Merge pull request #6968 from xclaesse/auto-promote

Merge wraps from subprojects into wraps from main project

14 files changed, 309 insertions, 187 deletions

diff --git a/docs/markdown/Builtin-options.md b/docs/markdown/Builtin-options.md
index febcc8a..afc1cde 100644
--- a/docs/markdown/Builtin-options.md
+++ b/docs/markdown/Builtin-options.md
@@ -79,7 +79,7 @@ for details.
 | unity_size {>=2}                     | 4             | Unity file block size                                          | no             | no                |
 | warning_level {0, 1, 2, 3}           | 1             | Set the warning level. From 0 = none to 3 = highest            | no             | yes               |
 | werror                               | false         | Treat warnings as errors                                       | no             | yes               |
-| wrap_mode {default, nofallback,<br>nodownload, forcefallback} | default | Wrap mode to use                            | no             | no                |
+| wrap_mode {default, nofallback,<br>nodownload, forcefallback, nopromote} | default | Wrap mode to use                 | no             | no                |
 | force_fallback_for                   | []            | Force fallback for those dependencies                          | no             | no                |
 
 <a name="build-type-options"></a>
diff --git a/docs/markdown/Subprojects.md b/docs/markdown/Subprojects.md
index 7e17afa..e8adc96 100644
--- a/docs/markdown/Subprojects.md
+++ b/docs/markdown/Subprojects.md
@@ -258,6 +258,13 @@ the following command-line options:
     `glib-2.0` must also be forced to fallback, in this case with
     `--force-fallback-for=glib,gsteamer`.
 
+* **--wrap-mode=nopromote**
+
+    *Since 0.56.0* Meson will automatically use wrap files found in subprojects
+    and copy them into the main project. That new behavior can be disabled by
+    passing `--wrap-mode=nopromote`. In that case only wraps found in the main
+    project will be used.
+
 ## `meson subprojects` command
 
 *Since 0.49.0*
diff --git a/docs/markdown/Using-wraptool.md b/docs/markdown/Using-wraptool.md
index f6023e8..ffa8309 100644
--- a/docs/markdown/Using-wraptool.md
+++ b/docs/markdown/Using-wraptool.md
@@ -76,24 +76,3 @@ straightforward:
 Wraptool can do other things besides these. Documentation for these
 can be found in the command line help, which can be accessed by
 `meson wrap --help`.
-
-## Promoting dependencies
-
-Meson will only search for subprojects from the top level
-`subprojects` directory. If you have subprojects that themselves have
-subprojects, you must transfer them to the top level. This can be done
-by going to your source root and issuing a promotion command.
-
-    meson wrap promote projname
-
-This will cause Meson to go through your entire project tree, find an
-embedded subproject and copy it to the top level.
-
-If there are multiple embedded copies of a subproject, Meson will not
-try to guess which one you want. Instead it will print all the
-possibilities. You can then manually select which one to promote by
-writing it out fully.
-
-    meson wrap promote subprojects/s1/subprojects/projname
-
-This functionality was added in Meson release 0.45.0.
diff --git a/docs/markdown/snippets/subsubproject.md b/docs/markdown/snippets/subsubproject.md
new file mode 100644
index 0000000..77f4a0d
--- /dev/null
+++ b/docs/markdown/snippets/subsubproject.md
@@ -0,0 +1,13 @@
+## Wraps from subprojects are automatically promoted
+
+It is not required to promote wrap files for subprojects into the main project
+any more. When configuring a subproject, meson will look for any wrap file or
+directory in the subproject's `subprojects/` directory and add them into the
+global list of available subprojects, to be used by any future `subproject()`
+call or `dependency()` fallback. If a subproject with the same name already exists,
+the new wrap file or directory is ignored. That means that the main project can
+always override any subproject's wrap files by providing their own, it also means
+the ordering in which subprojects are configured matters, if 2 subprojects provide
+foo.wrap only the one from the first subproject to be configured will be used.
+
+This new behavior can be disabled by passing `--wrap-mode=nopromote`.
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index f25a6f3..ad6f04e 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -1010,15 +1010,14 @@ class Test(InterpreterObject):
 
 class SubprojectHolder(InterpreterObject, ObjectHolder):
 
-    def __init__(self, subinterpreter, subproject_dir, name, warnings=0, disabled_feature=None,
+    def __init__(self, subinterpreter, subdir, warnings=0, disabled_feature=None,
                  exception=None):
         InterpreterObject.__init__(self)
         ObjectHolder.__init__(self, subinterpreter)
-        self.name = name
         self.warnings = warnings
         self.disabled_feature = disabled_feature
         self.exception = exception
-        self.subproject_dir = subproject_dir
+        self.subdir = PurePath(subdir).as_posix()
         self.methods.update({'get_variable': self.get_variable_method,
                              'found': self.found_method,
                              })
@@ -1037,8 +1036,7 @@ class SubprojectHolder(InterpreterObject, ObjectHolder):
         if len(args) < 1 or len(args) > 2:
             raise InterpreterException('Get_variable takes one or two arguments.')
         if not self.found():
-            raise InterpreterException('Subproject "%s/%s" disabled can\'t get_variable on it.' % (
-                self.subproject_dir, self.name))
+            raise InterpreterException('Subproject "%s" disabled can\'t get_variable on it.' % (self.subdir))
         varname = args[0]
         if not isinstance(varname, str):
             raise InterpreterException('Get_variable first argument must be a string.')
@@ -2171,7 +2169,7 @@ class MesonMain(InterpreterObject):
                                         self.interpreter.environment.build_dir)
             if not os.path.exists(abspath):
                 raise InterpreterException('Tried to override %s with a file that does not exist.' % name)
-            exe = OverrideProgram(abspath)
+            exe = OverrideProgram(name, abspath)
         if not isinstance(exe, (dependencies.ExternalProgram, build.Executable)):
             raise InterpreterException('Second argument must be an external program or executable.')
         self.interpreter.add_find_program_override(name, exe)
@@ -2840,84 +2838,75 @@ external dependencies (including libraries) must go to "dependencies".''')
     def func_subproject(self, nodes, args, kwargs):
         if len(args) != 1:
             raise InterpreterException('Subproject takes exactly one argument')
-        dirname = args[0]
-        return self.do_subproject(dirname, 'meson', kwargs)
+        subp_name = args[0]
+        return self.do_subproject(subp_name, 'meson', kwargs)
 
