From feb9054122736224fca99021218d2a14367d95a1 Mon Sep 17 00:00:00 2001
From: Kadir Can Ozden <101993364+bysiber@users.noreply.github.com>
Date: Fri, 20 Feb 2026 15:30:40 +0300
Subject: [PATCH] Fix KeyError in detailed_match_files for unmatched negation
 patterns
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When a negation pattern (include=False) matches files that were not
previously added by an inclusion pattern, the 'del return_files[file]'
raises a KeyError.

This happens when a negation pattern is broader than the preceding
inclusion patterns. For example, '*.txt' followed by 'checkout -b fix/detailed-match-files-keyerror master.log' — the
negation matches .log files that were never included.

Add a membership check before deletion to skip files that aren't in
the result set, consistent with how gitignore negation works (it can
only un-ignore files that were previously ignored).
---
 pathspec/util.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pathspec/util.py b/pathspec/util.py
index ea2dbee..79f6b56 100644
--- a/pathspec/util.py
+++ b/pathspec/util.py
@@ -156,7 +156,8 @@ def detailed_match_files(
 			else:
 				# Remove files.
 				for file in result_files:
-					del return_files[file]
+					if file in return_files:
+						del return_files[file]
 
 	return return_files