meson/mesonbuild/compilers/clike.py

# Copyright 2012-2017 The Meson development team

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


"""Mixin classes to be shared between C and C++ compilers.

Without this we'll end up with awful diamond inherintance problems. The goal
of this is to have mixin's, which are classes that are designed *not* to be
standalone, they only work through inheritance.
"""

import functools
import glob
import itertools
import os
import re
import subprocess
import typing
from pathlib import Path

from .. import mesonlib
from ..mesonlib import MachineChoice, LibType
from .. import mlog
from . import compilers

class CLikeCompiler:

    """Shared bits for the C and CPP Compilers."""

    # TODO: Replace this manual cache with functools.lru_cache
    library_dirs_cache = {}
    program_dirs_cache = {}
    find_library_cache = {}
    find_framework_cache = {}
    internal_libs = compilers.unixy_compiler_internal_libs

    def __init__(self, is_cross: bool, exe_wrapper: typing.Optional[str] = None):
        # If a child ObjC or CPP class has already set it, don't set it ourselves
        self.is_cross = is_cross
        self.can_compile_suffixes.add('h')
        # If the exe wrapper was not found, pretend it wasn't set so that the
        # sanity check is skipped and compiler checks use fallbacks.
        if not exe_wrapper or not exe_wrapper.found():
            self.exe_wrapper = None
        else:
            self.exe_wrapper = exe_wrapper.get_command()

        # Set to None until we actually need to check this
        self.has_fatal_warnings_link_arg = None

    def needs_static_linker(self):
        return True # When compiling static libraries, so yes.

    def get_always_args(self):
        '''
        Args that are always-on for all C compilers other than MSVC
        '''
        return ['-pipe'] + compilers.get_largefile_args(self)

    def get_linker_debug_crt_args(self):
        """
        Arguments needed to select a debug crt for the linker
        This is only needed for MSVC
        """
        return []

    def get_no_stdinc_args(self):
        return ['-nostdinc']

    def get_no_stdlib_link_args(self):
        return ['-nostdlib']

    def get_warn_args(self, level):
        return self.warn_args[level]

    def get_no_warn_args(self):
        # Almost every compiler uses this for disabling warnings
        return ['-w']

    def get_soname_args(self, *args):
        return []

    def split_shlib_to_parts(self, fname):
        return None, fname

    # The default behavior is this, override in MSVC
    @functools.lru_cache(maxsize=None)
    def build_rpath_args(self, build_dir, from_dir, rpath_paths, build_rpath, install_rpath):
        if self.compiler_type.is_windows_compiler:
            return []
        return self.build_unix_rpath_args(build_dir, from_dir, rpath_paths, build_rpath, install_rpath)

    def get_dependency_gen_args(self, outtarget, outfile):
        return ['-MD', '-MQ', outtarget, '-MF', outfile]

    def depfile_for_object(self, objfile):
        return objfile + '.' + self.get_depfile_suffix()

    def get_depfile_suffix(self):
        return 'd'

    def get_exelist(self):
        return self.exelist[:]

    def get_linker_exelist(self):
        return self.exelist[:]

    def get_preprocess_only_args(self):
        return ['-E', '-P']

    def get_compile_only_args(self):
        return ['-c']

    def get_no_optimization_args(self):
        return ['-O0']

    def get_compiler_check_args(self):
        '''
        Get arguments useful for compiler checks such as being permissive in
        the code quality and not doing any optimization.
        '''
        return self.get_no_optimization_args()

    def get_output_args(self, target):
        return ['-o', target]

    def get_linker_output_args(self, outputname):
        return ['-o', outputname]

    def get_coverage_args(self):
        return ['--coverage']

    def get_coverage_link_args(self):
        return ['--coverage']

    def get_werror_args(self):
        return ['-Werror']

    def get_std_exe_link_args(self):
        return []

    def get_include_args(self, path, is_system):
        if path == '':
            path = '.'
        if is_system:
            return ['-isystem', path]
        return ['-I' + path]

    def get_std_shared_lib_link_args(self):
        return ['-shared']

    @functools.lru_cache()
    def _get_search_dirs(self, env):
        extra_args = ['--print-search-dirs']
        stdo = None
        with self._build_wrapper('', env, extra_args=extra_args,
                                 dependencies=None, mode='compile',
                                 want_output=True) as p:
            stdo = p.stdo
        return stdo

    def _split_fetch_real_dirs(self, pathstr):
        # We need to use the path separator used by the compiler for printing
        # lists of paths ("gcc --print-search-dirs"). By default
        # we assume it uses the platform native separator.
        pathsep = os.pathsep

        # clang uses ':' instead of ';' on Windows https://reviews.llvm.org/D61121
        # so we need to repair things like 'C:\foo:C:\bar'
        if pathsep == ';':
            pathstr = re.sub(r':([^/\\])', r';\1', pathstr)