-    def disabled_subproject(self, dirname, disabled_feature=None, exception=None):
-        sub = SubprojectHolder(None, self.subproject_dir, dirname,
+    def disabled_subproject(self, subp_name, disabled_feature=None, exception=None):
+        sub = SubprojectHolder(None, os.path.join(self.subproject_dir, subp_name),
                                disabled_feature=disabled_feature, exception=exception)
-        self.subprojects[dirname] = sub
+        self.subprojects[subp_name] = sub
         return sub
 
-    def get_subproject(self, dirname):
-        sub = self.subprojects.get(dirname)
+    def get_subproject(self, subp_name):
+        sub = self.subprojects.get(subp_name)
         if sub and sub.found():
             return sub
         return None
 
-    def do_subproject(self, dirname: str, method: str, kwargs):
+    def do_subproject(self, subp_name: str, method: str, kwargs):
         disabled, required, feature = extract_required_kwarg(kwargs, self.subproject)
         if disabled:
-            mlog.log('Subproject', mlog.bold(dirname), ':', 'skipped: feature', mlog.bold(feature), 'disabled')
-            return self.disabled_subproject(dirname, disabled_feature=feature)
+            mlog.log('Subproject', mlog.bold(subp_name), ':', 'skipped: feature', mlog.bold(feature), 'disabled')
+            return self.disabled_subproject(subp_name, disabled_feature=feature)
 
         default_options = mesonlib.stringlistify(kwargs.get('default_options', []))
         default_options = coredata.create_options_dict(default_options)
 
-        if dirname == '':
-            raise InterpreterException('Subproject dir name must not be empty.')
-        if dirname[0] == '.':
-            raise InterpreterException('Subproject dir name must not start with a period.')
-        if '..' in dirname:
+        if subp_name == '':
+            raise InterpreterException('Subproject name must not be empty.')
+        if subp_name[0] == '.':
+            raise InterpreterException('Subproject name must not start with a period.')
+        if '..' in subp_name:
             raise InterpreterException('Subproject name must not contain a ".." path segment.')
-        if os.path.isabs(dirname):
+        if os.path.isabs(subp_name):
             raise InterpreterException('Subproject name must not be an absolute path.')
-        if has_path_sep(dirname):
+        if has_path_sep(subp_name):
             mlog.warning('Subproject name has a path separator. This may cause unexpected behaviour.',
                          location=self.current_node)
-        if dirname in self.subproject_stack:
-            fullstack = self.subproject_stack + [dirname]
+        if subp_name in self.subproject_stack:
+            fullstack = self.subproject_stack + [subp_name]
             incpath = ' => '.join(fullstack)
             raise InvalidCode('Recursive include of subprojects: %s.' % incpath)
-        if dirname in self.subprojects:
-            subproject = self.subprojects[dirname]
+        if subp_name in self.subprojects:
+            subproject = self.subprojects[subp_name]
             if required and not subproject.found():
-                raise InterpreterException('Subproject "%s/%s" required but not found.' % (
-                                           self.subproject_dir, dirname))
+                raise InterpreterException('Subproject "%s" required but not found.' % (subproject.subdir))
             return subproject
 
         r = self.environment.wrap_resolver
         try:
-            resolved = r.resolve(dirname, method, self.subproject)
+            subdir = r.resolve(subp_name, method, self.subproject)
         except wrap.WrapException as e:
-            subprojdir = os.path.join(self.subproject_dir, r.directory)
-            if isinstance(e, wrap.WrapNotFoundException):
-                # if the reason subproject execution failed was because
-                # the directory doesn't exist, try to give some helpful
-                # advice if it's a nested subproject that needs
-                # promotion...
-                self.print_nested_info(dirname)
             if not required:
                 mlog.log(e)
-                mlog.log('Subproject ', mlog.bold(subprojdir), 'is buildable:', mlog.red('NO'), '(disabling)')
-                return self.disabled_subproject(dirname, exception=e)
+                mlog.log('Subproject ', mlog.bold(subp_name), 'is buildable:', mlog.red('NO'), '(disabling)')
+                return self.disabled_subproject(subp_name, exception=e)
             raise e
 
-        subdir = os.path.join(self.subproject_dir, 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
 
         mlog.log()
         with mlog.nested():
-            mlog.log('Executing subproject', mlog.bold(dirname), 'method', mlog.bold(method), '\n')
+            mlog.log('Executing subproject', mlog.bold(subp_name), 'method', mlog.bold(method), '\n')
         try:
             if method == 'meson':
-                return self._do_subproject_meson(dirname, subdir, default_options, kwargs)
+                return self._do_subproject_meson(subp_name, subdir, default_options, kwargs)
             elif method == 'cmake':
-                return self._do_subproject_cmake(dirname, subdir, subdir_abs, default_options, kwargs)
+                return self._do_subproject_cmake(subp_name, subdir, subdir_abs, default_options, kwargs)
             else:
-                raise InterpreterException('The method {} is invalid for the subproject {}'.format(method, dirname))
+                raise InterpreterException('The method {} is invalid for the subproject {}'.format(method, subp_name))
         # Invalid code is always an error
         except InvalidCode:
             raise
@@ -2927,18 +2916,18 @@ external dependencies (including libraries) must go to "dependencies".''')
                     # Suppress the 'ERROR:' prefix because this exception is not
                     # fatal and VS CI treat any logs with "ERROR:" as fatal.
                     mlog.exception(e, prefix=mlog.yellow('Exception:'))
-                mlog.log('\nSubproject', mlog.bold(dirname), 'is buildable:', mlog.red('NO'), '(disabling)')
-                return self.disabled_subproject(dirname, exception=e)
+                mlog.log('\nSubproject', mlog.bold(subdir), 'is buildable:', mlog.red('NO'), '(disabling)')
+                return self.disabled_subproject(subp_name, exception=e)
             raise e
 
