Add compiler.has_define

Adds a new method to the compiler object, has_define.
This makes it possible to check if a preprocessor macro/define
is set or not.

This is especially helpful if the define in question is empty,
for example:

  #define MESON_EMPTY_DEFINE

This would yield the same results as a missing define with
the existing get_define method, as it would return an empty
string for both cases. Therefore this additional method is
needed.

2 files changed, 40 insertions, 9 deletions

diff --git a/mesonbuild/compilers/mixins/clike.py b/mesonbuild/compilers/mixins/clike.py
index 4999d60..f37bcf4 100644
--- a/mesonbuild/compilers/mixins/clike.py
+++ b/mesonbuild/compilers/mixins/clike.py
@@ -672,13 +672,15 @@ class CLikeCompiler(Compiler):
                    extra_args: T.Union[T.List[str], T.Callable[[CompileCheckMode], T.List[str]]],
                    dependencies: T.Optional[T.List['Dependency']],
                    disable_cache: bool = False) -> T.Tuple[str, bool]:
-        delim = '"MESON_GET_DEFINE_DELIMITER"'
+        delim_start = '"MESON_GET_DEFINE_DELIMITER_START"\n'
+        delim_end = '\n"MESON_GET_DEFINE_DELIMITER_END"'
+        sentinel_undef = '"MESON_GET_DEFINE_UNDEFINED_SENTINEL"'
         code = f'''
         {prefix}
         #ifndef {dname}
-        # define {dname}
+        # define {dname} {sentinel_undef}
         #endif
-        {delim}\n{dname}'''
+        {delim_start}{dname}{delim_end}'''
         args = self.build_wrapper_args(env, extra_args, dependencies,
                                        mode=CompileCheckMode.PREPROCESS).to_native()
         func = functools.partial(self.cached_compile, code, env.coredata, extra_args=args, mode=CompileCheckMode.PREPROCESS)
@@ -688,10 +690,21 @@ class CLikeCompiler(Compiler):
             cached = p.cached
             if p.returncode != 0:
                 raise mesonlib.EnvironmentException(f'Could not get define {dname!r}')
-        # Get the preprocessed value after the delimiter,
-        # minus the extra newline at the end and
-        # merge string literals.
-        return self._concatenate_string_literals(p.stdout.split(delim + '\n')[-1][:-1]).strip(), cached
+
+        # Get the preprocessed value between the delimiters
+        star_idx = p.stdout.find(delim_start)
+        end_idx = p.stdout.rfind(delim_end)
+        if (star_idx == -1) or (end_idx == -1) or (star_idx == end_idx):
+            raise AssertionError('BUG: Delimiters not found in preprocessor output!')
+        define_value = p.stdout[star_idx + len(delim_start):end_idx]
+
+        if define_value == sentinel_undef:
+            define_value = None
+        else:
+            # Merge string literals
+            define_value = self._concatenate_string_literals(define_value).strip()
+
+        return define_value, cached
 
     def get_return_value(self, fname: str, rtype: str, prefix: str,
                          env: 'Environment', extra_args: T.Optional[T.List[str]],
diff --git a/mesonbuild/interpreter/compiler.py b/mesonbuild/interpreter/compiler.py
index b85aa37..b6a1a85 100644
--- a/mesonbuild/interpreter/compiler.py
+++ b/mesonbuild/interpreter/compiler.py
@@ -189,6 +189,7 @@ class CompilerHolder(ObjectHolder['Compiler']):
                              'compute_int': self.compute_int_method,
                              'sizeof': self.sizeof_method,
                              'get_define': self.get_define_method,
+                             'has_define': self.has_define_method,
                              'check_header': self.check_header_method,
                              'has_header': self.has_header_method,
                              'has_header_symbol': self.has_header_symbol_method,
@@ -475,8 +476,25 @@ class CompilerHolder(ObjectHolder['Compiler']):
                                                  extra_args=extra_args,
                                                  dependencies=deps)
         cached_msg = mlog.blue('(cached)') if cached else ''
-        mlog.log('Fetching value of define', mlog.bold(element, True), msg, value, cached_msg)
-        return value
+        value_msg = '(undefined)' if value is None else value
+        mlog.log('Fetching value of define', mlog.bold(element, True), msg, value_msg, cached_msg)
+        return value if value is not None else ''
+
+    @FeatureNew('compiler.has_define', '1.3.0')
+    @typed_pos_args('compiler.has_define', str)
+    @typed_kwargs('compiler.has_define', *_COMMON_KWS)
+    def has_define_method(self, args: T.Tuple[str], kwargs: 'CommonKW') -> bool:
+        define_name = args[0]
+        extra_args = functools.partial(self._determine_args, kwargs)
+        deps, msg = self._determine_dependencies(kwargs['dependencies'], endl=None)
+        value, cached = self.compiler.get_define(define_name, kwargs['prefix'], self.environment,
+                                                 extra_args=extra_args,
+                                                 dependencies=deps)
+        cached_msg = mlog.blue('(cached)') if cached else ''
+        h = mlog.green('YES') if value is not None else mlog.red('NO')
+        mlog.log('Checking if define', mlog.bold(define_name, True), msg, 'exists:', h, cached_msg)
+
+        return value is not None
 
     @typed_pos_args('compiler.compiles', (str, mesonlib.File))
     @typed_kwargs('compiler.compiles', *_COMPILES_KWS)