feat(deps): support upgrading fish itself via cargo install fish

Fish 4.x is a Rust rewrite published to crates.io as 'fish'. Added the
crate to the catalog so fish-deps update will run cargo install --force
fish to upgrade it. A yellow restart reminder is printed after the
upgrade since the new binary won't take effect until the shell restarts.

README warning updated to mention cargo install fish as the upgrade
path for users stuck on Fish 3.x.

README.md

@@ -491,19 +491,28 @@ Named context shortcuts (e.g. `dcr`, `dck`) live in `~/.config/.user-dots/fish/l
 
 ### Required
 
-| Tool | Purpose |
-|---|---|
-| [Fish](https://fishshell.com/) | Shell |
-| [Fisher](https://github.com/jorgebucaran/fisher) | Plugin manager |
-| [Starship](https://starship.rs/) | Prompt |
-| [fzf](https://github.com/junegunn/fzf) | Fuzzy finder |
-| [zoxide](https://github.com/ajeetdsouza/zoxide) | Smart directory jumper |
-| [direnv](https://direnv.net/) | Per-directory env loading |
+| Tool | Version | Purpose |
+|---|---|---|
+| [Fish](https://fishshell.com/) | **≥ 4.0** | Shell |
+| [Fisher](https://github.com/jorgebucaran/fisher) | any | Plugin manager |
+| [Starship](https://starship.rs/) | any | Prompt |
+| [fzf](https://github.com/junegunn/fzf) | any | Fuzzy finder |
+| [zoxide](https://github.com/ajeetdsouza/zoxide) | any | Smart directory jumper |
+| [direnv](https://direnv.net/) | any | Per-directory env loading |
+
+> [!WARNING]
+> Fish **4.0 or newer is required.** This config uses `test` syntax and other constructs that are incompatible with Fish 3.x. Older versions will produce errors on startup.
+> If you are on an older Fish, you can upgrade via cargo (Fish 4.x is a Rust rewrite published to crates.io):
+> ```
+> cargo install fish
+> ```
+> Or run `fish-deps update` once cargo is available — it will upgrade Fish via cargo automatically.
 
 ### Recommended
 
 | Tool | Replaces |
 |---|---|
+| [Rust / cargo](https://www.rust-lang.org/tools/install) | Build tool for Rust-based CLI replacements below |
 | [paru](https://github.com/Morganamilo/paru) / [yay](https://github.com/Jguer/yay) | AUR helper (Arch only) |
 | [eza](https://github.com/eza-community/eza) | `ls` (preferred) |
 | [lsd](https://github.com/lsd-rs/lsd) | `ls` (fallback) |

functions/_fish_deps_catalog.fish

@@ -2,38 +2,40 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
 # Populates parallel arrays describing every managed dependency.
-# Callers must invoke this function before accessing _fdc_* variables.
+# Callers must invoke this function before accessing _fdc_* arrays.
 #
 # Array layout (same index across all sets):
 #   _fdc_bins    — binary name (what `type -q` checks)
 #   _fdc_tiers   — req | int | rec
 #   _fdc_cargo   — cargo crate name, or "" if not on crates.io
 #   _fdc_pm      — system PM package name, or "" if not in repos
-#   _fdc_special — special install key: fisher-bootstrap | fzf-update |
-#                  pipx | curl-installer | "" (none)
+#   _fdc_special — special install key: rustup-installer | fisher-bootstrap |
+#                  fzf-update | paru-build | pipx | curl-installer | "" (none)
+#
+# cargo is listed second so it is installed before Rust tools that depend on it.
 function _fish_deps_catalog
     set -g _fdc_bins \
-        fish fisher starship fzf zoxide direnv paru \
+        fish cargo fisher starship fzf zoxide direnv paru \
         wakatime tailscale \
         eza lsd bat btop dust duf prettyping most rg lazygit lazydocker trash kitty wezterm
 
     set -g _fdc_tiers \
-        req req req req req req rec \
+        req req req req req req req rec \
         int int \
         rec rec rec rec rec rec rec rec rec rec rec rec rec rec
 
     set -g _fdc_cargo \
-        "" "" starship "" zoxide "" "" \
+        fish "" "" starship "" zoxide "" "" \
         "" "" \
         eza lsd bat "" du-dust "" "" "" ripgrep "" "" trash-cli "" ""
 