-    def _do_subproject_meson(self, dirname, subdir, default_options, kwargs, ast=None, build_def_files=None):
+    def _do_subproject_meson(self, subp_name, subdir, default_options, kwargs, ast=None, build_def_files=None):
         with mlog.nested():
             new_build = self.build.copy()
-            subi = Interpreter(new_build, self.backend, dirname, subdir, self.subproject_dir,
+            subi = Interpreter(new_build, self.backend, subp_name, subdir, self.subproject_dir,
                                self.modules, default_options, ast=ast)
             subi.subprojects = self.subprojects
 
-            subi.subproject_stack = self.subproject_stack + [dirname]
+            subi.subproject_stack = self.subproject_stack + [subp_name]
             current_active = self.active_projectname
             current_warnings_counter = mlog.log_warnings_counter
             mlog.log_warnings_counter = 0
@@ -2946,7 +2935,7 @@ external dependencies (including libraries) must go to "dependencies".''')
             subi_warnings = mlog.log_warnings_counter
             mlog.log_warnings_counter = current_warnings_counter
 
-            mlog.log('Subproject', mlog.bold(dirname), 'finished.')
+            mlog.log('Subproject', mlog.bold(subp_name), 'finished.')
 
         mlog.log()
 
@@ -2954,22 +2943,21 @@ external dependencies (including libraries) must go to "dependencies".''')
             pv = subi.project_version
             wanted = kwargs['version']
             if pv == 'undefined' or not mesonlib.version_compare_many(pv, wanted)[0]:
-                raise InterpreterException('Subproject %s version is %s but %s required.' % (dirname, pv, wanted))
+                raise InterpreterException('Subproject %s version is %s but %s required.' % (subp_name, pv, wanted))
         self.active_projectname = current_active
         self.subprojects.update(subi.subprojects)
-        self.subprojects[dirname] = SubprojectHolder(subi, self.subproject_dir, dirname,
-                                                     warnings=subi_warnings)
+        self.subprojects[subp_name] = SubprojectHolder(subi, subdir, warnings=subi_warnings)
         # Duplicates are possible when subproject uses files from project root
         if build_def_files:
             self.build_def_files = list(set(self.build_def_files + build_def_files))
         else:
             self.build_def_files = list(set(self.build_def_files + subi.build_def_files))
         self.build.merge(subi.build)
-        self.build.subprojects[dirname] = subi.project_version
+        self.build.subprojects[subp_name] = subi.project_version
         self.summary.update(subi.summary)
-        return self.subprojects[dirname]
+        return self.subprojects[subp_name]
 
-    def _do_subproject_cmake(self, dirname, subdir, subdir_abs, default_options, kwargs):
+    def _do_subproject_cmake(self, subp_name, subdir, subdir_abs, default_options, kwargs):
         with mlog.nested():
             new_build = self.build.copy()
             prefix = self.coredata.builtins['prefix'].value
@@ -3007,7 +2995,7 @@ external dependencies (including libraries) must go to "dependencies".''')
                 mlog.cmd_ci_include(meson_filename)
                 mlog.log()
 
-            result = self._do_subproject_meson(dirname, subdir, default_options, kwargs, ast, cm_int.bs_files)
+            result = self._do_subproject_meson(subp_name, subdir, default_options, kwargs, ast, cm_int.bs_files)
             result.cm_interpreter = cm_int
 
         mlog.log()
@@ -3157,8 +3145,11 @@ external dependencies (including libraries) must go to "dependencies".''')
                                               'license': proj_license}
         if self.subproject in self.build.projects:
             raise InvalidCode('Second call to project().')
-        if not self.is_subproject() and 'subproject_dir' in kwargs:
-            spdirname = kwargs['subproject_dir']
+
+        # spdirname is the subproject_dir for this project, relative to self.subdir.
+        # self.subproject_dir is the subproject_dir for the main project, relative to top source dir.
+        spdirname = kwargs.get('subproject_dir')
+        if spdirname:
             if not isinstance(spdirname, str):
                 raise InterpreterException('Subproject_dir must be a string')
             if os.path.isabs(spdirname):
@@ -3167,13 +3158,21 @@ external dependencies (including libraries) must go to "dependencies".''')
                 raise InterpreterException('Subproject_dir must not begin with a period.')
             if '..' in spdirname:
                 raise InterpreterException('Subproject_dir must not contain a ".." segment.')
-            self.subproject_dir = spdirname
-
+            if not self.is_subproject():
+                self.subproject_dir = spdirname
+        else:
+            spdirname = 'subprojects'
         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)
+
+        # Load wrap files from this (sub)project.
+        wrap_mode = self.coredata.get_builtin_option('wrap_mode')
+        if not self.is_subproject() or wrap_mode != WrapMode.nopromote:
+            subdir = os.path.join(self.subdir, spdirname)
+            r = wrap.Resolver(self.environment.get_source_dir(), subdir, wrap_mode)
+            if self.is_subproject():
+                self.environment.wrap_resolver.merge_wraps(r)
+            else:
+                self.environment.wrap_resolver = r
 
         self.build.projects[self.subproject] = proj_name
         mlog.log('Project name:', mlog.bold(proj_name))
@@ -3376,7 +3375,7 @@ external dependencies (including libraries) must go to "dependencies".''')
                 return ExternalProgramHolder(prog, self.subproject)
         return None
 
