interpreter: Extract dependency() logic into its own helper class

The dependency lookup is a lot of complex code. This refactor it all
into a single file/class outside of interpreter main class. This new
design allows adding more fallbacks candidates in the future (e.g. using
cc.find_library()) but does not yet add any extra API.

1 files changed, 346 insertions, 0 deletions

diff --git a/mesonbuild/interpreter/dependencyfallbacks.py b/mesonbuild/interpreter/dependencyfallbacks.py
new file mode 100644
index 0000000..6edb129
--- /dev/null
+++ b/mesonbuild/interpreter/dependencyfallbacks.py
@@ -0,0 +1,346 @@
+from .interpreterobjects import DependencyHolder, SubprojectHolder, extract_required_kwarg
+
+from .. import mlog
+from .. import dependencies
+from .. import build
+from ..wrap import WrapMode
+from ..mesonlib import OptionKey, extract_as_list, stringlistify, version_compare_many
+from ..dependencies import DependencyException, NotFoundDependency
+from ..interpreterbase import (InterpreterObject, FeatureNew,
+                               InterpreterException, InvalidArguments,
+                               TYPE_nkwargs, TYPE_nvar)
+
+import typing as T
+if T.TYPE_CHECKING:
+    from .interpreter import Interpreter
+
+
+class DependencyFallbacksHolder(InterpreterObject):
+    def __init__(self, interpreter: 'Interpreter', names: T.List[str], allow_fallback: T.Optional[bool] = None) -> None:
+        super().__init__()
+        self.interpreter = interpreter
+        self.subproject = interpreter.subproject
+        self.coredata = interpreter.coredata
+        self.build = interpreter.build
+        self.environment = interpreter.environment
+        self.wrap_resolver = interpreter.environment.wrap_resolver
+        self.allow_fallback = allow_fallback
+        self.subproject_name = None
+        self.subproject_varname = None
+        self.subproject_kwargs = None
+        self.names: T.List[str] = []
+        for name in names:
+            if not name:
+                raise InterpreterException('dependency_fallbacks empty name \'\' is not allowed')
+            if '<' in name or '>' in name or '=' in name:
+                raise InvalidArguments('Characters <, > and = are forbidden in dependency names. To specify'
+                                       'version\n requirements use the \'version\' keyword argument instead.')
+            if name in self.names:
+                raise InterpreterException('dependency_fallbacks name {name!r} is duplicated')
+            self.names.append(name)
+
+    def set_fallback(self, fbinfo: T.Optional[T.Union[T.List[str], str]], default_options: T.Optional[T.List[str]] = None) -> None:
+        # Legacy: This converts dependency()'s fallback and default_options kwargs.
+        if fbinfo is None:
+            if default_options is not None:
+                mlog.warning('The "default_options" keyword argument does nothing without a fallback subproject.',
+                             location=self.interpreter.current_node)
+            return
+        fbinfo = stringlistify(fbinfo)
+        if len(fbinfo) == 1:
+            FeatureNew.single_use('Fallback without variable name', '0.53.0', self.subproject)
+            subp_name, varname = fbinfo[0], None
+        elif len(fbinfo) == 2:
+            subp_name, varname = fbinfo
+        else:
+            raise InterpreterException('Fallback info must have one or two items.')
+        kwargs = {'default_options': default_options or []}
+        self._subproject_impl(subp_name, varname, kwargs)
+
+    def _subproject_impl(self, subp_name: str, varname: str, kwargs: TYPE_nkwargs) -> None:
+        if not varname:
+            # If no variable name is specified, check if the wrap file has one.
+            # If the wrap file has a variable name, better use it because the
+            # subproject most probably is not using meson.override_dependency().
+            for name in self.names:
+                varname = self.wrap_resolver.get_varname(subp_name, name)
+                if varname:
+                    break
+        assert self.subproject_name is None
+        self.subproject_name = subp_name
+        self.subproject_varname = varname
+        self.subproject_kwargs = kwargs
+
+    def _do_dependency_cache(self, kwargs: TYPE_nkwargs, func_args: TYPE_nvar, func_kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        name = func_args[0]
+        cached_dep = self._get_cached_dep(name, kwargs)
+        if cached_dep:
+            self._verify_fallback_consistency(cached_dep)
+        return cached_dep
+
+    def _do_dependency(self, kwargs: TYPE_nkwargs, func_args: TYPE_nvar, func_kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        # Note that there is no df.dependency() method, this is called for names
+        # given as positional arguments to dependency_fallbacks(name1, ...).