        # pathlib treats empty paths as '.', so filter those out
        paths = [p for p in pathstr.split(pathsep) if p]

        result = []
        for p in paths:
            # GCC returns paths like this:
            # /usr/lib/gcc/x86_64-linux-gnu/8/../../../../x86_64-linux-gnu/lib
            # It would make sense to normalize them to get rid of the .. parts
            # Sadly when you are on a merged /usr fs it also kills these:
            # /lib/x86_64-linux-gnu
            # since /lib is a symlink to /usr/lib. This would mean
            # paths under /lib would be considered not a "system path",
            # which is wrong and breaks things. Store everything, just to be sure.
            pobj = Path(p)
            unresolved = pobj.as_posix()
            if pobj.exists():
                if unresolved not in result:
                    result.append(unresolved)
                try:
                    resolved = Path(p).resolve().as_posix()
                    if resolved not in result:
                        result.append(resolved)
                except FileNotFoundError:
                    pass
        return tuple(result)

    def get_compiler_dirs(self, env, name):
        '''
        Get dirs from the compiler, either `libraries:` or `programs:`
        '''
        stdo = self._get_search_dirs(env)
        for line in stdo.split('\n'):
            if line.startswith(name + ':'):
                return self._split_fetch_real_dirs(line.split('=', 1)[1])
        return ()

    @functools.lru_cache()
    def get_library_dirs(self, env, elf_class = None):
        dirs = self.get_compiler_dirs(env, 'libraries')
        if elf_class is None or elf_class == 0:
            return dirs

        # if we do have an elf class for 32-bit or 64-bit, we want to check that
        # the directory in question contains libraries of the appropriate class. Since
        # system directories aren't mixed, we only need to check one file for each
        # directory and go by that. If we can't check the file for some reason, assume
        # the compiler knows what it's doing, and accept the directory anyway.
        retval = []
        for d in dirs:
            files = [f for f in os.listdir(d) if f.endswith('.so') and os.path.isfile(os.path.join(d, f))]
            # if no files, accept directory and move on
            if not files:
                retval.append(d)
                continue
            file_to_check = os.path.join(d, files[0])
            with open(file_to_check, 'rb') as fd:
                header = fd.read(5)
                # if file is not an ELF file, it's weird, but accept dir
                # if it is elf, and the class matches, accept dir
                if header[1:4] != b'ELF' or int(header[4]) == elf_class:
                    retval.append(d)
                # at this point, it's an ELF file which doesn't match the
                # appropriate elf_class, so skip this one
                pass
        return tuple(retval)

    @functools.lru_cache()
    def get_program_dirs(self, env):
        '''
        Programs used by the compiler. Also where toolchain DLLs such as
        libstdc++-6.dll are found with MinGW.
        '''
        return self.get_compiler_dirs(env, 'programs')

    def get_pic_args(self):
        return ['-fPIC']

    def name_string(self):
        return ' '.join(self.exelist)

    def get_pch_use_args(self, pch_dir, header):
        return ['-include', os.path.basename(header)]

    def get_pch_name(self, header_name):
        return os.path.basename(header_name) + '.' + self.get_pch_suffix()

    def get_linker_search_args(self, dirname):
        return ['-L' + dirname]

    def get_default_include_dirs(self):
        return []

    def gen_export_dynamic_link_args(self, env):
        m = env.machines[self.for_machine]
        if m.is_windows() or m.is_cygwin():
            return ['-Wl,--export-all-symbols']
        elif mesonlib.for_darwin(env):
            return []
        else:
            return ['-Wl,-export-dynamic']

    def gen_import_library_args(self, implibname):
        """
        The name of the outputted import library

        This implementation is used only on Windows by compilers that use GNU ld
        """
        return ['-Wl,--out-implib=' + implibname]

    def sanity_check_impl(self, work_dir, environment, sname, code):
        mlog.debug('Sanity testing ' + self.get_display_language() + ' compiler:', ' '.join(self.exelist))
        mlog.debug('Is cross compiler: %s.' % str(self.is_cross))

        source_name = os.path.join(work_dir, sname)
        binname = sname.rsplit('.', 1)[0]
        mode = 'link'
        if self.is_cross:
            binname += '_cross'
            if self.exe_wrapper is None:
                # Linking cross built apps is painful. You can't really
                # tell if you should use -nostdlib or not and for example
                # on OSX the compiler binary is the same but you need
                # a ton of compiler flags to differentiate between
                # arm and x86_64. So just compile.
                mode = 'compile'
        extra_flags = self._get_basic_compiler_args(environment, mode)

        # Is a valid executable output for all toolchains and platforms
        binname += '.exe'
        # Write binary check source
        binary_name = os.path.join(work_dir, binname)
        with open(source_name, 'w') as ofile:
            ofile.write(code)
        # Compile sanity check
        cmdlist = self.exelist + extra_flags + [source_name] + self.get_output_args(binary_name)
        pc, stdo, stde = mesonlib.Popen_safe(cmdlist, cwd=work_dir)
        mlog.debug('Sanity check compiler command line:', ' '.join(cmdlist))
        mlog.debug('Sanity check compile stdout:')
        mlog.debug(stdo)
        mlog.debug('-----\nSanity check compile stderr:')
        mlog.debug(stde)
        mlog.debug('-----')
        if pc.returncode != 0:
            raise mesonlib.EnvironmentException('Compiler {0} can not compile programs.'.format(self.name_string()))
        # Run sanity check
        if self.is_cross:
            if self.exe_wrapper is None:
                # Can't check if the binaries run so we have to assume they do
                return
            cmdlist = self.exe_wrapper + [binary_name]
        else:
            cmdlist = [binary_name]
        mlog.debug('Running test binary command: ' + ' '.join(cmdlist))
        try:
            pe = subprocess.Popen(cmdlist)
        except Exception as e:
            raise mesonlib.EnvironmentException('Could not invoke sanity test executable: %s.' % str(e))
        pe.wait()
        if pe.returncode != 0:
            raise mesonlib.EnvironmentException('Executables created by {0} compiler {1} are not runnable.'.format(self.language, self.name_string()))

