Merge pull request #531 from centricular/has_function_impl_fix

cc.has_function: Also detect implementations and redefinitions by a provided header

2 files changed, 20 insertions, 8 deletions

diff --git a/mesonbuild/compilers.py b/mesonbuild/compilers.py
index a320e7d..d0950ef 100644
--- a/mesonbuild/compilers.py
+++ b/mesonbuild/compilers.py
@@ -680,6 +680,13 @@ int main(int argc, char **argv) {
         return align
 
     def has_function(self, funcname, prefix, env, extra_args=[]):
+        """
+        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.
+        """
         # Define the symbol to something else in case it is defined by the
         # includes or defines listed by the user `{0}` or by the compiler.
         # Then, undef the symbol to get rid of it completely.
@@ -725,12 +732,17 @@ int main(int argc, char **argv) {
                 raise EnvironmentException('Cross variable {0} is not a boolean.'.format(varname))
         if self.links(templ.format(prefix, funcname), extra_args):
             return True
+        # Add -O0 to ensure that the symbol isn't optimized away by the compiler
+        extra_args += self.get_no_optimization_args()
+        # Sometimes the implementation is provided by the header, or the header
+        # redefines the symbol to be something else. In that case, we want to
+        # still detect the function.
+        if self.links('{0}\nint main() {{ {1}; }}'.format(prefix, funcname), extra_args):
+            return True
         # Some functions like alloca() are defined as compiler built-ins which
         # are inlined by the compiler, so test for that instead. Built-ins are
         # special functions that ignore all includes and defines, so we just
         # directly try to link via main().
-        # Add -O0 to ensure that the symbol isn't optimized away by the compiler
-        extra_args += self.get_no_optimization_args()
         return self.links('int main() {{ {0}; }}'.format('__builtin_' + funcname), extra_args)
 
     def has_member(self, typename, membername, prefix, extra_args=[]):
diff --git a/test cases/common/43 has function/meson.build b/test cases/common/43 has function/meson.build
index 3736a3d..c7fe353 100644
--- a/test cases/common/43 has function/meson.build
+++ b/test cases/common/43 has function/meson.build
@@ -3,16 +3,16 @@ project('has function', 'c')
 cc = meson.get_compiler('c')
 
 if not cc.has_function('printf', prefix : '#include<stdio.h>')
-  error('Existing function not found.')
+  error('"printf" function not found (should always exist).')
 endif
 
 # Should also be able to detect it without specifying the header
 # We check for a different function here to make sure the result is
 # not taken from a cache (ie. the check above)
-assert(cc.has_function('fprintf'), 'Existing function not found without include')
+assert(cc.has_function('fprintf'), '"fprintf" function not found without include (should always exist).')
 
 if cc.has_function('hfkerhisadf', prefix : '#include<stdio.h>')
-  error('Found non-existant function.')
+  error('Found non-existent function "hfkerhisadf".')
 endif
 
 # With glibc on Linux lchmod is a stub that will always return an error,
@@ -21,9 +21,9 @@ endif
 # implemented in glibc it's probably not implemented in any other 'slimmer'
 # C library variants either, so the check should be safe either way hopefully.
 if host_machine.system() == 'linux' and cc.get_id() == 'gcc'
-  assert (cc.has_function('poll', prefix : '#include <poll.h>'), 'couldn\'t detect poll when defined by a header')
+  assert (cc.has_function('poll', prefix : '#include <poll.h>'), 'couldn\'t detect "poll" when defined by a header')
   assert (not cc.has_function('lchmod', prefix : '''#include <sys/stat.h>
-                                                    #include <unistd.h>'''), 'lchmod check should have failed')
+                                                    #include <unistd.h>'''), '"lchmod" check should have failed')
 endif
 
 # For some functions one needs to define _GNU_SOURCE before including the
@@ -31,5 +31,5 @@ endif
 # as well without any prefix
 if cc.has_header_symbol('sys/socket.h', 'recvmmsg', prefix : '#define _GNU_SOURCE')
   # We assume that if recvmmsg exists sendmmsg does too
-  assert (cc.has_function('sendmmsg'), 'Failed to detect existing function')
+  assert (cc.has_function('sendmmsg'), 'Failed to detect function "sendmmsg" (should always exist).')
 endif