Merge pull request #6532 from jon-turney/languages-native-kwarg

Add add_languages(native:)

12 files changed, 103 insertions, 18 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index 9bb791117..ea02cd40b 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -54,9 +54,9 @@ Like `add_global_arguments` but the arguments are passed to the linker.
   bool add_languages(*langs*)
 ```
 
-Add support for new programming languages. Equivalent to having them
-in the `project` declaration. This function is usually used to add
-languages that are only used on some platforms like this:
+Add programming languages used by the project. Equivalent to having them in the
+`project` declaration. This function is usually used to add languages that are
+only used under some conditions, like this:
 
 ```meson
 project('foobar', 'c')
@@ -68,12 +68,22 @@ if add_languages('cpp', required : false)
 endif
 ```
 
-Takes one keyword argument, `required`. It defaults to `true`, which
-means that if any of the languages specified is not found, Meson will
-halt. Returns true if all languages specified were found and false
-otherwise. Since *0.47.0* the value of a
-[`feature`](Build-options.md#features) option can also be passed to
-the `required` keyword argument.
+Takes the following keyword arguments:
+
+- `required` defaults to `true`, which means that if any of the languages
+specified is not found, Meson will halt. Since *0.47.0* the value of a
+[`feature`](Build-options.md#features) option can also be passed.
+
+- `native` if set to `true`, the language will be used to compile for the build
+  machine, if `false`, for the host machine. Since *0.54.0*.
+
+Returns `true` if all languages specified were found and `false` otherwise.
+
+If `native` is omitted, the languages may be used for either build or host
+machine, but are never required for the build machine.  (i.e. it is equivalent
+to `add_languages(*langs*, native: false, required: *required*) and
+add_languages(*langs*, native: true, required: false)`. This default behaviour
+may change to `native: false` in a future meson version.
 
 ### add_project_arguments()
 
diff --git a/docs/markdown/snippets/native_compiler_not_required.md b/docs/markdown/snippets/native_compiler_not_required.md
new file mode 100644
index 000000000..331b3c759
--- /dev/null
+++ b/docs/markdown/snippets/native_compiler_not_required.md
@@ -0,0 +1,20 @@
+## Native (build machine) compilers not always required
+
+`add_languages()` gained a `native:` keyword, indicating if a native or cross
+compiler is to be used.
+
+For the benefit of existing simple build definitions which don't contain any
+`native: true` targets, without breaking backwards compatibility for build
+definitions which assume that the native compiler is available after
+`add_languages()`, if the `native:` keyword is absent the languages may be used
+for either the build or host machine, but are never required for the build
+machine.
+
+This changes the behaviour of the following meson fragment (when cross-compiling
+but a native compiler is not available) from reporting an error at
+`add_language` to reporting an error at `executable`.
+
+```
+add_language('c')
+executable('main', 'main.c', native: true)
+```
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 6755dca79..61894fe8a 100644
--- a/mesonbuild/build.py
+++ b/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, unholder
 )
-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
 
@@ -651,14 +651,24 @@ 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])))
diff --git a/mesonbuild/compilers/__init__.py b/mesonbuild/compilers/__init__.py
index b378a63e7..a4e39432a 100644
--- a/mesonbuild/compilers/__init__.py
+++ b/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,
diff --git a/mesonbuild/compilers/compilers.py b/mesonbuild/compilers/compilers.py
index caa860032..366bb50fa 100644
--- a/mesonbuild/compilers/compilers.py
+++ b/mesonbuild/compilers/compilers.py
@@ -14,6 +14,7 @@
 
 import contextlib, os.path, re, tempfile
 import collections.abc
+import itertools
 import typing as T
 from functools import lru_cache
 
@@ -75,6 +76,7 @@ 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')
@@ -147,6 +149,13 @@ 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': [],
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index e8284bbc1..af6eda321 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2119,7 +2119,7 @@ _base_test_args = {'args', 'depends', 'env', 'should_fail', 'timeout', 'workdir'
 
 permitted_kwargs = {'add_global_arguments': {'language', 'native'},
                     'add_global_link_arguments': {'language', 'native'},
-                    'add_languages': {'required'},
+                    'add_languages': {'required', 'native'},
                     'add_project_link_arguments': {'language', 'native'},
                     'add_project_arguments': {'language', 'native'},