    def sanity_check(self, work_dir, environment):
        code = 'int main(int argc, char **argv) { int class=0; return class; }\n'
        return self.sanity_check_impl(work_dir, environment, 'sanitycheckc.c', code)

    def check_header(self, hname, prefix, env, *, extra_args=None, dependencies=None):
        fargs = {'prefix': prefix, 'header': hname}
        code = '''{prefix}
        #include <{header}>'''
        return self.compiles(code.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)

    def has_header(self, hname, prefix, env, *, extra_args=None, dependencies=None, disable_cache=False):
        fargs = {'prefix': prefix, 'header': hname}
        code = '''{prefix}
        #ifdef __has_include
         #if !__has_include("{header}")
          #error "Header '{header}' could not be found"
         #endif
        #else
         #include <{header}>
        #endif'''
        return self.compiles(code.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies, mode='preprocess', disable_cache=disable_cache)

    def has_header_symbol(self, hname, symbol, prefix, env, *, extra_args=None, dependencies=None):
        fargs = {'prefix': prefix, 'header': hname, 'symbol': symbol}
        t = '''{prefix}
        #include <{header}>
        int main () {{
            /* If it's not defined as a macro, try to use as a symbol */
            #ifndef {symbol}
                {symbol};
            #endif
        }}'''
        return self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)

    def _get_basic_compiler_args(self, env, mode):
        args = []
        # Select a CRT if needed since we're linking
        if mode == 'link':
            args += self.get_linker_debug_crt_args()
        if env.is_cross_build() and not self.is_cross:
            for_machine = MachineChoice.BUILD
        else:
            for_machine = MachineChoice.HOST
        if mode in {'compile', 'preprocess'}:
            # Add CFLAGS/CXXFLAGS/OBJCFLAGS/OBJCXXFLAGS and CPPFLAGS from the env
            sys_args = env.coredata.get_external_args(for_machine, self.language)
            # Apparently it is a thing to inject linker flags both
            # via CFLAGS _and_ LDFLAGS, even though the former are
            # also used during linking. These flags can break
            # argument checks. Thanks, Autotools.
            cleaned_sys_args = self.remove_linkerlike_args(sys_args)
            args += cleaned_sys_args
        elif mode == 'link':
            # Add LDFLAGS from the env
            args += env.coredata.get_external_link_args(for_machine, self.language)
        return args

    def _get_compiler_check_args(self, env, extra_args, dependencies, mode='compile'):
        if extra_args is None:
            extra_args = []
        else:
            extra_args = mesonlib.listify(extra_args)
        extra_args = mesonlib.listify([e(mode) if callable(e) else e for e in extra_args])

        if dependencies is None:
            dependencies = []
        elif not isinstance(dependencies, list):
            dependencies = [dependencies]
        # Collect compiler arguments
        args = compilers.CompilerArgs(self)
        for d in dependencies:
            # Add compile flags needed by dependencies
            args += d.get_compile_args()
            if mode == 'link':
                # Add link flags needed to find dependencies
                args += d.get_link_args()

        args += self._get_basic_compiler_args(env, mode)

        args += self.get_compiler_check_args()
        # extra_args must override all other arguments, so we add them last
        args += extra_args
        return args

    def compiles(self, code, env, *, extra_args=None, dependencies=None, mode='compile', disable_cache=False):
        with self._build_wrapper(code, env, extra_args, dependencies, mode, disable_cache=disable_cache) as p:
            return p.returncode == 0, p.cached

    def _build_wrapper(self, code, env, extra_args, dependencies=None, mode='compile', want_output=False, disable_cache=False):
        args = self._get_compiler_check_args(env, extra_args, dependencies, mode)
        if disable_cache or want_output:
            return self.compile(code, extra_args=args, mode=mode, want_output=want_output)
        return self.cached_compile(code, env.coredata, extra_args=args, mode=mode)

    def links(self, code, env, *, extra_args=None, dependencies=None, disable_cache=False):
        return self.compiles(code, env, extra_args=extra_args,
                             dependencies=dependencies, mode='link', disable_cache=disable_cache)

    def run(self, code: str, env, *, extra_args=None, dependencies=None):
        if self.is_cross and self.exe_wrapper is None:
            raise mesonlib.CrossNoRunException('Can not run test applications in this cross environment.')
        with self._build_wrapper(code, env, extra_args, dependencies, mode='link', want_output=True) as p:
            if p.returncode != 0:
                mlog.debug('Could not compile test file %s: %d\n' % (
                    p.input_name,
                    p.returncode))
                return compilers.RunResult(False)
            if self.is_cross:
                cmdlist = self.exe_wrapper + [p.output_name]
            else:
                cmdlist = p.output_name
            try:
                pe, so, se = mesonlib.Popen_safe(cmdlist)
            except Exception as e:
                mlog.debug('Could not run: %s (error: %s)\n' % (cmdlist, e))
                return compilers.RunResult(False)

        mlog.debug('Program stdout:\n')
        mlog.debug(so)
        mlog.debug('Program stderr:\n')
        mlog.debug(se)
        return compilers.RunResult(True, pe.returncode, so, se)

    def _compile_int(self, expression, prefix, env, extra_args, dependencies):
        fargs = {'prefix': prefix, 'expression': expression}
        t = '''#include <stdio.h>
        {prefix}
        int main() {{ static int a[1-2*!({expression})]; a[0]=0; return 0; }}'''
        return self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)[0]

    def cross_compute_int(self, expression, low, high, guess, prefix, env, extra_args, dependencies):
        # Try user's guess first
        if isinstance(guess, int):
            if self._compile_int('%s == %d' % (expression, guess), prefix, env, extra_args, dependencies):
                return guess

