Add fish shell completion

Makefile.am

@@ -144,6 +144,10 @@ zshcompletiondir = $(datadir)/zsh/site-functions
 zshcompletion_DATA = completion/_flatpak
 EXTRA_DIST += $(zshcompletion_DATA)
 
+fishcompletiondir = $(datadir)/fish/vendor_completions.d
+fishcompletion_DATA = completion/flatpak.fish
+EXTRA_DIST += $(fishcompletion_DATA)
+
 profiledir = $(PROFILE_DIR)
 profile_DATA = profile/flatpak.sh
 EXTRA_DIST += $(profile_DATA)

completion/flatpak.fish

@@ -0,0 +1,47 @@
+function __fish_complete_flatpak
+    set current_cmd (commandline -p)
+    set current_position (commandline -C)
+    set current_token (commandline -ct)
+    echo "CMD \"$current_cmd\" POS \"$current_position\" TOK \"$current_token\"" >> /tmp/fish-flatpak-debug.txt
+    command flatpak complete "$current_cmd" "$current_position" "$current_token" | while read fp_sugg
+        echo "SUG \"$fp_sugg\"" >> /tmp/fish-flatpak-debug.txt
+        set sugg (string trim -- "$fp_sugg")
+        switch "$sugg"
+            case __FLATPAK_FILE
+                __fish_complete_path "$current_token"
+            case __FLATPAK_BUNDLE_FILE
+                __fish_complete_suffix "$current_token" '.flatpak'
+            case __FLATPAK_BUNDLE_OR_REF_FILE
+                __fish_complete_suffix "$current_token" '.flatpak'
+                __fish_complete_suffix "$current_token" '.flatpakref'
+            case __FLATPAK_DIR
+                __fish_complete_directories "$current_token"
+            case '*'
+                # completing a value for option
+                if string match -- "--*=" "$current_token"
+                    echo "$current_token$sugg"
+                else
+                    echo "$sugg"
+                end
+        end
+    end
+    return
+end
+
+function __fish_flatpak_complete_files
+    if __fish_seen_subcommand_from run build
+        set pos_args 0
+        for t in (commandline -co)
+            if string match --invert -- "-*" "$t"
+                set pos_args (math "$pos_args+1")
+            end
+        end
+        if test $pos_args -gt 2
+            return 0
+        end
+    end
+    return 1
+end
+
+complete -c flatpak -f -n "not __fish_flatpak_complete_files" -a '(__fish_complete_flatpak)'
+complete -c flatpak -n "__fish_flatpak_complete_files" -a '(__fish_complete_flatpak)'