syn 3.0.3: syn::ExprIf

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Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify syn::ExprIf in pkg:cargo/syn@3.0.3
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:cargo/syn@3.0.3
Demonstrate these symbols/APIs:
  - syn::ExprIf

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

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  "kind": "HOW",
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  "symbols": [
    "syn::ExprIf"
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}

//! Clean-room verification sample for syn::ExprIf.

pub use syn::ExprIf;

use syn::{parse_str, Expr, ExprBinary, ExprBlock, ExprIf};

fn main() {
    // 1. syn::parse_str parses an if expression without else into ExprIf with else_branch as None
    let expr: ExprIf = parse_str("if enabled { do_work(); }").expect("valid if expr");
    assert!(expr.else_branch.is_none());
    assert_eq!(expr.then_branch.stmts.len(), 1);

    // 2. syn::parse_str parses an if-else expression into ExprIf with Block in else_branch
    let expr: ExprIf = parse_str("if count > 0 { count } else { 0 }").expect("valid if-else");
    assert!(expr.else_branch.is_some());
    let (_, else_expr) = expr.else_branch.as_ref().unwrap();
    match else_expr.as_ref() {
        Expr::Block(ExprBlock { block, .. }) => {
            assert_eq!(block.stmts.len(), 1);
        }
        _ => panic!("expected Expr::Block in else_branch"),
    }

    // 3. syn::parse_str parses an if-else-if chained expression into nested ExprIf in else_branch
    let expr: ExprIf = parse_str("if a { 1 } else if b { 2 } else { 3 }").expect("valid else-if");
    let (_, else_expr) = expr.else_branch.as_ref().unwrap();
    match else_expr.as_ref() {
        Expr::If(nested_if) => {
            assert!(nested_if.else_branch.is_some());
        }
        _ => panic!("expected nested Expr::If in else_branch"),
    }

    // 4. ExprIf cond field holds the conditional expression
    let expr: ExprIf = parse_str("if flag && ready { true }").expect("valid condition expr");
    match expr.cond.as_ref() {
        Expr::Binary(ExprBinary { op: syn::BinOp::And(_), .. }) => {}
        _ => panic!("expected binary condition expression"),
    }

    // 5. ExprIf then_branch contains the parsed block statements
    let expr: ExprIf = parse_str("if run { let x = 10; x + 1 }").expect("valid block expr");
    assert_eq!(expr.then_branch.stmts.len(), 2);

    // 6. syn::parse_str rejects invalid syntax for ExprIf with a parse error
    let invalid = parse_str::<ExprIf>("if { 1 }");
    assert!(invalid.is_err());
    let invalid_missing_body = parse_str::<ExprIf>("if true");
    assert!(invalid_missing_body.is_err());

    println!("All syn::ExprIf contract assertions passed successfully.");
}