        # If no bounds are given, compute them in the limit of int32
        maxint = 0x7fffffff
        minint = -0x80000000
        if not isinstance(low, int) or not isinstance(high, int):
            if self._compile_int('%s >= 0' % (expression), prefix, env, extra_args, dependencies):
                low = cur = 0
                while self._compile_int('%s > %d' % (expression, cur), prefix, env, extra_args, dependencies):
                    low = cur + 1
                    if low > maxint:
                        raise mesonlib.EnvironmentException('Cross-compile check overflowed')
                    cur = cur * 2 + 1
                    if cur > maxint:
                        cur = maxint
                high = cur
            else:
                low = cur = -1
                while self._compile_int('%s < %d' % (expression, cur), prefix, env, extra_args, dependencies):
                    high = cur - 1
                    if high < minint:
                        raise mesonlib.EnvironmentException('Cross-compile check overflowed')
                    cur = cur * 2
                    if cur < minint:
                        cur = minint
                low = cur
        else:
            # Sanity check limits given by user
            if high < low:
                raise mesonlib.EnvironmentException('high limit smaller than low limit')
            condition = '%s <= %d && %s >= %d' % (expression, high, expression, low)
            if not self._compile_int(condition, prefix, env, extra_args, dependencies):
                raise mesonlib.EnvironmentException('Value out of given range')

        # Binary search
        while low != high:
            cur = low + int((high - low) / 2)
            if self._compile_int('%s <= %d' % (expression, cur), prefix, env, extra_args, dependencies):
                high = cur
            else:
                low = cur + 1

        return low

    def compute_int(self, expression, low, high, guess, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        if self.is_cross:
            return self.cross_compute_int(expression, low, high, guess, prefix, env, extra_args, dependencies)
        fargs = {'prefix': prefix, 'expression': expression}
        t = '''#include<stdio.h>
        {prefix}
        int main(int argc, char **argv) {{
            printf("%ld\\n", (long)({expression}));
            return 0;
        }};'''
        res = self.run(t.format(**fargs), env, extra_args=extra_args,
                       dependencies=dependencies)
        if not res.compiled:
            return -1
        if res.returncode != 0:
            raise mesonlib.EnvironmentException('Could not run compute_int test binary.')
        return int(res.stdout)

    def cross_sizeof(self, typename, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        fargs = {'prefix': prefix, 'type': typename}
        t = '''#include <stdio.h>
        {prefix}
        int main(int argc, char **argv) {{
            {type} something;
        }}'''
        if not self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)[0]:
            return -1
        return self.cross_compute_int('sizeof(%s)' % typename, None, None, None, prefix, env, extra_args, dependencies)

    def sizeof(self, typename, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        fargs = {'prefix': prefix, 'type': typename}
        if self.is_cross:
            return self.cross_sizeof(typename, prefix, env, extra_args=extra_args,
                                     dependencies=dependencies)
        t = '''#include<stdio.h>
        {prefix}
        int main(int argc, char **argv) {{
            printf("%ld\\n", (long)(sizeof({type})));
            return 0;
        }};'''
        res = self.run(t.format(**fargs), env, extra_args=extra_args,
                       dependencies=dependencies)
        if not res.compiled:
            return -1
        if res.returncode != 0:
            raise mesonlib.EnvironmentException('Could not run sizeof test binary.')
        return int(res.stdout)

    def cross_alignment(self, typename, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        fargs = {'prefix': prefix, 'type': typename}
        t = '''#include <stdio.h>
        {prefix}
        int main(int argc, char **argv) {{
            {type} something;
        }}'''
        if not self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)[0]:
            return -1
        t = '''#include <stddef.h>
        {prefix}
        struct tmp {{
            char c;
            {type} target;
        }};'''
        return self.cross_compute_int('offsetof(struct tmp, target)', None, None, None, t.format(**fargs), env, extra_args, dependencies)

    def alignment(self, typename, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        if self.is_cross:
            return self.cross_alignment(typename, prefix, env, extra_args=extra_args,
                                        dependencies=dependencies)
        fargs = {'prefix': prefix, 'type': typename}
        t = '''#include <stdio.h>
        #include <stddef.h>
        {prefix}
        struct tmp {{
            char c;
            {type} target;
        }};
        int main(int argc, char **argv) {{
            printf("%d", (int)offsetof(struct tmp, target));
            return 0;
        }}'''
        res = self.run(t.format(**fargs), env, extra_args=extra_args,
                       dependencies=dependencies)
        if not res.compiled:
            raise mesonlib.EnvironmentException('Could not compile alignment test.')
        if res.returncode != 0:
            raise mesonlib.EnvironmentException('Could not run alignment test binary.')
        align = int(res.stdout)
        if align == 0:
            raise mesonlib.EnvironmentException('Could not determine alignment of %s. Sorry. You might want to file a bug.' % typename)
        return align

    def get_define(self, dname, prefix, env, extra_args, dependencies, disable_cache=False):
        delim = '"MESON_GET_DEFINE_DELIMITER"'
        fargs = {'prefix': prefix, 'define': dname, 'delim': delim}
        code = '''
        {prefix}
        #ifndef {define}
        # define {define}
        #endif
        {delim}\n{define}'''
        args = self._get_compiler_check_args(env, extra_args, dependencies,
                                             mode='preprocess').to_native()
        func = lambda: self.cached_compile(code.format(**fargs), env.coredata, extra_args=args, mode='preprocess')
        if disable_cache:
            func = lambda: self.compile(code.format(**fargs), extra_args=args, mode='preprocess')
        with func() as p:
            cached = p.cached
            if p.returncode != 0:
                raise mesonlib.EnvironmentException('Could not get define {!r}'.format(dname))
        # Get the preprocessed value after the delimiter,
        # minus the extra newline at the end and
        # merge string literals.
        return self.concatenate_string_literals(p.stdo.split(delim + '\n')[-1][:-1]), cached

    def get_return_value(self, fname, rtype, prefix, env, extra_args, dependencies):
        if rtype == 'string':
            fmt = '%s'
            cast = '(char*)'
        elif rtype == 'int':
            fmt = '%lli'
            cast = '(long long int)'
        else:
            raise AssertionError('BUG: Unknown return type {!r}'.format(rtype))
        fargs = {'prefix': prefix, 'f': fname, 'cast': cast, 'fmt': fmt}
        code = '''{prefix}
        #include <stdio.h>
        int main(int argc, char *argv[]) {{
            printf ("{fmt}", {cast} {f}());
        }}'''.format(**fargs)
        res = self.run(code, env, extra_args=extra_args, dependencies=dependencies)
        if not res.compiled:
            m = 'Could not get return value of {}()'
            raise mesonlib.EnvironmentException(m.format(fname))
        if rtype == 'string':
            return res.stdout
        elif rtype == 'int':
            try:
                return int(res.stdout.strip())
            except ValueError:
                m = 'Return value of {}() is not an int'
                raise mesonlib.EnvironmentException(m.format(fname))

    @staticmethod
    def _no_prototype_templ():
        """
        Try to find the function without a prototype from a header by defining
        our own dummy prototype and trying to link with the C library (and
        whatever else the compiler links in by default). This is very similar
        to the check performed by Autoconf for AC_CHECK_FUNCS.
        """
        # Define the symbol to something else since it is defined by the
        # includes or defines listed by the user or by the compiler. This may
        # include, for instance _GNU_SOURCE which must be defined before
        # limits.h, which includes features.h
        # Then, undef the symbol to get rid of it completely.
        head = '''
        #define {func} meson_disable_define_of_{func}
        {prefix}
        #include <limits.h>
        #undef {func}
        '''
        # Override any GCC internal prototype and declare our own definition for
        # the symbol. Use char because that's unlikely to be an actual return
        # value for a function which ensures that we override the definition.
        head += '''
        #ifdef __cplusplus
        extern "C"
        #endif
        char {func} ();
        '''
        # The actual function call
        main = '''
        int main () {{
          return {func} ();
        }}'''
        return head, main

    @staticmethod
    def _have_prototype_templ():
        """
        Returns a head-er and main() call that uses the headers listed by the
        user for the function prototype while checking if a function exists.
        """
        # Add the 'prefix', aka defines, includes, etc that the user provides
        # This may include, for instance _GNU_SOURCE which must be defined
        # before limits.h, which includes features.h
        head = '{prefix}\n#include <limits.h>\n'
        # We don't know what the function takes or returns, so return it as an int.
        # Just taking the address or comparing it to void is not enough because
        # compilers are smart enough to optimize it away. The resulting binary
        # is not run so we don't care what the return value is.
        main = '''\nint main() {{
            void *a = (void*) &{func};
            long b = (long) a;
            return (int) b;
        }}'''
        return head, main

    def has_function(self, funcname, prefix, env, *, extra_args=None, dependencies=None):
        """
        First, this function looks for the symbol in the default libraries
        provided by the compiler (stdlib + a few others usually). If that
        fails, it checks if any of the headers specified in the prefix provide
        an implementation of the function, and if that fails, it checks if it's
        implemented as a compiler-builtin.
        """
        if extra_args is None:
            extra_args = []

        # Short-circuit if the check is already provided by the cross-info file
        varname = 'has function ' + funcname
        varname = varname.replace(' ', '_')
        if self.is_cross:
            val = env.properties.host.get(varname, None)
            if val is not None:
                if isinstance(val, bool):
                    return val, False
                raise mesonlib.EnvironmentException('Cross variable {0} is not a boolean.'.format(varname))

        fargs = {'prefix': prefix, 'func': funcname}

        # glibc defines functions that are not available on Linux as stubs that
        # fail with ENOSYS (such as e.g. lchmod). In this case we want to fail
        # instead of detecting the stub as a valid symbol.
        # We already included limits.h earlier to ensure that these are defined
        # for stub functions.
        stubs_fail = '''
        #if defined __stub_{func} || defined __stub___{func}
        fail fail fail this function is not going to work
        #endif
        '''

        # If we have any includes in the prefix supplied by the user, assume
        # that the user wants us to use the symbol prototype defined in those
        # includes. If not, then try to do the Autoconf-style check with
        # a dummy prototype definition of our own.
        # This is needed when the linker determines symbol availability from an
        # SDK based on the prototype in the header provided by the SDK.
        # Ignoring this prototype would result in the symbol always being
        # marked as available.
        if '#include' in prefix:
            head, main = self._have_prototype_templ()
        else:
            head, main = self._no_prototype_templ()
        templ = head + stubs_fail + main

        res, cached = self.links(templ.format(**fargs), env, extra_args=extra_args,
                                 dependencies=dependencies)
        if res:
            return True, cached

