Make validation placeholders always available

system/Model.php

@@ -1432,10 +1432,6 @@ public function validate($data): bool
 			return true;
 		}
 
-		// Replace any placeholders (i.e. {id}) in the rules with
-		// the value found in $data, if exists.
-		$rules = $this->fillPlaceholders($rules, $data);
-
 		$this->validation->setRules($rules, $this->validationMessages);
 		$valid = $this->validation->run($data, null, $this->DBGroup);
 
@@ -1488,6 +1484,10 @@ protected function cleanValidationRules(array $rules, array $data = null): array
 	 *
 	 *  'required|is_unique[users,email,id,13]'
 	 *
+	 * @codeCoverageIgnore
+	 *
+	 * @deprecated use fillPlaceholders($rules, $data) from Validation instead
+	 *
 	 * @param array $rules
 	 * @param array $data
 	 *

system/Validation/Validation.php

@@ -155,6 +155,10 @@ public function run(array $data = null, string $group = null, string $db_group =
 			return false;
 		}
 
+		// Replace any placeholders (i.e. {id}) in the rules with
+		// the value found in $data, if exists.
+		$this->rules = $this->fillPlaceholders($this->rules, $data);
+
 		// Need this for searching arrays in validation.
 		helper('array');
 
@@ -603,6 +607,64 @@ public function loadRuleGroup(string $group = null)
 		return $this->rules;
 	}
 
+	//--------------------------------------------------------------------
+
+	/**
+	 * Replace any placeholders within the rules with the values that
+	 * match the 'key' of any properties being set. For example, if
+	 * we had the following $data array:
+	 *
+	 * [ 'id' => 13 ]
+	 *
+	 * and the following rule:
+	 *
+	 *  'required|is_unique[users,email,id,{id}]'
+	 *
+	 * The value of {id} would be replaced with the actual id in the form data:
+	 *
+	 *  'required|is_unique[users,email,id,13]'
+	 *
+	 * @param array $rules
+	 * @param array $data
+	 *
+	 * @return array
+	 */
+	protected function fillPlaceholders(array $rules, array $data): array
+	{
+		$replacements = [];
+
+		foreach ($data as $key => $value)
+		{
+			$replacements["{{$key}}"] = $value;
+		}
+
+		if (! empty($replacements))
+		{
+			foreach ($rules as &$rule)
+			{
+				if (is_array($rule))
+				{
+					foreach ($rule as &$row)
+					{
+						// Should only be an `errors` array
+						// which doesn't take placeholders.
+						if (is_array($row))
+						{
+							continue;
+						}
+
+						$row = strtr($row, $replacements);
+					}
+					continue;
+				}
+
+				$rule = strtr($rule, $replacements);
+			}
+		}
+
+		return $rules;
+	}
+
 	//--------------------------------------------------------------------
 	//--------------------------------------------------------------------
 	// Errors

tests/system/Validation/UniqueRulesTest.php

@@ -112,4 +112,35 @@ public function testIsUniqueIgnoresParams()
 	}
 
 	//--------------------------------------------------------------------
+
+	/**
+	 * @group DatabaseLive
+	 */
+	public function testIsUniqueIgnoresParamsPlaceholders()
+	{
+		$this->hasInDatabase('user', [
+			'name'    => 'Derek',
+			'email'   => '[email protected]',
+			'country' => 'GB',
+		]);
+
+		$db  = Database::connect();
+		$row = $db->table('user')
+				  ->limit(1)
+				  ->get()
+				  ->getRow();
+
+		$data = [
+			'id'    => $row->id,
+			'email' => '[email protected]',
+		];
+
+		$this->validation->setRules([
+			'email' => "is_unique[user.email,id,{id}]",
+		]);
+
+		$this->assertTrue($this->validation->run($data));
+	}
+
+	//--------------------------------------------------------------------
 }