                     'add_test_setup': {'exe_wrapper', 'gdb', 'timeout_multiplier', 'env', 'is_default'},
@@ -2951,11 +2951,13 @@ external dependencies (including libraries) must go to "dependencies".''')
         self.build.projects[self.subproject] = proj_name
         mlog.log('Project name:', mlog.bold(proj_name))
         mlog.log('Project version:', mlog.bold(self.project_version))
-        self.add_languages(proj_langs, True)
+        self.add_languages(proj_langs, True, MachineChoice.BUILD)
+        self.add_languages(proj_langs, True, MachineChoice.HOST)
         self.set_backend()
         if not self.is_subproject():
             self.check_stdlibs()
 
+    @FeatureNewKwargs('add_languages', '0.54.0', ['native'])
     @permittedKwargs(permitted_kwargs['add_languages'])
     @stringArgs
     def func_add_languages(self, node, args, kwargs):
@@ -2964,7 +2966,15 @@ external dependencies (including libraries) must go to "dependencies".''')
             for lang in sorted(args, key=compilers.sort_clink):
                 mlog.log('Compiler for language', mlog.bold(lang), 'skipped: feature', mlog.bold(feature), 'disabled')
             return False
-        return self.add_languages(args, required)
+        if 'native' in kwargs:
+            return self.add_languages(args, required, self.machine_from_native_kwarg(kwargs))
+        else:
+            # absent 'native' means 'both' for backwards compatibility
+            mlog.warning('add_languages is missing native:, assuming languages are wanted for both host and build.',
+                         location=self.current_node)
+            success = self.add_languages(args, False, MachineChoice.BUILD)
+            success &= self.add_languages(args, required, MachineChoice.HOST)
+            return success
 
     def get_message_string_arg(self, arg):
         if isinstance(arg, list):
@@ -3060,9 +3070,8 @@ external dependencies (including libraries) must go to "dependencies".''')
         self.validate_arguments(args, 0, [])
         raise Exception()
 
-    def add_languages(self, args: T.Sequence[str], required: bool) -> bool:
-        success = self.add_languages_for(args, required, MachineChoice.BUILD)
-        success &= self.add_languages_for(args, required, MachineChoice.HOST)
+    def add_languages(self, args: T.Sequence[str], required: bool, for_machine: MachineChoice) -> bool:
+        success = self.add_languages_for(args, required, for_machine)
         if not self.coredata.is_cross_build():
             self.coredata.copy_build_options_from_regular_ones()
         return success
diff --git a/test cases/common/85 add language/meson.build b/test cases/common/85 add language/meson.build
index d9bc0fa2b..aa4972abd 100644
--- a/test cases/common/85 add language/meson.build
+++ b/test cases/common/85 add language/meson.build
@@ -6,3 +6,6 @@ assert(add_languages('cpp'), 'Add_languages returned false on success')
 assert(not add_languages('klingon', required : false), 'Add_languages returned true on failure.')
 
 test('C++', executable('cppprog', 'prog.cc'))
+
+add_languages('c', native: true)
+add_languages('c', native: false)
diff --git a/test cases/failing/100 no native compiler/main.c b/test cases/failing/100 no native compiler/main.c
new file mode 100644
index 000000000..9b6bdc2ec
--- /dev/null
+++ b/test cases/failing/100 no native compiler/main.c
@@ -0,0 +1,3 @@
+int main(void) {
+    return 0;
+}
diff --git a/test cases/failing/100 no native compiler/meson.build b/test cases/failing/100 no native compiler/meson.build
new file mode 100644
index 000000000..f0126ac15
--- /dev/null
+++ b/test cases/failing/100 no native compiler/meson.build
@@ -0,0 +1,12 @@
+project('no native compiler')
+
+if not meson.is_cross_build()
+   error('MESON_SKIP_TEST test only applicable when cross building.')
+endif
+
+if add_languages('c', required: false, native: true)
+  error('MESON_SKIP_TEST test only applicable when native compiler not available.')
+endif
+
+add_languages('c')
+executable('main', 'main.c', native: true)
diff --git a/test cases/failing/101 no lang/main.c b/test cases/failing/101 no lang/main.c
new file mode 100644
index 000000000..9b6bdc2ec
--- /dev/null
+++ b/test cases/failing/101 no lang/main.c
@@ -0,0 +1,3 @@
+int main(void) {
+    return 0;
+}
diff --git a/test cases/failing/101 no lang/meson.build b/test cases/failing/101 no lang/meson.build
new file mode 100644
index 000000000..85c5db8e5
--- /dev/null
+++ b/test cases/failing/101 no lang/meson.build
@@ -0,0 +1,2 @@
+project('target without lang')
+executable('main', 'main.c')
diff --git a/test cases/warning/2 languages missing native/meson.build b/test cases/warning/2 languages missing native/meson.build
new file mode 100644
index 000000000..f4aa9567a
--- /dev/null
+++ b/test cases/warning/2 languages missing native/meson.build
@@ -0,0 +1,2 @@
+project('languages missing native')
+add_languages('c')