Can combine D and C++ in a single target. Closes #3125.

5 files changed, 34 insertions, 15 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index ed7c118..6499105 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -318,21 +318,18 @@ class Backend:
             self.write_benchmark_file(datafile)
         return test_data, benchmark_data
 
-    def determine_linker(self, target):
+    def determine_linker_and_stdlib_args(self, target):
         '''
         If we're building a static library, there is only one static linker.
         Otherwise, we query the target for the dynamic linker.
         '''
         if isinstance(target, build.StaticLibrary):
             if target.is_cross:
-                return self.build.static_cross_linker
+                return self.build.static_cross_linker, []
             else:
-                return self.build.static_linker
-        l = target.get_clike_dynamic_linker()
-        if not l:
-            m = "Couldn't determine linker for target {!r}"
-            raise MesonException(m.format(target.name))
-        return l
+                return self.build.static_linker, []
+        l, stdlib_args = target.get_clike_dynamic_linker_and_stdlibs()
+        return l, stdlib_args
 
     def rpaths_for_bundled_shared_libraries(self, target):
         paths = []
diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index 6dd04da..1d8d011 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -470,8 +470,8 @@ int dummy;
         if is_unity:
             for src in self.generate_unity_files(target, unity_src):
                 obj_list.append(self.generate_single_compile(target, outfile, src, True, unity_deps + header_deps))
-        linker = self.determine_linker(target)
-        elem = self.generate_link(target, outfile, outname, obj_list, linker, pch_objects)
+        linker, stdlib_args = self.determine_linker_and_stdlib_args(target)
+        elem = self.generate_link(target, outfile, outname, obj_list, linker, pch_objects, stdlib_args=stdlib_args)
         self.generate_shlib_aliases(target, self.get_target_dir(target))
         elem.write(outfile)
 
@@ -2485,7 +2485,7 @@ rule FORTRAN_DEP_HACK%s
 
         return guessed_dependencies + absolute_libs
 
-    def generate_link(self, target, outfile, outname, obj_list, linker, extra_args=[]):
+    def generate_link(self, target, outfile, outname, obj_list, linker, extra_args=[], stdlib_args=[]):
         if isinstance(target, build.StaticLibrary):
             linker_base = 'STATIC'
         else:
@@ -2496,7 +2496,6 @@ rule FORTRAN_DEP_HACK%s
         if target.is_cross:
             crstr = '_CROSS'
         linker_rule = linker_base + crstr + '_LINKER'
-
         # Create an empty commands list, and start adding link arguments from
         # various sources in the order in which they must override each other
         # starting from hard-coded defaults followed by build options and so on.
@@ -2602,6 +2601,7 @@ rule FORTRAN_DEP_HACK%s
         custom_target_libraries = self.get_custom_target_provided_libraries(target)
         commands += extra_args
         commands += custom_target_libraries
+        commands += stdlib_args # Standard library arguments go last, because they never depend on anything.
         # Convert from GCC-style link argument naming to the naming used by the
         # current compiler.
         commands = commands.to_native()
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index a2d024a..5d1163b 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -989,6 +989,8 @@ You probably should put it in link_with instead.''')
         langs = []
         # Check if any of the external libraries were written in this language
         for dep in self.external_deps:
+            if dep.language is None:
+                continue
             if dep.language not in langs:
                 langs.append(dep.language)
         # Check if any of the internal libraries this target links to were
@@ -999,7 +1001,7 @@ You probably should put it in link_with instead.''')
                     langs.append(language)
         return langs
 
-    def get_clike_dynamic_linker(self):
+    def get_clike_dynamic_linker_and_stdlibs(self):
         '''
         We use the order of languages in `clike_langs` to determine which
         linker to use in case the target has sources compiled with multiple
@@ -1021,12 +1023,19 @@ You probably should put it in link_with instead.''')
         for l in clike_langs:
             if l in self.compilers or l in dep_langs:
                 try:
-                    return all_compilers[l]
+                    linker = all_compilers[l]
                 except KeyError:
                     raise MesonException(
                         'Could not get a dynamic linker for build target {!r}. '
                         'Requires a linker for language "{}", but that is not '
                         'a project language.'.format(self.name, l))
+                stdlib_args = []
+                added_languages = set()
+                for dl in itertools.chain(self.compilers, dep_langs):
+                    if dl != linker.language:
+                        stdlib_args += all_compilers[dl].language_stdlib_only_link_flags()
+                        added_languages.add(dl)
+                return linker, stdlib_args
 
         m = 'Could not get a dynamic linker for build target {!r}'
         raise AssertionError(m.format(self.name))
@@ -1049,7 +1058,8 @@ You probably should put it in link_with instead.''')
         2. If the target contains only objects, process_compilers guesses and
            picks the first compiler that smells right.
         '''
-        linker = self.get_clike_dynamic_linker()
+        linker, _ = self.get_clike_dynamic_linker_and_stdlibs()
+        # Mixing many languages with MSVC is not supported yet so ignore stdlibs.
         if linker and linker.get_id() == 'msvc':
             return True
         return False
diff --git a/mesonbuild/compilers/compilers.py b/mesonbuild/compilers/compilers.py
index a2c6668..02faed2 100644
--- a/mesonbuild/compilers/compilers.py
+++ b/mesonbuild/compilers/compilers.py
@@ -938,6 +938,12 @@ class Compiler:
     def openmp_flags(self):
         raise EnvironmentException('Language %s does not support OpenMP flags.' % self.get_display_language())
 
+    def language_stdlib_only_link_flags(self):
+        # The linker flags needed to link the standard library of the current
+        # language in. This is needed in cases where you e.g. combine D and C++
+        # and both of which need to link their runtime library in or otherwise
+        # building fails with undefined symbols.
+        return []
 
 GCC_STANDARD = 0
 GCC_OSX = 1
diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index 4c48052..051f922 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -93,6 +93,9 @@ class ClangCPPCompiler(ClangCompiler, CPPCompiler):
     def get_option_link_args(self, options):
         return []
 
+    def language_stdlib_only_link_flags(self):
+        return ['-lstdc++']
+
 
 class GnuCPPCompiler(GnuCompiler, CPPCompiler):
     def __init__(self, exelist, version, gcc_type, is_cross, exe_wrap, defines, **kwargs):
@@ -134,6 +137,9 @@ class GnuCPPCompiler(GnuCompiler, CPPCompiler):
     def get_pch_use_args(self, pch_dir, header):
         return ['-fpch-preprocess', '-include', os.path.basename(header)]
 
+    def language_stdlib_only_link_flags(self):
+        return ['-lstdc++']
+
 
 class ElbrusCPPCompiler(GnuCPPCompiler, ElbrusCompiler):
     def __init__(self, exelist, version, gcc_type, is_cross, exe_wrapper=None, defines=None, **kwargs):