+        # We use kwargs from the dependency() function, for things like version,
+        # module, etc.
+        name = func_args[0]
+        self._handle_featurenew_dependencies(name)
+        dep = dependencies.find_external_dependency(name, self.environment, kwargs)
+        if dep.found():
+            for_machine = self.interpreter.machine_from_native_kwarg(kwargs)
+            identifier = dependencies.get_dep_identifier(name, kwargs)
+            self.coredata.deps[for_machine].put(identifier, dep)
+            return DependencyHolder(dep, self.subproject)
+        return None
+
+    def _do_existing_subproject(self, kwargs: TYPE_nkwargs, func_args: TYPE_nvar, func_kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        subp_name = func_args[0]
+        varname = self.subproject_varname
+        if subp_name and self._get_subproject(subp_name):
+            return self._get_subproject_dep(subp_name, varname, kwargs)
+        return None
+
+    def _do_subproject(self, kwargs: TYPE_nkwargs, func_args: TYPE_nvar, func_kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        if self.nofallback:
+            mlog.log('Not looking for a fallback subproject for the dependency',
+                     mlog.bold(self.display_name), 'because:\nUse of fallback dependencies is disabled.')
+            return None
+        if self.forcefallback:
+            mlog.log('Looking for a fallback subproject for the dependency',
+                     mlog.bold(self.display_name), 'because:\nUse of fallback dependencies is forced.')
+        else:
+            mlog.log('Looking for a fallback subproject for the dependency',
+                     mlog.bold(self.display_name))
+
+        # Configure the subproject
+        subp_name = self.subproject_name
+        varname = self.subproject_varname
+        self.interpreter.do_subproject(subp_name, 'meson', func_kwargs)
+        return self._get_subproject_dep(subp_name, varname, kwargs)
+
+    def _get_subproject(self, subp_name: str) -> T.Optional[SubprojectHolder]:
+        sub = self.interpreter.subprojects.get(subp_name)
+        if sub and sub.found():
+            return sub
+        return None
+
+    def _get_subproject_dep(self, subp_name: str, varname: str, kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        # Verify the subproject is found
+        subproject = self._get_subproject(subp_name)
+        if not subproject:
+            mlog.log('Dependency', mlog.bold(self.display_name), 'from subproject',
+                     mlog.bold(subp_name), 'found:', mlog.red('NO'),
+                     mlog.blue('(subproject failed to configure)'))
+            return None
+
+        # The subproject has been configured. If for any reason the dependency
+        # cannot be found in this subproject we have to return not-found object
+        # instead of None, because we don't want to continue the lookup on the
+        # system.
+
+        # Check if the subproject overridden at least one of the names we got.
+        cached_dep = None
+        for name in self.names:
+            cached_dep = self._get_cached_dep(name, kwargs)
+            if cached_dep:
+                break
+
+        # If we have cached_dep we did all the checks and logging already in
+        # self._get_cached_dep().
+        if cached_dep:
+            self._verify_fallback_consistency(cached_dep)
+            return cached_dep
+
+        # Legacy: Use the variable name if provided instead of relying on the
+        # subproject to override one of our dependency names
+        if not varname:
+            mlog.warning(f'Subproject {subp_name!r} did not override {self.display_name!r} dependency and no variable name specified')
+            mlog.log('Dependency', mlog.bold(self.display_name), 'from subproject',
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'))
+            return self._notfound_dependency()
+
+        var_dep = self._get_subproject_variable(subproject, varname) or self._notfound_dependency()
+        if not var_dep.found():
+            mlog.log('Dependency', mlog.bold(self.display_name), 'from subproject',
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'))
+            return var_dep
+
+        wanted = stringlistify(kwargs.get('version', []))
+        found = var_dep.held_object.get_version()
+        if not self._check_version(wanted, found):
+            mlog.log('Dependency', mlog.bold(self.display_name), 'from subproject',
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'),
+                     'found', mlog.normal_cyan(found), 'but need:',
+                     mlog.bold(', '.join([f"'{e}'" for e in wanted])))
+            return self._notfound_dependency()
+
+        mlog.log('Dependency', mlog.bold(self.display_name), 'from subproject',
+                 mlog.bold(subproject.subdir), 'found:', mlog.green('YES'),
+                 mlog.normal_cyan(found) if found else None)
+        return var_dep
+
+    def _get_cached_dep(self, name: str, kwargs: TYPE_nkwargs) -> T.Optional[DependencyHolder]:
+        # Unlike other methods, this one returns not-found dependency instead
+        # of None in the case the dependency is cached as not-found, or if cached
+        # version does not match. In that case we don't want to continue with
+        # other candidates.