-    def program_from_system(self, args, search_dirs, silent=False):
+    def program_from_system(self, args, search_dirs, extra_info):
         # Search for scripts relative to current subdir.
         # Do not cache found programs because find_program('foobar')
         # might give different results when run from different source dirs.
@@ -3399,9 +3398,10 @@ external dependencies (including libraries) must go to "dependencies".''')
                                        'files, not {!r}'.format(exename))
             extprog = dependencies.ExternalProgram(exename, search_dir=search_dir,
                                                    extra_search_dirs=extra_search_dirs,
-                                                   silent=silent)
+                                                   silent=True)
             progobj = ExternalProgramHolder(extprog, self.subproject)
             if progobj.found():
+                extra_info.append('({})'.format(' '.join(progobj.get_command())))
                 return progobj
 
     def program_from_overrides(self, command_names, extra_info):
@@ -3459,7 +3459,7 @@ external dependencies (including libraries) must go to "dependencies".''')
             if not is_found:
                 mlog.log('Program', mlog.bold(progobj.get_name()), 'found:', mlog.red('NO'),
                          'found', mlog.normal_cyan(version), 'but need:',
-                         mlog.bold(', '.join(["'{}'".format(e) for e in not_found])))
+                         mlog.bold(', '.join(["'{}'".format(e) for e in not_found])), *extra_info)
                 if required:
                     m = 'Invalid version of program, need {!r} {!r} found {!r}.'
                     raise InterpreterException(m.format(progobj.get_name(), not_found, version))
@@ -3485,7 +3485,7 @@ external dependencies (including libraries) must go to "dependencies".''')
 
         progobj = self.program_from_file_for(for_machine, args)
         if progobj is None:
-            progobj = self.program_from_system(args, search_dirs, silent=True)
+            progobj = self.program_from_system(args, search_dirs, extra_info)
         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
@@ -3582,8 +3582,8 @@ external dependencies (including libraries) must go to "dependencies".''')
     def notfound_dependency(self):
         return DependencyHolder(NotFoundDependency(self.environment), self.subproject)
 
-    def verify_fallback_consistency(self, dirname, varname, cached_dep):
-        subi = self.get_subproject(dirname)
+    def verify_fallback_consistency(self, subp_name, varname, cached_dep):
+        subi = self.get_subproject(subp_name)
         if not cached_dep or not varname or not subi or not cached_dep.found():
             return
         dep = subi.get_variable_method([varname], {})
@@ -3591,63 +3591,77 @@ external dependencies (including libraries) must go to "dependencies".''')
             m = 'Inconsistency: Subproject has overridden the dependency with another variable than {!r}'
             raise DependencyException(m.format(varname))
 
-    def get_subproject_dep(self, name, display_name, dirname, varname, kwargs):
+    def get_subproject_dep(self, name, display_name, subp_name, varname, kwargs):
         required = kwargs.get('required', True)
         wanted = mesonlib.stringlistify(kwargs.get('version', []))
-        subproj_path = os.path.join(self.subproject_dir, dirname)
         dep = self.notfound_dependency()
+
+        # Verify the subproject is found
+        subproject = self.subprojects.get(subp_name)
+        if not subproject or not subproject.found():
+            mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'),
+                     mlog.blue('(subproject failed to configure)'))
+            if required:
+                m = 'Subproject {} failed to configure for dependency {}'
+                raise DependencyException(m.format(subproject.subdir, display_name))
+            return dep
+
+        extra_info = []
         try:
-            subproject = self.subprojects[dirname]
+            # Check if the subproject overridden the dependency
             _, cached_dep = self._find_cached_dep(name, display_name, kwargs)
-            if varname is None:
-                # Assuming the subproject overridden the dependency we want
-                if cached_dep:
-                    if required and not cached_dep.found():
-                        m = 'Dependency {!r} is not satisfied'
-                        raise DependencyException(m.format(display_name))
-                    return DependencyHolder(cached_dep, self.subproject)
-                else:
-                    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], {})
+            if cached_dep:
+                if varname:
+                    self.verify_fallback_consistency(subp_name, varname, cached_dep)
+                if required and not cached_dep.found():
+                    m = 'Dependency {!r} is not satisfied'
+                    raise DependencyException(m.format(display_name))
+                return DependencyHolder(cached_dep, self.subproject)
+            elif varname is None:
+                mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
+                         mlog.bold(subproject.subdir), 'found:', mlog.red('NO'))
+                if required:
+                    m = 'Subproject {} did not override dependency {}'
+                    raise DependencyException(m.format(subproject.subdir, display_name))
+                return self.notfound_dependency()
+            else:
+                # The subproject did not override the dependency, but we know the
+                # variable name to take.
+                dep = subproject.get_variable_method([varname], {})
         except InvalidArguments:
-            pass
+            # This is raised by get_variable_method() if varname does no exist
+            # in the subproject. Just add the reason in the not-found message
+            # that will be printed later.
+            extra_info.append(mlog.blue('(Variable {!r} not found)'.format(varname)))
 
         if not isinstance(dep, DependencyHolder):
             raise InvalidCode('Fetched variable {!r} in the subproject {!r} is '
-                              'not a dependency object.'.format(varname, dirname))
+                              'not a dependency object.'.format(varname, subp_name))
 
         if not dep.found():
+            mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'), *extra_info)
             if required:
                 raise DependencyException('Could not find dependency {} in subproject {}'
-                                          ''.format(varname, dirname))
-            # If the dependency is not required, don't raise an exception
-            mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
-                     mlog.bold(subproj_path), 'found:', mlog.red('NO'))
+                                          ''.format(varname, subp_name))
             return dep
 