        # MSVC does not have compiler __builtin_-s.
        if self.get_id() in {'msvc', 'intel-cl'}:
            return False, False

        # Detect function as a built-in
        #
        # Some functions like alloca() are defined as compiler built-ins which
        # are inlined by the compiler and you can't take their address, so we
        # need to look for them differently. On nice compilers like clang, we
        # can just directly use the __has_builtin() macro.
        fargs['no_includes'] = '#include' not in prefix
        t = '''{prefix}
        int main() {{
        #ifdef __has_builtin
            #if !__has_builtin(__builtin_{func})
                #error "__builtin_{func} not found"
            #endif
        #elif ! defined({func})
            /* Check for __builtin_{func} only if no includes were added to the
             * prefix above, which means no definition of {func} can be found.
             * We would always check for this, but we get false positives on
             * MSYS2 if we do. Their toolchain is broken, but we can at least
             * give them a workaround. */
            #if {no_includes:d}
                __builtin_{func};
            #else
                #error "No definition for __builtin_{func} found in the prefix"
            #endif
        #endif
        }}'''
        return self.links(t.format(**fargs), env, extra_args=extra_args,
                          dependencies=dependencies)

    def has_members(self, typename, membernames, prefix, env, *, extra_args=None, dependencies=None):
        if extra_args is None:
            extra_args = []
        fargs = {'prefix': prefix, 'type': typename, 'name': 'foo'}
        # Create code that accesses all members
        members = ''
        for member in membernames:
            members += '{}.{};\n'.format(fargs['name'], member)
        fargs['members'] = members
        t = '''{prefix}
        void bar() {{
            {type} {name};
            {members}
        }};'''
        return self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)

    def has_type(self, typename, prefix, env, extra_args, dependencies=None):
        fargs = {'prefix': prefix, 'type': typename}
        t = '''{prefix}
        void bar() {{
            sizeof({type});
        }};'''
        return self.compiles(t.format(**fargs), env, extra_args=extra_args,
                             dependencies=dependencies)

    def symbols_have_underscore_prefix(self, env):
        '''
        Check if the compiler prefixes an underscore to global C symbols
        '''
        symbol_name = b'meson_uscore_prefix'
        code = '''#ifdef __cplusplus
        extern "C" {
        #endif
        void ''' + symbol_name.decode() + ''' () {}
        #ifdef __cplusplus
        }
        #endif
        '''
        args = self.get_compiler_check_args()
        n = 'symbols_have_underscore_prefix'
        with self.compile(code, extra_args=args, mode='compile', want_output=True) as p:
            if p.returncode != 0:
                m = 'BUG: Unable to compile {!r} check: {}'
                raise RuntimeError(m.format(n, p.stdo))
            if not os.path.isfile(p.output_name):
                m = 'BUG: Can\'t find compiled test code for {!r} check'
                raise RuntimeError(m.format(n))
            with open(p.output_name, 'rb') as o:
                for line in o:
                    # Check if the underscore form of the symbol is somewhere
                    # in the output file.
                    if b'_' + symbol_name in line:
                        return True
                    # Else, check if the non-underscored form is present
                    elif symbol_name in line:
                        return False
        raise RuntimeError('BUG: {!r} check failed unexpectedly'.format(n))

    def _get_patterns(self, env, prefixes, suffixes, shared=False):
        patterns = []
        for p in prefixes:
            for s in suffixes:
                patterns.append(p + '{}.' + s)
        if shared and mesonlib.for_openbsd(env):
            # Shared libraries on OpenBSD can be named libfoo.so.X.Y:
            # https://www.openbsd.org/faq/ports/specialtopics.html#SharedLibs
            #
            # This globbing is probably the best matching we can do since regex
            # is expensive. It's wrong in many edge cases, but it will match
            # correctly-named libraries and hopefully no one on OpenBSD names
            # their files libfoo.so.9a.7b.1.0
            for p in prefixes:
                patterns.append(p + '{}.so.[0-9]*.[0-9]*')
        return patterns

    def get_library_naming(self, env, libtype: LibType, strict=False):
        '''
        Get library prefixes and suffixes for the target platform ordered by
        priority
        '''
        stlibext = ['a']
        # We've always allowed libname to be both `foo` and `libfoo`, and now
        # people depend on it. Also, some people use prebuilt `foo.so` instead
        # of `libfoo.so` for unknown reasons, and may also want to create
        # `foo.so` by setting name_prefix to ''
        if strict and not isinstance(self, compilers.VisualStudioLikeCompiler): # lib prefix is not usually used with msvc
            prefixes = ['lib']
        else:
            prefixes = ['lib', '']
        # Library suffixes and prefixes
        if mesonlib.for_darwin(env):
            shlibext = ['dylib', 'so']
        elif mesonlib.for_windows(env):
            # FIXME: .lib files can be import or static so we should read the
            # file, figure out which one it is, and reject the wrong kind.
            if isinstance(self, compilers.VisualStudioLikeCompiler):
                shlibext = ['lib']
            else:
                shlibext = ['dll.a', 'lib', 'dll']
            # Yep, static libraries can also be foo.lib
            stlibext += ['lib']
        elif mesonlib.for_cygwin(env):
            shlibext = ['dll', 'dll.a']
            prefixes = ['cyg'] + prefixes
        else:
            # Linux/BSDs
            shlibext = ['so']
        # Search priority
        if libtype is LibType.PREFER_SHARED:
            patterns = self._get_patterns(env, prefixes, shlibext, True)
            patterns.extend([x for x in self._get_patterns(env, prefixes, stlibext, False) if x not in patterns])
        elif libtype is LibType.PREFER_STATIC:
            patterns = self._get_patterns(env, prefixes, stlibext, False)
            patterns.extend([x for x in self._get_patterns(env, prefixes, shlibext, True) if x not in patterns])
        elif libtype is LibType.SHARED:
            patterns = self._get_patterns(env, prefixes, shlibext, True)
        else:
            assert libtype is LibType.STATIC
            patterns = self._get_patterns(env, prefixes, stlibext, False)
        return tuple(patterns)