+        for_machine = self.interpreter.machine_from_native_kwarg(kwargs)
+        identifier = dependencies.get_dep_identifier(name, kwargs)
+        wanted_vers = stringlistify(kwargs.get('version', []))
+
+        override = self.build.dependency_overrides[for_machine].get(identifier)
+        if override:
+            info = [mlog.blue('(overridden)' if override.explicit else '(cached)')]
+            cached_dep = override.dep
+            # We don't implicitly override not-found dependencies, but user could
+            # have explicitly called meson.override_dependency() with a not-found
+            # dep.
+            if not cached_dep.found():
+                mlog.log('Dependency', mlog.bold(self.display_name),
+                         'found:', mlog.red('NO'), *info)
+                return DependencyHolder(cached_dep, self.subproject)
+        else:
+            info = [mlog.blue('(cached)')]
+            cached_dep = self.coredata.deps[for_machine].get(identifier)
+
+        if cached_dep:
+            found_vers = cached_dep.get_version()
+            if not self._check_version(wanted_vers, found_vers):
+                mlog.log('Dependency', mlog.bold(name),
+                         'found:', mlog.red('NO'),
+                         'found', mlog.normal_cyan(found_vers), 'but need:',
+                         mlog.bold(', '.join([f"'{e}'" for e in wanted_vers])),
+                         *info)
+                return self._notfound_dependency()
+            if found_vers:
+                info = [mlog.normal_cyan(found_vers), *info]
+            mlog.log('Dependency', mlog.bold(self.display_name),
+                     'found:', mlog.green('YES'), *info)
+            return DependencyHolder(cached_dep, self.subproject)
+        return None
+
+    def _get_subproject_variable(self, subproject: SubprojectHolder, varname: str) -> T.Optional[DependencyHolder]:
+        var_dep = subproject.held_object.variables.get(varname)
+        if not isinstance(var_dep, DependencyHolder):
+            mlog.warning(f'Variable {varname!r} in the subproject {subproject.subdir!r} is',
+                         'not found' if var_dep is None else 'not a dependency object')
+            return None
+        return var_dep
+
+    def _verify_fallback_consistency(self, cached_dep: DependencyHolder):
+        subp_name = self.subproject_name
+        varname = self.subproject_varname
+        subproject = self._get_subproject(subp_name)
+        if subproject and varname:
+            var_dep = self._get_subproject_variable(subproject, varname)
+            if var_dep and cached_dep.found() and var_dep.held_object != cached_dep.held_object:
+                mlog.warning(f'Inconsistency: Subproject has overridden the dependency with another variable than {varname!r}')
+
+    def _handle_featurenew_dependencies(self, name: str) -> None:
+        'Do a feature check on dependencies used by this subproject'
+        if name == 'mpi':
+            FeatureNew.single_use('MPI Dependency', '0.42.0', self.subproject)
+        elif name == 'pcap':
+            FeatureNew.single_use('Pcap Dependency', '0.42.0', self.subproject)
+        elif name == 'vulkan':
+            FeatureNew.single_use('Vulkan Dependency', '0.42.0', self.subproject)
+        elif name == 'libwmf':
+            FeatureNew.single_use('LibWMF Dependency', '0.44.0', self.subproject)
+        elif name == 'openmp':
+            FeatureNew.single_use('OpenMP Dependency', '0.46.0', self.subproject)
+
+    def _notfound_dependency(self) -> DependencyHolder:
+        return DependencyHolder(NotFoundDependency(self.environment), self.subproject)
+
+    @staticmethod
+    def _check_version(wanted: T.Optional[str], found: str) -> bool:
+        if not wanted:
+            return True
+        if found == 'undefined' or not version_compare_many(found, wanted)[0]:
+            return False
+        return True
+
+    def _get_candidates(self) -> T.List[T.Tuple[T.Callable[[TYPE_nkwargs, TYPE_nvar, TYPE_nkwargs], T.Optional[DependencyHolder]], TYPE_nvar, TYPE_nkwargs]]:
+        candidates = []
+        # 1. check if any of the names is cached already.
