Disable setting fields in case we use environment variables

src/Core/Config/Capability/IManageConfigValues.php

@@ -58,6 +58,16 @@ interface IManageConfigValues
 	 */
 	public function get(string $cat, string $key = null, $default_value = null);
 
+	/**
+	 * Returns true, if the current config cannot be changed
+	 *
+	 * @param string $cat The category of the configuration value
+	 * @param string $key The configuration key to query
+	 *
+	 * @return bool true, if set is disabled
+	 */
+	public function isSetDisabled(string $cat, string $key): bool;
+
 	/**
 	 * Sets a configuration value for system config
 	 *

src/Core/Config/Model/DatabaseConfig.php

@@ -80,6 +80,12 @@ class DatabaseConfig implements IManageConfigValues
 		return $this->cache->get($cat, $key) ?? $default_value;
 	}
 
+	/** {@inheritDoc} */
+	public function isSetDisabled(string $cat, string $key): bool
+	{
+		return $this->cache->getSource($cat, $key) >= Cache::SOURCE_ENV;
+	}
+
 	/** {@inheritDoc} */
 	public function set(string $cat, string $key, $value): bool
 	{

src/Core/Config/Model/ReadOnlyFileConfig.php

@@ -68,6 +68,12 @@ class ReadOnlyFileConfig implements IManageConfigValues
 		return $this->configCache->get($cat, $key) ?? $default_value;
 	}
 
+	/** {@inheritDoc} */
+	public function isSetDisabled(string $cat, string $key): bool
+	{
+		return $this->configCache->getSource($cat, $key) >= Cache::SOURCE_ENV;
+	}
+
 	/** {@inheritDoc} */
 	public function set(string $cat, string $key, $value): bool
 	{

src/Core/Config/ValueObject/Cache.php

@@ -31,6 +31,15 @@ use ParagonIE\HiddenString\HiddenString;
  */
 class Cache
 {
+	/** @var int[] A list of valid config source  */
+	const VALID_SOURCES = [
+		self::SOURCE_STATIC,
+		self::SOURCE_FILE,
+		self::SOURCE_DATA,
+		self::SOURCE_ENV,
+		self::SOURCE_FIX,
+	];
+
 	/** @var int Indicates that the cache entry is a default value - Lowest Priority */
 	const SOURCE_STATIC = 0;
 	/** @var int Indicates that the cache entry is set by file - Low Priority */