    @staticmethod
    def _sort_shlibs_openbsd(libs):
        filtered = []
        for lib in libs:
            # Validate file as a shared library of type libfoo.so.X.Y
            ret = lib.rsplit('.so.', maxsplit=1)
            if len(ret) != 2:
                continue
            try:
                float(ret[1])
            except ValueError:
                continue
            filtered.append(lib)
        float_cmp = lambda x: float(x.rsplit('.so.', maxsplit=1)[1])
        return sorted(filtered, key=float_cmp, reverse=True)

    @classmethod
    def _get_trials_from_pattern(cls, pattern, directory, libname):
        f = Path(directory) / pattern.format(libname)
        # Globbing for OpenBSD
        if '*' in pattern:
            # NOTE: globbing matches directories and broken symlinks
            # so we have to do an isfile test on it later
            return [Path(x) for x in cls._sort_shlibs_openbsd(glob.glob(str(f)))]
        return [f]

    @staticmethod
    def _get_file_from_list(env, files: typing.List[str]) -> Path:
        '''
        We just check whether the library exists. We can't do a link check
        because the library might have unresolved symbols that require other
        libraries. On macOS we check if the library matches our target
        architecture.
        '''
        # If not building on macOS for Darwin, do a simple file check
        files = [Path(f) for f in files]
        if not env.machines.host.is_darwin() or not env.machines.build.is_darwin():
            for f in files:
                if f.is_file():
                    return f
        # Run `lipo` and check if the library supports the arch we want
        for f in files:
            if not f.is_file():
                continue
            archs = mesonlib.darwin_get_object_archs(f)
            if archs and env.machines.host.cpu_family in archs:
                return f
            else:
                mlog.debug('Rejected {}, supports {} but need {}'
                           .format(f, archs, env.machines.host.cpu_family))
        return None

    @functools.lru_cache()
    def output_is_64bit(self, env):
        '''
        returns true if the output produced is 64-bit, false if 32-bit
        '''
        return self.sizeof('void *', '', env) == 8

    def find_library_real(self, libname, env, extra_dirs, code, libtype: LibType):
        # First try if we can just add the library as -l.
        # Gcc + co seem to prefer builtin lib dirs to -L dirs.
        # Only try to find std libs if no extra dirs specified.
        # The built-in search procedure will always favour .so and then always
        # search for .a. This is only allowed if libtype is LibType.PREFER_SHARED
        if ((not extra_dirs and libtype is LibType.PREFER_SHARED) or
                libname in self.internal_libs):
            args = ['-l' + libname]
            largs = self.linker_to_compiler_args(self.get_allow_undefined_link_args())
            if self.links(code, env, extra_args=(args + largs), disable_cache=True)[0]:
                return args
            # Don't do a manual search for internal libs
            if libname in self.internal_libs:
                return None
        # Not found or we want to use a specific libtype? Try to find the
        # library file itself.
        patterns = self.get_library_naming(env, libtype)
        # try to detect if we are 64-bit or 32-bit. If we can't
        # detect, we will just skip path validity checks done in
        # get_library_dirs() call
        try:
            if self.output_is_64bit(env):
                elf_class = 2
            else:
                elf_class = 1
        except (mesonlib.MesonException, KeyError): # TODO evaluate if catching KeyError is wanted here
            elf_class = 0
        # Search in the specified dirs, and then in the system libraries
        for d in itertools.chain(extra_dirs, self.get_library_dirs(env, elf_class)):
            for p in patterns:
                trial = self._get_trials_from_pattern(p, d, libname)
                if not trial:
                    continue
                trial = self._get_file_from_list(env, trial)
                if not trial:
                    continue
                return [trial.as_posix()]
        return None

    def find_library_impl(self, libname, env, extra_dirs, code, libtype: LibType):
        # These libraries are either built-in or invalid
        if libname in self.ignore_libs:
            return []
        if isinstance(extra_dirs, str):
            extra_dirs = [extra_dirs]
        key = (tuple(self.exelist), libname, tuple(extra_dirs), code, libtype)
        if key not in self.find_library_cache:
            value = self.find_library_real(libname, env, extra_dirs, code, libtype)
            self.find_library_cache[key] = value
        else:
            value = self.find_library_cache[key]
        if value is None:
            return None
        return value[:]

    def find_library(self, libname, env, extra_dirs, libtype: LibType = LibType.PREFER_SHARED):
        code = 'int main(int argc, char **argv) { return 0; }'
        return self.find_library_impl(libname, env, extra_dirs, code, libtype)

