From 4cd29f9a85b2d9402fb864a0c05ecc728619f42f Mon Sep 17 00:00:00 2001
From: Henry <henryoberholtzer@gmail.com>
Date: Fri, 9 Jan 2026 18:08:56 -0800
Subject: [PATCH] Fixes and refinements, 100% coverage.

---
 beetsplug/fromfilename.py         | 28 +++++++++++++---------------
 docs/plugins/fromfilename.rst     |  2 +-
 test/plugins/test_fromfilename.py |  2 +-
 3 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/beetsplug/fromfilename.py b/beetsplug/fromfilename.py
index 35b35bec9..a95d63b19 100644
--- a/beetsplug/fromfilename.py
+++ b/beetsplug/fromfilename.py
@@ -112,11 +112,12 @@ RE_BRACKETS = re.compile(r"[\(\[\{].*?[\)\]\}]")
 
 
 class FilenameMatch(MutableMapping[str, str | None]):
-    def __init__(self, matches: dict[str, str] = {}) -> None:
+    def __init__(self, matches: dict[str, str] | None = None) -> None:
         self._matches: dict[str, str] = {}
-        for key, value in matches.items():
-            if value is not None:
-                self._matches[key.lower()] = str(value).strip()
+        if matches:
+            for key, value in matches.items():
+                if value is not None:
+                    self._matches[key.lower()] = str(value).strip()
 
     def __getitem__(self, key: str) -> str | None:
         return self._matches.get(key, None)
@@ -159,13 +160,13 @@ class FromFilenamePlugin(BeetsPlugin):
             }
         )
         self.fields = set(self.config["fields"].as_str_seq())
-        # Evaluate the user patterns to expand the fields
         self.file_patterns = self._user_pattern_to_regex(
             self.config["patterns"]["file"].as_str_seq()
         )
         self.folder_patterns = self._user_pattern_to_regex(
             self.config["patterns"]["folder"].as_str_seq()
         )
+        self.session_fields: set[str] = set()
         self.register_listener("import_task_start", self.filename_task)
 
     @cached_property
@@ -209,16 +210,13 @@ class FromFilenamePlugin(BeetsPlugin):
         If no fields are detect that need to be processed,
         return false to shortcut the plugin.
         """
-        remove = set()
+        self.session_fields = set({})
         for field in self.fields:
             # If any field is a bad field
             if any([True for item in items if self._bad_field(item[field])]):
-                continue
-            else:
-                remove.add(field)
-        self.fields = self.fields - remove
+                self.session_fields.add(field)
         # If all fields have been removed, there is nothing to do
-        if not len(self.fields):
+        if not len(self.session_fields):
             return False
         return True
 
@@ -335,13 +333,13 @@ class FromFilenamePlugin(BeetsPlugin):
         track_matches: dict[Item, FilenameMatch],
     ) -> None:
         """Apply all valid matched fields to all items in the match dictionary."""
-        match = album_match
+        match = dict(album_match._matches)
         for item in track_matches:
-            match.update(track_matches[item])
+            match.update(track_matches[item]._matches)
             found_data: dict[str, int | str] = {}
             self._log.debug(f"Attempting keys: {match.keys()}")
             for key in match.keys():
-                if key in self.fields:
+                if key in self.session_fields:
                     old_value = item.get(key)
                     new_value = match[key]
                     if self._bad_field(old_value) and new_value:
@@ -445,7 +443,7 @@ class FromFilenamePlugin(BeetsPlugin):
         for f in fields:
             pattern = re.sub(rf"\\\${f}", f"(?P<{f}>.+)", pattern)
             self.fields.add(f)
-        return rf"{pattern}"
+        return pattern
 
     @staticmethod
     def _mutate_string(text: str, span: tuple[int, int]) -> str:
diff --git a/docs/plugins/fromfilename.rst b/docs/plugins/fromfilename.rst
index fae2cf12d..98ea92f94 100644
--- a/docs/plugins/fromfilename.rst
+++ b/docs/plugins/fromfilename.rst
@@ -63,7 +63,7 @@ Default
     of the file.
 
     If ``fromfilename`` can't match the entire string to the given pattern, it will
-    falls back to the default pattern.
+    fall back to the default pattern.
 
     The following custom patterns will match this path and retrieve the specified
     fields.
diff --git a/test/plugins/test_fromfilename.py b/test/plugins/test_fromfilename.py
index 8800ee04d..4f09deee1 100644
--- a/test/plugins/test_fromfilename.py
+++ b/test/plugins/test_fromfilename.py
@@ -746,7 +746,7 @@ class TestFromFilename(PluginMixin):
             ) as mock:
                 f = FromFilenamePlugin()
                 f.filename_task(task, Session())
-                assert len(f.fields) == 1
+                assert len(f.session_fields) == 1
                 assert "title" in f.fields
                 mock.assert_called()