Add support for meson.options as a replacement for meson_options.txt

We will still try to load `meson_options.txt` if `meson.options` doesn't
exist. Because there are some advantages to using `meson.options` even
with older versions of meson (such as better text editor handling)
we will not warn about the existence of a `meson.options` file if a
`meson_options.txt` file or symlink also exists.

The name `meson.options` was picked instead of alternative proposals,
such as `meson_options.build` for a couple of reasons:

  1. meson.options is shorter
  2. While the syntax is the same, only the `option()` function may be
     called in meson.options, while, it may not be called in meson.build
  3. While the two files share a syntax and elementary types (strings,
     arrays, etc), they have different purposes: `meson.build` declares
     build targets, `meson.options` declares options. This is similar to
     the difference between C's `.c` and `.h` extensions.

As an implementation detail `Interpreter.option_file` has been removed,
as it is used exactly once, in the `project()` call to read the options,
and we can just calculate it there and not store it.

Fixes: #11176

4 files changed, 32 insertions, 13 deletions

diff --git a/mesonbuild/ast/introspection.py b/mesonbuild/ast/introspection.py
index 98f03fd..e811f11 100644
--- a/mesonbuild/ast/introspection.py
+++ b/mesonbuild/ast/introspection.py
@@ -76,7 +76,6 @@ class IntrospectionInterpreter(AstInterpreter):
             self.environment = env
         self.subproject_dir = subproject_dir
         self.coredata = self.environment.get_coredata()
-        self.option_file = os.path.join(self.source_root, self.subdir, 'meson_options.txt')
         self.backend = backend
         self.default_options = {OptionKey('backend'): self.backend}
         self.project_data = {}    # type: T.Dict[str, T.Any]
@@ -113,9 +112,12 @@ class IntrospectionInterpreter(AstInterpreter):
             proj_vers = 'undefined'
         self.project_data = {'descriptive_name': proj_name, 'version': proj_vers}
 
-        if os.path.exists(self.option_file):
+        optfile = os.path.join(self.source_root, self.subdir, 'meson.options')
+        if not os.path.exists(optfile):
+            optfile = os.path.join(self.source_root, self.subdir, 'meson_options.txt')
+        if os.path.exists(optfile):
             oi = optinterpreter.OptionInterpreter(self.subproject)
-            oi.process(self.option_file)
+            oi.process(optfile)
             self.coredata.update_project_options(oi.options)
 
         def_opts = self.flatten_args(kwargs.get('default_options', []))
diff --git a/mesonbuild/backend/xcodebackend.py b/mesonbuild/backend/xcodebackend.py
index e4195e2..b5cf83a 100644
--- a/mesonbuild/backend/xcodebackend.py
+++ b/mesonbuild/backend/xcodebackend.py
@@ -1025,6 +1025,7 @@ class XCodeBackend(backends.Backend):
             group_id = self.write_group_target_entry(objects_dict, target)
             children_array.add_item(group_id)
         potentials = [os.path.join(current_subdir, 'meson.build'),
+                      os.path.join(current_subdir, 'meson.options'),
                       os.path.join(current_subdir, 'meson_options.txt')]
         for bf in potentials:
             i = self.fileref_ids.get(bf, None)
diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index a033c4f..72bc8e2 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -23,8 +23,9 @@ from .. import compilers
 from .. import envconfig
 from ..wrap import wrap, WrapMode
 from .. import mesonlib
-from ..mesonlib import (MesonBugException, HoldableObject, FileMode, MachineChoice, OptionKey,
-                        listify, extract_as_list, has_path_sep, PerMachine)
+from ..mesonlib import (MesonBugException, MesonException, HoldableObject,
+                        FileMode, MachineChoice, OptionKey, listify,
+                        extract_as_list, has_path_sep, PerMachine)
 from ..programs import ExternalProgram, NonExistingExternalProgram
 from ..dependencies import Dependency
 from ..depfile import DepFile
@@ -290,7 +291,6 @@ class Interpreter(InterpreterBase, HoldableObject):
         # be different for dependencies provided by wrap files.
         self.subproject_directory_name = subdir.split(os.path.sep)[-1]
         self.subproject_dir = subproject_dir
-        self.option_file = os.path.join(self.source_root, self.subdir, 'meson_options.txt')
         self.relaxations = relaxations or set()
         if not mock and ast is None:
             self.load_root_meson_file()
@@ -1174,11 +1174,27 @@ class Interpreter(InterpreterBase, HoldableObject):
         if kwargs['meson_version']:
             self.handle_meson_version(kwargs['meson_version'], node)
 
-        if os.path.exists(self.option_file):
+        # Load "meson.options" before "meson_options.txt", and produce a warning if
+        # it is being used with an old version. I have added check that if both
+        # exist the warning isn't raised
+        option_file = os.path.join(self.source_root, self.subdir, 'meson.options')
+        old_option_file = os.path.join(self.source_root, self.subdir, 'meson_options.txt')
+
+        if os.path.exists(option_file):
+            if os.path.exists(old_option_file):
+                if os.path.samefile(option_file, old_option_file):
+                    mlog.debug("Not warning about meson.options with version minimum < 1.1 because meson_options.txt also exists")
+                else:
+                    raise MesonException("meson.options and meson_options.txt both exist, but are not the same file.")
+            else:
+                FeatureNew.single_use('meson.options file', '1.1', self.subproject, 'Use meson_options.txt instead')
+        else:
+            option_file = old_option_file
+        if os.path.exists(option_file):
             oi = optinterpreter.OptionInterpreter(self.subproject)
-            oi.process(self.option_file)
+            oi.process(option_file)
             self.coredata.update_project_options(oi.options)
-            self.add_build_def_file(self.option_file)
+            self.add_build_def_file(option_file)
 
         # Do not set default_options on reconfigure otherwise it would override
         # values previously set from command line. That means that changing
diff --git a/mesonbuild/mintro.py b/mesonbuild/mintro.py
index 68820d6..1842313 100644
--- a/mesonbuild/mintro.py
+++ b/mesonbuild/mintro.py
@@ -329,12 +329,12 @@ def list_buildoptions(coredata: cdata.CoreData, subprojects: T.Optional[T.List[s
     return optlist
 
 def find_buildsystem_files_list(src_dir: str) -> T.List[str]:
+    build_files = frozenset({'meson.build', 'meson.options', 'meson_options.txt'})
     # I feel dirty about this. But only slightly.
-    filelist = []  # type: T.List[str]
+    filelist: T.List[str] = []
     for root, _, files in os.walk(src_dir):
-        for f in files:
-            if f in {'meson.build', 'meson_options.txt'}:
-                filelist.append(os.path.relpath(os.path.join(root, f), src_dir))
+        filelist.extend(os.path.relpath(os.path.join(root, f), src_dir)
+                        for f in build_files.intersection(files))
     return filelist
 
 def list_buildsystem_files(builddata: build.Build, interpreter: Interpreter) -> T.List[str]: