Merge pull request #6902 from xclaesse/auto-fallback

Implicit dependency fallback when a subproject wrap or dir exists

19 files changed, 366 insertions, 63 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index dad8c12..9bca74b 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -456,7 +456,11 @@ arguments:
   *(since 0.54.0)* `'subproj_dep'` argument can be omitted in the case the
   subproject used `meson.override_dependency('dependency_name', subproj_dep)`.
   In that case, the `fallback` keyword argument can be a single string instead
-  of a list of 2 strings.
+  of a list of 2 strings. *Since 0.55.0* the `fallback` keyword argument can be
+  omitted when there is a wrap file or a directory with the same `dependency_name`,
+  and subproject registered the dependency using
+  `meson.override_dependency('dependency_name', subproj_dep)`, or when the wrap
+  file has `dependency_name` in its `[provide]` section.
 - `language` *(since 0.42.0)*: defines what language-specific
   dependency to find if it's available for multiple languages.
 - `method`: defines the way the dependency is detected, the default is
diff --git a/docs/markdown/Wrap-dependency-system-manual.md b/docs/markdown/Wrap-dependency-system-manual.md
index e59a6be..0ff304d 100644
--- a/docs/markdown/Wrap-dependency-system-manual.md
+++ b/docs/markdown/Wrap-dependency-system-manual.md
@@ -71,6 +71,7 @@ revision = head
 - `directory` - name of the subproject root directory, defaults to the name of the wrap.
 
 Since *0.55.0* those can be used in all wrap types, they were previously reserved to `wrap-file`:
+
 - `patch_url` - download url to retrieve an optional overlay archive
 - `patch_fallback_url` - fallback URL to be used when download from `patch_url` fails *Since: 0.55.0*
 - `patch_filename` - filename of the downloaded overlay archive
@@ -105,7 +106,7 @@ of downloading the file, even if `--wrap-mode` option is set to
   valid value (such as a git tag) for the VCS's `checkout` command, or
   (for git) `head` to track upstream's default branch. Required.
 
-## Specific to wrap-git
+### Specific to wrap-git
 - `depth` - shallowly clone the repository to X number of commits. Note
   that git always allow shallowly cloning branches, but in order to
   clone commit ids shallowly, the server must support
@@ -138,6 +139,62 @@ put them somewhere where you can download them.
 Meson build patches are only supported for wrap-file mode. When using
 wrap-git, the repository must contain all Meson build definitions.
 
+## `provide` section
+
+*Since *0.55.0*
+
+Wrap files can define the dependencies it provides in the `[provide]` section.
+When a wrap file provides the dependency `foo` any call do `dependency('foo')`
+will automatically fallback to that subproject even if no `fallback` keyword
+argument is given. It is recommended for subprojects to call
+`meson.override_dependency('foo', foo_dep)`, dependency name can then be added into
+the special `dependency_names` entry which takes comma separated list of dependency
+names. For backward compatibility with subprojects that does not call
+`meson.override_dependency()`, the variable name can be provided in the wrap file
+with entries in the format `dependency_name = variable_name`,
+where `dependency_name` usually match the corresponding pkg-config name and
+`variable_name` is the name of a variable defined in the subproject that should
+be returned for that dependency.
+
+For example when using a recent enough version of glib that uses
+`meson.override_dependency()` to override `glib-2.0`, `gobject-2.0` and `gio-2.0`,
+a wrap file would look like:
+```ini
+[wrap-git]
+url=https://gitlab.gnome.org/GNOME/glib.git
+revision=glib-2-62
+
+[provide]
+dependency_names = glib-2.0, gobject-2.0, gio-2.0
+```
+
+With older version of glib dependency variable names need to be specified:
+```ini
+[wrap-git]
+url=https://gitlab.gnome.org/GNOME/glib.git
+revision=glib-2-62
+
+[provide]
+glib-2.0=glib_dep
+gobject-2.0=gobject_dep
+gio-2.0=gio_dep
+```
+
+With such wrap file, `dependency('glib-2.0')` will automatically fallback to use
+`glib.wrap` and return `glib_dep` variable from the subproject.
+
+Programs can also be provided by wrap files, with the `program_names` key:
+```ini
+[wrap-git]
+...
+
+[provide]
+program_names = myprog, otherprog
+```
+
+With such wrap file, `find_program('myprog')` will automatically fallback to use
+the subproject, assuming it uses `meson.override_find_program('myprog')`.
+
 ## Using wrapped projects
 
 Wraps provide a convenient way of obtaining a project into your subproject directory.
diff --git a/docs/markdown/snippets/implicit_fallback.md b/docs/markdown/snippets/implicit_fallback.md
new file mode 100644
index 0000000..3d5a833
--- /dev/null
+++ b/docs/markdown/snippets/implicit_fallback.md
@@ -0,0 +1,21 @@
+## Implicit dependency fallback
+
+`dependency('foo')` now automatically fallback if the dependency is not found on
+the system but a subproject wrap file or directory exists with the same name.
+
+That means that simply adding `subprojects/foo.wrap` is enough to add fallback
+to any `dependency('foo')` call. It is however requires that the subproject call
+`meson.override_dependency('foo', foo_dep)` to specify which dependency object
+should be used for `foo`.
+
+## Wrap file `provide` section
+
+Wrap files can define the dependencies it provides in the `[provide]` section.
+When a wrap file provides the dependency `foo` any call do `dependency('foo')`
+will automatically fallback to that subproject even if no `fallback` keyword
+argument is given. See [Wrap documentation](Wrap-dependency-system-manual.md#provide_section).
+
+## `find_program()` fallback
+
+When a program cannot be found on the system but a wrap file has its name in the
+`[provide]` section, that subproject will be used as fallback.
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 487bdd6..12d6cde 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2779,10 +2779,9 @@ external dependencies (including libraries) must go to "dependencies".''')
                                            self.subproject_dir, dirname))
             return subproject
 
-        subproject_dir_abs = os.path.join(self.environment.get_source_dir(), self.subproject_dir)
-        r = wrap.Resolver(subproject_dir_abs, self.coredata.get_builtin_option('wrap_mode'), current_subproject=self.subproject)
+        r = self.environment.wrap_resolver
         try:
-            resolved = r.resolve(dirname, method)
+            resolved = r.resolve(dirname, method, self.subproject)
         except wrap.WrapException as e:
             subprojdir = os.path.join(self.subproject_dir, r.directory)
             if isinstance(e, wrap.WrapNotFoundException):
@@ -2798,7 +2797,7 @@ external dependencies (including libraries) must go to "dependencies".''')
             raise e
 
         subdir = os.path.join(self.subproject_dir, resolved)
-        subdir_abs = os.path.join(subproject_dir_abs, resolved)
+        subdir_abs = os.path.join(self.environment.get_source_dir(), subdir)
         os.makedirs(os.path.join(self.build.environment.get_build_dir(), subdir), exist_ok=True)
         self.global_args_frozen = True
 
@@ -3062,6 +3061,10 @@ external dependencies (including libraries) must go to "dependencies".''')
             self.subproject_dir = spdirname
 
         self.build.subproject_dir = self.subproject_dir
+        if not self.is_subproject():
+            wrap_mode = self.coredata.get_builtin_option('wrap_mode')
+            subproject_dir_abs = os.path.join(self.environment.get_source_dir(), self.subproject_dir)
+            self.environment.wrap_resolver = wrap.Resolver(subproject_dir_abs, wrap_mode)
 
         self.build.projects[self.subproject] = proj_name
         mlog.log('Project name:', mlog.bold(proj_name))
@@ -3248,7 +3251,7 @@ external dependencies (including libraries) must go to "dependencies".''')
 
         return success
 
-    def program_from_file_for(self, for_machine, prognames, silent):
+    def program_from_file_for(self, for_machine, prognames):
         for p in unholder(prognames):
             if isinstance(p, mesonlib.File):
                 continue # Always points to a local (i.e. self generated) file.
@@ -3287,15 +3290,13 @@ external dependencies (including libraries) must go to "dependencies".''')
             if progobj.found():
                 return progobj
 
-    def program_from_overrides(self, command_names, silent=False):
+    def program_from_overrides(self, command_names, extra_info):
         for name in command_names:
             if not isinstance(name, str):
                 continue
             if name in self.build.find_overrides:
                 exe = self.build.find_overrides[name]
-                if not silent:
-                    mlog.log('Program', mlog.bold(name), 'found:', mlog.green('YES'),
-                             '(overridden: %s)' % exe.description())
+                extra_info.append(mlog.blue('(overriden)'))
                 return ExternalProgramHolder(exe, self.subproject, self.backend)
         return None
 
@@ -3313,40 +3314,75 @@ external dependencies (including libraries) must go to "dependencies".''')
                                        % name)
         self.build.find_overrides[name] = exe
 
+    def notfound_program(self, args):
+        return ExternalProgramHolder(dependencies.NonExistingExternalProgram(' '.join(args)), self.subproject)
+
     # TODO update modules to always pass `for_machine`. It is bad-form to assume
     # the host machine.
     def find_program_impl(self, args, for_machine: MachineChoice = MachineChoice.HOST,
                           required=True, silent=True, wanted='', search_dirs=None):
-        if not isinstance(args, list):
-            args = [args]
+        args = mesonlib.listify(args)
 
-        progobj = self.program_from_overrides(args, silent=silent)
+        extra_info = []
+        progobj = self.program_lookup(args, for_machine, required, search_dirs, extra_info)
         if progobj is None:
-            progobj = self.program_from_file_for(for_machine, args, silent=silent)
-        if progobj is None:
-            progobj = self.program_from_system(args, search_dirs, silent=silent)
-        if progobj is None and args[0].endswith('python3'):
-            prog = dependencies.ExternalProgram('python3', mesonlib.python_command, silent=True)
-            progobj = ExternalProgramHolder(prog, self.subproject)
-        if required and (progobj is None or not progobj.found()):
-            raise InvalidArguments('Program(s) {!r} not found or not executable'.format(args))
-        if progobj is None:
-            return ExternalProgramHolder(dependencies.NonExistingExternalProgram(' '.join(args)), self.subproject)
-        # Only store successful lookups
-        self.store_name_lookups(args)
+            progobj = self.notfound_program(args)
+
+        if not progobj.found():
+            mlog.log('Program', mlog.bold(progobj.get_name()), 'found:', mlog.red('NO'))
+            if required:
+                m = 'Program {!r} not found'
+                raise InterpreterException(m.format(progobj.get_name()))
+            return progobj
+
         if wanted:
             version = progobj.get_version(self)
             is_found, not_found, found = mesonlib.version_compare_many(version, wanted)
             if not is_found:
                 mlog.log('Program', mlog.bold(progobj.get_name()), 'found:', mlog.red('NO'),
-                         'found {!r} but need:'.format(version),
-                         ', '.join(["'{}'".format(e) for e in not_found]))
+                         'found', mlog.normal_cyan(version), 'but need:',
+                         mlog.bold(', '.join(["'{}'".format(e) for e in not_found])))
                 if required:
                     m = 'Invalid version of program, need {!r} {!r} found {!r}.'
-                    raise InvalidArguments(m.format(progobj.get_name(), not_found, version))
-                return ExternalProgramHolder(dependencies.NonExistingExternalProgram(' '.join(args)), self.subproject)
+                    raise InterpreterException(m.format(progobj.get_name(), not_found, version))
+                return self.notfound_program(args)
+            extra_info.insert(0, mlog.normal_cyan(version))
+
+        # Only store successful lookups
+        self.store_name_lookups(args)
+        mlog.log('Program', mlog.bold(progobj.get_name()), 'found:', mlog.green('YES'), *extra_info)
+        return progobj
+
+    def program_lookup(self, args, for_machine, required, search_dirs, extra_info):
+        progobj = self.program_from_overrides(args, extra_info)
+        if progobj:
+            return progobj
+
+        fallback = None
+        wrap_mode = self.coredata.get_builtin_option('wrap_mode')
+        if wrap_mode != WrapMode.nofallback:
+            fallback = self.environment.wrap_resolver.find_program_provider(args)
+        if fallback and wrap_mode == WrapMode.forcefallback:
+            return self.find_program_fallback(fallback, args, required, extra_info)
+
+        progobj = self.program_from_file_for(for_machine, args)
+        if progobj is None:
+            progobj = self.program_from_system(args, search_dirs, silent=True)
+        if progobj is None and args[0].endswith('python3'):
+            prog = dependencies.ExternalProgram('python3', mesonlib.python_command, silent=True)
+            progobj = ExternalProgramHolder(prog, self.subproject) if prog.found() else None
+        if progobj is None and fallback and required:
+            progobj = self.find_program_fallback(fallback, args, required, extra_info)
+
         return progobj
 
+    def find_program_fallback(self, fallback, args, required, extra_info):
+        mlog.log('Fallback to subproject', mlog.bold(fallback), 'which provides program',
+                 mlog.bold(' '.join(args)))
+        sp_kwargs = { 'required': required }
+        self.do_subproject(fallback, 'meson', sp_kwargs)
+        return self.program_from_overrides(args, extra_info)
+
     @FeatureNewKwargs('find_program', '0.53.0', ['dirs'])
     @FeatureNewKwargs('find_program', '0.52.0', ['version'])
     @FeatureNewKwargs('find_program', '0.49.0', ['disabler'])
@@ -3359,7 +3395,7 @@ external dependencies (including libraries) must go to "dependencies".''')
         disabled, required, feature = extract_required_kwarg(kwargs, self.subproject)
         if disabled:
             mlog.log('Program', mlog.bold(' '.join(args)), 'skipped: feature', mlog.bold(feature), 'disabled')
-            return ExternalProgramHolder(dependencies.NonExistingExternalProgram(' '.join(args)), self.subproject)
+            return self.notfound_program(args)
 
         search_dirs = extract_search_dirs(kwargs)
         wanted = mesonlib.stringlistify(kwargs.get('version', []))
@@ -3453,8 +3489,12 @@ external dependencies (including libraries) must go to "dependencies".''')
                         raise DependencyException(m.format(display_name))
                     return DependencyHolder(cached_dep, self.subproject)
                 else:
-                    m = 'Subproject {} did not override dependency {}'
-                    raise DependencyException(m.format(subproj_path, display_name))
+                    if required:
+                        m = 'Subproject {} did not override dependency {}'
+                        raise DependencyException(m.format(subproj_path, display_name))
+                    mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
+                             mlog.bold(subproj_path), 'found:', mlog.red('NO'))
+                    return self.notfound_dependency()
             if subproject.found():
                 self.verify_fallback_consistency(dirname, varname, cached_dep)
                 dep = self.subprojects[dirname].get_variable_method([varname], {})
@@ -3549,6 +3589,18 @@ external dependencies (including libraries) must go to "dependencies".''')
             return self.notfound_dependency()
 
         has_fallback = 'fallback' in kwargs
+        if not has_fallback and name:
+            # Add an implicit fallback if we have a wrap file or a directory with the same name,
+            # but only if this dependency is required. It is common to first check for a pkg-config,
+            # then fallback to use find_library() and only afterward check again the dependency
+            # with a fallback. If the fallback has already been configured then we have to use it
+            # even if the dependency is not required.
+            provider = self.environment.wrap_resolver.find_dep_provider(name)
+            dirname = mesonlib.listify(provider)[0]
+            if provider and (required or dirname in self.subprojects):
+                kwargs['fallback'] = provider
+                has_fallback = True
+
         if 'default_options' in kwargs and not has_fallback:
             mlog.warning('The "default_options" keyworg argument does nothing without a "fallback" keyword argument.',
                          location=self.current_node)
diff --git a/mesonbuild/mdist.py b/mesonbuild/mdist.py
index 5ab0ad4..9d94ace 100644
--- a/mesonbuild/mdist.py
+++ b/mesonbuild/mdist.py
@@ -259,7 +259,7 @@ def run(options):
     if options.include_subprojects:
         subproject_dir = os.path.join(src_root, b.subproject_dir)
         for sub in b.subprojects:
-            _, directory = wrap.get_directory(subproject_dir, sub)
+            directory = wrap.get_directory(subproject_dir, sub)
             subprojects.append(os.path.join(b.subproject_dir, directory))
         extra_meson_args.append('-Dwrap_mode=nodownload')
 
diff --git a/mesonbuild/wrap/wrap.py b/mesonbuild/wrap/wrap.py
index 689fb4f..e0c7a04 100644
--- a/mesonbuild/wrap/wrap.py
+++ b/mesonbuild/wrap/wrap.py
@@ -103,14 +103,31 @@ class WrapNotFoundException(WrapException):
 
 class PackageDefinition:
     def __init__(self, fname: str):
-        self.filename = fname
+        self.type = None
+        self.values = {} # type: T.Dict[str, str]
+        self.provided_deps = {} # type: T.Dict[str, T.Optional[str]]
+        self.provided_programs = [] # type: T.List[str]
         self.basename = os.path.basename(fname)
-        self.name = self.basename[:-5]
+        self.name = self.basename
+        if self.name.endswith('.wrap'):
+            self.name = self.name[:-5]
+        self.provided_deps[self.name] = None
+        if fname.endswith('.wrap'):
+            self.parse_wrap(fname)
+        self.directory = self.values.get('directory', self.name)
+        if os.path.dirname(self.directory):
+            raise WrapException('Directory key must be a name and not a path')
+
+    def parse_wrap(self, fname: str):
         try:
             self.config = configparser.ConfigParser(interpolation=None)
             self.config.read(fname)
         except configparser.Error:
             raise WrapException('Failed to parse {}'.format(self.basename))
+        self.parse_wrap_section()
+        self.parse_provide_section()
+
+    def parse_wrap_section(self):
         if len(self.config.sections()) < 1:
             raise WrapException('Missing sections in {}'.format(self.basename))
         self.wrap_section = self.config.sections()[0]
@@ -120,6 +137,27 @@ class PackageDefinition:
         self.type = self.wrap_section[5:]
         self.values = dict(self.config[self.wrap_section])
 
+    def parse_provide_section(self):
+        if self.config.has_section('provide'):
+            for k, v in self.config['provide'].items():
+                if k == 'dependency_names':
+                    # A comma separated list of dependency names that does not
+                    # need a variable name
+                    names = {n.strip(): None for n in v.split(',')}
+                    self.provided_deps.update(names)
+                    continue
+                if k == 'program_names':
+                    # A comma separated list of program names
+                    names = [n.strip() for n in v.split(',')]
+                    self.provided_programs += names
+                    continue
+                if not v:
+                    m = ('Empty dependency variable name for {!r} in {}. '
+                         'If the subproject uses meson.override_dependency() '
+                         'it can be added in the "dependency_names" special key.')
+                    raise WrapException(m.format(k, self.basename))
+                self.provided_deps[k] = v
+
     def get(self, key: str) -> str:
         try:
             return self.values[key]
@@ -127,35 +165,87 @@ class PackageDefinition:
             m = 'Missing key {!r} in {}'
             raise WrapException(m.format(key, self.basename))
 
-def load_wrap(subdir_root: str, packagename: str) -> PackageDefinition:
+def get_directory(subdir_root: str, packagename: str) -> str:
     fname = os.path.join(subdir_root, packagename + '.wrap')
     if os.path.isfile(fname):
-        return PackageDefinition(fname)
-    return None
-
-def get_directory(subdir_root: str, packagename: str):
-    directory = packagename
-    # We always have to load the wrap file, if it exists, because it could
-    # override the default directory name.
-    wrap = load_wrap(subdir_root, packagename)
-    if wrap and 'directory' in wrap.values:
-        directory = wrap.get('directory')
-        if os.path.dirname(directory):
-            raise WrapException('Directory key must be a name and not a path')
-    return wrap, directory
+        wrap = PackageDefinition(fname)
+        return wrap.directory
+    return packagename
 
 class Resolver:
-    def __init__(self, subdir_root: str, wrap_mode=WrapMode.default, current_subproject: str = ''):
+    def __init__(self, subdir_root: str, wrap_mode=WrapMode.default):
         self.wrap_mode = wrap_mode
         self.subdir_root = subdir_root
-        self.current_subproject = current_subproject
         self.cachedir = os.path.join(self.subdir_root, 'packagecache')
         self.filesdir = os.path.join(self.subdir_root, 'packagefiles')
+        self.wraps = {} # type: T.Dict[str, PackageDefinition]
+        self.provided_deps = {} # type: T.Dict[str, PackageDefinition]
+        self.provided_programs = {} # type: T.Dict[str, PackageDefinition]
+        self.load_wraps()
 
-    def resolve(self, packagename: str, method: str) -> str:
+    def load_wraps(self):
+        if not os.path.isdir(self.subdir_root):
+            return
+        root, dirs, files = next(os.walk(self.subdir_root))
+        for i in files:
+            if not i.endswith('.wrap'):
+                continue
+            fname = os.path.join(self.subdir_root, i)
+            wrap = PackageDefinition(fname)
+            self.wraps[wrap.name] = wrap
+            if wrap.directory in dirs:
+                dirs.remove(wrap.directory)
+        # Add dummy package definition for directories not associated with a wrap file.
+        for i in dirs:
+            if i in ['packagecache', 'packagefiles']:
+                continue
+            fname = os.path.join(self.subdir_root, i)
+            wrap = PackageDefinition(fname)
+            self.wraps[wrap.name] = wrap
+
+        for wrap in self.wraps.values():
+            for k in wrap.provided_deps.keys():
+                if k in self.provided_deps:
+                    prev_wrap = self.provided_deps[k]
+                    m = 'Multiple wrap files provide {!r} dependency: {} and {}'
+                    raise WrapException(m.format(k, wrap.basename, prev_wrap.basename))
+                self.provided_deps[k] = wrap
+            for k in wrap.provided_programs:
+                if k in self.provided_programs:
+                    prev_wrap = self.provided_programs[k]
+                    m = 'Multiple wrap files provide {!r} program: {} and {}'
+                    raise WrapException(m.format(k, wrap.basename, prev_wrap.basename))
+                self.provided_programs[k] = wrap
+
+    def find_dep_provider(self, packagename: str):
+        # Return value is in the same format as fallback kwarg:
+        # ['subproject_name', 'variable_name'], or 'subproject_name'.
+        wrap = self.provided_deps.get(packagename)
+        if wrap:
+            dep_var = wrap.provided_deps.get(packagename)
+            if dep_var:
+                return [wrap.name, dep_var]
+            return wrap.name
+        return None
+
+    def find_program_provider(self, names: T.List[str]):
+        for name in names:
+            wrap = self.provided_programs.get(name)
+            if wrap:
+                return wrap.name
+        return None
+
+    def resolve(self, packagename: str, method: str, current_subproject: str = '') -> str:
+        self.current_subproject = current_subproject
         self.packagename = packagename
-        self.wrap, self.directory = get_directory(self.subdir_root, self.packagename)
+        self.directory = packagename
+        self.wrap = self.wraps.get(packagename)
+        if not self.wrap:
+            m = 'Subproject directory not found and {}.wrap file not found'
+            raise WrapNotFoundException(m.format(self.packagename))
+        self.directory = self.wrap.directory
         self.dirname = os.path.join(self.subdir_root, self.directory)
+
         meson_file = os.path.join(self.dirname, 'meson.build')
         cmake_file = os.path.join(self.dirname, 'CMakeLists.txt')
 
@@ -175,11 +265,6 @@ class Resolver:
             if not os.path.isdir(self.dirname):
                 raise WrapException('Path already exists but is not a directory')
         else:
-            # A wrap file is required to download
-            if not self.wrap:
-                m = 'Subproject directory not found and {}.wrap file not found'
-                raise WrapNotFoundException(m.format(self.packagename))
-
             if self.wrap.type == 'file':
                 self.get_file()
             else:
diff --git a/run_unittests.py b/run_unittests.py
index c4978c2..2f9fb7f 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -4081,6 +4081,11 @@ recommended as it is not supported on some platforms''')
                     'version': '1.0'
                 },
                 {
+                    'descriptive_name': 'sub_implicit',
+                    'name': 'sub_implicit',
+                    'version': '1.0',
+                },
+                {
                     'descriptive_name': 'sub-novar',
                     'name': 'sub_novar',
                     'version': '1.0',
diff --git a/test cases/common/102 subproject subdir/meson.build b/test cases/common/102 subproject subdir/meson.build
index 8299a37..a891ca9 100644
--- a/test cases/common/102 subproject subdir/meson.build
+++ b/test cases/common/102 subproject subdir/meson.build
@@ -25,3 +25,32 @@ dependency('sub-novar', fallback : 'sub_novar')
 # Verify a subproject can force a dependency to be not-found
 d = dependency('sub-notfound', fallback : 'sub_novar', required : false)
 assert(not d.found(), 'Dependency should be not-found')
+
+# Verify that implicit fallback works because subprojects/sub_implicit directory exists
+d = dependency('sub_implicit')
+assert(d.found(), 'Should implicitly fallback')
+
+# Verify that implicit fallback works because sub_implicit.wrap has
+# `dependency_names=sub_implicit_provide1` and the subproject overrides sub_implicit_provide1.
+d = dependency('sub_implicit_provide1')
+assert(d.found(), 'Should implicitly fallback')
+
+# Verify that implicit fallback works because sub_implicit.wrap has
+# `sub_implicit_provide2=sub_implicit_provide2_dep` and does not override
+# sub_implicit_provide2.
+d = dependency('sub_implicit_provide2')
+assert(d.found(), 'Should implicitly fallback')
+
+# sub_implicit.wrap provides glib-2.0 and we already configured that subproject,
+# so we must not return the system dependency here. Using glib-2.0 here because
+# some CI runners have it installed.
+d = dependency('glib-2.0', required : false)
+assert(d.found())
+assert(d.type_name() == 'internal')
+
+# sub_implicit.wrap provides gobject-2.0 and we already configured that subproject,
+# so we must not return the system dependency here. But since the subproject did
+# not override that dependency and its not required, not-found should be returned.
+# Using gobject-2.0 here because some CI runners have it installed.
+d = dependency('gobject-2.0', required : false)
+assert(not d.found())
diff --git a/test cases/common/102 subproject subdir/subprojects/sub_implicit.wrap b/test cases/common/102 subproject subdir/subprojects/sub_implicit.wrap
new file mode 100644
index 0000000..a809c43
--- /dev/null
+++ b/test cases/common/102 subproject subdir/subprojects/sub_implicit.wrap
@@ -0,0 +1,6 @@
+[wrap-file]
+
+[provide]
+glib-2.0 = glib_dep
+dependency_names = sub_implicit_provide1, gobject-2.0
+sub_implicit_provide2 = sub_implicit_provide2_dep
diff --git a/test cases/common/102 subproject subdir/subprojects/sub_implicit/meson.build b/test cases/common/102 subproject subdir/subprojects/sub_implicit/meson.build
new file mode 100644
index 0000000..24609ae
--- /dev/null
+++ b/test cases/common/102 subproject subdir/subprojects/sub_implicit/meson.build
@@ -0,0 +1,11 @@
+project('sub_implicit', 'c', version : '1.0')
+
+dep = declare_dependency()
+meson.override_dependency('sub_implicit', dep)
+meson.override_dependency('sub_implicit_provide1', dep)
+
+# This one is not overriden but the wrap file tells the variable name to use.
+sub_implicit_provide2_dep = dep
+
+# This one is not overriden but the wrap file tells the variable name to use.
+glib_dep = dep
diff --git a/test cases/common/187 find override/meson.build b/test cases/common/187 find override/meson.build
index 3b8af80..b277459 100644
--- a/test cases/common/187 find override/meson.build
+++ b/test cases/common/187 find override/meson.build
@@ -10,3 +10,6 @@ if not gencodegen.found()
 endif
 
