symbol_new_for_short_literal

Default Severity: warn

What it does

Detects calls to Symbol::new(&env, "literal") where the string literal is short enough (≤ 9 characters) and contains only valid short-symbol characters (a-zA-Z0-9_). Such symbols can be created at compile time using the symbol_short! macro instead.

Why is this bad?

DANGER

Symbol::new creates symbols at runtime, which incurs CPU overhead on every call. Short symbols (≤ 9 chars, alphanumeric + underscore) can be created at compile time using symbol_short!, producing a const Symbol with zero runtime cost.

Example

// ❌ Bad: runtime symbol creation for a short literal
let sym = Symbol::new(&env, "hello");

Suggested Fix

TIP

Use symbol_short! macro for compile-time symbol creation:

// ✅ Good: compile-time symbol creation
let sym = symbol_short!("hello");

Cost impact

Every Symbol::new(&env, "literal") call crosses the Wasm–host boundary to allocate and register the symbol at runtime — even for short, compile-time-knowable literals. symbol_short! produces a const Symbol with zero runtime cost.

Measured with Env::default() in the cost_benchmarks crate (cargo test -- --nocapture):

Pattern	Iterations	CPU instructions (delta)	Memory bytes (delta)
Symbol::new(&env, "hello") (bad)	100	run cargo test -- --nocapture in cost_benchmarks/	run cargo test -- --nocapture in cost_benchmarks/
symbol_short!("hello") (good)	100	≈ 0 (compile-time constant)	≈ 0 (compile-time constant)

INFO

The saving per call is small in absolute terms, but many contracts create dozens of symbols at init. Using symbol_short! where possible eliminates every one of those host crossings.

How to reproduce

cd cost_benchmarks
cargo test bench_symbol_new_vs_short -- --nocapture

The test calls each pattern 100 times and prints the budget delta.

Valid Characters and Length

• Maximum length: 9 characters
• Valid characters: a-z, A-Z, 0-9, _ (underscore)

Non-Flagged Cases

The lint does not trigger for:

• String literals longer than 9 characters
• String literals containing invalid characters (e.g., -, ., spaces)
• Non-literal string arguments (variables, expressions)
• Empty strings