         found = dep.held_object.get_version()
         if not self.check_version(wanted, found):
-            if required:
-                raise DependencyException('Version {} of subproject dependency {} already '
-                                          'cached, requested incompatible version {} for '
-                                          'dep {}'.format(found, dirname, wanted, display_name))
-
             mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
-                     mlog.bold(subproj_path), 'found:', mlog.red('NO'),
+                     mlog.bold(subproject.subdir), 'found:', mlog.red('NO'),
                      'found', mlog.normal_cyan(found), 'but need:',
                      mlog.bold(', '.join(["'{}'".format(e) for e in wanted])))
+            if required:
+                raise DependencyException('Version {} of subproject dependency {} already '
+                                          'cached, requested incompatible version {} for '
+                                          'dep {}'.format(found, subp_name, wanted, display_name))
             return self.notfound_dependency()
 
         found = mlog.normal_cyan(found) if found else None
         mlog.log('Dependency', mlog.bold(display_name), 'from subproject',
-                 mlog.bold(subproj_path), 'found:', mlog.green('YES'), found)
+                 mlog.bold(subproject.subdir), 'found:', mlog.green('YES'), found)
         return dep
 
     def _handle_featurenew_dependencies(self, name):
@@ -3733,8 +3747,8 @@ external dependencies (including libraries) must go to "dependencies".''')
             provider = self.environment.wrap_resolver.find_dep_provider(name)
             if not provider and allow_fallback is True:
                 raise InvalidArguments('Fallback wrap or subproject not found for dependency \'%s\'' % name)
-            dirname = mesonlib.listify(provider)[0]
-            if provider and (allow_fallback is True or required or self.get_subproject(dirname)):
+            subp_name = mesonlib.listify(provider)[0]
+            if provider and (allow_fallback is True or required or self.get_subproject(subp_name)):
                 fallback = provider
 
         if 'default_options' in kwargs and not fallback:
@@ -3752,8 +3766,8 @@ external dependencies (including libraries) must go to "dependencies".''')
         identifier, cached_dep = self._find_cached_dep(name, display_name, kwargs)
         if cached_dep:
             if fallback:
-                dirname, varname = self.get_subproject_infos(fallback)
-                self.verify_fallback_consistency(dirname, varname, cached_dep)
+                subp_name, varname = self.get_subproject_infos(fallback)
+                self.verify_fallback_consistency(subp_name, varname, cached_dep)
             if required and not cached_dep.found():
                 m = 'Dependency {!r} was already checked and was not found'
                 raise DependencyException(m.format(display_name))
@@ -3762,16 +3776,16 @@ external dependencies (including libraries) must go to "dependencies".''')
         if fallback:
             # If the dependency has already been configured, possibly by
             # a higher level project, try to use it first.
-            dirname, varname = self.get_subproject_infos(fallback)
-            if self.get_subproject(dirname):
-                return self.get_subproject_dep(name, display_name, dirname, varname, kwargs)
+            subp_name, varname = self.get_subproject_infos(fallback)
+            if self.get_subproject(subp_name):
+                return self.get_subproject_dep(name, display_name, subp_name, varname, kwargs)
 
             wrap_mode = self.coredata.get_builtin_option('wrap_mode')
             force_fallback_for = self.coredata.get_builtin_option('force_fallback_for')
             force_fallback = (force_fallback or
                               wrap_mode == WrapMode.forcefallback or
                               name in force_fallback_for or
-                              dirname in force_fallback_for)
+                              subp_name in force_fallback_for)
 
         if name != '' and (not fallback or not force_fallback):
             self._handle_featurenew_dependencies(name)
@@ -3798,23 +3812,6 @@ external dependencies (including libraries) must go to "dependencies".''')
     def func_disabler(self, node, args, kwargs):
         return Disabler()
 
-    def print_nested_info(self, dependency_name):
-        message = ['Dependency', mlog.bold(dependency_name), 'not found but it is available in a sub-subproject.\n' +
-                   'To use it in the current project, promote it by going in the project source\n'
-                   'root and issuing']
-        sprojs = mesonlib.detect_subprojects('subprojects', self.source_root)
-        if dependency_name not in sprojs:
-            return
-        found = sprojs[dependency_name]
-        if len(found) > 1:
-            message.append('one of the following commands:')
-        else:
-            message.append('the following command:')
-        command_templ = '\nmeson wrap promote {}'
-        for l in found:
-            message.append(mlog.bold(command_templ.format(l[len(self.source_root) + 1:])))
-        mlog.warning(*message, location=self.current_node)
-
     def get_subproject_infos(self, fbinfo):
         fbinfo = mesonlib.stringlistify(fbinfo)
         if len(fbinfo) == 1:
@@ -3825,13 +3822,13 @@ external dependencies (including libraries) must go to "dependencies".''')
         return fbinfo
 
     def dependency_fallback(self, name, display_name, fallback, kwargs):
-        dirname, varname = self.get_subproject_infos(fallback)
+        subp_name, varname = self.get_subproject_infos(fallback)
         required = kwargs.get('required', True)
 
         # Explicitly listed fallback preferences for specific subprojects
         # take precedence over wrap-mode
         force_fallback_for = self.coredata.get_builtin_option('force_fallback_for')
-        if name in force_fallback_for or dirname in force_fallback_for:
+        if name in force_fallback_for or subp_name in force_fallback_for:
             mlog.log('Looking for a fallback subproject for the dependency',
                      mlog.bold(display_name), 'because:\nUse of fallback was forced for that specific subproject')
         elif self.coredata.get_builtin_option('wrap_mode') == WrapMode.nofallback:
@@ -3852,8 +3849,8 @@ external dependencies (including libraries) must go to "dependencies".''')
             'default_options': kwargs.get('default_options', []),
             'required': required,
         }
-        self.do_subproject(dirname, 'meson', sp_kwargs)
-        return self.get_subproject_dep(name, display_name, dirname, varname, kwargs)
+        self.do_subproject(subp_name, 'meson', sp_kwargs)
+        return self.get_subproject_dep(name, display_name, subp_name, varname, kwargs)
 
