Improve error reported when language has no compiler

This gives consistent reporting of this error for all platforms.

Also, reporting this error when constructing the BuildTarget, rather
than discovering the problem during backend generation means that the
error is reported against with a location.

mesonbuild/build.py

@@ -28,7 +28,7 @@ from .mesonlib import (
     extract_as_list, typeslistify, stringlistify, classify_unity_sources,
     get_filenames_templates_dict, substitute_values, has_path_sep,
 )
-from .compilers import Compiler, is_object, clink_langs, sort_clink, lang_suffixes
+from .compilers import Compiler, is_object, clink_langs, sort_clink, lang_suffixes, is_known_suffix
 from .linkers import StaticLinker
 from .interpreterbase import FeatureNew
 
@@ -652,14 +652,24 @@ class BuildTarget(Target):
                     sources.append(s)
         if sources:
             # 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.
+            #
+            # If it has a suffix that belongs to a known language, we must have
+            # a compiler for that language.
+            #
+            # Otherwise, it's ok if no compilers can compile it, 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:
+                    if is_known_suffix(s):
+                        raise MesonException('No {} machine compiler for "{}"'.
+                                             format(self.for_machine.get_lower_case_name(), s))
+
             # Re-sort according to clink_langs
             self.compilers = OrderedDict(sorted(self.compilers.items(),
                                                 key=lambda t: sort_clink(t[0])))

mesonbuild/compilers/__init__.py

@@ -30,6 +30,7 @@ __all__ = [
     'is_llvm_ir',
     'is_object',
     'is_source',
+    'is_known_suffix',
     'lang_suffixes',
     'sort_clink',
 
@@ -115,6 +116,7 @@ from .compilers import (
     is_llvm_ir,
     is_object,
     is_library,
+    is_known_suffix,
     lang_suffixes,
     sort_clink,
     CompilerArgs,

mesonbuild/compilers/compilers.py

@@ -14,6 +14,7 @@
 
 import contextlib, os.path, re, tempfile
 import collections.abc
+import itertools
 import typing as T
 
 from ..linkers import StaticLinker, GnuLikeDynamicLinkerMixin, SolarisDynamicLinker
@@ -72,6 +73,7 @@ clink_suffixes = ()
 for _l in clink_langs + ('vala',):
     clink_suffixes += lang_suffixes[_l]
 clink_suffixes += ('h', 'll', 's')
+all_suffixes = set(itertools.chain(*lang_suffixes.values(), clink_suffixes))
 
 # Languages that should use LDFLAGS arguments when linking.
 languages_using_ldflags = ('objcpp', 'cpp', 'objc', 'c', 'fortran', 'd', 'cuda')
@@ -144,6 +146,13 @@ def is_library(fname):
     suffix = fname.split('.')[-1]
     return suffix in lib_suffixes
 
+def is_known_suffix(fname):
+    if hasattr(fname, 'fname'):
+        fname = fname.fname
+    suffix = fname.split('.')[-1]
+
+    return suffix in all_suffixes
+
 cuda_buildtype_args = {'plain': [],
                        'debug': [],
                        'debugoptimized': [],