Allow later contract fields to reference earlier fields (#229)

[palacharlanarendra]

Allow later contract fields to reference earlier fields #229

Contract field initializers can reference constructor parameters and constants, and static checking accepts references to earlier contract fields. However, bytecode compilation evaluates each field initializer without adding previously resolved fields to the constant environment. This causes compilation to fail with RuntimeEvaluationRequired when a later field references an earlier field.

We resolve this by accumulating successfully resolved contract fields into the constant environment sequentially in declaration order during compilation.

The Defect

In silverscript-lang/src/compiler/compile/helpers.rs, the compiler compiles contract fields in compile_contract_fields by iterating over them and resolving constant references using only base_constants:

let resolved = resolve_constant_references(field.expr.clone(), base_constants, &mut resolve_visiting)?;

base_constants only contains constructor parameters and global constants. Because the resolved expressions of preceding fields are not accumulated, references to earlier fields (e.g. mirrored = amount) remain unresolved as raw ExprKind::Identifier expressions.

When the compiler attempts to encode the value as a constant push (for fixed-size types like int), it fails to encode the identifier and aborts with RuntimeEvaluationRequired.

The Fix

1. Accumulate Constants: Clone base_constants into a mutable environment map current_constants at the beginning of compile_contract_fields.
2. Propagate Resolved Fields: After a field's initializer is resolved and compiled, insert its resolved expression into current_constants.
3. Sequential Reference Resolution: Pass current_constants to resolve_constant_references, fixed_type_size, encode_value_with_constant_size, and the expression environment ExprEnv.
4. Validation: Undefined variables, forward references, and cyclic dependencies continue to be rejected by the compiler's sequential static check pass.

Tests

We added three regression tests in silverscript-lang/tests/compiler_tests.rs:

• contract_field_initializer_accepts_a_reference_to_an_earlier_field: Verifies that compiling a contract with prior field references succeeds and matches the expected behavior.
• contract_field_initializer_rejects_forward_and_undefined_references: Verifies that undefined variables and forward-references to fields declared later are clearly rejected during static checks.
• contract_field_initializer_rejects_cyclic_references: Verifies that circular field reference dependencies are clearly rejected.