Compiled SpEL expression fails if #root or #this is a non-public type

[sbrannen]

If a SpEL expression references the root context object via the #root or #this variables, we currently insert a checkcast in the generated byte code that casts the object to its concrete type.

However if the root context object's type is non-public, that results in an IllegalAccessError when the compiled byte code is executed.

See the following test, for an example.

spring-framework/spring-expression/src/test/java/org/springframework/expression/spel/SpelCompilationCoverageTests.java

Lines 514 to 525 in a29c84f

	// custom CompilableMapAccessor via explicit #root & array index
	expression = parser.parseExpression("#root.foo[1]");
	assertThat(expression.getValue(context, map)).isEqualTo(2);
	assertCanCompile(expression);
	// TODO If map is created via Map.of(), the following fails with an IllegalAccessError.
	//
	// IllegalAccessError: failed to access class java.util.ImmutableCollections$Map1 from class
	// spel.Ex2774 (java.util.ImmutableCollections$Map1 is in module java.base of loader 'bootstrap';
	// spel.Ex2774 is in unnamed module of loader
	// org.springframework.expression.spel.standard.SpelCompiler$ChildClassLoader @359b650b)
	assertThat(expression.getValue(context, map)).isEqualTo(2);

Interestingly enough, VariableReference.getValueInternal(ExpressionState) already contains a "workaround" for global variables which inserts a checkcast to Object in the generated byte code instead of to the object's concrete non-public type.

I have a local fix that applies the same logic to #root/#this and global variables. Thus, this issue is here to provide public visibility and raise awareness.