Consider compilers used in static_library parents

Currently meson only considers what compiler/linker were used by a
Target's immediate sources or objects, not the sources of libraries it's
linked with by the link_with and link_while keywords. This means that if
given 3 libraries: libA which is C++, libB which is C, and libC which is
also C, and libC links with libB which links with libA then linking libC
will be attempted with the C linker, and will fail.

This patch corrects that by adding the compilers used by sub libraries
to the collection of compilers considered by meson when picking a
linker.

This adds a new process_compilers_late method to the BuildTarget class,
which is evaluated after process_kwargs is called. This is needed
because some D options need to be evaluated after compilers are
selected, while for C-like languages we need to check the link* targets
for language requirements, and link* targets are passed by kwargs.

This implementation is recursive, since each Target adds it's parent's
dependencies.

mesonbuild/build.py

@@ -359,6 +359,7 @@ class BuildTarget(Target):
         self.check_unknown_kwargs(kwargs)
         if not self.sources and not self.generated and not self.objects:
             raise InvalidArguments('Build target %s has no sources.' % name)
+        self.process_compilers_late()
         self.validate_sources()
         self.validate_cross_install(environment)
 
@@ -439,6 +440,39 @@ class BuildTarget(Target):
                 removed = True
         return removed
 
+    def process_compilers_late(self):
+        """Processes additional compilers after kwargs have been evaluated.
+
+        This can add extra compilers that might be required by keyword
+        arguments, such as link_with or dependencies. It will also try to guess
+        which compiler to use if one hasn't been selected already.
+        """
+        # Populate list of compilers
+        if self.is_cross:
+            compilers = self.environment.coredata.cross_compilers
+        else:
+            compilers = self.environment.coredata.compilers
+
+        # If this library is linked against another library we need to consider
+        # the languages of those libraries as well.
+        if self.link_targets or self.link_whole_targets:
+            extra = set()
+            for t in itertools.chain(self.link_targets, self.link_whole_targets):
+                for name, compiler in t.compilers.items():
+                    if name in clike_langs:
+                        extra.add((name, compiler))
+            for name, compiler in sorted(extra, key=lambda p: sort_clike(p[0])):
+                self.compilers[name] = compiler
+
+        if not self.compilers:
+            # No source files or parent targets, target consists of only object
+            # files of unknown origin. Just add the first clike compiler
+            # that we have and hope that it can link these objects
+            for lang in clike_langs:
+                if lang in compilers:
+                    self.compilers[lang] = compilers[lang]
+                    break
+
     def process_compilers(self):
         '''
         Populate self.compilers, which is the list of compilers that this
@@ -487,14 +521,7 @@ class BuildTarget(Target):
             # Re-sort according to clike_langs
             self.compilers = OrderedDict(sorted(self.compilers.items(),
                                                 key=lambda t: sort_clike(t[0])))
-        else:
-            # No source files, target consists of only object files of unknown
-            # origin. Just add the first clike compiler that we have and hope
-            # that it can link these objects
-            for lang in clike_langs:
-                if lang in compilers:
-                    self.compilers[lang] = compilers[lang]
-                    break
+
         # If all our sources are Vala, our target also needs the C compiler but
         # it won't get added above.
         if 'vala' in self.compilers and 'c' not in self.compilers:

test cases/common/146 C and CPP link/meson.build

@@ -65,10 +65,44 @@ libfoo = shared_library(
 #
 # VS2010 lacks the /WHOLEARCHIVE option that later versions of MSVC support, so
 # don't run this tests on that backend.
-if meson.backend() != 'vs2010'
+if not (cxx.get_id() == 'msvc' and cxx.version().version_compare('<19'))
   libfoowhole = shared_library(
     'foowhole',
     ['foobar.c', 'foobar.h'],
     link_whole : [libc, libcpp],
   )
 endif
+
+# Test sublinking (linking C and C++, then linking that to C)
+libfoo_static = static_library(
+  'foo_static',
+  ['foobar.c', 'foobar.h'],
+  link_with : [libc, libcpp],
+)
+
+libsub = shared_library(
+  'sub',
+  ['sub.c', 'sub.h'],
+  link_with : libfoo_static,
+)
+
+if not (cxx.get_id() == 'msvc' and cxx.version().version_compare('<19'))
+  libsubwhole = shared_library(
+    'subwhole',
+    ['sub.c', 'sub.h'],
+    link_whole : libfoo_static,
+  )
+endif
+
+# Test that it really is recursive
+libsub_static = static_library(
+  'sub_static',
+  ['sub.c', 'sub.h'],
+  link_with : libfoo_static,
+)
+
+libsubsub = shared_library(
+  'subsub',
+  ['dummy.c'],
+  link_with : libsub_static,
+)

test cases/common/146 C and CPP link/sub.c

@@ -0,0 +1,19 @@
+/* Copyright © 2017 Dylan Baker
+ *
+ * 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.
+ */
+#include "sub.h"
+
+float a_half(void) {
+    return .5;
+}

test cases/common/146 C and CPP link/sub.h

@@ -0,0 +1,16 @@
+/* Copyright © 2017 Dylan Baker
+ *
+ * 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.
+ */
+
+float a_half(void);