus_compiler_test.v

@@ -0,0 +1,19 @@
+module main
+
+#flag @VMODROOT/implementation.o
+#include "@VMODROOT/implementation.h"
+
+fn C.sizeof_char() int
+
+fn test_the_implementation_object_file_was_compiled_with_a_c_plus_plus_compiler() {
+	res := C.sizeof_char()
+	dump(res)
+	if res == sizeof(int) {
+		eprintln('implementation.o was compiled with a C compiler. Fail.')
+	} else if res == sizeof(char) {
+		println('implementation.o was compiled with a C++ compiler. Good.')
+	} else {
+		eprintln('¯\\_(ツ)_/¯ ... unknown C/C++ compiler')
+	}
+	assert res == sizeof(char)
+}

vlib/v/tests/project_with_cpp_code/implementation.cpp

@@ -0,0 +1,9 @@
+// This file should be compiled with a C++ compiler:
+extern "C" {
+	int sizeof_char(void);
+}
+
+int sizeof_char(void) {
+   // see https://stackoverflow.com/a/12887719/1023403
+   return sizeof('a'); // 4 for C compilers, 1 for C++ compilers
+}

vlib/v/tests/project_with_cpp_code/implementation.h

@@ -0,0 +1 @@
+int sizeof_char(void);

vlib/v/tests/project_with_cpp_code/v.mod

@@ -0,0 +1,5 @@
+Module {
+	name: 'project_with_cpp_code',
+	description: 'A simple project, containing a .cpp file with C++ code, that has to be compiled with a C++ compiler.',
+	dependencies: []
+}