`unsafe-cross-contract-input` taint tracking doesn't clear on variable shadowing — false positive on validated re-bindings

[unrealtim-tech]

Labels: bug, checks-crate
Crate: checks

Description
crates/checks/src/xc_input.rs's taint set xc_bindings: HashSet<String> (lines ~74-88) is keyed purely by variable name, and entries are never removed:

if let Stmt::Local(local) = stmt {
    if let Some(init) = &local.init {
        if is_invoke_contract(&init.expr) {
            if let Pat::Ident(pi) = &local.pat {
                self.xc_bindings.insert(pi.ident.to_string());
            }
        }
    }
}

Rust code that shadows a tainted binding with a validated value under the same name still trips the check:

let result = env.invoke_contract(&callee, &sym, ());   // tainted, "result" inserted
let result = if result > 0 { result } else { 0 };      // shadowed/validated
env.storage().persistent().set(&k, &result);           // false positive: "result" still tainted

The existing passing test sidesteps this by using a different variable name for the validated value, so this shadowing case has no coverage.

Acceptance Criteria

• Clear (or replace) a binding's taint status when it is shadowed by a new let with the same name and a non-tainted initializer.
• Add a test using the shadowing pattern above, asserting no finding once the shadowed value is validated.

Difficulty: intermediate

[Ebby46]

@Ebby46 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, pls i will like to work on this issue

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[Handynfts2]

@Handynfts2 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

hi maintainer, i would love to fix this issue.
kindly assign me.

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[abdulquadri123]

@abdulquadri123 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hey Maintainer,
As a blockchain developer, I will delighted to handle this issue and solve it diligently once assigned to me.
Thanks.

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