New compiler method: check_header

This checks not only for existence, but also for usability of the
header, which means it does a full compilation and not just
pre-processing or __has_include.

Fixes https://github.com/mesonbuild/meson/issues/2246

mesonbuild/compilers/c.py

@@ -266,6 +266,12 @@ class CCompiler(Compiler):
         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, dependencies)
+
     def has_header(self, hname, prefix, env, extra_args=None, dependencies=None):
         fargs = {'prefix': prefix, 'header': hname}
         code = '''{prefix}

mesonbuild/compilers/compilers.py

@@ -710,6 +710,9 @@ class Compiler:
     def get_option_link_args(self, options):
         return []
 
+    def check_header(self, *args, **kwargs):
+        raise EnvironmentException('Language %s does not support header checks.' % self.get_display_language())
+
     def has_header(self, *args, **kwargs):
         raise EnvironmentException('Language %s does not support header checks.' % self.get_display_language())
 

mesonbuild/interpreter.py

@@ -843,6 +843,7 @@ class CompilerHolder(InterpreterObject):
                              'compute_int': self.compute_int_method,
                              'sizeof': self.sizeof_method,
                              'get_define': self.get_define_method,
+                             'check_header': self.check_header_method,
                              'has_header': self.has_header_method,
                              'has_header_symbol': self.has_header_symbol_method,
                              'run': self.run_method,
@@ -1229,6 +1230,31 @@ class CompilerHolder(InterpreterObject):
             mlog.log('Checking if "', mlog.bold(testname), '" links: ', h, sep='')
         return result
 
+    @permittedKwargs({
+        'prefix',
+        'no_builtin_args',
+        'include_directories',
+        'args',
+        'dependencies',
+    })
+    def check_header_method(self, args, kwargs):
+        if len(args) != 1:
+            raise InterpreterException('check_header method takes exactly one argument.')
+        check_stringlist(args)
+        hname = args[0]
+        prefix = kwargs.get('prefix', '')
+        if not isinstance(prefix, str):
+            raise InterpreterException('Prefix argument of has_header must be a string.')
+        extra_args = self.determine_args(kwargs)
+        deps = self.determine_dependencies(kwargs)
+        haz = self.compiler.check_header(hname, prefix, self.environment, extra_args, deps)
+        if haz:
+            h = mlog.green('YES')
+        else:
+            h = mlog.red('NO')
+        mlog.log('Check usable header "%s":' % hname, h)
+        return haz
+
     @permittedKwargs({
         'prefix',
         'no_builtin_args',

test cases/common/200 check header/meson.build

@@ -0,0 +1,48 @@
+project('check header', 'c', 'cpp')
+
+host_system = host_machine.system()
+
+non_existant_header = 'ouagadougou.h'
+
+# Copy it into the builddir to ensure that it isn't found even if it's there
+configure_file(input : non_existant_header,
+  output : non_existant_header,
+  copy: true)
+
+fallback = ''
+
+foreach comp : [meson.get_compiler('c'), meson.get_compiler('cpp')]
+  assert(comp.check_header('stdio.h', prefix : fallback), 'Stdio missing.')
+
+  # stdio.h doesn't actually need stdlib.h, but just test that setting the
+  # prefix does not result in an error.
+  assert(comp.check_header('stdio.h', prefix : '#include <stdlib.h>' + fallback),
+         'Stdio missing.')
+
+  # Test that check_header behaves differently than has_header. The second
+  # check without windows.h will fail with check_header.
+  # We only do this check on MSVC because MinGW often defines its own wrappers
+  # that pre-include windows.h
+  if comp.get_id() == 'msvc'
+    assert(comp.check_header('XInput.h', prefix : '#include <windows.h>' + fallback),
+           'XInput.h should not be missing on Windows')
+    assert(not comp.check_header('XInput.h'), 'XInput.h needs windows.h')
+  endif
+
+  # Test that the following GCC bug doesn't happen:
+  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80005
+  # https://github.com/mesonbuild/meson/issues/1458
+  if host_system == 'linux'
+    assert(comp.check_header('linux/if.h', prefix : fallback),
+           'Could not find <linux/if.h>')
+    if comp.has_header('intrin.h', prefix : fallback)
+      assert(not comp.check_header('intrin.h'),
+             'intrin.h should not be usable on linux')
+    endif
+  endif
+
+  # This header exists in the source and the builddir, but we still must not
+  # find it since we are looking in the system directories.
+  assert(not comp.check_header(non_existant_header, prefix : fallback),
+         'Found non-existant header.')
+endforeach

test cases/common/200 check header/ouagadougou.h

@@ -0,0 +1 @@
+#define OMG_THIS_SHOULDNT_BE_FOUND