    def find_framework_paths(self, env):
        '''
        These are usually /Library/Frameworks and /System/Library/Frameworks,
        unless you select a particular macOS SDK with the -isysroot flag.
        You can also add to this by setting -F in CFLAGS.
        '''
        if self.id != 'clang':
            raise mesonlib.MesonException('Cannot find framework path with non-clang compiler')
        # Construct the compiler command-line
        commands = self.get_exelist() + ['-v', '-E', '-']
        commands += self.get_always_args()
        # Add CFLAGS/CXXFLAGS/OBJCFLAGS/OBJCXXFLAGS from the env
        if env.is_cross_build() and not self.is_cross:
            for_machine = MachineChoice.BUILD
        else:
            for_machine = MachineChoice.HOST
        commands += env.coredata.get_external_args(for_machine, self.language)
        mlog.debug('Finding framework path by running: ', ' '.join(commands), '\n')
        os_env = os.environ.copy()
        os_env['LC_ALL'] = 'C'
        _, _, stde = mesonlib.Popen_safe(commands, env=os_env, stdin=subprocess.PIPE)
        paths = []
        for line in stde.split('\n'):
            if '(framework directory)' not in line:
                continue
            # line is of the form:
            # ` /path/to/framework (framework directory)`
            paths.append(line[:-21].strip())
        return paths

    def find_framework_real(self, name, env, extra_dirs, allow_system):
        code = 'int main(int argc, char **argv) { return 0; }'
        link_args = []
        for d in extra_dirs:
            link_args += ['-F' + d]
        # We can pass -Z to disable searching in the system frameworks, but
        # then we must also pass -L/usr/lib to pick up libSystem.dylib
        extra_args = [] if allow_system else ['-Z', '-L/usr/lib']
        link_args += ['-framework', name]
        if self.links(code, env, extra_args=(extra_args + link_args), disable_cache=True)[0]:
            return link_args

    def find_framework_impl(self, name, env, extra_dirs, allow_system):
        if isinstance(extra_dirs, str):
            extra_dirs = [extra_dirs]
        key = (tuple(self.exelist), name, tuple(extra_dirs), allow_system)
        if key in self.find_framework_cache:
            value = self.find_framework_cache[key]
        else:
            value = self.find_framework_real(name, env, extra_dirs, allow_system)
            self.find_framework_cache[key] = value
        if value is None:
            return None
        return value[:]

    def find_framework(self, name, env, extra_dirs, allow_system=True):
        '''
        Finds the framework with the specified name, and returns link args for
        the same or returns None when the framework is not found.
        '''
        if self.id != 'clang':
            raise mesonlib.MesonException('Cannot find frameworks with non-clang compiler')
        return self.find_framework_impl(name, env, extra_dirs, allow_system)

    def thread_flags(self, env):
        if mesonlib.for_haiku(env) or mesonlib.for_darwin(env):
            return []
        return ['-pthread']

    def thread_link_flags(self, env):
        if mesonlib.for_haiku(env) or mesonlib.for_darwin(env):
            return []
        return ['-pthread']

    def linker_to_compiler_args(self, args):
        return args

    def has_arguments(self, args, env, code, mode):
        return self.compiles(code, env, extra_args=args, mode=mode)

    def has_multi_arguments(self, args, env):
        for arg in args[:]:
            # some compilers, e.g. GCC, don't warn for unsupported warning-disable
            # flags, so when we are testing a flag like "-Wno-forgotten-towel", also
            # check the equivalent enable flag too "-Wforgotten-towel"
            if arg.startswith('-Wno-'):
                args.append('-W' + arg[5:])
            if arg.startswith('-Wl,'):
                mlog.warning('{} looks like a linker argument, '
                             'but has_argument and other similar methods only '
                             'support checking compiler arguments. Using them '
                             'to check linker arguments are never supported, '
                             'and results are likely to be wrong regardless of '
                             'the compiler you are using. has_link_argument or '
                             'other similar method can be used instead.'
                             .format(arg))
        code = 'int i;\n'
        return self.has_arguments(args, env, code, mode='compile')

    def has_multi_link_arguments(self, args, env):
        # First time we check for link flags we need to first check if we have
        # --fatal-warnings, otherwise some linker checks could give some
        # false positive.
        fatal_warnings_args = ['-Wl,--fatal-warnings']
        if self.has_fatal_warnings_link_arg is None:
            self.has_fatal_warnings_link_arg = False
            self.has_fatal_warnings_link_arg = self.has_multi_link_arguments(fatal_warnings_args, env)[0]

        if self.has_fatal_warnings_link_arg:
            args = fatal_warnings_args + args

        args = self.linker_to_compiler_args(args)
        code = 'int main(int argc, char **argv) { return 0; }'
        return self.has_arguments(args, env, code, mode='link')

    @staticmethod
    def concatenate_string_literals(s):
        pattern = re.compile(r'(?P<pre>.*([^\\]")|^")(?P<str1>([^\\"]|\\.)*)"\s+"(?P<str2>([^\\"]|\\.)*)(?P<post>".*)')
        ret = s
        m = pattern.match(ret)
        while m:
            ret = ''.join(m.group('pre', 'str1', 'str2', 'post'))
            m = pattern.match(ret)
        return ret

    def has_func_attribute(self, name, env):
        # Just assume that if we're not on windows that dllimport and dllexport
        # don't work
        if not (mesonlib.for_windows(env) or
                mesonlib.for_cygwin(env)):
            if name in ['dllimport', 'dllexport']:
                return False, False

        # Clang and GCC both return warnings if the __attribute__ is undefined,
        # so set -Werror
        return self.compiles(self.attribute_check_func(name), env, extra_args='-Werror')