     @FeatureNewKwargs('executable', '0.42.0', ['implib'])
     @permittedKwargs(permitted_kwargs['executable'])
@@ -4709,11 +4706,11 @@ This will probably not work.
 Try setting b_lundef to false instead.'''.format(self.coredata.base_options['b_sanitize'].value),
                          location=self.current_node)
 
-    def evaluate_subproject_info(self, path_from_source_root, subproject_dirname):
+    def evaluate_subproject_info(self, path_from_source_root, subproject_dir):
         depth = 0
         subproj_name = ''
         segs = PurePath(path_from_source_root).parts
-        segs_spd = PurePath(subproject_dirname).parts
+        segs_spd = PurePath(subproject_dir).parts
         while segs and segs[0] == segs_spd[0]:
             if len(segs_spd) == 1:
                 subproj_name = segs[1]
@@ -4926,14 +4923,8 @@ This will become a hard error in the future.''', location=self.current_node)
 
     # Only permit object extraction from the same subproject
     def validate_extraction(self, buildtarget: InterpreterObject) -> None:
-        if not self.subdir.startswith(self.subproject_dir):
-            if buildtarget.subdir.startswith(self.subproject_dir):
-                raise InterpreterException('Tried to extract objects from a subproject target.')
-        else:
-            if not buildtarget.subdir.startswith(self.subproject_dir):
-                raise InterpreterException('Tried to extract objects from the main project from a subproject.')
-            if self.subdir.split('/')[1] != buildtarget.subdir.split('/')[1]:
-                raise InterpreterException('Tried to extract objects from a different subproject.')
+        if self.subproject != buildtarget.subproject:
+            raise InterpreterException('Tried to extract objects from a different subproject.')
 
     def is_subproject(self):
         return self.subproject != ''
diff --git a/mesonbuild/msubprojects.py b/mesonbuild/msubprojects.py
index b628a47..20639cb 100755
--- a/mesonbuild/msubprojects.py
+++ b/mesonbuild/msubprojects.py
@@ -364,7 +364,7 @@ def run(options):
     if not os.path.isdir(subprojects_dir):
         mlog.log('Directory', mlog.bold(src_dir), 'does not seem to have subprojects.')
         return 0
-    r = Resolver(subprojects_dir)
+    r = Resolver(src_dir, 'subprojects')
     if options.subprojects:
         wraps = [wrap for name, wrap in r.wraps.items() if name in options.subprojects]
     else:
diff --git a/mesonbuild/wrap/__init__.py b/mesonbuild/wrap/__init__.py
index 1771146..653f42a 100644
--- a/mesonbuild/wrap/__init__.py
+++ b/mesonbuild/wrap/__init__.py
@@ -40,6 +40,7 @@ string_to_value = {'default': 1,
                    'nofallback': 2,
                    'nodownload': 3,
                    'forcefallback': 4,
+                   'nopromote': 5,
                    }
 
 class WrapMode(Enum):
@@ -47,6 +48,7 @@ class WrapMode(Enum):
     nofallback = 2
     nodownload = 3
     forcefallback = 4
+    nopromote = 5
 
     def __str__(self) -> str:
         return self.name
diff --git a/mesonbuild/wrap/wrap.py b/mesonbuild/wrap/wrap.py
index a0a4801..a4e0b25 100644
--- a/mesonbuild/wrap/wrap.py
+++ b/mesonbuild/wrap/wrap.py
@@ -26,6 +26,7 @@ import subprocess
 import sys
 import configparser
 import typing as T
+import textwrap
 
 from .._pathlib import Path
 from . import WrapMode
@@ -97,25 +98,47 @@ class PackageDefinition:
         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
-        if self.name.endswith('.wrap'):
-            self.name = self.name[:-5]
+        self.has_wrap = self.basename.endswith('.wrap')
+        self.name = self.basename[:-5] if self.has_wrap else self.basename
+        self.directory = self.name
         self.provided_deps[self.name] = None
-        if fname.endswith('.wrap'):
-            self.parse_wrap(fname)
+        if self.has_wrap:
+            self.parse_wrap()
         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')
         if self.type and self.type not in ALL_TYPES:
             raise WrapException('Unknown wrap type {!r}'.format(self.type))
+        self.filesdir = os.path.join(os.path.dirname(self.filename), 'packagefiles')
 
-    def parse_wrap(self, fname: str) -> None:
+    def parse_wrap(self) -> None:
         try:
             self.config = configparser.ConfigParser(interpolation=None)
-            self.config.read(fname)
+            self.config.read(self.filename)
         except configparser.Error:
             raise WrapException('Failed to parse {}'.format(self.basename))
         self.parse_wrap_section()
+        if self.type == 'redirect':
+            # [wrap-redirect] have a `filename` value pointing to the real wrap
+            # file we should parse instead. It must be relative to the current
+            # wrap file location and must be in the form foo/subprojects/bar.wrap.
+            dirname = Path(self.filename).parent
+            fname = Path(self.values['filename'])
+            for i, p in enumerate(fname.parts):
+                if i % 2 == 0:
+                    if p == '..':
+                        raise WrapException('wrap-redirect filename cannot contain ".."')
+                else:
+                    if p != 'subprojects':
+                        raise WrapException('wrap-redirect filename must be in the form foo/subprojects/bar.wrap')
+            if fname.suffix != '.wrap':
+                raise WrapException('wrap-redirect filename must be a .wrap file')
+            fname = dirname / fname
+            if not fname.is_file():
+                raise WrapException('wrap-redirect filename does not exist')
+            self.filename = str(fname)
+            self.parse_wrap()
+            return
         self.parse_provide_section()
 
     def parse_wrap_section(self) -> None:
@@ -164,11 +187,12 @@ def get_directory(subdir_root: str, packagename: str) -> str:
     return packagename
 
 class Resolver:
-    def __init__(self, subdir_root: str, wrap_mode: WrapMode = WrapMode.default) -> None:
+    def __init__(self, source_dir: str, subdir: str, wrap_mode: WrapMode = WrapMode.default) -> None:
+        self.source_dir = source_dir
+        self.subdir = subdir
         self.wrap_mode = wrap_mode
-        self.subdir_root = subdir_root
+        self.subdir_root = os.path.join(source_dir, subdir)
         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]
@@ -208,6 +232,14 @@ class Resolver:
                     raise WrapException(m.format(k, wrap.basename, prev_wrap.basename))
                 self.provided_programs[k] = wrap
 
