add std/strings.nix

nib/std/strings.nix

@@ -0,0 +1,38 @@
+{nib, ...}: let
+  inherit
+    (builtins)
+    isPath
+    substring
+    stringLength
+    ;
+
+  inherit
+    (nib.trivial)
+    warnIf
+    ;
+in rec {
+  # re-export builtin string methods
+  inherit
+    substring
+    stringLength
+    ;
+
+  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.
+    warnIf (isPath suffix)
+    ''
+      lib.strings.removeSuffix: The first argument (${toString suffix}) is a path value, but only strings are supported.
+          There is almost certainly a bug in the calling code, since this function never removes any suffix 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.''
+    (
+      let
+        sufLen = stringLength suffix;
+        sLen = stringLength str;
+      in
+        if sufLen <= sLen && suffix == substring (sLen - sufLen) sufLen str
+        then substring 0 (sLen - sufLen) str
+        else str
+    );
+}