syn 3.0.3: syn::parse_str

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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::parse_str 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::parse_str

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:sha256:5f7ea67518789db64c763d1cc09ef5ff3826aa9fbb52186de395e174c3f76f25","contract":["syn::parse_str parses expressions into syn::Expr syntax tree nodes","syn::parse_str parses struct definitions into syn::ItemStruct syntax tree nodes","syn::parse_str parses types into syn::Type syntax tree nodes","syn::parse_str parses enum definitions into syn::DeriveInput syntax tree nodes","syn::parse_str rejects invalid syntax with syn::Error","syn::parse_str enforces complete consumption of input and rejects trailing unparsed tokens"],"goal":"verify syn::parse_str in pkg:cargo/syn@3.0.3","kind":"HOW","packages":["pkg:cargo/syn@3.0.3"],"schemaVersion":1,"symbols":["syn::parse_str"]},"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::parse_str"],"verifierAdapter":"cargo@1"}

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

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

pub use syn::parse_str;

use syn::{parse_str, DeriveInput, Expr, ItemStruct, Type};

fn main() {
    // 1. syn::parse_str parses expressions into syn::Expr syntax tree nodes
    let expr: Expr = parse_str("1 + 2 * 3").expect("parse binary expression");
    match expr {
        Expr::Binary(ref bin) => {
            assert!(matches!(*bin.left, Expr::Lit(_)));
            assert!(matches!(*bin.right, Expr::Binary(_)));
        }
        _ => panic!("expected Expr::Binary"),
    }

    // 2. syn::parse_str parses struct definitions into syn::ItemStruct syntax tree nodes
    let item: ItemStruct = parse_str("struct Point { x: f64, y: f64 }").expect("parse struct");
    assert_eq!(item.ident.to_string(), "Point");
    assert_eq!(item.fields.len(), 2);

    // 3. syn::parse_str parses types into syn::Type syntax tree nodes
    let ty: Type = parse_str("Vec<Option<String>>").expect("parse type");
    assert!(matches!(ty, Type::Path(_)));

    // 4. syn::parse_str parses enum definitions into syn::DeriveInput syntax tree nodes
    let derive_input: DeriveInput = parse_str("enum Status { Active, Inactive }").expect("parse enum");
    assert_eq!(derive_input.ident.to_string(), "Status");
    match derive_input.data {
        syn::Data::Enum(ref data_enum) => {
            assert_eq!(data_enum.variants.len(), 2);
        }
        _ => panic!("expected Data::Enum"),
    }

    // 5. syn::parse_str rejects invalid syntax with syn::Error
    let err_invalid = parse_str::<Expr>("struct Foo {}");
    assert!(err_invalid.is_err());

    // 6. syn::parse_str enforces complete consumption of input and rejects trailing unparsed tokens
    let err_trailing = parse_str::<Expr>("1 + 2 trailing_tokens");
    assert!(err_trailing.is_err());

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