improve collapsible if in complex cases with same expressions

Description

if a {
    if b {
        f();
    }
} else {
    f();
}

if !a || b {
    f();
}

Contributor guide

Tech stack

rust

Domain

toolingdeveloper experience

Issue type

feature

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-2 days

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

RustClippy internalsAST knowledgeLogical expressions

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

45

Research direction

Examine the current implementation of the collapsible if lint in rust clippy (file clippy lints/src/collapsible if.rs). Understand how it currently detects simple nested if statements. The enhancement would require adding logic to detect cases where the else branch contains the same expression as the if body, and transform to a single conditional. Look for any existing discussions or attempts (the issue is assigned but no PR). The maintainer might have input on desired approach. Focus on the AST patterns for the given example.