Make library folder discovery case-insensitive

Steam will go out of its way to perform certain operations
case-insensitively. For example, when a Steam library folder has been
added, Steam will automatically discover it even if it is renamed to ALL
CAPS. The configuration will not be updated to use the new name,
however, so we have to perform this search ourselves as well.

Adjust Steam library folder discovery to account for this.

Refs #433

Author: Matoking

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+### Fixed
+ - Fix Steam library folder discovery by using case-insensitive directory name matching
+
 ## [1.13.0] - 2025-08-11
 ### Added
  - Improve compatibility by setting additional Proton related environment variables when applicable

src/protontricks/steam.py

@@ -1016,6 +1016,54 @@ def parse_library_folders(data):
             if is_library_folder_xdg_steam and is_flatpak_steam:
                 path = flatpak_steam_path
 
+            # Steam matches library folders case-insensitively.
+            candidates = [
+                candidate
+                for candidate in path.parent.iterdir()
+                if candidate.name.lower() == path.name.lower()
+            ]
+
+            logger.debug(
+                "Following candidates found for the Steam library path %s: %s",
+                path, candidates
+            )
+
+            if not candidates:
+                logger.warning(
+                    "Steam library folder %s in Steam configuration does not "
+                    "exist",
+                    path
+                )
+                continue
+
+            # In case of multiple matches, prioritize those that contain
+            # a 'steamapps' subdirectory
+            candidates.sort(
+                key=lambda path: any(
+                    path.name.lower() == "steamapps"
+                    for path in path.iterdir()
+                ),
+                reverse=True
+            )
+
+            # In case multiple directories match, pick the first one,
+            # log a warning and hope for the best
+            if len(candidates) > 1:
+                logger.warning(
+                    "Multiple Steam library folders with name %s were found. "
+                    "Selecting %s.",
+                    path, candidates[0]
+                )
+
+            if candidates[0].name != path.name:
+                logger.warning(
+                    "Steam library folder %s in configuration differs from "
+                    "found path %s. Was this directory renamed?",
+                    path, candidates[0]
+                )
+
+            path = candidates[0]
+
             logger.debug(
                 "Found Steam library folder %s. Is Flatpak path: %s, "
                 "Is XDG Steam path: %s.",

tests/test_steam.py

@@ -527,6 +527,57 @@ def test_get_steam_lib_paths_adjust_flatpak_steam_path(
         assert len(library_paths) == 1
         assert str(library_paths[0]) == str(flatpak_steam_dir)
 
+    def test_get_steam_lib_paths_multiple_case_insensitive_matches(
+            self, steam_dir, steam_library_factory, home_dir, caplog):
+        """
+        Retrieve Steam library folders ensuring that when multiple
+        case-insensitive matches are found for one configured path, the first
+        path with 'steamapps' directory inside it is picked and a warning
+        is printed
+        """
+        library_dir = steam_library_factory("TestLibrary")
+        shutil.copytree(library_dir, library_dir.parent / "TESTLIBRARY")
+        shutil.copytree(library_dir, library_dir.parent / "testlibrary")
+
+        # Add 'steamapps' subdir to 'TESTLIBRARY' to ensure it's prioritized
+        expected_path = library_dir.parent / "TESTLIBRARY"
+        (expected_path / "steamapps").mkdir()
+
+        lib_paths = get_steam_lib_paths(steam_dir)
+
+        assert expected_path in lib_paths
+        assert library_dir not in lib_paths
+
+        assert any(
+            record for record in caplog.records
+            if record.levelname == "WARNING"
+            and f"Multiple Steam library folders with name {library_dir}"
+            in record.getMessage()
+        )
+
+    def test_get_steam_lib_paths_renamed_library(
+            self, steam_dir, steam_library_factory, home_dir, caplog):
+        """
+        Retrieve Steam library folders ensuring that a renamed library folder
+        can be found if it still matches the old name case-insensitively
+
+        Regression test for #433
+        """
+        library_dir = steam_library_factory("TestLibrary")
+        library_dir.rename(library_dir.parent / "testlibrary")
+
+        lib_paths = get_steam_lib_paths(steam_dir)
+
+        assert library_dir not in lib_paths
+        assert library_dir.parent / "testlibrary" in lib_paths
+
+        assert any(
+            record for record in caplog.records
+            if record.levelname == "WARNING"
+            and f"Steam library folder {library_dir} in configuration"
+            in record.getMessage()
+        )
+
 
 class TestFindAppidProtonPrefix:
     def test_find_appid_proton_prefix_steamapps_case(