     set -g _fdc_pm \
-        fish "" starship fzf zoxide direnv "" \
+        fish cargo "" starship fzf zoxide direnv "" \
         wakatime tailscale \
         eza lsd bat btop dust duf prettyping most ripgrep lazygit lazydocker trash kitty wezterm
 
     set -g _fdc_special \
-        "" fisher-bootstrap curl-installer fzf-update "" "" "" \
+        "" rustup-installer fisher-bootstrap curl-installer fzf-update "" "" paru-build \
         pipx "" \
         "" "" "" "" "" "" "" "" "" "" "" "" "" ""
 end

functions/_fish_deps_install.fish

@@ -20,25 +20,31 @@ function _fish_deps_install
             set -l methods
             set -l method_labels
 
-            # Cargo first — preferred for Rust tools; gets the latest crate version
+            # Cargo — preferred for Rust tools; gets the latest crate version
             if test -n "$cargo_crate"
                 if type -q cargo
                     set -a methods cargo
                     set -a method_labels "cargo ($cargo_crate)"
                 else
                     set_color brblack
-                    echo "  note: cargo not found — install rustup for the latest $bin"
+                    echo "  note: cargo not found — install cargo first for the latest $bin"
                     set_color normal
                 end
             end
 
-            # System PM — after cargo so cargo is always the default when available
+            # rustup installer — listed before system PM so it is the default for cargo itself
+            if test "$special" = rustup-installer
+                set -a methods special-rustup
+                set -a method_labels "rustup installer (curl | sh)"
+            end
+
+            # System PM — after cargo/rustup so those are always the default when available
             if test -n "$pm_pkg"; and test -n "$pm"
                 set -a methods pm
                 set -a method_labels "$pm ($pm_pkg)"
             end
 
-            # Special methods
+            # Remaining special methods
             switch $special
                 case fzf-update
                     set -a methods special-fzf
@@ -49,6 +55,16 @@ function _fish_deps_install
                 case curl-installer
                     set -a methods special-curl
                     set -a method_labels "curl installer"
+                case paru-build
+                    # Only offered on Arch-based systems where pacman is present
+                    if type -q yay
+                        set -a methods special-yay-paru
+                        set -a method_labels "yay -S paru"
+                    end
+                    if type -q pacman
+                        set -a methods special-paru
+                        set -a method_labels "build from AUR (makepkg)"
+                    end
                 case pipx
                     if type -q pipx
                         set -a methods special-pipx
@@ -98,6 +114,8 @@ function _fish_deps_install
                     cargo install $cargo_crate
                 case pm
                     _fish_deps_pm_install $pm_pkg
+                case special-rustup
+                    curl https://sh.rustup.rs -sSf | sh
                 case special-fzf
                     fzf-update
                 case special-fisher
@@ -107,6 +125,15 @@ function _fish_deps_install
                     if test "$bin" = starship
                         curl -sS https://starship.rs/install.sh | sh
                     end
+                case special-yay-paru
+                    yay -S --noconfirm paru
+                case special-paru
+                    set -l _build_dir (mktemp -d)
+                    git clone https://aur.archlinux.org/paru.git $_build_dir
+                    and pushd $_build_dir
+                    and makepkg -si --noconfirm
+                    and popd
+                    rm -rf $_build_dir
                 case special-pipx
                     pipx install $bin
                 case special-pip

functions/_fish_deps_update.fish

@@ -28,6 +28,17 @@ function _fish_deps_update
         set -l pm_pkg       $_fdc_pm[$i]
         set -l special      $_fdc_special[$i]
 
+        # cargo: update via rustup
+        if test "$special" = rustup-installer
+            if type -q rustup
+                echo "Updating $bin..."
+                rustup update
+                set updated_any 1
+            end
+            set i (math $i + 1)
+            continue
+        end
+
         # fzf: always use fzf-update (git-based)
         if test "$special" = fzf-update
             echo "Updating $bin..."
@@ -64,6 +75,11 @@ function _fish_deps_update
             echo "Updating $bin..."
             cargo install --force $cargo_crate
             set updated_any 1
+            if test "$bin" = fish
+                set_color yellow
+                echo "  Fish updated — restart your shell to use the new version."
+                set_color normal
+            end
             set i (math $i + 1)
             continue
         end