fix: Interpret custom_dir relative to current directory, not config directory

The custom theme dir handling was not working in case the mkdocs config
  file was not in the top-level directory. Since mkdocs itself seems only
  to work in the top-level directory, this PR modifies mkdocs_semiliterate
  to interpret custom theme dirs relative to the current directory.

  Also, improves the harmonization between current mkdocs_simple_plugin
  code and this code.

  Resolves #28.

mkdocs_semiliterate/plugin.py

@@ -14,6 +14,9 @@ of the `simple` plugin.)
 
 from mkdocs import utils
 from mkdocs.config import config_options
+from mkdocs.config.defaults import MkDocsConfig
+from mkdocs.structure.files import File, Files
+
 from mkdocs_simple_plugin.semiliterate import (
     Semiliterate, LazyFile, ExtractionPattern, StreamExtract)
 from mkdocs_simple_plugin.simple import (Simple, SimplePath)
@@ -23,6 +26,7 @@ import os
 import re
 import subprocess
 import sys
+import time
 import tempfile
 import yaml
 
@@ -352,12 +356,13 @@ terminate: '^\s*\)'
         saved_includes = self.config['include']
         new_config = super().on_config(config, **kwargs)
         self.config['saved_includes'] = saved_includes
-        cfpath = os.path.dirname(config.config_file_path)
+        curpath = os.path.abspath('.')
         self.custom_dir = None
         for themedir in config['theme'].dirs:
-            common = os.path.commonpath([cfpath, themedir])
-            if common == cfpath:
-                self.custom_dir = os.path.relpath(themedir, cfpath)
+            common = os.path.commonpath(
+                [os.path.abspath('.'), os.path.abspath(themedir)])
+            if common == curpath:
+                self.custom_dir = os.path.relpath(themedir, curpath)
                 newthemedir = os.path.join(
                     self.config['build_dir'], self.custom_dir)
                 utils.log.debug(
@@ -368,7 +373,39 @@ terminate: '^\s*\)'
                 break
         return new_config
 
-    def on_files(self, files, config):
+    # Override rather than extend so that we use Semisimple instead of simple
+    # Note code must track mkdocs_simple_plugin, with the added section for
+    # the custom_dir at the bottom.
+    def on_files(self, files: Files, /, *,
+                 config: MkDocsConfig):
+        """Update files based on plugin settings."""
+        # Configure Semisimple
+        semisimple = Semisimple(**self.config)
+
+        # Save paths to add to watch if serving
+        do_copy = self.config["copy"]
+        self.paths = semisimple.build_docs(
+            self.dirty, self.last_build_time, do_copy)
+        self.last_build_time = time.time()
+
+        if not self.config["merge_docs_dir"]:
+            # If not merging, remove files that are from the docs dir
+            abs_docs_dir = os.path.abspath(config['docs_dir'])
+            for _, file in files.src_uris.items():
+                if file.abs_src_path.startswith(abs_docs_dir):
+                    files.remove(file)
+
+        for path in self.paths:
+            file = File(
+                src_dir=os.path.abspath(path.output_root),
+                path=path.output_relpath,
+                dest_dir=config.site_dir,
+                use_directory_urls=config["use_directory_urls"]
+            )
+            if file.src_uri in files.src_uris:
+                files.remove(file)
+            files.append(file)
+
         # If we designated a subdirectory for the theme, ignore files in it
         if self.custom_dir:
             sources = files.src_paths
@@ -379,15 +416,7 @@ terminate: '^\s*\)'
                         + f"from theme directory {self.custom_dir}")
                     files.remove(sources[path])
 
-    def on_pre_build(self, *, config):
-        """Build documentation directory with files according to settings."""
-        semisimple = Semisimple(**self.config)
-
-        # Merge docs
-        if self.config["merge_docs_dir"]:
-            semisimple.merge_docs(self.orig_docs_dir)
-        # Copy all of the valid doc files into build_docs_dir
-        self.paths = semisimple.build_docs()
+        return files
 
 
 class Semisimple(Simple):