+        for name in self.names:
+            candidates.append((self._do_dependency_cache, [name], {}))
+        # 2. check if the subproject fallback has already been configured.
+        if self.subproject_name:
+            candidates.append((self._do_existing_subproject, [self.subproject_name], self.subproject_kwargs))
+        # 3. check external dependency if we are not forced to use subproject
+        if not self.forcefallback or not self.subproject_name:
+            for name in self.names:
+                candidates.append((self._do_dependency, [name], {}))
+        # 4. configure the subproject
+        if self.subproject_name:
+            candidates.append((self._do_subproject, [self.subproject_name], self.subproject_kwargs))
+        return candidates
+
+    def lookup(self, kwargs: TYPE_nkwargs, force_fallback: bool = False) -> DependencyHolder:
+        self.display_name = self.names[0] if self.names else '(anonymous)'
+        mods = extract_as_list(kwargs, 'modules')
+        if mods:
+            self.display_name += ' (modules: {})'.format(', '.join(str(i) for i in mods))
+
+        disabled, required, feature = extract_required_kwarg(kwargs, self.subproject)
+        if disabled:
+            mlog.log('Dependency', mlog.bold(self.display_name), 'skipped: feature', mlog.bold(feature), 'disabled')
+            return self._notfound_dependency()
+
+        # Check if usage of the subproject fallback is forced
+        wrap_mode = self.coredata.get_option(OptionKey('wrap_mode'))
+        force_fallback_for = self.coredata.get_option(OptionKey('force_fallback_for'))
+        self.nofallback = wrap_mode == WrapMode.nofallback
+        self.forcefallback = (force_fallback or
+                              wrap_mode == WrapMode.forcefallback or
+                              any(name in force_fallback_for for name in self.names) or
+                              self.subproject_name in force_fallback_for)
+
+        # Add an implicit subproject fallback if none has been set explicitly,
+        # unless implicit fallback is not allowed.
+        # Legacy: self.allow_fallback can be None when that kwarg is not defined
+        # in dependency('name'). In that case we don't want to use implicit
+        # fallback when required is false because user will typically fallback
+        # manually using cc.find_library() for example.
+        if not self.subproject_name and self.allow_fallback is not False:
+            for name in self.names:
+                subp_name, varname = self.wrap_resolver.find_dep_provider(name)
+                if subp_name:
+                    self.forcefallback |= subp_name in force_fallback_for
+                    if self.forcefallback or self.allow_fallback is True or required or self._get_subproject(subp_name):
+                        self._subproject_impl(subp_name, varname, {})
+                    break
+
+        candidates = self._get_candidates()
+
+        # writing just "dependency('')" is an error, because it can only fail
+        if not candidates and required:
+            raise InvalidArguments('Dependency is required but has no candidates.')
+
+        # Try all candidates, only the last one is really required.
+        last = len(candidates) - 1
+        for i, item in enumerate(candidates):
+            func, func_args, func_kwargs = item
+            func_kwargs['required'] = required and (i == last)
+            kwargs['required'] = required and (i == last)
+            dep = func(kwargs, func_args, func_kwargs)
+            if dep and dep.held_object.found():
+                # Override this dependency to have consistent results in subsequent
+                # dependency lookups.
+                for name in self.names:
+                    for_machine = self.interpreter.machine_from_native_kwarg(kwargs)
+                    identifier = dependencies.get_dep_identifier(name, kwargs)
+                    if identifier not in self.build.dependency_overrides[for_machine]:
+                        self.build.dependency_overrides[for_machine][identifier] = \
+                            build.DependencyOverride(dep.held_object, self.interpreter.current_node, explicit=False)
+                return dep
+            elif required and (dep or i == last):
+                # This was the last candidate or the dependency has been cached
+                # as not-found, or cached dependency version does not match,
+                # otherwise func() would have returned None instead.
+                raise DependencyException(f'Dependency {self.display_name!r} is required but not found.')
+            elif dep:
+                # Same as above, but the dependency is not required.
+                return dep
+        return self._notfound_dependency()