+    def merge_wraps(self, other_resolver: 'Resolver') -> None:
+        for k, v in other_resolver.wraps.items():
+            self.wraps.setdefault(k, v)
+        for k, v in other_resolver.provided_deps.items():
+            self.provided_deps.setdefault(k, v)
+        for k, v in other_resolver.provided_programs.items():
+            self.provided_programs.setdefault(k, v)
+
     def find_dep_provider(self, packagename: str) -> T.Optional[T.Union[str, T.List[str]]]:
         # Return value is in the same format as fallback kwarg:
         # ['subproject_name', 'variable_name'], or 'subproject_name'.
@@ -235,7 +267,29 @@ class Resolver:
             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)
+
+        if self.wrap.has_wrap:
+            # We have a .wrap file, source code will be placed into main
+            # project's subproject_dir even if the wrap file comes from another
+            # subproject.
+            self.dirname = os.path.join(self.subdir_root, self.directory)
+            # Check if the wrap comes from the main project.
+            main_fname = os.path.join(self.subdir_root, self.wrap.basename)
+            if self.wrap.filename != main_fname:
+                rel = os.path.relpath(self.wrap.filename, self.source_dir)
+                mlog.log('Using', mlog.bold(rel))
+                # Write a dummy wrap file in main project that redirect to the
+                # wrap we picked.
+                with open(main_fname, 'w') as f:
+                    f.write(textwrap.dedent('''\
+                        [wrap-redirect]
+                        filename = {}
+                        '''.format(os.path.relpath(self.wrap.filename, self.subdir_root))))
+        else:
+            # No wrap file, it's a dummy package definition for an existing
+            # directory. Use the source code in place.
+            self.dirname = self.wrap.filename
+        rel_path = os.path.relpath(self.dirname, self.source_dir)
 
         meson_file = os.path.join(self.dirname, 'meson.build')
         cmake_file = os.path.join(self.dirname, 'CMakeLists.txt')
@@ -245,9 +299,9 @@ class Resolver:
 
         # The directory is there and has meson.build? Great, use it.
         if method == 'meson' and os.path.exists(meson_file):
-            return self.directory
+            return rel_path
         if method == 'cmake' and os.path.exists(cmake_file):
-            return self.directory
+            return rel_path
 
         # Check if the subproject is a git submodule
         self.resolve_git_submodule()
@@ -276,7 +330,7 @@ class Resolver:
         if method == 'cmake' and not os.path.exists(cmake_file):
             raise WrapException('Subproject exists but has no CMakeLists.txt file')
 
-        return self.directory
+        return rel_path
 
     def check_can_download(self) -> None:
         # Don't download subproject data based on wrap file if requested.
@@ -487,7 +541,7 @@ class Resolver:
         else:
             from ..interpreterbase import FeatureNew
             FeatureNew('Local wrap patch files without {}_url'.format(what), '0.55.0').use(self.current_subproject)
-            path = Path(self.filesdir) / filename
+            path = Path(self.wrap.filesdir) / filename
 
             if not path.exists():
                 raise WrapException('File "{}" does not exist'.format(path))
@@ -511,7 +565,7 @@ class Resolver:
             from ..interpreterbase import FeatureNew
             FeatureNew('patch_directory', '0.55.0').use(self.current_subproject)
             patch_dir = self.wrap.values['patch_directory']
-            src_dir = os.path.join(self.filesdir, patch_dir)
+            src_dir = os.path.join(self.wrap.filesdir, patch_dir)
             if not os.path.isdir(src_dir):
                 raise WrapException('patch directory does not exists: {}'.format(patch_dir))
             self.copy_tree(src_dir, self.dirname)
diff --git a/run_unittests.py b/run_unittests.py
index 22e7cdc..f6adcee 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -69,6 +69,8 @@ import mesonbuild.modules.pkgconfig
 
 from mesonbuild.mtest import TAPParser, TestResult
 
+from mesonbuild.wrap.wrap import PackageDefinition, WrapException
+
 from run_tests import (
     Backend, FakeBuild, FakeCompilerOptions,
     ensure_backend_detects_changes, exe_suffix, get_backend_commands,
@@ -4183,6 +4185,16 @@ recommended as it is not supported on some platforms''')
                     'name': 'sub_novar',
                     'version': '1.0',
                 },
+                {
+                    'descriptive_name': 'subsub',
+                    'name': 'subsub',
+                    'version': 'undefined'
+                },
+                {
+                    'descriptive_name': 'subsubsub',
+                    'name': 'subsubsub',
+                    'version': 'undefined'
+                },
             ]
         }
         res['subprojects'] = sorted(res['subprojects'], key=lambda i: i['name'])
@@ -5156,6 +5168,52 @@ recommended as it is not supported on some platforms''')
         out = self.init(testdir)
         self.assertNotRegex(out, r'WARNING')
 
