vs2010backend: avoid duplicated directory structure in vcxproj.filters

Root the vcxproj.filters at the directory containing the meson.build
defining the target.

Co-authored-by: Joshua Ashton <joshua@froggi.es>

mesonbuild/backend/vs2010backend.py

@@ -20,7 +20,7 @@ import xml.dom.minidom
 import xml.etree.ElementTree as ET
 import uuid
 import typing as T
-from pathlib import Path, PurePath
+from pathlib import Path, PurePath, PureWindowsPath
 import re
 from collections import Counter
 
@@ -1809,8 +1809,76 @@ class Vs2010Backend(backends.Backend):
             # build system as possible.
             self.add_target_deps(root, target)
         self._prettyprint_vcxproj_xml(ET.ElementTree(root), ofname)
+        if self.environment.coredata.get_option(OptionKey('layout')) == 'mirror':
+            self.gen_vcxproj_filters(target, ofname)
         return True
 
+    def gen_vcxproj_filters(self, target, ofname):
+        # Generate pitchfork of filters based on directory structure.
+        root = ET.Element('Project', {'ToolsVersion': '4.0',
+                                      'xmlns': 'http://schemas.microsoft.com/developer/msbuild/2003'})
+        filter_folders = ET.SubElement(root, 'ItemGroup')
+        filter_items = ET.SubElement(root, 'ItemGroup')
+        mlog.debug(f'Generating vcxproj filters {target.name}.')
+
+        def relative_to_defined_in(file):
+            # Get the relative path to file's directory from the location of the meson.build that defines this target.
+            return os.path.dirname(self.relpath(PureWindowsPath(file.subdir, file.fname), self.get_target_dir(target)))
+
+        found_folders_to_filter = {}
+        all_files = target.sources + target.extra_files
+
+        # Build a dictionary of all used relative paths (i.e. from the meson.build defining this target)
+        # for all sources.
+        for i in all_files:
+            if not os.path.isabs(i.fname):
+                dirname = relative_to_defined_in(i)
+                if dirname:
+                    found_folders_to_filter[dirname] = ''
+
+        # Now walk up each of those relative paths checking for empty intermediate dirs to generate the filter.
+        for folder in found_folders_to_filter:
+            dirname = folder
+            filter = ''
+
+            while dirname:
+                basename = os.path.basename(dirname)
+
+                if filter == '':
+                    filter = basename
+                else:
+                    # Use '/' to squash empty dirs. To actually get a '\', use '%255c'.
+                    filter = basename + ('\\' if dirname in found_folders_to_filter else '/') + filter
+
+                dirname = os.path.dirname(dirname)
+
+            # Don't add an empty filter, breaks all other (?) filters.
+            if filter != '':
+                found_folders_to_filter[folder] = filter
+                filter_element = ET.SubElement(filter_folders, 'Filter', {'Include': filter})
+                uuid_element = ET.SubElement(filter_element, 'UniqueIdentifier')
+                uuid_element.text = '{' + str(uuid.uuid4()).upper() + '}'
+
+        sources, headers, objects, _ = self.split_sources(all_files)
+        down = self.target_to_build_root(target)
+
+        def add_element(type_name, elements):
+            for i in elements:
+                if not os.path.isabs(i.fname):
+                    dirname = relative_to_defined_in(i)
+
+                    if dirname and dirname in found_folders_to_filter:
+                        relpath = os.path.join(down, i.rel_to_builddir(self.build_to_src))
+                        target_element = ET.SubElement(filter_items, type_name, {'Include': relpath})
+                        filter_element = ET.SubElement(target_element, 'Filter')
+                        filter_element.text = found_folders_to_filter[dirname]
+
+        add_element('ClCompile', sources)
+        add_element('ClInclude', headers)
+        add_element('Object', objects)
+
+        self._prettyprint_vcxproj_xml(ET.ElementTree(root), ofname + '.filters')
+
     def gen_regenproj(self):
         # To fully adapt the REGEN work for a 'genvslite' solution, to check timestamps, settings, and regenerate the
         # '[builddir]_vs' solution/vcxprojs, as well as regenerating the accompanying buildtype-suffixed ninja build