feat: add immutable URI query variable helpers

system/HTTP/URI.php

@@ -875,6 +875,56 @@ public function addQuery(string $key, $value = null)
         return $this;
     }
 
+    /**
+     * Return an instance with one query var added, replaced, or removed.
+     *
+     * Note: Method not in PSR-7
+     *
+     * @param int|string|null $value Null removes the query var.
+     *
+     * @return static
+     */
+    public function withQueryVar(string $key, $value)
+    {
+        $uri = clone $this;
+
+        if ($value === null) {
+            unset($uri->query[$key]);
+
+            return $uri;
+        }
+
+        $uri->query[$key] = $value;
+
+        return $uri;
+    }
+
+    /**
+     * Return an instance with multiple query vars added, replaced, or removed.
+     *
+     * Note: Method not in PSR-7
+     *
+     * @param array<string, int|string|null> $params Null values remove query vars.
+     *
+     * @return static
+     */
+    public function withQueryVars(array $params)
+    {
+        $uri = clone $this;
+
+        foreach ($params as $key => $value) {
+            if ($value === null) {
+                unset($uri->query[$key]);
+
+                continue;
+            }
+
+            $uri->query[$key] = $value;
+        }
+
+        return $uri;
+    }
+
     /**
      * Removes one or more query vars from the URI.
      *

tests/system/HTTP/URITest.php

@@ -835,6 +835,65 @@ public function testAddQueryVarRespectsExistingQueryVars(): void
         $this->assertSame('http://example.com/foo?bar=baz&baz=foz', (string) $uri);
     }
 
+    public function testWithQueryVarAddsQueryVarWithoutMutatingOriginal(): void
+    {
+        $base = 'http://example.com/foo';
+        $uri  = new URI($base);
+
+        $new = $uri->withQueryVar('bar', 'baz');
+
+        $this->assertSame('http://example.com/foo?bar=baz', (string) $new);
+        $this->assertSame('http://example.com/foo', (string) $uri);
+    }
+
+    public function testWithQueryVarReplacesQueryVarAndPreservesFragment(): void
+    {
+        $base = 'http://example.com/foo?bar=baz#section';
+        $uri  = new URI($base);
+
+        $new = $uri->withQueryVar('bar', 'foz');
+
+        $this->assertSame('http://example.com/foo?bar=foz#section', (string) $new);
+        $this->assertSame('http://example.com/foo?bar=baz#section', (string) $uri);
+    }
+
+    public function testWithQueryVarRemovesQueryVarWhenValueIsNull(): void
+    {
+        $base = 'http://example.com/foo?foo=bar&bar=baz&baz=foz';
+        $uri  = new URI($base);
+
+        $new = $uri->withQueryVar('bar', null);
+
+        $this->assertSame('http://example.com/foo?foo=bar&baz=foz', (string) $new);
+        $this->assertSame('http://example.com/foo?foo=bar&bar=baz&baz=foz', (string) $uri);
+    }
+
+    public function testWithQueryVarKeepsEmptyStringQueryVar(): void
+    {
+        $base = 'http://example.com/foo?bar=baz';
+        $uri  = new URI($base);
+
+        $new = $uri->withQueryVar('bar', '');
+
+        $this->assertSame('http://example.com/foo?bar=', (string) $new);
+        $this->assertSame('http://example.com/foo?bar=baz', (string) $uri);
+    }
+
+    public function testWithQueryVarsAddsReplacesAndRemovesWithoutMutatingOriginal(): void
+    {
+        $base = 'http://example.com/foo?foo=bar&bar=baz&baz=foz#section';
+        $uri  = new URI($base);
+
+        $new = $uri->withQueryVars([
+            'bar' => null,
+            'baz' => 'updated',
+            'new' => 'value',
+        ]);
+
+        $this->assertSame('http://example.com/foo?foo=bar&baz=updated&new=value#section', (string) $new);
+        $this->assertSame('http://example.com/foo?foo=bar&bar=baz&baz=foz#section', (string) $uri);
+    }
+
     public function testStripQueryVars(): void
     {
         $base = 'http://example.com/foo?foo=bar&bar=baz&baz=foz';

user_guide_src/source/changelogs/v4.8.0.rst

@@ -276,6 +276,7 @@ HTTP
 - ``CLIRequest`` now supports options with values specified using an equals sign (e.g., ``--option=value``) in addition to the existing space-separated syntax (e.g., ``--option value``).
   This provides more flexibility in how you can pass options to CLI requests.
 - Added ``$enableStyleNonce`` and ``$enableScriptNonce`` options to ``Config\App`` to automatically add nonces to control whether to add nonces to style-* and script-* directives in the Content Security Policy (CSP) header when CSP is enabled. See :ref:`csp-control-nonce-generation` for details.
+- Added ``URI::withQueryVar()`` and ``URI::withQueryVars()`` to return a cloned URI with query variables added, replaced, or removed.
 - ``URI`` now accepts an optional boolean second parameter in the constructor, defaulting to ``false``, to control how the query string is parsed in instantiation.
   This is the behavior of ``->useRawQueryString()`` brought into the constructor for convenience. Previously, you need to call ``$uri->useRawQueryString(true)->setURI($uri)`` to get this behavior.
   Now you can simply do ``new URI($uri, true)``.

user_guide_src/source/libraries/uri.rst

@@ -188,6 +188,19 @@ parameter is the name of the variable, and the second parameter is the value:
 
 .. literalinclude:: uri/019.php
 
+Changing Query Values Without Mutation
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionadded:: 4.8.0
+
+You can return a new URI instance with one or more query variables changed by using the ``withQueryVar()``
+and ``withQueryVars()`` methods. Existing query variables are preserved unless they are replaced or removed.
+Passing ``null`` removes a query variable:
+
+.. literalinclude:: uri/028.php
+
+The original URI instance is not modified.
+
 Filtering Query Values
 ^^^^^^^^^^^^^^^^^^^^^^
 

user_guide_src/source/libraries/uri/028.php

@@ -0,0 +1,16 @@
+<?php
+
+$uri = new \CodeIgniter\HTTP\URI('https://example.com/users?q=bob&page=1');
+
+$nextPage = $uri->withQueryVar('page', 2);
+// https://example.com/users?q=bob&page=2
+
+$withoutSearch = $uri->withQueryVar('q', null);
+// https://example.com/users?page=1
+
+$filtered = $uri->withQueryVars([
+    'q'    => null,
+    'page' => 1,
+    'role' => 'admin',
+]);
+// https://example.com/users?page=1&role=admin