Feature: Desktop Entry Locator

Purpose

The project must find the *.desktop files that the GNOME desktop would find, using the same directory order and identifier rules, so that a reader can resolve a desktop file by identifier and can enumerate installed entries.

The search rules implemented here are recorded in documents/09-desktop-file-search-paths.md.

Requirements

• The locator must build the application search path from $XDG_DATA_HOME and $XDG_DATA_DIRS.
• The locator must use $HOME/.local/share when $XDG_DATA_HOME is unset or empty.
• The locator must use /usr/local/share:/usr/share when $XDG_DATA_DIRS is unset or empty.
• The locator must ignore a relative path in either variable.
• The locator must append the applications component to each data directory.
• The locator must place the user data directory before every system data directory.
• The locator must preserve the order of $XDG_DATA_DIRS.
• The locator must skip a directory that does not exist and must not report it as an error.
• The locator must build the autostart search path from $XDG_CONFIG_HOME and $XDG_CONFIG_DIRS.
• The locator must use $HOME/.config when $XDG_CONFIG_HOME is unset or empty.
• The locator must use /etc/xdg when $XDG_CONFIG_DIRS is unset or empty.
• The locator must not append the applications component to an autostart directory.
• The locator must expose the ordered list of directories it searched.
• The locator must compute a desktop file identifier from a path relative to a data directory.
• The locator must remove the applications/ prefix and replace / with - when computing an identifier.
• The locator must return no identifier for a file outside an applications component.
• The locator must resolve an identifier by searching the path in order and returning the first match.
• The locator must support the prefix-to-subdirectory mapping, so that an identifier kde-foo.desktop also matches <dir>/applications/kde/foo.desktop.
• The locator must enumerate entries with a first-match-wins rule for duplicate identifiers.
• The locator must not require any environment variable to be set.
• The locator must be read-only and must not create, modify, or delete any file.

Behavior

• Given no environment overrides, the application search path starts with $HOME/.local/share/applications and ends with the applications subdirectory of every $XDG_DATA_DIRS entry.
• Given a temporary $XDG_DATA_HOME with one desktop file, enumeration returns exactly that entry.
• Given the same identifier in two data directories, resolution returns the file in the earlier directory.
• Given an identifier with a dash, resolution also finds the nested subdirectory form.
• Given an environment with a relative $XDG_DATA_DIRS entry, that entry is skipped.

Dependencies

• None.
• The locator supplies paths to the AppImage Reader and the Desktop Entry Reader, but does not depend on them.