readline: Add support for keynames (#3947)

Kenames like `Control-n` or `meta-p` should not be quoted or they don't work.

Keyseqs like `\C-p` or `ab` must continue to be quoted.

See also: https://www.gnu.org/software/bash/manual/html_node/Readline-Init-File-Syntax.html

Fixes https://github.com/nix-community/home-manager/issues/3611

modules/programs/readline.nix

@@ -21,7 +21,14 @@ let
           abort ("values ${toPretty v} is of unsupported type");
     in "set ${n} ${mkValueStr v}";
 
-  mkBindingStr = k: v: ''"${k}": ${v}'';
+  mkBindingStr = k: v:
+    let
+      isKeynameNotKeyseq = k:
+        builtins.elem (builtins.head (lib.splitString "-" (toLower k))) [
+          "control"
+          "meta"
+        ];
+    in if isKeynameNotKeyseq k then "${k}: ${v}" else ''"${k}": ${v}'';
 
 in {
   options.programs.readline = {

tests/modules/programs/readline/using-all-options.nix

@@ -7,7 +7,10 @@ with lib;
     programs.readline = {
       enable = true;
 
-      bindings = { "\\C-h" = "backward-kill-word"; };
+      bindings = {
+        "\\C-h" = "backward-kill-word";
+        "Control-p" = ''"whups"'';
+      };
 
       variables = {
         bell-style = "audible";

tests/modules/programs/readline/using-all-options.txt

@@ -4,6 +4,7 @@ $include /etc/inputrc
 set bell-style audible
 set completion-map-case on
 set completion-prefix-display-length 2
+Control-p: "whups"
 "\C-h": backward-kill-word
 $if mode=emacs
 "\e[1~": beginning-of-line