add hasInfix to nib.strings

nib/std/strings.nix

@@ -2,6 +2,7 @@
   inherit
     (builtins)
     isPath
+    genList
     replaceStrings
     substring
     stringLength
@@ -19,6 +20,21 @@ in rec {
     stringLength
     ;
 
+  escape = list: replaceStrings list (map (c: "\\${c}") list);
+
+  escapeRegex = escape (stringToCharacters "\\[{()^$?*+|.");
+
+  hasInfix = infix: content:
+  # Before 23.05, paths would be copied to the store before converting them
+  # to strings and comparing. This was surprising and confusing.
+    warnIf (isPath infix)
+    ''
+      lib.strings.hasInfix: The first argument (${toString infix}) is a path value, but only strings are supported.
+          There is almost certainly a bug in the calling code, since this function always returns `false` in such a case.
+          This function also copies the path to the Nix store, which may not be what you want.
+          This behavior is deprecated and will throw an error in the future.''
+    (builtins.match ".*${escapeRegex infix}.*" "${content}" != null);
+
   removeSuffix = suffix: str:
   # Before 23.05, paths would be copied to the store before converting them
   # to strings and comparing. This was surprising and confusing.
@@ -37,4 +53,6 @@ in rec {
         then substring 0 (sLen - sufLen) str
         else str
     );
+
+  stringToCharacters = s: genList (p: substring p 1 s) (stringLength s);
 }