 subdir('otherdir')
+
+tool = find_program('sometool')
+assert(tool.found())
diff --git a/test cases/common/187 find override/subprojects/sub.wrap b/test cases/common/187 find override/subprojects/sub.wrap
new file mode 100644
index 0000000..17aa332
--- /dev/null
+++ b/test cases/common/187 find override/subprojects/sub.wrap
@@ -0,0 +1,5 @@
+[wrap-file]
+directory = sub
+
+[provide]
+program_names = sometool
diff --git a/test cases/common/187 find override/subprojects/sub/meson.build b/test cases/common/187 find override/subprojects/sub/meson.build
new file mode 100644
index 0000000..640f270
--- /dev/null
+++ b/test cases/common/187 find override/subprojects/sub/meson.build
@@ -0,0 +1,4 @@
+project('tools')
+
+exe = find_program('gencodegen')
+meson.override_find_program('sometool', exe)
diff --git a/test cases/failing/106 fallback consistency/meson.build b/test cases/failing/106 fallback consistency/meson.build
new file mode 100644
index 0000000..1b007f5
--- /dev/null
+++ b/test cases/failing/106 fallback consistency/meson.build
@@ -0,0 +1,3 @@
+project('fallback consistency')
+
+dependency('foo')
diff --git a/test cases/failing/106 fallback consistency/subprojects/foo.wrap b/test cases/failing/106 fallback consistency/subprojects/foo.wrap
new file mode 100644
index 0000000..28055d9
--- /dev/null
+++ b/test cases/failing/106 fallback consistency/subprojects/foo.wrap
@@ -0,0 +1,6 @@
+[wrap-file]
+source_url = http://host.invalid/foo.tar.gz
+source_filename = foo.tar.gz
+
+[provide]
+foo = bar_dep
diff --git a/test cases/failing/106 fallback consistency/subprojects/foo/meson.build b/test cases/failing/106 fallback consistency/subprojects/foo/meson.build
new file mode 100644
index 0000000..fb58a4a
--- /dev/null
+++ b/test cases/failing/106 fallback consistency/subprojects/foo/meson.build
@@ -0,0 +1,6 @@
+project('sub')
+
+foo_dep = declare_dependency()
+meson.override_dependency('foo', foo_dep)
+
+bar_dep = declare_dependency()
diff --git a/test cases/failing/106 fallback consistency/test.json b/test cases/failing/106 fallback consistency/test.json
new file mode 100644
index 0000000..af1a429
--- /dev/null
+++ b/test cases/failing/106 fallback consistency/test.json
@@ -0,0 +1,7 @@
+{
+  "stdout": [
+    {
+      "line": "test cases/failing/106 fallback consistency/meson.build:3:0: ERROR: Inconsistency: Subproject has overridden the dependency with another variable than 'bar_dep'"
+    }
+  ]
+}
diff --git a/test cases/linuxlike/5 dependency versions/meson.build b/test cases/linuxlike/5 dependency versions/meson.build
index 94f424d..164e679 100644
--- a/test cases/linuxlike/5 dependency versions/meson.build
+++ b/test cases/linuxlike/5 dependency versions/meson.build
@@ -31,10 +31,10 @@ dependency('somebrokenlib', version : '>=1.0', required : false)
 
 # Search for an external dependency that won't be found, but must later be
 # found via fallbacks
-somelibnotfound = dependency('somelib', required : false)
+somelibnotfound = dependency('somelib1', required : false)
 assert(somelibnotfound.found() == false, 'somelibnotfound was found?')
 # Find internal dependency without version
-somelibver = dependency('somelib',
+somelibver = dependency('somelib1',
   fallback : ['somelibnover', 'some_dep'])
 assert(somelibver.type_name() == 'internal', 'somelibver should be of type "internal", not ' + somelibver.type_name())
 # Find an internal dependency again with the same name and a specific version
diff --git a/test cases/unit/12 promote/subprojects/s2/subprojects/athing.wrap b/test cases/unit/12 promote/subprojects/s2/subprojects/athing.wrap
index 09ba4e8..11b2178 100644
--- a/test cases/unit/12 promote/subprojects/s2/subprojects/athing.wrap
+++ b/test cases/unit/12 promote/subprojects/s2/subprojects/athing.wrap
@@ -1,2 +1 @@
-The contents of this wrap file are never evaluated so they
-can be anything.
+[wrap-file]