syn 3.0.3: syn::ItemFn

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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::ItemFn 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::ItemFn

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.

{"case":{"caseId":"case:sha256:3ed0e1b9590f2c9f2e1c41ab5417e145d1154e4b9c7096a8cf029108ab619b32","contract":["parse_str parses a standard function into ItemFn with identifier and visibility","parse_str parses an async function into ItemFn with asyncness modifier","parse_str parses a const unsafe function with generic parameters into ItemFn","parse_str parses an ItemFn with outer attributes","ItemFn exposes modifiers with defaultness field"],"goal":"verify syn::ItemFn in pkg:cargo/syn@3.0.3","kind":"HOW","packages":["pkg:cargo/syn@3.0.3"],"schemaVersion":1,"symbols":["syn::ItemFn"]},"contractCommand":["cargo","run","--offline"],"environment":{"arch":"x64","distro":"alpine","ecosystem":"cargo","libc":"musl","os":"linux","packageManager":"cargo","schemaVersion":1},"license":"MIT-0","packages":["pkg:cargo/syn@3.0.3"],"schemaVersion":1,"subject":"pkg:cargo/syn@3.0.3","symbols":["syn::ItemFn"],"verifierAdapter":"cargo@1"}

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  "kind": "HOW",
  "packages": [
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  ],
  "symbols": [
    "syn::ItemFn"
  ]
}

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

pub use syn::*;

use syn::{parse_str, ItemFn, ReturnType, Safety, Visibility};

fn main() {
    // 1. parse_str parses a standard function into ItemFn with identifier and visibility
    let fn_code = "pub fn calculate_sum(a: i32, b: i32) -> i32 { a + b }";
    let item_fn: ItemFn = parse_str(fn_code).expect("failed to parse standard function");
    assert_eq!(item_fn.sig.ident.to_string(), "calculate_sum");
    assert!(matches!(item_fn.vis, Visibility::Public(_)));
    assert_eq!(item_fn.sig.inputs.len(), 2);
    assert!(matches!(item_fn.sig.output, ReturnType::Type(_, _)));
    assert_eq!(item_fn.block.stmts.len(), 1);

    // 2. parse_str parses an async function into ItemFn with asyncness modifier
    let async_code = "async fn fetch_resource() { }";
    let async_fn: ItemFn = parse_str(async_code).expect("failed to parse async function");
    assert_eq!(async_fn.sig.ident.to_string(), "fetch_resource");
    assert!(async_fn.sig.asyncness.is_some());
    assert!(async_fn.sig.constness.is_none());
    assert!(matches!(async_fn.sig.safety, Safety::Default));
    assert!(matches!(async_fn.vis, Visibility::Inherited));

    // 3. parse_str parses a const unsafe function with generic parameters into ItemFn
    let const_code = "const unsafe fn identity<T>(value: T) -> T { value }";
    let const_fn: ItemFn = parse_str(const_code).expect("failed to parse const unsafe function");
    assert_eq!(const_fn.sig.ident.to_string(), "identity");
    assert!(const_fn.sig.constness.is_some());
    assert!(matches!(const_fn.sig.safety, Safety::Unsafe(_)));
    assert_eq!(const_fn.sig.generics.params.len(), 1);

    // 4. parse_str parses an ItemFn with outer attributes
    let attr_code = "#[inline]\n#[must_use]\nfn get_zero() -> usize { 0 }";
    let attr_fn: ItemFn = parse_str(attr_code).expect("failed to parse attributed function");
    assert_eq!(attr_fn.attrs.len(), 2);
    assert!(attr_fn.attrs[0].path().is_ident("inline"));
    assert!(attr_fn.attrs[1].path().is_ident("must_use"));

    // 5. ItemFn exposes modifiers with defaultness field
    let simple_code = "fn standard_fn() {}";
    let simple_fn: ItemFn = parse_str(simple_code).expect("failed to parse simple function");
    assert!(simple_fn.modifiers.defaultness.is_none());

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