nixos/zsh-autosuggestions: ZSH_AUTOSUGGEST_STRATEGY array

zsh-autosuggestions supports having fallback strategies expressed
through the ZSH_AUTOSUGGEST_STRATEGY array. For example,
`ZSH_AUTOSUGGEST_STRATEGY=(history completion)`. We should also support
this.

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -846,6 +846,12 @@
           compatibilty, but will be removed at a later date.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <literal>programs.zsh.autosuggestions.strategy</literal> now
+          takes a list of strings instead of a string.
+        </para>
+      </listitem>
       <listitem>
         <para>
           The <literal>services.unifi.openPorts</literal> option default

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -278,6 +278,8 @@ In addition to numerous new and upgraded packages, this release has the followin
   combined `influxdb2` package is still provided in this release for
   backwards compatibilty, but will be removed at a later date.
 
+- `programs.zsh.autosuggestions.strategy` now takes a list of strings instead of a string.
+
 - The `services.unifi.openPorts` option default value of `true` is now deprecated and will be changed to `false` in 22.11.
   Configurations using this default will print a warning when rebuilt.
 

nixos/modules/programs/zsh/zsh-autosuggestions.nix

@@ -22,17 +22,18 @@ in
     };
 
     strategy = mkOption {
-      type = types.enum [ "history" "match_prev_cmd" ];
-      default = "history";
+      type = types.listOf (types.enum [ "history" "completion" "match_prev_cmd" ]);
+      default = [ "history" ];
       description = ''
-        Set ZSH_AUTOSUGGEST_STRATEGY to choose the strategy for generating suggestions.
-        There are currently two to choose from:
+        `ZSH_AUTOSUGGEST_STRATEGY` is an array that specifies how suggestions should be generated.
+        The strategies in the array are tried successively until a suggestion is found.
+        There are currently three built-in strategies to choose from:
 
-          * history: Chooses the most recent match.
-          * match_prev_cmd: Chooses the most recent match whose preceding history item matches
-            the most recently executed command (more info). Note that this strategy won't work as
-            expected with ZSH options that don't preserve the history order such as
-            HIST_IGNORE_ALL_DUPS or HIST_EXPIRE_DUPS_FIRST.
+        - `history`: Chooses the most recent match from history.
+        - `completion`: Chooses a suggestion based on what tab-completion would suggest. (requires `zpty` module)
+        - `match_prev_cmd`: Like `history`, but chooses the most recent match whose preceding history item matches
+            the most recently executed command. Note that this strategy won't work as expected with ZSH options that
+            don't preserve the history order such as `HIST_IGNORE_ALL_DUPS` or `HIST_EXPIRE_DUPS_FIRST`.
       '';
     };
 
@@ -62,7 +63,7 @@ in
       source ${pkgs.zsh-autosuggestions}/share/zsh-autosuggestions/zsh-autosuggestions.zsh
 
       export ZSH_AUTOSUGGEST_HIGHLIGHT_STYLE="${cfg.highlightStyle}"
-      export ZSH_AUTOSUGGEST_STRATEGY=("${cfg.strategy}")
+      export ZSH_AUTOSUGGEST_STRATEGY=(${concatStringsSep " " cfg.strategy})
       ${optionalString (!cfg.async) "unset ZSH_AUTOSUGGEST_USE_ASYNC"}
 
       ${concatStringsSep "\n" (mapAttrsToList (key: value: ''export ${key}="${value}"'') cfg.extraConfig)}