+    def test_wrap_redirect(self):
+        redirect_wrap = os.path.join(self.builddir, 'redirect.wrap')
+        real_wrap = os.path.join(self.builddir, 'foo/subprojects/real.wrap')
+        os.makedirs(os.path.dirname(real_wrap))
+
+        # Invalid redirect, filename must have .wrap extension
+        with open(redirect_wrap, 'w') as f:
+            f.write(textwrap.dedent('''
+                [wrap-redirect]
+                filename = foo/subprojects/real.wrapper
+                '''))
+        with self.assertRaisesRegex(WrapException, 'wrap-redirect filename must be a .wrap file'):
+            PackageDefinition(redirect_wrap)
+
+        # Invalid redirect, filename cannot be in parent directory
+        with open(redirect_wrap, 'w') as f:
+            f.write(textwrap.dedent('''
+                [wrap-redirect]
+                filename = ../real.wrap
+                '''))
+        with self.assertRaisesRegex(WrapException, 'wrap-redirect filename cannot contain ".."'):
+            PackageDefinition(redirect_wrap)
+
+        # Invalid redirect, filename must be in foo/subprojects/real.wrap
+        with open(redirect_wrap, 'w') as f:
+            f.write(textwrap.dedent('''
+                [wrap-redirect]
+                filename = foo/real.wrap
+                '''))
+        with self.assertRaisesRegex(WrapException, 'wrap-redirect filename must be in the form foo/subprojects/bar.wrap'):
+            wrap = PackageDefinition(redirect_wrap)
+
+        # Correct redirect
+        with open(redirect_wrap, 'w') as f:
+            f.write(textwrap.dedent('''
+                [wrap-redirect]
+                filename = foo/subprojects/real.wrap
+                '''))
+        with open(real_wrap, 'w') as f:
+            f.write(textwrap.dedent('''
+                [wrap-git]
+                url = http://invalid
+                '''))
+        wrap = PackageDefinition(redirect_wrap)
+        self.assertEqual(wrap.get('url'), 'http://invalid')
+
 class FailureTests(BasePlatformTests):
     '''
     Tests that test failure conditions. Build files here should be dynamically
@@ -5365,16 +5423,16 @@ class FailureTests(BasePlatformTests):
            correct message when the fallback subproject is found but the
            variable inside it is not.
         4. A fallback dependency is found from the subproject parsed in (3)
-        5. The correct message is outputted when the .wrap file is missing for
-           a sub-subproject.
+        5. A wrap file from a subproject is used but fails because it does not
+           contain required keys.
         '''
         tdir = os.path.join(self.unit_test_dir, '20 subproj dep variables')
         out = self.init(tdir, inprocess=True)
         self.assertRegex(out, r"Subproject directory not found and .*nosubproj.wrap.* file not found")
         self.assertRegex(out, r'Function does not take positional arguments.')
-        self.assertRegex(out, r'WARNING:.* Dependency .*subsubproject.* not found but it is available in a sub-subproject.')
-        self.assertRegex(out, r'Subproject directory not found and .*subsubproject.wrap.* file not found')
+        self.assertRegex(out, r'Dependency .*somenotfounddep.* from subproject .*subprojects/somesubproj.* found: .*NO.*')
         self.assertRegex(out, r'Dependency .*zlibproxy.* from subproject .*subprojects.*somesubproj.* found: .*YES.*')
+        self.assertRegex(out, r'Missing key .*source_filename.* in subsubproject.wrap')
 
     def test_exception_exit_status(self):
         '''
diff --git a/test cases/common/102 subproject subdir/meson.build b/test cases/common/102 subproject subdir/meson.build
index a891ca9..36e48a7 100644
--- a/test cases/common/102 subproject subdir/meson.build
+++ b/test cases/common/102 subproject subdir/meson.build
@@ -54,3 +54,14 @@ assert(d.type_name() == 'internal')
 # Using gobject-2.0 here because some CI runners have it installed.
 d = dependency('gobject-2.0', required : false)
 assert(not d.found())
+
+# Verify that implicit fallback works because subprojects/sub_implicit/subprojects/subsub
+# directory exists.
+d = dependency('subsub')
+assert(d.found(), 'Should be able to fallback to sub-subproject')
+
+# Verify that implicit fallback works because
+# subprojects/sub_implicit/subprojects/subsub/subprojects/subsubsub.wrap
+# file exists.
+d = dependency('subsubsub')
+assert(d.found(), 'Should be able to fallback to sub-sub-subproject')
diff --git a/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/meson.build b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/meson.build
new file mode 100644
index 0000000..18e2cea
--- /dev/null
+++ b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/meson.build
@@ -0,0 +1,3 @@
+project('subsub')
+
+meson.override_dependency('subsub', declare_dependency())
diff --git a/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/packagefiles/subsubsub-1.0.zip b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/packagefiles/subsubsub-1.0.zip
new file mode 100644
index 0000000..dfb7576
--- /dev/null
+++ b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/packagefiles/subsubsub-1.0.zip
diff --git a/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/subsubsub.wrap b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/subsubsub.wrap
new file mode 100644
index 0000000..6567ed0
--- /dev/null
+++ b/test cases/common/102 subproject subdir/subprojects/sub_implicit/subprojects/subsub/subprojects/subsubsub.wrap
@@ -0,0 +1,4 @@
+[wrap-file]
+directory = subsubsub-1.0
+source_filename = subsubsub-1.0.zip
+source_hash = c073a96b7251937e53216578f6f03d91b84816618a0f1ce3ecfb867beddf1498
diff --git a/test cases/failing/16 extract from subproject/test.json b/test cases/failing/16 extract from subproject/test.json
index 78d45a5..2e32904 100644
--- a/test cases/failing/16 extract from subproject/test.json
+++ b/test cases/failing/16 extract from subproject/test.json
@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/16 extract from subproject/meson.build:6:0: ERROR: Tried to extract objects from a subproject target."
+      "line": "test cases/failing/16 extract from subproject/meson.build:6:0: ERROR: Tried to extract objects from a different subproject."
     }
   ]
 }