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MAINT008-large-impl-block — Large impl Block or Class

Dimension: Maintainability Default severity: Low Languages: All (Rust impl blocks, Python classes; JS/TS produce no findings) CWE: (none) Last reviewed: 2026-05-07

What it detects​

Flags impl blocks (Rust) and classes (Python) that contain more methods than a configurable threshold (default 30). A type with a very large number of methods is a common code-smell that signals a violation of the Single Responsibility Principle — the type is likely doing too many things.

Configuration​

[rules."MAINT008-large-impl-block"]
threshold = 30   # default; method count strictly > threshold triggers the rule

Example — flagged​

Rust (31 methods, default threshold 30):

pub struct God;

impl God {
    pub fn do_thing_1(&self) {}
    pub fn do_thing_2(&self) {}
    // … 29 more methods …
    pub fn do_thing_31(&self) {}
}
// Finding: `God` has 31 methods (threshold 30); consider splitting into smaller types

Python (31 methods, default threshold 30):

class GodClass:
    def do_thing_1(self): pass
    def do_thing_2(self): pass
    # … 29 more methods …
    def do_thing_31(self): pass
# Finding: `GodClass` has 31 methods (threshold 30); consider splitting into smaller types

Example — not flagged​

pub struct Focused;

impl Focused {
    pub fn step_1(&self) {}
    pub fn step_2(&self) {}
    // … up to 30 methods total — at or below threshold → clean
}

Fix guidance​

  • Extract a logically cohesive subset of methods into a dedicated helper type or trait.
  • Separate I/O concerns from pure business logic.
  • Use the Facade pattern: keep a thin public surface and delegate to smaller focused types.

Implementation​

  • Source: crates/zuit-analyzers/src/large_impl_block.rs
  • Threshold read via Config::rule_threshold("MAINT008-large-impl-block", 30).
  • One finding is emitted per exceeding group, located at the span of the first method (best available proxy for the block header).
  • Languages without parent_name support (JS/TS) produce no findings.

References​