lib: add upperFirstChar

A util function to capitalize the first character of a string.

lib/utils.nix

@@ -67,6 +67,31 @@ with lib;
     in
     concatStrings (map processWord words);
 
+  /**
+    Capitalize a string by making the first character uppercase.
+
+    # Example
+
+    ```nix
+    upperFirstChar "hello, world!"
+    => "Hello, world!"
+    ```
+
+    # Type
+
+    ```
+    upperFirstChar :: String -> String
+    ```
+  */
+  upperFirstChar =
+    s:
+    let
+      first = substring 0 1 s;
+      rest = substring 1 (stringLength s) s;
+      result = (toUpper first) + rest;
+    in
+    optionalString (s != "") result;
+
   mkIfNonNull' = x: y: (mkIf (x != null) y);
 
   mkIfNonNull = x: (mkIfNonNull' x x);

tests/lib-tests.nix

@@ -113,6 +113,23 @@ let
       };
       expected = ''{["c"] = { },["d"] = {["g"] = { }}}'';
     };
+
+    testUpperFirstChar = {
+      expr = map helpers.upperFirstChar [
+        "foo"
+        " foo"
+        "foo bar"
+        "UPPER"
+        "mIxEd"
+      ];
+      expected = [
+        "Foo"
+        " foo"
+        "Foo bar"
+        "UPPER"
+        "MIxEd"
+      ];
+    };
   };
 in
 if results == [ ] then