Try harder to use the C compiler for compiling asm

Use an ordered dict for the compiler dictionary and sort it according
to a priority order: fortran, c, c++, etc.

This also ensures that builds are reproducible because it would be
a toss-up whether a C or a C++ compiler would be used based on the
order in which compilers.items() would return items.

Closes https://github.com/mesonbuild/meson/issues/1370

mesonbuild/build.py

@@ -390,13 +390,6 @@ class BuildTarget(Target):
                 msg = 'Bad source of type {!r} in target {!r}.'.format(type(s).__name__, self.name)
                 raise InvalidArguments(msg)
 
-    @staticmethod
-    def can_compile_sources(compiler, sources):
-        for s in sources:
-            if compiler.can_compile(s):
-                return True
-        return False
-
     @staticmethod
     def can_compile_remove_sources(compiler, sources):
         removed = False
@@ -442,13 +435,15 @@ class BuildTarget(Target):
                 if not s.endswith(lang_suffixes['vala']):
                     sources.append(s)
         if sources:
-            # Add compilers based on the above sources
-            for lang, compiler in compilers.items():
-                # We try to be conservative because sometimes people add files
-                # in the list of sources that we can't determine the type based
-                # just on the suffix.
-                if self.can_compile_sources(compiler, sources):
-                    self.compilers[lang] = compiler
+            # For each source, try to add one compiler that can compile it.
+            # It's ok if no compilers can do so, because users are expected to
+            # be able to add arbitrary non-source files to the sources list.
+            for s in sources:
+                for lang, compiler in compilers.items():
+                    if compiler.can_compile(s):
+                        if lang not in self.compilers:
+                            self.compilers[lang] = compiler
+                        break
         else:
             # No source files, target consists of only object files of unknown
             # origin. Just add the first clike compiler that we have and hope

mesonbuild/coredata.py

@@ -14,6 +14,7 @@
 
 import pickle, os, uuid
 from pathlib import PurePath
+from collections import OrderedDict
 from .mesonlib import MesonException, commonpath
 from .mesonlib import default_libdir, default_libexecdir, default_prefix
 
@@ -128,8 +129,8 @@ class CoreData:
         else:
             self.cross_file = None
         self.wrap_mode = options.wrap_mode
-        self.compilers = {}
-        self.cross_compilers = {}
+        self.compilers = OrderedDict()
+        self.cross_compilers = OrderedDict()
         self.deps = {}
         self.modules = {}
         # Only to print a warning if it changes between Meson invocations.

mesonbuild/interpreter.py

@@ -1752,10 +1752,22 @@ class Interpreter(InterpreterBase):
         self.coredata.compiler_options = new_options
         return comp, cross_comp
 
+    @staticmethod
+    def sort_clike(lang):
+        '''
+        Sorting function to sort the list of languages according to
+        reversed(compilers.clike_langs) and append the unknown langs in the end.
+        The purpose is to prefer C over C++ for files that can be compiled by
+        both such as assembly, C, etc. Also applies to ObjC, ObjC++, etc.
+        '''
+        if lang not in compilers.clike_langs:
+            return 1
+        return -compilers.clike_langs.index(lang)
+
     def add_languages(self, args, required):
         success = True
         need_cross_compiler = self.environment.is_cross_build() and self.environment.cross_info.need_cross_compiler()
-        for lang in args:
+        for lang in sorted(args, key=self.sort_clike):
             lang = lang.lower()
             if lang in self.coredata.compilers:
                 comp = self.coredata.compilers[lang]